The great generics revisiting.

33 files changed, 1155 insertions, 1209 deletions

diff --git a/csharp/ProtocolBuffers.Test/AbstractMessageTest.cs b/csharp/ProtocolBuffers.Test/AbstractMessageTest.cs
index d1af0dca..4178c92e 100644
--- a/csharp/ProtocolBuffers.Test/AbstractMessageTest.cs
+++ b/csharp/ProtocolBuffers.Test/AbstractMessageTest.cs
@@ -10,15 +10,13 @@ namespace Google.ProtocolBuffers {
 
     [Test]
     public void Clear() {
-      AbstractMessageWrapper message = (AbstractMessageWrapper)
-        new AbstractMessageWrapper.Builder(TestAllTypes.CreateBuilder(TestUtil.GetAllSet())).Clear().Build();
+      AbstractMessageWrapper message = new AbstractMessageWrapper.Builder(TestAllTypes.CreateBuilder(TestUtil.GetAllSet())).Clear().Build();
       TestUtil.AssertClear((TestAllTypes) message.WrappedMessage);
     }
 
     [Test]
     public void Copy() {
-      AbstractMessageWrapper message = (AbstractMessageWrapper)
-        new AbstractMessageWrapper.Builder(TestAllTypes.CreateBuilder()).MergeFrom(TestUtil.GetAllSet()).Build();
+      AbstractMessageWrapper message = new AbstractMessageWrapper.Builder(TestAllTypes.CreateBuilder()).MergeFrom(TestUtil.GetAllSet()).Build();
       TestUtil.AssertAllFieldsSet((TestAllTypes) message.WrappedMessage);
     }
 
@@ -40,7 +38,7 @@ namespace Google.ProtocolBuffers {
     [Test]
     public void Parsing() {
       IBuilder builder = new AbstractMessageWrapper.Builder(TestAllTypes.CreateBuilder());
-      AbstractMessageWrapper message = (AbstractMessageWrapper) builder.MergeFrom(TestUtil.GetAllSet().ToByteString()).Build();
+      AbstractMessageWrapper message = (AbstractMessageWrapper) builder.WeakMergeFrom(TestUtil.GetAllSet().ToByteString()).WeakBuild();
       TestUtil.AssertAllFieldsSet((TestAllTypes) message.WrappedMessage);
     }
 
@@ -177,7 +175,7 @@ namespace Google.ProtocolBuffers {
       Assert.AreEqual(message, message);
       
       // Object should be equal to a dynamic copy of itself.
-      DynamicMessage dynamic = (DynamicMessage) ((IBuilder) DynamicMessage.CreateBuilder(message)).Build();
+      DynamicMessage dynamic = DynamicMessage.CreateBuilder(message).Build();
       Assert.AreEqual(message, dynamic);
       Assert.AreEqual(dynamic, message);
       Assert.AreEqual(dynamic.GetHashCode(), message.GetHashCode());
@@ -207,7 +205,7 @@ namespace Google.ProtocolBuffers {
     /// test that AbstractMessage's implementations work even if the wrapped
     /// object does not use them.
     /// </summary>
-    private class AbstractMessageWrapper : AbstractMessage {
+    private class AbstractMessageWrapper : AbstractMessage<AbstractMessageWrapper, AbstractMessageWrapper.Builder> {
       private readonly IMessage wrappedMessage;
 
       public IMessage WrappedMessage {
@@ -222,8 +220,8 @@ namespace Google.ProtocolBuffers {
         get { return wrappedMessage.DescriptorForType; }
       }
 
-      protected override IMessage DefaultInstanceForTypeImpl {
-        get { return new AbstractMessageWrapper(wrappedMessage.DefaultInstanceForType); }
+      public override AbstractMessageWrapper DefaultInstanceForType {
+        get { return new AbstractMessageWrapper(wrappedMessage.WeakDefaultInstanceForType); }
       }
 
       public override IDictionary<FieldDescriptor, object> AllFields {
@@ -250,17 +248,26 @@ namespace Google.ProtocolBuffers {
         get { return wrappedMessage.UnknownFields; }
       }
 
-      protected override IBuilder CreateBuilderForTypeImpl() {
-        return new Builder(wrappedMessage.CreateBuilderForType());
+      public override Builder CreateBuilderForType() {
+        return new Builder(wrappedMessage.WeakCreateBuilderForType());
       }
 
-      internal class Builder : AbstractBuilder {
+      internal class Builder : AbstractBuilder<AbstractMessageWrapper, Builder> {
         private readonly IBuilder wrappedBuilder;
 
+        protected override Builder ThisBuilder {
+          get { return this; }
+        }
+
         internal Builder(IBuilder wrappedBuilder) {
           this.wrappedBuilder = wrappedBuilder;
         }
 
+        public override Builder MergeFrom(AbstractMessageWrapper other) {
+          wrappedBuilder.WeakMergeFrom(other.wrappedMessage);
+          return this;
+        }
+
         public override bool IsInitialized {
           get { return wrappedBuilder.IsInitialized; }
         }
@@ -296,29 +303,29 @@ namespace Google.ProtocolBuffers {
           set { wrappedBuilder.UnknownFields = value; }
         }
 
-        protected override IMessage BuildImpl() {
-          return new AbstractMessageWrapper(wrappedBuilder.Build());
+        public override AbstractMessageWrapper Build() {
+          return new AbstractMessageWrapper(wrappedBuilder.WeakBuild());
         }
 
-        protected override IMessage BuildPartialImpl() {
-          return new AbstractMessageWrapper(wrappedBuilder.BuildPartial());
+        public override AbstractMessageWrapper BuildPartial() {
+          return new AbstractMessageWrapper(wrappedBuilder.WeakBuildPartial());
         }
 
-        protected override IBuilder CloneImpl() {
-          return new Builder(wrappedBuilder.Clone());
+        public override Builder Clone() {
+          return new Builder(wrappedBuilder.WeakClone());
         }
 
-        protected override IMessage DefaultInstanceForTypeImpl {
-          get { return wrappedBuilder.DefaultInstanceForType; }
+        public override AbstractMessageWrapper DefaultInstanceForType {
+          get { return new AbstractMessageWrapper(wrappedBuilder.WeakDefaultInstanceForType); }
         }
 
-        protected override IBuilder ClearFieldImpl(FieldDescriptor field) {
-          wrappedBuilder.ClearField(field);
+        public override Builder ClearField(FieldDescriptor field) {
+          wrappedBuilder.WeakClearField(field);
           return this;
         }
 
-        protected override IBuilder AddRepeatedFieldImpl(FieldDescriptor field, object value) {
-          wrappedBuilder.AddRepeatedField(field, value);
+        public override Builder AddRepeatedField(FieldDescriptor field, object value) {
+          wrappedBuilder.WeakAddRepeatedField(field, value);
           return this;
         }
 
@@ -327,13 +334,13 @@ namespace Google.ProtocolBuffers {
           return this;
         }
 
-        public override IBuilder MergeFrom(IMessage other) {
-          wrappedBuilder.MergeFrom(other);
+        public override Builder MergeFrom(IMessage other) {
+          wrappedBuilder.WeakMergeFrom(other);
           return this;
         }
 
-        protected override IBuilder MergeFromImpl(CodedInputStream input, ExtensionRegistry extensionRegistry) {
-          wrappedBuilder.MergeFrom(input, extensionRegistry);
+        public override Builder MergeFrom(CodedInputStream input, ExtensionRegistry extensionRegistry) {
+          wrappedBuilder.WeakMergeFrom(input, extensionRegistry);
           return this;
         }
       }
diff --git a/csharp/ProtocolBuffers.Test/DynamicMessageTest.cs b/csharp/ProtocolBuffers.Test/DynamicMessageTest.cs
index dcf6e0fb..5f9f6bee 100644
--- a/csharp/ProtocolBuffers.Test/DynamicMessageTest.cs
+++ b/csharp/ProtocolBuffers.Test/DynamicMessageTest.cs
@@ -21,7 +21,7 @@ namespace Google.ProtocolBuffers {
     public void DynamicMessageAccessors() {
       IBuilder builder = DynamicMessage.CreateBuilder(TestAllTypes.Descriptor);
       reflectionTester.SetAllFieldsViaReflection(builder);
-      IMessage message = builder.Build();
+      IMessage message = builder.WeakBuild();
       reflectionTester.AssertAllFieldsSetViaReflection(message);
     }
 
@@ -32,7 +32,7 @@ namespace Google.ProtocolBuffers {
     // It treats them just like any other fields.
     IBuilder builder = DynamicMessage.CreateBuilder(TestAllExtensions.Descriptor);
     extensionsReflectionTester.SetAllFieldsViaReflection(builder);
-    IMessage message = builder.Build();
+    IMessage message = builder.WeakBuild();
     extensionsReflectionTester.AssertAllFieldsSetViaReflection(message);
   }
 
@@ -41,7 +41,7 @@ namespace Google.ProtocolBuffers {
       IBuilder builder = DynamicMessage.CreateBuilder(TestAllTypes.Descriptor);
       reflectionTester.SetAllFieldsViaReflection(builder);
       reflectionTester.ModifyRepeatedFieldsViaReflection(builder);
-      IMessage message = builder.Build();
+      IMessage message = builder.WeakBuild();
       reflectionTester.AssertRepeatedFieldsModifiedViaReflection(message);
     }
 
@@ -57,7 +57,7 @@ namespace Google.ProtocolBuffers {
 
       IBuilder dynamicBuilder = DynamicMessage.CreateBuilder(TestAllTypes.Descriptor);
       reflectionTester.SetAllFieldsViaReflection(dynamicBuilder);
-      IMessage dynamicMessage = dynamicBuilder.Build();
+      IMessage dynamicMessage = dynamicBuilder.WeakBuild();
 
       Assert.AreEqual(message.SerializedSize, dynamicMessage.SerializedSize);
     }
@@ -66,7 +66,7 @@ namespace Google.ProtocolBuffers {
     public void DynamicMessageSerialization() {
       IBuilder builder =  DynamicMessage.CreateBuilder(TestAllTypes.Descriptor);
       reflectionTester.SetAllFieldsViaReflection(builder);
-      IMessage message = builder.Build();
+      IMessage message = builder.WeakBuild();
 
       ByteString rawBytes = message.ToByteString();
       TestAllTypes message2 = TestAllTypes.ParseFrom(rawBytes);
diff --git a/csharp/ProtocolBuffers.Test/MessageTest.cs b/csharp/ProtocolBuffers.Test/MessageTest.cs
index 60aa3d17..04bea0a5 100644
--- a/csharp/ProtocolBuffers.Test/MessageTest.cs
+++ b/csharp/ProtocolBuffers.Test/MessageTest.cs
@@ -153,8 +153,7 @@ namespace Google.ProtocolBuffers {
       builder[descriptor.FindDescriptor<FieldDescriptor>("optional_message")] = TestRequiredInitialized;
       Assert.IsTrue(builder.IsInitialized);
 
-      // TODO(jonskeet): Remove this nastiness by making IBuilder always generic.
-      ((IBuilder) builder).AddRepeatedField(descriptor.FindDescriptor<FieldDescriptor>("repeated_message"), TestRequiredUninitialized);
+      builder.AddRepeatedField(descriptor.FindDescriptor<FieldDescriptor>("repeated_message"), TestRequiredUninitialized);
       Assert.IsFalse(builder.IsInitialized);
 
       builder.SetRepeatedField(descriptor.FindDescriptor<FieldDescriptor>("repeated_message"), 0, TestRequiredInitialized);
@@ -266,8 +265,7 @@ namespace Google.ProtocolBuffers {
     [Test]
     public void DynamicBuildPartial() {
       // We're mostly testing that no exception is thrown.
-      // TODO(jonskeet): Fix this ghastly casting mess
-      DynamicMessage message = (DynamicMessage) ((IBuilder) DynamicMessage.CreateBuilder(TestRequired.Descriptor)).BuildPartial();
+      DynamicMessage message = DynamicMessage.CreateBuilder(TestRequired.Descriptor).BuildPartial();
       Assert.IsFalse(message.Initialized);
     }
 
diff --git a/csharp/ProtocolBuffers.Test/ReflectionTester.cs b/csharp/ProtocolBuffers.Test/ReflectionTester.cs
index 3c57c653..67c26106 100644
--- a/csharp/ProtocolBuffers.Test/ReflectionTester.cs
+++ b/csharp/ProtocolBuffers.Test/ReflectionTester.cs
@@ -170,7 +170,7 @@ namespace Google.ProtocolBuffers {
         ExtensionInfo extension = extensionRegistry[field.ContainingType, field.FieldNumber];
         Assert.IsNotNull(extension);
         Assert.IsNotNull(extension.DefaultInstance);
-        return extension.DefaultInstance.CreateBuilderForType();
+        return extension.DefaultInstance.WeakCreateBuilderForType();
       }
     }
 
@@ -196,10 +196,10 @@ namespace Google.ProtocolBuffers {
       message[f("optional_string"  )] = "115";
       message[f("optional_bytes")] = TestUtil.ToBytes("116");
 
-      message[f("optionalgroup")] = CreateBuilderForField(message, f("optionalgroup")).SetField(groupA, 117).Build();
-      message[f("optional_nested_message")] = CreateBuilderForField(message, f("optional_nested_message")).SetField(nestedB, 118).Build();
-      message[f("optional_foreign_message")] = CreateBuilderForField(message, f("optional_foreign_message")).SetField(foreignC, 119).Build();
-      message[f("optional_import_message")] = CreateBuilderForField(message, f("optional_import_message")).SetField(importD, 120).Build();
+      message[f("optionalgroup")] = CreateBuilderForField(message, f("optionalgroup")).SetField(groupA, 117).WeakBuild();
+      message[f("optional_nested_message")] = CreateBuilderForField(message, f("optional_nested_message")).SetField(nestedB, 118).WeakBuild();
+      message[f("optional_foreign_message")] = CreateBuilderForField(message, f("optional_foreign_message")).SetField(foreignC, 119).WeakBuild();
+      message[f("optional_import_message")] = CreateBuilderForField(message, f("optional_import_message")).SetField(importD, 120).WeakBuild();
 
       message[f("optional_nested_enum" )] =  nestedBaz;
       message[f("optional_foreign_enum")] = foreignBaz;
@@ -210,71 +210,71 @@ namespace Google.ProtocolBuffers {
 
       // -----------------------------------------------------------------
 
-      message.AddRepeatedField(f("repeated_int32"   ), 201 );
-      message.AddRepeatedField(f("repeated_int64"   ), 202L);
-      message.AddRepeatedField(f("repeated_uint32"  ), 203U );
-      message.AddRepeatedField(f("repeated_uint64"  ), 204UL);
-      message.AddRepeatedField(f("repeated_sint32"  ), 205 );
-      message.AddRepeatedField(f("repeated_sint64"  ), 206L);
-      message.AddRepeatedField(f("repeated_fixed32" ), 207U );
-      message.AddRepeatedField(f("repeated_fixed64" ), 208UL);
-      message.AddRepeatedField(f("repeated_sfixed32"), 209 );
-      message.AddRepeatedField(f("repeated_sfixed64"), 210L);
-      message.AddRepeatedField(f("repeated_float"   ), 211F);
-      message.AddRepeatedField(f("repeated_double"  ), 212D);
-      message.AddRepeatedField(f("repeated_bool"    ), true);
-      message.AddRepeatedField(f("repeated_string"  ), "215");
-      message.AddRepeatedField(f("repeated_bytes"   ), TestUtil.ToBytes("216"));
-
-
-      message.AddRepeatedField(f("repeatedgroup"), CreateBuilderForField(message, f("repeatedgroup")).SetField(repeatedGroupA, 217).Build());
-      message.AddRepeatedField(f("repeated_nested_message"), CreateBuilderForField(message, f("repeated_nested_message")).SetField(nestedB, 218).Build());
-      message.AddRepeatedField(f("repeated_foreign_message"), CreateBuilderForField(message, f("repeated_foreign_message")).SetField(foreignC, 219).Build());
-      message.AddRepeatedField(f("repeated_import_message"), CreateBuilderForField(message, f("repeated_import_message")).SetField(importD, 220).Build());
-
-      message.AddRepeatedField(f("repeated_nested_enum" ),  nestedBar);
-      message.AddRepeatedField(f("repeated_foreign_enum"), foreignBar);
-      message.AddRepeatedField(f("repeated_import_enum" ),  importBar);
-
-      message.AddRepeatedField(f("repeated_string_piece" ), "224");
-      message.AddRepeatedField(f("repeated_cord" ), "225");
+      message.WeakAddRepeatedField(f("repeated_int32"   ), 201 );
+      message.WeakAddRepeatedField(f("repeated_int64"   ), 202L);
+      message.WeakAddRepeatedField(f("repeated_uint32"  ), 203U );
+      message.WeakAddRepeatedField(f("repeated_uint64"  ), 204UL);
+      message.WeakAddRepeatedField(f("repeated_sint32"  ), 205 );
+      message.WeakAddRepeatedField(f("repeated_sint64"  ), 206L);
+      message.WeakAddRepeatedField(f("repeated_fixed32" ), 207U );
+      message.WeakAddRepeatedField(f("repeated_fixed64" ), 208UL);
+      message.WeakAddRepeatedField(f("repeated_sfixed32"), 209 );
+      message.WeakAddRepeatedField(f("repeated_sfixed64"), 210L);
+      message.WeakAddRepeatedField(f("repeated_float"   ), 211F);
+      message.WeakAddRepeatedField(f("repeated_double"  ), 212D);
+      message.WeakAddRepeatedField(f("repeated_bool"    ), true);
+      message.WeakAddRepeatedField(f("repeated_string"  ), "215");
+      message.WeakAddRepeatedField(f("repeated_bytes"   ), TestUtil.ToBytes("216"));
+
+
+      message.WeakAddRepeatedField(f("repeatedgroup"), CreateBuilderForField(message, f("repeatedgroup")).SetField(repeatedGroupA, 217).WeakBuild());
+      message.WeakAddRepeatedField(f("repeated_nested_message"), CreateBuilderForField(message, f("repeated_nested_message")).SetField(nestedB, 218).WeakBuild());
+      message.WeakAddRepeatedField(f("repeated_foreign_message"), CreateBuilderForField(message, f("repeated_foreign_message")).SetField(foreignC, 219).WeakBuild());
+      message.WeakAddRepeatedField(f("repeated_import_message"), CreateBuilderForField(message, f("repeated_import_message")).SetField(importD, 220).WeakBuild());
+
+      message.WeakAddRepeatedField(f("repeated_nested_enum" ),  nestedBar);
+      message.WeakAddRepeatedField(f("repeated_foreign_enum"), foreignBar);
+      message.WeakAddRepeatedField(f("repeated_import_enum" ),  importBar);
+
+      message.WeakAddRepeatedField(f("repeated_string_piece" ), "224");
+      message.WeakAddRepeatedField(f("repeated_cord" ), "225");
 
       // Add a second one of each field.
-      message.AddRepeatedField(f("repeated_int32"   ), 301 );
-      message.AddRepeatedField(f("repeated_int64"   ), 302L);
-      message.AddRepeatedField(f("repeated_uint32"  ), 303U );
-      message.AddRepeatedField(f("repeated_uint64"  ), 304UL);
-      message.AddRepeatedField(f("repeated_sint32"  ), 305 );
-      message.AddRepeatedField(f("repeated_sint64"  ), 306L);
-      message.AddRepeatedField(f("repeated_fixed32" ), 307U );
-      message.AddRepeatedField(f("repeated_fixed64" ), 308UL);
-      message.AddRepeatedField(f("repeated_sfixed32"), 309 );
-      message.AddRepeatedField(f("repeated_sfixed64"), 310L);
-      message.AddRepeatedField(f("repeated_float"   ), 311F);
-      message.AddRepeatedField(f("repeated_double"  ), 312D);
-      message.AddRepeatedField(f("repeated_bool"    ), false);
-      message.AddRepeatedField(f("repeated_string"  ), "315");
-      message.AddRepeatedField(f("repeated_bytes"   ), TestUtil.ToBytes("316"));
-
-      message.AddRepeatedField(f("repeatedgroup"),
+      message.WeakAddRepeatedField(f("repeated_int32"   ), 301 );
+      message.WeakAddRepeatedField(f("repeated_int64"   ), 302L);
+      message.WeakAddRepeatedField(f("repeated_uint32"  ), 303U );
+      message.WeakAddRepeatedField(f("repeated_uint64"  ), 304UL);
+      message.WeakAddRepeatedField(f("repeated_sint32"  ), 305 );
+      message.WeakAddRepeatedField(f("repeated_sint64"  ), 306L);
+      message.WeakAddRepeatedField(f("repeated_fixed32" ), 307U );
+      message.WeakAddRepeatedField(f("repeated_fixed64" ), 308UL);
+      message.WeakAddRepeatedField(f("repeated_sfixed32"), 309 );
+      message.WeakAddRepeatedField(f("repeated_sfixed64"), 310L);
+      message.WeakAddRepeatedField(f("repeated_float"   ), 311F);
+      message.WeakAddRepeatedField(f("repeated_double"  ), 312D);
+      message.WeakAddRepeatedField(f("repeated_bool"    ), false);
+      message.WeakAddRepeatedField(f("repeated_string"  ), "315");
+      message.WeakAddRepeatedField(f("repeated_bytes"   ), TestUtil.ToBytes("316"));
+
+      message.WeakAddRepeatedField(f("repeatedgroup"),
         CreateBuilderForField(message, f("repeatedgroup"))
-               .SetField(repeatedGroupA, 317).Build());
-      message.AddRepeatedField(f("repeated_nested_message"),
+               .SetField(repeatedGroupA, 317).WeakBuild());
+      message.WeakAddRepeatedField(f("repeated_nested_message"),
         CreateBuilderForField(message, f("repeated_nested_message"))
-               .SetField(nestedB, 318).Build());
-      message.AddRepeatedField(f("repeated_foreign_message"),
+               .SetField(nestedB, 318).WeakBuild());
+      message.WeakAddRepeatedField(f("repeated_foreign_message"),
         CreateBuilderForField(message, f("repeated_foreign_message"))
-               .SetField(foreignC, 319).Build());
-      message.AddRepeatedField(f("repeated_import_message"),
+               .SetField(foreignC, 319).WeakBuild());
+      message.WeakAddRepeatedField(f("repeated_import_message"),
         CreateBuilderForField(message, f("repeated_import_message"))
-               .SetField(importD, 320).Build());
+               .SetField(importD, 320).WeakBuild());
 
-      message.AddRepeatedField(f("repeated_nested_enum" ),  nestedBaz);
-      message.AddRepeatedField(f("repeated_foreign_enum"), foreignBaz);
-      message.AddRepeatedField(f("repeated_import_enum" ),  importBaz);
+      message.WeakAddRepeatedField(f("repeated_nested_enum" ),  nestedBaz);
+      message.WeakAddRepeatedField(f("repeated_foreign_enum"), foreignBaz);
+      message.WeakAddRepeatedField(f("repeated_import_enum" ),  importBaz);
 
-      message.AddRepeatedField(f("repeated_string_piece" ), "324");
-      message.AddRepeatedField(f("repeated_cord" ), "325");
+      message.WeakAddRepeatedField(f("repeated_string_piece" ), "324");
+      message.WeakAddRepeatedField(f("repeated_cord" ), "325");
 
       // -----------------------------------------------------------------
 
@@ -326,10 +326,10 @@ namespace Google.ProtocolBuffers {
       message[f("repeated_string"  ), 1] = "515";
       message.SetRepeatedField(f("repeated_bytes"   ), 1, TestUtil.ToBytes("516"));
 
-      message.SetRepeatedField(f("repeatedgroup"), 1, CreateBuilderForField(message, f("repeatedgroup")).SetField(repeatedGroupA, 517).Build());
-      message.SetRepeatedField(f("repeated_nested_message"), 1, CreateBuilderForField(message, f("repeated_nested_message")).SetField(nestedB, 518).Build());
-      message.SetRepeatedField(f("repeated_foreign_message"), 1, CreateBuilderForField(message, f("repeated_foreign_message")).SetField(foreignC, 519).Build());
-      message.SetRepeatedField(f("repeated_import_message"), 1, CreateBuilderForField(message, f("repeated_import_message")).SetField(importD, 520).Build());
+      message.SetRepeatedField(f("repeatedgroup"), 1, CreateBuilderForField(message, f("repeatedgroup")).SetField(repeatedGroupA, 517).WeakBuild());
+      message.SetRepeatedField(f("repeated_nested_message"), 1, CreateBuilderForField(message, f("repeated_nested_message")).SetField(nestedB, 518).WeakBuild());
+      message.SetRepeatedField(f("repeated_foreign_message"), 1, CreateBuilderForField(message, f("repeated_foreign_message")).SetField(foreignC, 519).WeakBuild());
+      message.SetRepeatedField(f("repeated_import_message"), 1, CreateBuilderForField(message, f("repeated_import_message")).SetField(importD, 520).WeakBuild());
 
       message[f("repeated_nested_enum" ), 1] =  nestedFoo;
       message[f("repeated_foreign_enum"), 1] = foreignFoo;
diff --git a/csharp/ProtocolBuffers.Test/TestProtos/MessageWithNoOuter.cs b/csharp/ProtocolBuffers.Test/TestProtos/MessageWithNoOuter.cs
index 860b7a03..6c5ec24f 100644
--- a/csharp/ProtocolBuffers.Test/TestProtos/MessageWithNoOuter.cs
+++ b/csharp/ProtocolBuffers.Test/TestProtos/MessageWithNoOuter.cs
@@ -95,12 +95,16 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
         
         public static Builder CreateBuilder() { return new Builder(); }
-        public override IBuilder<self::MessageWithNoOuter.Types.NestedMessage> CreateBuilderForType() { return new Builder(); }
+        public override Builder CreateBuilderForType() { return new Builder(); }
         public static Builder CreateBuilder(self::MessageWithNoOuter.Types.NestedMessage prototype) {
           return (Builder) new Builder().MergeFrom(prototype);
         }
         
         public sealed partial class Builder : pb::GeneratedBuilder<self::MessageWithNoOuter.Types.NestedMessage, Builder> {
+          protected override Builder ThisBuilder {
+            get { return this; }
+          }
+          
           // Construct using self::MessageWithNoOuter.Types.NestedMessage.CreateBuilder()
           internal Builder() {}
           
@@ -110,12 +114,12 @@ namespace Google.ProtocolBuffers.TestProtos {
             get { return result; }
           }
           
-          public override IBuilder<self::MessageWithNoOuter.Types.NestedMessage> Clear() {
+          public override Builder Clear() {
             result = new self::MessageWithNoOuter.Types.NestedMessage();
             return this;
           }
           
-          public override IBuilder<self::MessageWithNoOuter.Types.NestedMessage> Clone() {
+          public override Builder Clone() {
             return new Builder().MergeFrom(result);
           }
           
@@ -231,12 +235,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::MessageWithNoOuter> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::MessageWithNoOuter prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::MessageWithNoOuter, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::MessageWithNoOuter.CreateBuilder()
       internal Builder() {}
       
@@ -246,12 +254,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::MessageWithNoOuter> Clear() {
+      public override Builder Clear() {
         result = new self::MessageWithNoOuter();
         return this;
       }
       
-      public override IBuilder<self::MessageWithNoOuter> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
diff --git a/csharp/ProtocolBuffers.Test/TestProtos/MultiFileProto.cs b/csharp/ProtocolBuffers.Test/TestProtos/MultiFileProto.cs
index 05a99876..a96aae0d 100644
--- a/csharp/ProtocolBuffers.Test/TestProtos/MultiFileProto.cs
+++ b/csharp/ProtocolBuffers.Test/TestProtos/MultiFileProto.cs
@@ -59,8 +59,8 @@ namespace Google.ProtocolBuffers.TestProtos {
     #endregion
     
     #region Extensions
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, int> ExtensionWithOuter =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, int>.CreateInstance(Descriptor.Extensions[0]);
+    public static readonly pb::GeneratedExtensionBase<int> ExtensionWithOuter =
+          pb::GeneratedSingleExtension<int>.CreateInstance(Descriptor.Extensions[0]);
     #endregion
     
     #region Static variables
diff --git a/csharp/ProtocolBuffers.Test/TestProtos/ServiceWithNoOuter.cs b/csharp/ProtocolBuffers.Test/TestProtos/ServiceWithNoOuter.cs
index 61dfcc3c..8b5d97ee 100644
--- a/csharp/ProtocolBuffers.Test/TestProtos/ServiceWithNoOuter.cs
+++ b/csharp/ProtocolBuffers.Test/TestProtos/ServiceWithNoOuter.cs
@@ -95,7 +95,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           controller,
           request,
           self::TestAllTypes.DefaultInstance,
-          pb::RpcUtil.GeneralizeCallback(done, self::TestAllTypes.DefaultInstance));
+          pb::RpcUtil.GeneralizeCallback<self::TestAllTypes, self::TestAllTypes.Builder>(done, self::TestAllTypes.DefaultInstance));
       }
     }
   }
diff --git a/csharp/ProtocolBuffers.Test/TestProtos/UnitTestEmbedOptimizeForProtoFile.cs b/csharp/ProtocolBuffers.Test/TestProtos/UnitTestEmbedOptimizeForProtoFile.cs
index b96c7c9e..d9459e29 100644
--- a/csharp/ProtocolBuffers.Test/TestProtos/UnitTestEmbedOptimizeForProtoFile.cs
+++ b/csharp/ProtocolBuffers.Test/TestProtos/UnitTestEmbedOptimizeForProtoFile.cs
@@ -174,12 +174,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::TestEmbedOptimizedForSize> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::TestEmbedOptimizedForSize prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::TestEmbedOptimizedForSize, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::TestEmbedOptimizedForSize.CreateBuilder()
       internal Builder() {}
       
@@ -189,12 +193,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::TestEmbedOptimizedForSize> Clear() {
+      public override Builder Clear() {
         result = new self::TestEmbedOptimizedForSize();
         return this;
       }
       
-      public override IBuilder<self::TestEmbedOptimizedForSize> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -215,11 +219,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::TestEmbedOptimizedForSize) {
           return MergeFrom((self::TestEmbedOptimizedForSize) other);
         } else {
@@ -228,7 +228,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
       }
       
-      public override IBuilder<self::TestEmbedOptimizedForSize> MergeFrom(self::TestEmbedOptimizedForSize other) {
+      public override Builder MergeFrom(self::TestEmbedOptimizedForSize other) {
         if (other == self::TestEmbedOptimizedForSize.DefaultInstance) return this;
         if (other.HasOptionalMessage) {
           MergeOptionalMessage(other.OptionalMessage);
@@ -243,11 +243,11 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       
-      public override IBuilder<self::TestEmbedOptimizedForSize> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::TestEmbedOptimizedForSize> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
diff --git a/csharp/ProtocolBuffers.Test/TestProtos/UnitTestImportProtoFile.cs b/csharp/ProtocolBuffers.Test/TestProtos/UnitTestImportProtoFile.cs
index d798070c..5d5a546b 100644
--- a/csharp/ProtocolBuffers.Test/TestProtos/UnitTestImportProtoFile.cs
+++ b/csharp/ProtocolBuffers.Test/TestProtos/UnitTestImportProtoFile.cs
@@ -150,12 +150,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::ImportMessage> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::ImportMessage prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::ImportMessage, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::ImportMessage.CreateBuilder()
       internal Builder() {}
       
@@ -165,12 +169,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::ImportMessage> Clear() {
+      public override Builder Clear() {
         result = new self::ImportMessage();
         return this;
       }
       
-      public override IBuilder<self::ImportMessage> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -188,11 +192,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::ImportMessage) {
           return MergeFrom((self::ImportMessage) other);
         } else {
@@ -201,7 +201,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
       }
       
-      public override IBuilder<self::ImportMessage> MergeFrom(self::ImportMessage other) {
+      public override Builder MergeFrom(self::ImportMessage other) {
         if (other == self::ImportMessage.DefaultInstance) return this;
         if (other.HasD) {
           D = other.D;
@@ -210,11 +210,11 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       
-      public override IBuilder<self::ImportMessage> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::ImportMessage> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
diff --git a/csharp/ProtocolBuffers.Test/TestProtos/UnitTestMessageSetProtoFile.cs b/csharp/ProtocolBuffers.Test/TestProtos/UnitTestMessageSetProtoFile.cs
index dc2c62b1..8599f65b 100644
--- a/csharp/ProtocolBuffers.Test/TestProtos/UnitTestMessageSetProtoFile.cs
+++ b/csharp/ProtocolBuffers.Test/TestProtos/UnitTestMessageSetProtoFile.cs
@@ -188,12 +188,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::TestMessageSet> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::TestMessageSet prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::ExtendableBuilder<self::TestMessageSet, self::TestMessageSet.Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::TestMessageSet.CreateBuilder()
       internal Builder() {}
       
@@ -203,12 +207,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::TestMessageSet> Clear() {
+      public override Builder Clear() {
         result = new self::TestMessageSet();
         return this;
       }
       
-      public override IBuilder<self::TestMessageSet> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -226,11 +230,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::TestMessageSet) {
           return MergeFrom((self::TestMessageSet) other);
         } else {
@@ -239,17 +239,17 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
       }
       
-      public override IBuilder<self::TestMessageSet> MergeFrom(self::TestMessageSet other) {
+      public override Builder MergeFrom(self::TestMessageSet other) {
         if (other == self::TestMessageSet.DefaultInstance) return this;
         this.MergeUnknownFields(other.UnknownFields);
         return this;
       }
       
-      public override IBuilder<self::TestMessageSet> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::TestMessageSet> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -368,12 +368,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::TestMessageSetContainer> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::TestMessageSetContainer prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::TestMessageSetContainer, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::TestMessageSetContainer.CreateBuilder()
       internal Builder() {}
       
@@ -383,12 +387,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::TestMessageSetContainer> Clear() {
+      public override Builder Clear() {
         result = new self::TestMessageSetContainer();
         return this;
       }
       
-      public override IBuilder<self::TestMessageSetContainer> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -406,11 +410,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::TestMessageSetContainer) {
           return MergeFrom((self::TestMessageSetContainer) other);
         } else {
@@ -419,7 +419,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
       }
       
-      public override IBuilder<self::TestMessageSetContainer> MergeFrom(self::TestMessageSetContainer other) {
+      public override Builder MergeFrom(self::TestMessageSetContainer other) {
         if (other == self::TestMessageSetContainer.DefaultInstance) return this;
         if (other.HasMessageSet) {
           MergeMessageSet(other.MessageSet);
@@ -428,11 +428,11 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       
-      public override IBuilder<self::TestMessageSetContainer> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::TestMessageSetContainer> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -520,8 +520,8 @@ namespace Google.ProtocolBuffers.TestProtos {
     
     #region Nested types
     public static class Types {
-      public static readonly pb::GeneratedExtensionBase<self::TestMessageSet, self::TestMessageSetExtension1> MessageSetExtension =
-            pb::GeneratedSingleExtension<self::TestMessageSet, self::TestMessageSetExtension1>.CreateInstance(Descriptor.Extensions[0]);
+      public static readonly pb::GeneratedExtensionBase<self::TestMessageSetExtension1> MessageSetExtension =
+            pb::GeneratedSingleExtension<self::TestMessageSetExtension1>.CreateInstance(Descriptor.Extensions[0]);
     }
     #endregion
     
@@ -599,12 +599,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::TestMessageSetExtension1> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::TestMessageSetExtension1 prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::TestMessageSetExtension1, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::TestMessageSetExtension1.CreateBuilder()
       internal Builder() {}
       
@@ -614,12 +618,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::TestMessageSetExtension1> Clear() {
+      public override Builder Clear() {
         result = new self::TestMessageSetExtension1();
         return this;
       }
       
-      public override IBuilder<self::TestMessageSetExtension1> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -637,11 +641,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::TestMessageSetExtension1) {
           return MergeFrom((self::TestMessageSetExtension1) other);
         } else {
@@ -650,7 +650,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
       }
       
-      public override IBuilder<self::TestMessageSetExtension1> MergeFrom(self::TestMessageSetExtension1 other) {
+      public override Builder MergeFrom(self::TestMessageSetExtension1 other) {
         if (other == self::TestMessageSetExtension1.DefaultInstance) return this;
         if (other.HasI) {
           I = other.I;
@@ -659,11 +659,11 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       
-      public override IBuilder<self::TestMessageSetExtension1> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::TestMessageSetExtension1> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -730,8 +730,8 @@ namespace Google.ProtocolBuffers.TestProtos {
     
     #region Nested types
     public static class Types {
-      public static readonly pb::GeneratedExtensionBase<self::TestMessageSet, self::TestMessageSetExtension2> MessageSetExtension =
-            pb::GeneratedSingleExtension<self::TestMessageSet, self::TestMessageSetExtension2>.CreateInstance(Descriptor.Extensions[0]);
+      public static readonly pb::GeneratedExtensionBase<self::TestMessageSetExtension2> MessageSetExtension =
+            pb::GeneratedSingleExtension<self::TestMessageSetExtension2>.CreateInstance(Descriptor.Extensions[0]);
     }
     #endregion
     
@@ -809,12 +809,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::TestMessageSetExtension2> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::TestMessageSetExtension2 prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::TestMessageSetExtension2, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::TestMessageSetExtension2.CreateBuilder()
       internal Builder() {}
       
@@ -824,12 +828,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::TestMessageSetExtension2> Clear() {
+      public override Builder Clear() {
         result = new self::TestMessageSetExtension2();
         return this;
       }
       
-      public override IBuilder<self::TestMessageSetExtension2> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -847,11 +851,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::TestMessageSetExtension2) {
           return MergeFrom((self::TestMessageSetExtension2) other);
         } else {
@@ -860,7 +860,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
       }
       
-      public override IBuilder<self::TestMessageSetExtension2> MergeFrom(self::TestMessageSetExtension2 other) {
+      public override Builder MergeFrom(self::TestMessageSetExtension2 other) {
         if (other == self::TestMessageSetExtension2.DefaultInstance) return this;
         if (other.HasStr) {
           Str = other.Str;
@@ -869,11 +869,11 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       
-      public override IBuilder<self::TestMessageSetExtension2> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::TestMessageSetExtension2> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -1050,12 +1050,16 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
         
         public static Builder CreateBuilder() { return new Builder(); }
-        public override IBuilder<self::RawMessageSet.Types.Item> CreateBuilderForType() { return new Builder(); }
+        public override Builder CreateBuilderForType() { return new Builder(); }
         public static Builder CreateBuilder(self::RawMessageSet.Types.Item prototype) {
           return (Builder) new Builder().MergeFrom(prototype);
         }
         
         public sealed partial class Builder : pb::GeneratedBuilder<self::RawMessageSet.Types.Item, Builder> {
+          protected override Builder ThisBuilder {
+            get { return this; }
+          }
+          
           // Construct using self::RawMessageSet.Types.Item.CreateBuilder()
           internal Builder() {}
           
@@ -1065,12 +1069,12 @@ namespace Google.ProtocolBuffers.TestProtos {
             get { return result; }
           }
           
-          public override IBuilder<self::RawMessageSet.Types.Item> Clear() {
+          public override Builder Clear() {
             result = new self::RawMessageSet.Types.Item();
             return this;
           }
           
-          public override IBuilder<self::RawMessageSet.Types.Item> Clone() {
+          public override Builder Clone() {
             return new Builder().MergeFrom(result);
           }
           
@@ -1088,11 +1092,7 @@ namespace Google.ProtocolBuffers.TestProtos {
             return returnMe;
           }
           
-          protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-            return MergeFrom(data, extensionRegistry);
-          }
-          
-          public override IBuilder MergeFrom(pb::IMessage other) {
+          public override Builder MergeFrom(pb::IMessage other) {
             if (other is self::RawMessageSet.Types.Item) {
               return MergeFrom((self::RawMessageSet.Types.Item) other);
             } else {
@@ -1101,7 +1101,7 @@ namespace Google.ProtocolBuffers.TestProtos {
             }
           }
           
-          public override IBuilder<self::RawMessageSet.Types.Item> MergeFrom(self::RawMessageSet.Types.Item other) {
+          public override Builder MergeFrom(self::RawMessageSet.Types.Item other) {
             if (other == self::RawMessageSet.Types.Item.DefaultInstance) return this;
             if (other.HasTypeId) {
               TypeId = other.TypeId;
@@ -1113,11 +1113,11 @@ namespace Google.ProtocolBuffers.TestProtos {
             return this;
           }
           
-          public override IBuilder<self::RawMessageSet.Types.Item> MergeFrom(pb::CodedInputStream input) {
+          public override Builder MergeFrom(pb::CodedInputStream input) {
             return MergeFrom(input, pb::ExtensionRegistry.Empty);
           }
           
-          public override IBuilder<self::RawMessageSet.Types.Item> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+          public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
             pb::UnknownFieldSet.Builder unknownFields =
               pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
             while (true) {
@@ -1269,12 +1269,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::RawMessageSet> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::RawMessageSet prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::RawMessageSet, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::RawMessageSet.CreateBuilder()
       internal Builder() {}
       
@@ -1284,12 +1288,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::RawMessageSet> Clear() {
+      public override Builder Clear() {
         result = new self::RawMessageSet();
         return this;
       }
       
-      public override IBuilder<self::RawMessageSet> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -1310,11 +1314,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::RawMessageSet) {
           return MergeFrom((self::RawMessageSet) other);
         } else {
@@ -1323,7 +1323,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
       }
       
-      public override IBuilder<self::RawMessageSet> MergeFrom(self::RawMessageSet other) {
+      public override Builder MergeFrom(self::RawMessageSet other) {
         if (other == self::RawMessageSet.DefaultInstance) return this;
         if (other.item_.Count != 0) {
           if (result.item_.Count == 0) {
@@ -1335,11 +1335,11 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       
-      public override IBuilder<self::RawMessageSet> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::RawMessageSet> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
diff --git a/csharp/ProtocolBuffers.Test/TestProtos/UnitTestOptimizeForProtoFile.cs b/csharp/ProtocolBuffers.Test/TestProtos/UnitTestOptimizeForProtoFile.cs
index fd647c1a..b38a26b1 100644
--- a/csharp/ProtocolBuffers.Test/TestProtos/UnitTestOptimizeForProtoFile.cs
+++ b/csharp/ProtocolBuffers.Test/TestProtos/UnitTestOptimizeForProtoFile.cs
@@ -77,8 +77,8 @@ namespace Google.ProtocolBuffers.TestProtos {
     
     #region Nested types
     public static class Types {
-      public static readonly pb::GeneratedExtensionBase<self::TestOptimizedForSize, int> TestExtension =
-            pb::GeneratedSingleExtension<self::TestOptimizedForSize, int>.CreateInstance(Descriptor.Extensions[0]);
+      public static readonly pb::GeneratedExtensionBase<int> TestExtension =
+            pb::GeneratedSingleExtension<int>.CreateInstance(Descriptor.Extensions[0]);
     }
     #endregion
     
@@ -137,12 +137,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::TestOptimizedForSize> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::TestOptimizedForSize prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::ExtendableBuilder<self::TestOptimizedForSize, self::TestOptimizedForSize.Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::TestOptimizedForSize.CreateBuilder()
       internal Builder() {}
       
@@ -152,12 +156,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::TestOptimizedForSize> Clear() {
+      public override Builder Clear() {
         result = new self::TestOptimizedForSize();
         return this;
       }
       
-      public override IBuilder<self::TestOptimizedForSize> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
diff --git a/csharp/ProtocolBuffers.Test/TestProtos/UnitTestProtoFile.cs b/csharp/ProtocolBuffers.Test/TestProtos/UnitTestProtoFile.cs
index bf6a3543..4c7dd75d 100644
--- a/csharp/ProtocolBuffers.Test/TestProtos/UnitTestProtoFile.cs
+++ b/csharp/ProtocolBuffers.Test/TestProtos/UnitTestProtoFile.cs
@@ -632,170 +632,170 @@ namespace Google.ProtocolBuffers.TestProtos {
     #endregion
     
     #region Extensions
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, int> OptionalInt32Extension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, int>.CreateInstance(Descriptor.Extensions[0]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, long> OptionalInt64Extension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, long>.CreateInstance(Descriptor.Extensions[1]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, uint> OptionalUint32Extension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, uint>.CreateInstance(Descriptor.Extensions[2]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, ulong> OptionalUint64Extension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, ulong>.CreateInstance(Descriptor.Extensions[3]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, int> OptionalSint32Extension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, int>.CreateInstance(Descriptor.Extensions[4]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, long> OptionalSint64Extension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, long>.CreateInstance(Descriptor.Extensions[5]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, uint> OptionalFixed32Extension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, uint>.CreateInstance(Descriptor.Extensions[6]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, ulong> OptionalFixed64Extension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, ulong>.CreateInstance(Descriptor.Extensions[7]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, int> OptionalSfixed32Extension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, int>.CreateInstance(Descriptor.Extensions[8]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, long> OptionalSfixed64Extension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, long>.CreateInstance(Descriptor.Extensions[9]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, float> OptionalFloatExtension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, float>.CreateInstance(Descriptor.Extensions[10]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, double> OptionalDoubleExtension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, double>.CreateInstance(Descriptor.Extensions[11]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, bool> OptionalBoolExtension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, bool>.CreateInstance(Descriptor.Extensions[12]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, string> OptionalStringExtension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, string>.CreateInstance(Descriptor.Extensions[13]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, pb::ByteString> OptionalBytesExtension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, pb::ByteString>.CreateInstance(Descriptor.Extensions[14]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, self::OptionalGroup_extension> OptionalGroupExtension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, self::OptionalGroup_extension>.CreateInstance(Descriptor.Extensions[15]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, self::TestAllTypes.Types.NestedMessage> OptionalNestedMessageExtension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, self::TestAllTypes.Types.NestedMessage>.CreateInstance(Descriptor.Extensions[16]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, self::ForeignMessage> OptionalForeignMessageExtension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, self::ForeignMessage>.CreateInstance(Descriptor.Extensions[17]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, self::ImportMessage> OptionalImportMessageExtension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, self::ImportMessage>.CreateInstance(Descriptor.Extensions[18]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, self::TestAllTypes.Types.NestedEnum> OptionalNestedEnumExtension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, self::TestAllTypes.Types.NestedEnum>.CreateInstance(Descriptor.Extensions[19]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, self::ForeignEnum> OptionalForeignEnumExtension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, self::ForeignEnum>.CreateInstance(Descriptor.Extensions[20]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, self::ImportEnum> OptionalImportEnumExtension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, self::ImportEnum>.CreateInstance(Descriptor.Extensions[21]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, string> OptionalStringPieceExtension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, string>.CreateInstance(Descriptor.Extensions[22]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, string> OptionalCordExtension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, string>.CreateInstance(Descriptor.Extensions[23]);
+    public static readonly pb::GeneratedExtensionBase<int> OptionalInt32Extension =
+          pb::GeneratedSingleExtension<int>.CreateInstance(Descriptor.Extensions[0]);
+    public static readonly pb::GeneratedExtensionBase<long> OptionalInt64Extension =
+          pb::GeneratedSingleExtension<long>.CreateInstance(Descriptor.Extensions[1]);
+    public static readonly pb::GeneratedExtensionBase<uint> OptionalUint32Extension =
+          pb::GeneratedSingleExtension<uint>.CreateInstance(Descriptor.Extensions[2]);
+    public static readonly pb::GeneratedExtensionBase<ulong> OptionalUint64Extension =
+          pb::GeneratedSingleExtension<ulong>.CreateInstance(Descriptor.Extensions[3]);
+    public static readonly pb::GeneratedExtensionBase<int> OptionalSint32Extension =
+          pb::GeneratedSingleExtension<int>.CreateInstance(Descriptor.Extensions[4]);
+    public static readonly pb::GeneratedExtensionBase<long> OptionalSint64Extension =
+          pb::GeneratedSingleExtension<long>.CreateInstance(Descriptor.Extensions[5]);
+    public static readonly pb::GeneratedExtensionBase<uint> OptionalFixed32Extension =
+          pb::GeneratedSingleExtension<uint>.CreateInstance(Descriptor.Extensions[6]);
+    public static readonly pb::GeneratedExtensionBase<ulong> OptionalFixed64Extension =
+          pb::GeneratedSingleExtension<ulong>.CreateInstance(Descriptor.Extensions[7]);
+    public static readonly pb::GeneratedExtensionBase<int> OptionalSfixed32Extension =
+          pb::GeneratedSingleExtension<int>.CreateInstance(Descriptor.Extensions[8]);
+    public static readonly pb::GeneratedExtensionBase<long> OptionalSfixed64Extension =
+          pb::GeneratedSingleExtension<long>.CreateInstance(Descriptor.Extensions[9]);
+    public static readonly pb::GeneratedExtensionBase<float> OptionalFloatExtension =
+          pb::GeneratedSingleExtension<float>.CreateInstance(Descriptor.Extensions[10]);
+    public static readonly pb::GeneratedExtensionBase<double> OptionalDoubleExtension =
+          pb::GeneratedSingleExtension<double>.CreateInstance(Descriptor.Extensions[11]);
+    public static readonly pb::GeneratedExtensionBase<bool> OptionalBoolExtension =
+          pb::GeneratedSingleExtension<bool>.CreateInstance(Descriptor.Extensions[12]);
+    public static readonly pb::GeneratedExtensionBase<string> OptionalStringExtension =
+          pb::GeneratedSingleExtension<string>.CreateInstance(Descriptor.Extensions[13]);
+    public static readonly pb::GeneratedExtensionBase<pb::ByteString> OptionalBytesExtension =
+          pb::GeneratedSingleExtension<pb::ByteString>.CreateInstance(Descriptor.Extensions[14]);
+    public static readonly pb::GeneratedExtensionBase<self::OptionalGroup_extension> OptionalGroupExtension =
+          pb::GeneratedSingleExtension<self::OptionalGroup_extension>.CreateInstance(Descriptor.Extensions[15]);
+    public static readonly pb::GeneratedExtensionBase<self::TestAllTypes.Types.NestedMessage> OptionalNestedMessageExtension =
+          pb::GeneratedSingleExtension<self::TestAllTypes.Types.NestedMessage>.CreateInstance(Descriptor.Extensions[16]);
+    public static readonly pb::GeneratedExtensionBase<self::ForeignMessage> OptionalForeignMessageExtension =
+          pb::GeneratedSingleExtension<self::ForeignMessage>.CreateInstance(Descriptor.Extensions[17]);
+    public static readonly pb::GeneratedExtensionBase<self::ImportMessage> OptionalImportMessageExtension =
+          pb::GeneratedSingleExtension<self::ImportMessage>.CreateInstance(Descriptor.Extensions[18]);
+    public static readonly pb::GeneratedExtensionBase<self::TestAllTypes.Types.NestedEnum> OptionalNestedEnumExtension =
+          pb::GeneratedSingleExtension<self::TestAllTypes.Types.NestedEnum>.CreateInstance(Descriptor.Extensions[19]);
+    public static readonly pb::GeneratedExtensionBase<self::ForeignEnum> OptionalForeignEnumExtension =
+          pb::GeneratedSingleExtension<self::ForeignEnum>.CreateInstance(Descriptor.Extensions[20]);
+    public static readonly pb::GeneratedExtensionBase<self::ImportEnum> OptionalImportEnumExtension =
+          pb::GeneratedSingleExtension<self::ImportEnum>.CreateInstance(Descriptor.Extensions[21]);
+    public static readonly pb::GeneratedExtensionBase<string> OptionalStringPieceExtension =
+          pb::GeneratedSingleExtension<string>.CreateInstance(Descriptor.Extensions[22]);
+    public static readonly pb::GeneratedExtensionBase<string> OptionalCordExtension =
+          pb::GeneratedSingleExtension<string>.CreateInstance(Descriptor.Extensions[23]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<int>> RepeatedInt32Extension =
-          pb::GeneratedRepeatExtension<self::TestAllExtensions, int>.CreateInstance(Descriptor.Extensions[24]);
+      pb::GeneratedExtensionBase<scg::IList<int>> RepeatedInt32Extension =
+          pb::GeneratedRepeatExtension<int>.CreateInstance(Descriptor.Extensions[24]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<long>> RepeatedInt64Extension =
-          pb::GeneratedRepeatExtension<self::TestAllExtensions, long>.CreateInstance(Descriptor.Extensions[25]);
+      pb::GeneratedExtensionBase<scg::IList<long>> RepeatedInt64Extension =
+          pb::GeneratedRepeatExtension<long>.CreateInstance(Descriptor.Extensions[25]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<uint>> RepeatedUint32Extension =
-          pb::GeneratedRepeatExtension<self::TestAllExtensions, uint>.CreateInstance(Descriptor.Extensions[26]);
+      pb::GeneratedExtensionBase<scg::IList<uint>> RepeatedUint32Extension =
+          pb::GeneratedRepeatExtension<uint>.CreateInstance(Descriptor.Extensions[26]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<ulong>> RepeatedUint64Extension =
-          pb::GeneratedRepeatExtension<self::TestAllExtensions, ulong>.CreateInstance(Descriptor.Extensions[27]);
+      pb::GeneratedExtensionBase<scg::IList<ulong>> RepeatedUint64Extension =
+          pb::GeneratedRepeatExtension<ulong>.CreateInstance(Descriptor.Extensions[27]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<int>> RepeatedSint32Extension =
-          pb::GeneratedRepeatExtension<self::TestAllExtensions, int>.CreateInstance(Descriptor.Extensions[28]);
+      pb::GeneratedExtensionBase<scg::IList<int>> RepeatedSint32Extension =
+          pb::GeneratedRepeatExtension<int>.CreateInstance(Descriptor.Extensions[28]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<long>> RepeatedSint64Extension =
-          pb::GeneratedRepeatExtension<self::TestAllExtensions, long>.CreateInstance(Descriptor.Extensions[29]);
+      pb::GeneratedExtensionBase<scg::IList<long>> RepeatedSint64Extension =
+          pb::GeneratedRepeatExtension<long>.CreateInstance(Descriptor.Extensions[29]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<uint>> RepeatedFixed32Extension =
-          pb::GeneratedRepeatExtension<self::TestAllExtensions, uint>.CreateInstance(Descriptor.Extensions[30]);
+      pb::GeneratedExtensionBase<scg::IList<uint>> RepeatedFixed32Extension =
+          pb::GeneratedRepeatExtension<uint>.CreateInstance(Descriptor.Extensions[30]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<ulong>> RepeatedFixed64Extension =
-          pb::GeneratedRepeatExtension<self::TestAllExtensions, ulong>.CreateInstance(Descriptor.Extensions[31]);
+      pb::GeneratedExtensionBase<scg::IList<ulong>> RepeatedFixed64Extension =
+          pb::GeneratedRepeatExtension<ulong>.CreateInstance(Descriptor.Extensions[31]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<int>> RepeatedSfixed32Extension =
-          pb::GeneratedRepeatExtension<self::TestAllExtensions, int>.CreateInstance(Descriptor.Extensions[32]);
+      pb::GeneratedExtensionBase<scg::IList<int>> RepeatedSfixed32Extension =
+          pb::GeneratedRepeatExtension<int>.CreateInstance(Descriptor.Extensions[32]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<long>> RepeatedSfixed64Extension =
-          pb::GeneratedRepeatExtension<self::TestAllExtensions, long>.CreateInstance(Descriptor.Extensions[33]);
+      pb::GeneratedExtensionBase<scg::IList<long>> RepeatedSfixed64Extension =
+          pb::GeneratedRepeatExtension<long>.CreateInstance(Descriptor.Extensions[33]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<float>> RepeatedFloatExtension =
-          pb::GeneratedRepeatExtension<self::TestAllExtensions, float>.CreateInstance(Descriptor.Extensions[34]);
+      pb::GeneratedExtensionBase<scg::IList<float>> RepeatedFloatExtension =
+          pb::GeneratedRepeatExtension<float>.CreateInstance(Descriptor.Extensions[34]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<double>> RepeatedDoubleExtension =
-          pb::GeneratedRepeatExtension<self::TestAllExtensions, double>.CreateInstance(Descriptor.Extensions[35]);
+      pb::GeneratedExtensionBase<scg::IList<double>> RepeatedDoubleExtension =
+          pb::GeneratedRepeatExtension<double>.CreateInstance(Descriptor.Extensions[35]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<bool>> RepeatedBoolExtension =
-          pb::GeneratedRepeatExtension<self::TestAllExtensions, bool>.CreateInstance(Descriptor.Extensions[36]);
+      pb::GeneratedExtensionBase<scg::IList<bool>> RepeatedBoolExtension =
+          pb::GeneratedRepeatExtension<bool>.CreateInstance(Descriptor.Extensions[36]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<string>> RepeatedStringExtension =
-          pb::GeneratedRepeatExtension<self::TestAllExtensions, string>.CreateInstance(Descriptor.Extensions[37]);
+      pb::GeneratedExtensionBase<scg::IList<string>> RepeatedStringExtension =
+          pb::GeneratedRepeatExtension<string>.CreateInstance(Descriptor.Extensions[37]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<pb::ByteString>> RepeatedBytesExtension =
-          pb::GeneratedRepeatExtension<self::TestAllExtensions, pb::ByteString>.CreateInstance(Descriptor.Extensions[38]);
+      pb::GeneratedExtensionBase<scg::IList<pb::ByteString>> RepeatedBytesExtension =
+          pb::GeneratedRepeatExtension<pb::ByteString>.CreateInstance(Descriptor.Extensions[38]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<self::RepeatedGroup_extension>> RepeatedGroupExtension =
-          pb::GeneratedRepeatExtension<self::TestAllExtensions, self::RepeatedGroup_extension>.CreateInstance(Descriptor.Extensions[39]);
+      pb::GeneratedExtensionBase<scg::IList<self::RepeatedGroup_extension>> RepeatedGroupExtension =
+          pb::GeneratedRepeatExtension<self::RepeatedGroup_extension>.CreateInstance(Descriptor.Extensions[39]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<self::TestAllTypes.Types.NestedMessage>> RepeatedNestedMessageExtension =
-          pb::GeneratedRepeatExtension<self::TestAllExtensions, self::TestAllTypes.Types.NestedMessage>.CreateInstance(Descriptor.Extensions[40]);
+      pb::GeneratedExtensionBase<scg::IList<self::TestAllTypes.Types.NestedMessage>> RepeatedNestedMessageExtension =
+          pb::GeneratedRepeatExtension<self::TestAllTypes.Types.NestedMessage>.CreateInstance(Descriptor.Extensions[40]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<self::ForeignMessage>> RepeatedForeignMessageExtension =
-          pb::GeneratedRepeatExtension<self::TestAllExtensions, self::ForeignMessage>.CreateInstance(Descriptor.Extensions[41]);
+      pb::GeneratedExtensionBase<scg::IList<self::ForeignMessage>> RepeatedForeignMessageExtension =
+          pb::GeneratedRepeatExtension<self::ForeignMessage>.CreateInstance(Descriptor.Extensions[41]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<self::ImportMessage>> RepeatedImportMessageExtension =
-          pb::GeneratedRepeatExtension<self::TestAllExtensions, self::ImportMessage>.CreateInstance(Descriptor.Extensions[42]);
+      pb::GeneratedExtensionBase<scg::IList<self::ImportMessage>> RepeatedImportMessageExtension =
+          pb::GeneratedRepeatExtension<self::ImportMessage>.CreateInstance(Descriptor.Extensions[42]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<self::TestAllTypes.Types.NestedEnum>> RepeatedNestedEnumExtension =
-          pb::GeneratedRepeatExtension<self::TestAllExtensions, self::TestAllTypes.Types.NestedEnum>.CreateInstance(Descriptor.Extensions[43]);
+      pb::GeneratedExtensionBase<scg::IList<self::TestAllTypes.Types.NestedEnum>> RepeatedNestedEnumExtension =
+          pb::GeneratedRepeatExtension<self::TestAllTypes.Types.NestedEnum>.CreateInstance(Descriptor.Extensions[43]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<self::ForeignEnum>> RepeatedForeignEnumExtension =
-          pb::GeneratedRepeatExtension<self::TestAllExtensions, self::ForeignEnum>.CreateInstance(Descriptor.Extensions[44]);
+      pb::GeneratedExtensionBase<scg::IList<self::ForeignEnum>> RepeatedForeignEnumExtension =
+          pb::GeneratedRepeatExtension<self::ForeignEnum>.CreateInstance(Descriptor.Extensions[44]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<self::ImportEnum>> RepeatedImportEnumExtension =
-          pb::GeneratedRepeatExtension<self::TestAllExtensions, self::ImportEnum>.CreateInstance(Descriptor.Extensions[45]);
+      pb::GeneratedExtensionBase<scg::IList<self::ImportEnum>> RepeatedImportEnumExtension =
+          pb::GeneratedRepeatExtension<self::ImportEnum>.CreateInstance(Descriptor.Extensions[45]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<string>> RepeatedStringPieceExtension =
-          pb::GeneratedRepeatExtension<self::TestAllExtensions, string>.CreateInstance(Descriptor.Extensions[46]);
+      pb::GeneratedExtensionBase<scg::IList<string>> RepeatedStringPieceExtension =
+          pb::GeneratedRepeatExtension<string>.CreateInstance(Descriptor.Extensions[46]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<string>> RepeatedCordExtension =
-          pb::GeneratedRepeatExtension<self::TestAllExtensions, string>.CreateInstance(Descriptor.Extensions[47]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, int> DefaultInt32Extension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, int>.CreateInstance(Descriptor.Extensions[48]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, long> DefaultInt64Extension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, long>.CreateInstance(Descriptor.Extensions[49]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, uint> DefaultUint32Extension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, uint>.CreateInstance(Descriptor.Extensions[50]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, ulong> DefaultUint64Extension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, ulong>.CreateInstance(Descriptor.Extensions[51]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, int> DefaultSint32Extension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, int>.CreateInstance(Descriptor.Extensions[52]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, long> DefaultSint64Extension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, long>.CreateInstance(Descriptor.Extensions[53]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, uint> DefaultFixed32Extension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, uint>.CreateInstance(Descriptor.Extensions[54]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, ulong> DefaultFixed64Extension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, ulong>.CreateInstance(Descriptor.Extensions[55]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, int> DefaultSfixed32Extension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, int>.CreateInstance(Descriptor.Extensions[56]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, long> DefaultSfixed64Extension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, long>.CreateInstance(Descriptor.Extensions[57]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, float> DefaultFloatExtension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, float>.CreateInstance(Descriptor.Extensions[58]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, double> DefaultDoubleExtension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, double>.CreateInstance(Descriptor.Extensions[59]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, bool> DefaultBoolExtension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, bool>.CreateInstance(Descriptor.Extensions[60]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, string> DefaultStringExtension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, string>.CreateInstance(Descriptor.Extensions[61]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, pb::ByteString> DefaultBytesExtension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, pb::ByteString>.CreateInstance(Descriptor.Extensions[62]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, self::TestAllTypes.Types.NestedEnum> DefaultNestedEnumExtension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, self::TestAllTypes.Types.NestedEnum>.CreateInstance(Descriptor.Extensions[63]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, self::ForeignEnum> DefaultForeignEnumExtension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, self::ForeignEnum>.CreateInstance(Descriptor.Extensions[64]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, self::ImportEnum> DefaultImportEnumExtension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, self::ImportEnum>.CreateInstance(Descriptor.Extensions[65]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, string> DefaultStringPieceExtension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, string>.CreateInstance(Descriptor.Extensions[66]);
-    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, string> DefaultCordExtension =
-          pb::GeneratedSingleExtension<self::TestAllExtensions, string>.CreateInstance(Descriptor.Extensions[67]);
-    public static readonly pb::GeneratedExtensionBase<self::TestFieldOrderings, string> MyExtensionString =
-          pb::GeneratedSingleExtension<self::TestFieldOrderings, string>.CreateInstance(Descriptor.Extensions[68]);
-    public static readonly pb::GeneratedExtensionBase<self::TestFieldOrderings, int> MyExtensionInt =
-          pb::GeneratedSingleExtension<self::TestFieldOrderings, int>.CreateInstance(Descriptor.Extensions[69]);
+      pb::GeneratedExtensionBase<scg::IList<string>> RepeatedCordExtension =
+          pb::GeneratedRepeatExtension<string>.CreateInstance(Descriptor.Extensions[47]);
+    public static readonly pb::GeneratedExtensionBase<int> DefaultInt32Extension =
+          pb::GeneratedSingleExtension<int>.CreateInstance(Descriptor.Extensions[48]);
+    public static readonly pb::GeneratedExtensionBase<long> DefaultInt64Extension =
+          pb::GeneratedSingleExtension<long>.CreateInstance(Descriptor.Extensions[49]);
+    public static readonly pb::GeneratedExtensionBase<uint> DefaultUint32Extension =
+          pb::GeneratedSingleExtension<uint>.CreateInstance(Descriptor.Extensions[50]);
+    public static readonly pb::GeneratedExtensionBase<ulong> DefaultUint64Extension =
+          pb::GeneratedSingleExtension<ulong>.CreateInstance(Descriptor.Extensions[51]);
+    public static readonly pb::GeneratedExtensionBase<int> DefaultSint32Extension =
+          pb::GeneratedSingleExtension<int>.CreateInstance(Descriptor.Extensions[52]);
+    public static readonly pb::GeneratedExtensionBase<long> DefaultSint64Extension =
+          pb::GeneratedSingleExtension<long>.CreateInstance(Descriptor.Extensions[53]);
+    public static readonly pb::GeneratedExtensionBase<uint> DefaultFixed32Extension =
+          pb::GeneratedSingleExtension<uint>.CreateInstance(Descriptor.Extensions[54]);
+    public static readonly pb::GeneratedExtensionBase<ulong> DefaultFixed64Extension =
+          pb::GeneratedSingleExtension<ulong>.CreateInstance(Descriptor.Extensions[55]);
+    public static readonly pb::GeneratedExtensionBase<int> DefaultSfixed32Extension =
+          pb::GeneratedSingleExtension<int>.CreateInstance(Descriptor.Extensions[56]);
+    public static readonly pb::GeneratedExtensionBase<long> DefaultSfixed64Extension =
+          pb::GeneratedSingleExtension<long>.CreateInstance(Descriptor.Extensions[57]);
+    public static readonly pb::GeneratedExtensionBase<float> DefaultFloatExtension =
+          pb::GeneratedSingleExtension<float>.CreateInstance(Descriptor.Extensions[58]);
+    public static readonly pb::GeneratedExtensionBase<double> DefaultDoubleExtension =
+          pb::GeneratedSingleExtension<double>.CreateInstance(Descriptor.Extensions[59]);
+    public static readonly pb::GeneratedExtensionBase<bool> DefaultBoolExtension =
+          pb::GeneratedSingleExtension<bool>.CreateInstance(Descriptor.Extensions[60]);
+    public static readonly pb::GeneratedExtensionBase<string> DefaultStringExtension =
+          pb::GeneratedSingleExtension<string>.CreateInstance(Descriptor.Extensions[61]);
+    public static readonly pb::GeneratedExtensionBase<pb::ByteString> DefaultBytesExtension =
+          pb::GeneratedSingleExtension<pb::ByteString>.CreateInstance(Descriptor.Extensions[62]);
+    public static readonly pb::GeneratedExtensionBase<self::TestAllTypes.Types.NestedEnum> DefaultNestedEnumExtension =
+          pb::GeneratedSingleExtension<self::TestAllTypes.Types.NestedEnum>.CreateInstance(Descriptor.Extensions[63]);
+    public static readonly pb::GeneratedExtensionBase<self::ForeignEnum> DefaultForeignEnumExtension =
+          pb::GeneratedSingleExtension<self::ForeignEnum>.CreateInstance(Descriptor.Extensions[64]);
+    public static readonly pb::GeneratedExtensionBase<self::ImportEnum> DefaultImportEnumExtension =
+          pb::GeneratedSingleExtension<self::ImportEnum>.CreateInstance(Descriptor.Extensions[65]);
+    public static readonly pb::GeneratedExtensionBase<string> DefaultStringPieceExtension =
+          pb::GeneratedSingleExtension<string>.CreateInstance(Descriptor.Extensions[66]);
+    public static readonly pb::GeneratedExtensionBase<string> DefaultCordExtension =
+          pb::GeneratedSingleExtension<string>.CreateInstance(Descriptor.Extensions[67]);
+    public static readonly pb::GeneratedExtensionBase<string> MyExtensionString =
+          pb::GeneratedSingleExtension<string>.CreateInstance(Descriptor.Extensions[68]);
+    public static readonly pb::GeneratedExtensionBase<int> MyExtensionInt =
+          pb::GeneratedSingleExtension<int>.CreateInstance(Descriptor.Extensions[69]);
     #endregion
     
     #region Static variables
@@ -1150,12 +1150,16 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
         
         public static Builder CreateBuilder() { return new Builder(); }
-        public override IBuilder<self::TestAllTypes.Types.NestedMessage> CreateBuilderForType() { return new Builder(); }
+        public override Builder CreateBuilderForType() { return new Builder(); }
         public static Builder CreateBuilder(self::TestAllTypes.Types.NestedMessage prototype) {
           return (Builder) new Builder().MergeFrom(prototype);
         }
         
         public sealed partial class Builder : pb::GeneratedBuilder<self::TestAllTypes.Types.NestedMessage, Builder> {
+          protected override Builder ThisBuilder {
+            get { return this; }
+          }
+          
           // Construct using self::TestAllTypes.Types.NestedMessage.CreateBuilder()
           internal Builder() {}
           
@@ -1165,12 +1169,12 @@ namespace Google.ProtocolBuffers.TestProtos {
             get { return result; }
           }
           
-          public override IBuilder<self::TestAllTypes.Types.NestedMessage> Clear() {
+          public override Builder Clear() {
             result = new self::TestAllTypes.Types.NestedMessage();
             return this;
           }
           
-          public override IBuilder<self::TestAllTypes.Types.NestedMessage> Clone() {
+          public override Builder Clone() {
             return new Builder().MergeFrom(result);
           }
           
@@ -1188,11 +1192,7 @@ namespace Google.ProtocolBuffers.TestProtos {
             return returnMe;
           }
           
-          protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-            return MergeFrom(data, extensionRegistry);
-          }
-          
-          public override IBuilder MergeFrom(pb::IMessage other) {
+          public override Builder MergeFrom(pb::IMessage other) {
             if (other is self::TestAllTypes.Types.NestedMessage) {
               return MergeFrom((self::TestAllTypes.Types.NestedMessage) other);
             } else {
@@ -1201,7 +1201,7 @@ namespace Google.ProtocolBuffers.TestProtos {
             }
           }
           
-          public override IBuilder<self::TestAllTypes.Types.NestedMessage> MergeFrom(self::TestAllTypes.Types.NestedMessage other) {
+          public override Builder MergeFrom(self::TestAllTypes.Types.NestedMessage other) {
             if (other == self::TestAllTypes.Types.NestedMessage.DefaultInstance) return this;
             if (other.HasBb) {
               Bb = other.Bb;
@@ -1210,11 +1210,11 @@ namespace Google.ProtocolBuffers.TestProtos {
             return this;
           }
           
-          public override IBuilder<self::TestAllTypes.Types.NestedMessage> MergeFrom(pb::CodedInputStream input) {
+          public override Builder MergeFrom(pb::CodedInputStream input) {
             return MergeFrom(input, pb::ExtensionRegistry.Empty);
           }
           
-          public override IBuilder<self::TestAllTypes.Types.NestedMessage> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+          public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
             pb::UnknownFieldSet.Builder unknownFields =
               pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
             while (true) {
@@ -1353,12 +1353,16 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
         
         public static Builder CreateBuilder() { return new Builder(); }
-        public override IBuilder<self::TestAllTypes.Types.OptionalGroup> CreateBuilderForType() { return new Builder(); }
+        public override Builder CreateBuilderForType() { return new Builder(); }
         public static Builder CreateBuilder(self::TestAllTypes.Types.OptionalGroup prototype) {
           return (Builder) new Builder().MergeFrom(prototype);
         }
         
         public sealed partial class Builder : pb::GeneratedBuilder<self::TestAllTypes.Types.OptionalGroup, Builder> {
+          protected override Builder ThisBuilder {
+            get { return this; }
+          }
+          
           // Construct using self::TestAllTypes.Types.OptionalGroup.CreateBuilder()
           internal Builder() {}
           
@@ -1368,12 +1372,12 @@ namespace Google.ProtocolBuffers.TestProtos {
             get { return result; }
           }
           
-          public override IBuilder<self::TestAllTypes.Types.OptionalGroup> Clear() {
+          public override Builder Clear() {
             result = new self::TestAllTypes.Types.OptionalGroup();
             return this;
           }
           
-          public override IBuilder<self::TestAllTypes.Types.OptionalGroup> Clone() {
+          public override Builder Clone() {
             return new Builder().MergeFrom(result);
           }
           
@@ -1391,11 +1395,7 @@ namespace Google.ProtocolBuffers.TestProtos {
             return returnMe;
           }
           
-          protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-            return MergeFrom(data, extensionRegistry);
-          }
-          
-          public override IBuilder MergeFrom(pb::IMessage other) {
+          public override Builder MergeFrom(pb::IMessage other) {
             if (other is self::TestAllTypes.Types.OptionalGroup) {
               return MergeFrom((self::TestAllTypes.Types.OptionalGroup) other);
             } else {
@@ -1404,7 +1404,7 @@ namespace Google.ProtocolBuffers.TestProtos {
             }
           }
           
-          public override IBuilder<self::TestAllTypes.Types.OptionalGroup> MergeFrom(self::TestAllTypes.Types.OptionalGroup other) {
+          public override Builder MergeFrom(self::TestAllTypes.Types.OptionalGroup other) {
             if (other == self::TestAllTypes.Types.OptionalGroup.DefaultInstance) return this;
             if (other.HasA) {
               A = other.A;
@@ -1413,11 +1413,11 @@ namespace Google.ProtocolBuffers.TestProtos {
             return this;
           }
           
-          public override IBuilder<self::TestAllTypes.Types.OptionalGroup> MergeFrom(pb::CodedInputStream input) {
+          public override Builder MergeFrom(pb::CodedInputStream input) {
             return MergeFrom(input, pb::ExtensionRegistry.Empty);
           }
           
-          public override IBuilder<self::TestAllTypes.Types.OptionalGroup> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+          public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
             pb::UnknownFieldSet.Builder unknownFields =
               pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
             while (true) {
@@ -1556,12 +1556,16 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
         
         public static Builder CreateBuilder() { return new Builder(); }
-        public override IBuilder<self::TestAllTypes.Types.RepeatedGroup> CreateBuilderForType() { return new Builder(); }
+        public override Builder CreateBuilderForType() { return new Builder(); }
         public static Builder CreateBuilder(self::TestAllTypes.Types.RepeatedGroup prototype) {
           return (Builder) new Builder().MergeFrom(prototype);
         }
         
         public sealed partial class Builder : pb::GeneratedBuilder<self::TestAllTypes.Types.RepeatedGroup, Builder> {
+          protected override Builder ThisBuilder {
+            get { return this; }
+          }
+          
           // Construct using self::TestAllTypes.Types.RepeatedGroup.CreateBuilder()
           internal Builder() {}
           
@@ -1571,12 +1575,12 @@ namespace Google.ProtocolBuffers.TestProtos {
             get { return result; }
           }
           
-          public override IBuilder<self::TestAllTypes.Types.RepeatedGroup> Clear() {
+          public override Builder Clear() {
             result = new self::TestAllTypes.Types.RepeatedGroup();
             return this;
           }
           
-          public override IBuilder<self::TestAllTypes.Types.RepeatedGroup> Clone() {
+          public override Builder Clone() {
             return new Builder().MergeFrom(result);
           }
           
@@ -1594,11 +1598,7 @@ namespace Google.ProtocolBuffers.TestProtos {
             return returnMe;
           }
           
-          protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-            return MergeFrom(data, extensionRegistry);
-          }
-          
-          public override IBuilder MergeFrom(pb::IMessage other) {
+          public override Builder MergeFrom(pb::IMessage other) {
             if (other is self::TestAllTypes.Types.RepeatedGroup) {
               return MergeFrom((self::TestAllTypes.Types.RepeatedGroup) other);
             } else {
@@ -1607,7 +1607,7 @@ namespace Google.ProtocolBuffers.TestProtos {
             }
           }
           
-          public override IBuilder<self::TestAllTypes.Types.RepeatedGroup> MergeFrom(self::TestAllTypes.Types.RepeatedGroup other) {
+          public override Builder MergeFrom(self::TestAllTypes.Types.RepeatedGroup other) {
             if (other == self::TestAllTypes.Types.RepeatedGroup.DefaultInstance) return this;
             if (other.HasA) {
               A = other.A;
@@ -1616,11 +1616,11 @@ namespace Google.ProtocolBuffers.TestProtos {
             return this;
           }
           
-          public override IBuilder<self::TestAllTypes.Types.RepeatedGroup> MergeFrom(pb::CodedInputStream input) {
+          public override Builder MergeFrom(pb::CodedInputStream input) {
             return MergeFrom(input, pb::ExtensionRegistry.Empty);
           }
           
-          public override IBuilder<self::TestAllTypes.Types.RepeatedGroup> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+          public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
             pb::UnknownFieldSet.Builder unknownFields =
               pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
             while (true) {
@@ -2878,12 +2878,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::TestAllTypes> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::TestAllTypes prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::TestAllTypes, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::TestAllTypes.CreateBuilder()
       internal Builder() {}
       
@@ -2893,12 +2897,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::TestAllTypes> Clear() {
+      public override Builder Clear() {
         result = new self::TestAllTypes();
         return this;
       }
       
-      public override IBuilder<self::TestAllTypes> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -2948,11 +2952,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::TestAllTypes) {
           return MergeFrom((self::TestAllTypes) other);
         } else {
@@ -2961,7 +2961,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
       }
       
-      public override IBuilder<self::TestAllTypes> MergeFrom(self::TestAllTypes other) {
+      public override Builder MergeFrom(self::TestAllTypes other) {
         if (other == self::TestAllTypes.DefaultInstance) return this;
         if (other.HasOptionalInt32) {
           OptionalInt32 = other.OptionalInt32;
@@ -3243,11 +3243,11 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       
-      public override IBuilder<self::TestAllTypes> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::TestAllTypes> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -5447,12 +5447,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::ForeignMessage> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::ForeignMessage prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::ForeignMessage, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::ForeignMessage.CreateBuilder()
       internal Builder() {}
       
@@ -5462,12 +5466,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::ForeignMessage> Clear() {
+      public override Builder Clear() {
         result = new self::ForeignMessage();
         return this;
       }
       
-      public override IBuilder<self::ForeignMessage> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -5485,11 +5489,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::ForeignMessage) {
           return MergeFrom((self::ForeignMessage) other);
         } else {
@@ -5498,7 +5498,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
       }
       
-      public override IBuilder<self::ForeignMessage> MergeFrom(self::ForeignMessage other) {
+      public override Builder MergeFrom(self::ForeignMessage other) {
         if (other == self::ForeignMessage.DefaultInstance) return this;
         if (other.HasC) {
           C = other.C;
@@ -5507,11 +5507,11 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       
-      public override IBuilder<self::ForeignMessage> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::ForeignMessage> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -5638,12 +5638,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::TestAllExtensions> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::TestAllExtensions prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::ExtendableBuilder<self::TestAllExtensions, self::TestAllExtensions.Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::TestAllExtensions.CreateBuilder()
       internal Builder() {}
       
@@ -5653,12 +5657,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::TestAllExtensions> Clear() {
+      public override Builder Clear() {
         result = new self::TestAllExtensions();
         return this;
       }
       
-      public override IBuilder<self::TestAllExtensions> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -5676,11 +5680,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::TestAllExtensions) {
           return MergeFrom((self::TestAllExtensions) other);
         } else {
@@ -5689,17 +5689,17 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
       }
       
-      public override IBuilder<self::TestAllExtensions> MergeFrom(self::TestAllExtensions other) {
+      public override Builder MergeFrom(self::TestAllExtensions other) {
         if (other == self::TestAllExtensions.DefaultInstance) return this;
         this.MergeUnknownFields(other.UnknownFields);
         return this;
       }
       
-      public override IBuilder<self::TestAllExtensions> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::TestAllExtensions> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -5815,12 +5815,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::OptionalGroup_extension> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::OptionalGroup_extension prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::OptionalGroup_extension, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::OptionalGroup_extension.CreateBuilder()
       internal Builder() {}
       
@@ -5830,12 +5834,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::OptionalGroup_extension> Clear() {
+      public override Builder Clear() {
         result = new self::OptionalGroup_extension();
         return this;
       }
       
-      public override IBuilder<self::OptionalGroup_extension> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -5853,11 +5857,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::OptionalGroup_extension) {
           return MergeFrom((self::OptionalGroup_extension) other);
         } else {
@@ -5866,7 +5866,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
       }
       
-      public override IBuilder<self::OptionalGroup_extension> MergeFrom(self::OptionalGroup_extension other) {
+      public override Builder MergeFrom(self::OptionalGroup_extension other) {
         if (other == self::OptionalGroup_extension.DefaultInstance) return this;
         if (other.HasA) {
           A = other.A;
@@ -5875,11 +5875,11 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       
-      public override IBuilder<self::OptionalGroup_extension> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::OptionalGroup_extension> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -6018,12 +6018,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::RepeatedGroup_extension> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::RepeatedGroup_extension prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::RepeatedGroup_extension, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::RepeatedGroup_extension.CreateBuilder()
       internal Builder() {}
       
@@ -6033,12 +6037,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::RepeatedGroup_extension> Clear() {
+      public override Builder Clear() {
         result = new self::RepeatedGroup_extension();
         return this;
       }
       
-      public override IBuilder<self::RepeatedGroup_extension> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -6056,11 +6060,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::RepeatedGroup_extension) {
           return MergeFrom((self::RepeatedGroup_extension) other);
         } else {
@@ -6069,7 +6069,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
       }
       
-      public override IBuilder<self::RepeatedGroup_extension> MergeFrom(self::RepeatedGroup_extension other) {
+      public override Builder MergeFrom(self::RepeatedGroup_extension other) {
         if (other == self::RepeatedGroup_extension.DefaultInstance) return this;
         if (other.HasA) {
           A = other.A;
@@ -6078,11 +6078,11 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       
-      public override IBuilder<self::RepeatedGroup_extension> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::RepeatedGroup_extension> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -6149,11 +6149,11 @@ namespace Google.ProtocolBuffers.TestProtos {
     
     #region Nested types
     public static class Types {
-      public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, self::TestRequired> Single =
-            pb::GeneratedSingleExtension<self::TestAllExtensions, self::TestRequired>.CreateInstance(Descriptor.Extensions[0]);
+      public static readonly pb::GeneratedExtensionBase<self::TestRequired> Single =
+            pb::GeneratedSingleExtension<self::TestRequired>.CreateInstance(Descriptor.Extensions[0]);
       public static readonly
-        pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<self::TestRequired>> Multi =
-            pb::GeneratedRepeatExtension<self::TestAllExtensions, self::TestRequired>.CreateInstance(Descriptor.Extensions[1]);
+        pb::GeneratedExtensionBase<scg::IList<self::TestRequired>> Multi =
+            pb::GeneratedRepeatExtension<self::TestRequired>.CreateInstance(Descriptor.Extensions[1]);
     }
     #endregion
     
@@ -6746,12 +6746,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::TestRequired> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::TestRequired prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::TestRequired, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::TestRequired.CreateBuilder()
       internal Builder() {}
       
@@ -6761,12 +6765,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::TestRequired> Clear() {
+      public override Builder Clear() {
         result = new self::TestRequired();
         return this;
       }
       
-      public override IBuilder<self::TestRequired> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -6784,11 +6788,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::TestRequired) {
           return MergeFrom((self::TestRequired) other);
         } else {
@@ -6797,7 +6797,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
       }
       
-      public override IBuilder<self::TestRequired> MergeFrom(self::TestRequired other) {
+      public override Builder MergeFrom(self::TestRequired other) {
         if (other == self::TestRequired.DefaultInstance) return this;
         if (other.HasA) {
           A = other.A;
@@ -6902,11 +6902,11 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       
-      public override IBuilder<self::TestRequired> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::TestRequired> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -7821,12 +7821,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::TestRequiredForeign> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::TestRequiredForeign prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::TestRequiredForeign, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::TestRequiredForeign.CreateBuilder()
       internal Builder() {}
       
@@ -7836,12 +7840,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::TestRequiredForeign> Clear() {
+      public override Builder Clear() {
         result = new self::TestRequiredForeign();
         return this;
       }
       
-      public override IBuilder<self::TestRequiredForeign> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -7862,11 +7866,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::TestRequiredForeign) {
           return MergeFrom((self::TestRequiredForeign) other);
         } else {
@@ -7875,7 +7875,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
       }
       
-      public override IBuilder<self::TestRequiredForeign> MergeFrom(self::TestRequiredForeign other) {
+      public override Builder MergeFrom(self::TestRequiredForeign other) {
         if (other == self::TestRequiredForeign.DefaultInstance) return this;
         if (other.HasOptionalMessage) {
           MergeOptionalMessage(other.OptionalMessage);
@@ -7893,11 +7893,11 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       
-      public override IBuilder<self::TestRequiredForeign> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::TestRequiredForeign> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -8130,12 +8130,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::TestForeignNested> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::TestForeignNested prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::TestForeignNested, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::TestForeignNested.CreateBuilder()
       internal Builder() {}
       
@@ -8145,12 +8149,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::TestForeignNested> Clear() {
+      public override Builder Clear() {
         result = new self::TestForeignNested();
         return this;
       }
       
-      public override IBuilder<self::TestForeignNested> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -8168,11 +8172,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::TestForeignNested) {
           return MergeFrom((self::TestForeignNested) other);
         } else {
@@ -8181,7 +8181,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
       }
       
-      public override IBuilder<self::TestForeignNested> MergeFrom(self::TestForeignNested other) {
+      public override Builder MergeFrom(self::TestForeignNested other) {
         if (other == self::TestForeignNested.DefaultInstance) return this;
         if (other.HasForeignNested) {
           MergeForeignNested(other.ForeignNested);
@@ -8190,11 +8190,11 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       
-      public override IBuilder<self::TestForeignNested> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::TestForeignNested> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -8338,12 +8338,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::TestEmptyMessage> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::TestEmptyMessage prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::TestEmptyMessage, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::TestEmptyMessage.CreateBuilder()
       internal Builder() {}
       
@@ -8353,12 +8357,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::TestEmptyMessage> Clear() {
+      public override Builder Clear() {
         result = new self::TestEmptyMessage();
         return this;
       }
       
-      public override IBuilder<self::TestEmptyMessage> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -8376,11 +8380,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::TestEmptyMessage) {
           return MergeFrom((self::TestEmptyMessage) other);
         } else {
@@ -8389,17 +8389,17 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
       }
       
-      public override IBuilder<self::TestEmptyMessage> MergeFrom(self::TestEmptyMessage other) {
+      public override Builder MergeFrom(self::TestEmptyMessage other) {
         if (other == self::TestEmptyMessage.DefaultInstance) return this;
         this.MergeUnknownFields(other.UnknownFields);
         return this;
       }
       
-      public override IBuilder<self::TestEmptyMessage> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::TestEmptyMessage> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -8503,12 +8503,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::TestEmptyMessageWithExtensions> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::TestEmptyMessageWithExtensions prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::ExtendableBuilder<self::TestEmptyMessageWithExtensions, self::TestEmptyMessageWithExtensions.Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::TestEmptyMessageWithExtensions.CreateBuilder()
       internal Builder() {}
       
@@ -8518,12 +8522,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::TestEmptyMessageWithExtensions> Clear() {
+      public override Builder Clear() {
         result = new self::TestEmptyMessageWithExtensions();
         return this;
       }
       
-      public override IBuilder<self::TestEmptyMessageWithExtensions> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -8541,11 +8545,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::TestEmptyMessageWithExtensions) {
           return MergeFrom((self::TestEmptyMessageWithExtensions) other);
         } else {
@@ -8554,17 +8554,17 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
       }
       
-      public override IBuilder<self::TestEmptyMessageWithExtensions> MergeFrom(self::TestEmptyMessageWithExtensions other) {
+      public override Builder MergeFrom(self::TestEmptyMessageWithExtensions other) {
         if (other == self::TestEmptyMessageWithExtensions.DefaultInstance) return this;
         this.MergeUnknownFields(other.UnknownFields);
         return this;
       }
       
-      public override IBuilder<self::TestEmptyMessageWithExtensions> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::TestEmptyMessageWithExtensions> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -8696,12 +8696,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::TestReallyLargeTagNumber> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::TestReallyLargeTagNumber prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::TestReallyLargeTagNumber, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::TestReallyLargeTagNumber.CreateBuilder()
       internal Builder() {}
       
@@ -8711,12 +8715,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::TestReallyLargeTagNumber> Clear() {
+      public override Builder Clear() {
         result = new self::TestReallyLargeTagNumber();
         return this;
       }
       
-      public override IBuilder<self::TestReallyLargeTagNumber> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -8734,11 +8738,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::TestReallyLargeTagNumber) {
           return MergeFrom((self::TestReallyLargeTagNumber) other);
         } else {
@@ -8747,7 +8747,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
       }
       
-      public override IBuilder<self::TestReallyLargeTagNumber> MergeFrom(self::TestReallyLargeTagNumber other) {
+      public override Builder MergeFrom(self::TestReallyLargeTagNumber other) {
         if (other == self::TestReallyLargeTagNumber.DefaultInstance) return this;
         if (other.HasA) {
           A = other.A;
@@ -8759,11 +8759,11 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       
-      public override IBuilder<self::TestReallyLargeTagNumber> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::TestReallyLargeTagNumber> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -8941,12 +8941,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::TestRecursiveMessage> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::TestRecursiveMessage prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::TestRecursiveMessage, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::TestRecursiveMessage.CreateBuilder()
       internal Builder() {}
       
@@ -8956,12 +8960,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::TestRecursiveMessage> Clear() {
+      public override Builder Clear() {
         result = new self::TestRecursiveMessage();
         return this;
       }
       
-      public override IBuilder<self::TestRecursiveMessage> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -8979,11 +8983,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::TestRecursiveMessage) {
           return MergeFrom((self::TestRecursiveMessage) other);
         } else {
@@ -8992,7 +8992,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
       }
       
-      public override IBuilder<self::TestRecursiveMessage> MergeFrom(self::TestRecursiveMessage other) {
+      public override Builder MergeFrom(self::TestRecursiveMessage other) {
         if (other == self::TestRecursiveMessage.DefaultInstance) return this;
         if (other.HasA) {
           MergeA(other.A);
@@ -9004,11 +9004,11 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       
-      public override IBuilder<self::TestRecursiveMessage> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::TestRecursiveMessage> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -9191,12 +9191,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::TestMutualRecursionA> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::TestMutualRecursionA prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::TestMutualRecursionA, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::TestMutualRecursionA.CreateBuilder()
       internal Builder() {}
       
@@ -9206,12 +9210,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::TestMutualRecursionA> Clear() {
+      public override Builder Clear() {
         result = new self::TestMutualRecursionA();
         return this;
       }
       
-      public override IBuilder<self::TestMutualRecursionA> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -9229,11 +9233,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::TestMutualRecursionA) {
           return MergeFrom((self::TestMutualRecursionA) other);
         } else {
@@ -9242,7 +9242,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
       }
       
-      public override IBuilder<self::TestMutualRecursionA> MergeFrom(self::TestMutualRecursionA other) {
+      public override Builder MergeFrom(self::TestMutualRecursionA other) {
         if (other == self::TestMutualRecursionA.DefaultInstance) return this;
         if (other.HasBb) {
           MergeBb(other.Bb);
@@ -9251,11 +9251,11 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       
-      public override IBuilder<self::TestMutualRecursionA> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::TestMutualRecursionA> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -9431,12 +9431,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::TestMutualRecursionB> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::TestMutualRecursionB prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::TestMutualRecursionB, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::TestMutualRecursionB.CreateBuilder()
       internal Builder() {}
       
@@ -9446,12 +9450,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::TestMutualRecursionB> Clear() {
+      public override Builder Clear() {
         result = new self::TestMutualRecursionB();
         return this;
       }
       
-      public override IBuilder<self::TestMutualRecursionB> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -9469,11 +9473,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::TestMutualRecursionB) {
           return MergeFrom((self::TestMutualRecursionB) other);
         } else {
@@ -9482,7 +9482,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
       }
       
-      public override IBuilder<self::TestMutualRecursionB> MergeFrom(self::TestMutualRecursionB other) {
+      public override Builder MergeFrom(self::TestMutualRecursionB other) {
         if (other == self::TestMutualRecursionB.DefaultInstance) return this;
         if (other.HasA) {
           MergeA(other.A);
@@ -9494,11 +9494,11 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       
-      public override IBuilder<self::TestMutualRecursionB> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::TestMutualRecursionB> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -9701,12 +9701,16 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
         
         public static Builder CreateBuilder() { return new Builder(); }
-        public override IBuilder<self::TestDupFieldNumber.Types.Foo> CreateBuilderForType() { return new Builder(); }
+        public override Builder CreateBuilderForType() { return new Builder(); }
         public static Builder CreateBuilder(self::TestDupFieldNumber.Types.Foo prototype) {
           return (Builder) new Builder().MergeFrom(prototype);
         }
         
         public sealed partial class Builder : pb::GeneratedBuilder<self::TestDupFieldNumber.Types.Foo, Builder> {
+          protected override Builder ThisBuilder {
+            get { return this; }
+          }
+          
           // Construct using self::TestDupFieldNumber.Types.Foo.CreateBuilder()
           internal Builder() {}
           
@@ -9716,12 +9720,12 @@ namespace Google.ProtocolBuffers.TestProtos {
             get { return result; }
           }
           
-          public override IBuilder<self::TestDupFieldNumber.Types.Foo> Clear() {
+          public override Builder Clear() {
             result = new self::TestDupFieldNumber.Types.Foo();
             return this;
           }
           
-          public override IBuilder<self::TestDupFieldNumber.Types.Foo> Clone() {
+          public override Builder Clone() {
             return new Builder().MergeFrom(result);
           }
           
@@ -9739,11 +9743,7 @@ namespace Google.ProtocolBuffers.TestProtos {
             return returnMe;
           }
           
-          protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-            return MergeFrom(data, extensionRegistry);
-          }
-          
-          public override IBuilder MergeFrom(pb::IMessage other) {
+          public override Builder MergeFrom(pb::IMessage other) {
             if (other is self::TestDupFieldNumber.Types.Foo) {
               return MergeFrom((self::TestDupFieldNumber.Types.Foo) other);
             } else {
@@ -9752,7 +9752,7 @@ namespace Google.ProtocolBuffers.TestProtos {
             }
           }
           
-          public override IBuilder<self::TestDupFieldNumber.Types.Foo> MergeFrom(self::TestDupFieldNumber.Types.Foo other) {
+          public override Builder MergeFrom(self::TestDupFieldNumber.Types.Foo other) {
             if (other == self::TestDupFieldNumber.Types.Foo.DefaultInstance) return this;
             if (other.HasA) {
               A = other.A;
@@ -9761,11 +9761,11 @@ namespace Google.ProtocolBuffers.TestProtos {
             return this;
           }
           
-          public override IBuilder<self::TestDupFieldNumber.Types.Foo> MergeFrom(pb::CodedInputStream input) {
+          public override Builder MergeFrom(pb::CodedInputStream input) {
             return MergeFrom(input, pb::ExtensionRegistry.Empty);
           }
           
-          public override IBuilder<self::TestDupFieldNumber.Types.Foo> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+          public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
             pb::UnknownFieldSet.Builder unknownFields =
               pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
             while (true) {
@@ -9904,12 +9904,16 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
         
         public static Builder CreateBuilder() { return new Builder(); }
-        public override IBuilder<self::TestDupFieldNumber.Types.Bar> CreateBuilderForType() { return new Builder(); }
+        public override Builder CreateBuilderForType() { return new Builder(); }
         public static Builder CreateBuilder(self::TestDupFieldNumber.Types.Bar prototype) {
           return (Builder) new Builder().MergeFrom(prototype);
         }
         
         public sealed partial class Builder : pb::GeneratedBuilder<self::TestDupFieldNumber.Types.Bar, Builder> {
+          protected override Builder ThisBuilder {
+            get { return this; }
+          }
+          
           // Construct using self::TestDupFieldNumber.Types.Bar.CreateBuilder()
           internal Builder() {}
           
@@ -9919,12 +9923,12 @@ namespace Google.ProtocolBuffers.TestProtos {
             get { return result; }
           }
           
-          public override IBuilder<self::TestDupFieldNumber.Types.Bar> Clear() {
+          public override Builder Clear() {
             result = new self::TestDupFieldNumber.Types.Bar();
             return this;
           }
           
-          public override IBuilder<self::TestDupFieldNumber.Types.Bar> Clone() {
+          public override Builder Clone() {
             return new Builder().MergeFrom(result);
           }
           
@@ -9942,11 +9946,7 @@ namespace Google.ProtocolBuffers.TestProtos {
             return returnMe;
           }
           
-          protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-            return MergeFrom(data, extensionRegistry);
-          }
-          
-          public override IBuilder MergeFrom(pb::IMessage other) {
+          public override Builder MergeFrom(pb::IMessage other) {
             if (other is self::TestDupFieldNumber.Types.Bar) {
               return MergeFrom((self::TestDupFieldNumber.Types.Bar) other);
             } else {
@@ -9955,7 +9955,7 @@ namespace Google.ProtocolBuffers.TestProtos {
             }
           }
           
-          public override IBuilder<self::TestDupFieldNumber.Types.Bar> MergeFrom(self::TestDupFieldNumber.Types.Bar other) {
+          public override Builder MergeFrom(self::TestDupFieldNumber.Types.Bar other) {
             if (other == self::TestDupFieldNumber.Types.Bar.DefaultInstance) return this;
             if (other.HasA) {
               A = other.A;
@@ -9964,11 +9964,11 @@ namespace Google.ProtocolBuffers.TestProtos {
             return this;
           }
           
-          public override IBuilder<self::TestDupFieldNumber.Types.Bar> MergeFrom(pb::CodedInputStream input) {
+          public override Builder MergeFrom(pb::CodedInputStream input) {
             return MergeFrom(input, pb::ExtensionRegistry.Empty);
           }
           
-          public override IBuilder<self::TestDupFieldNumber.Types.Bar> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+          public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
             pb::UnknownFieldSet.Builder unknownFields =
               pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
             while (true) {
@@ -10124,12 +10124,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::TestDupFieldNumber> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::TestDupFieldNumber prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::TestDupFieldNumber, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::TestDupFieldNumber.CreateBuilder()
       internal Builder() {}
       
@@ -10139,12 +10143,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::TestDupFieldNumber> Clear() {
+      public override Builder Clear() {
         result = new self::TestDupFieldNumber();
         return this;
       }
       
-      public override IBuilder<self::TestDupFieldNumber> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -10162,11 +10166,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::TestDupFieldNumber) {
           return MergeFrom((self::TestDupFieldNumber) other);
         } else {
@@ -10175,7 +10175,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
       }
       
-      public override IBuilder<self::TestDupFieldNumber> MergeFrom(self::TestDupFieldNumber other) {
+      public override Builder MergeFrom(self::TestDupFieldNumber other) {
         if (other == self::TestDupFieldNumber.DefaultInstance) return this;
         if (other.HasA) {
           A = other.A;
@@ -10190,11 +10190,11 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       
-      public override IBuilder<self::TestDupFieldNumber> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::TestDupFieldNumber> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -10462,12 +10462,16 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
         
         public static Builder CreateBuilder() { return new Builder(); }
-        public override IBuilder<self::TestNestedMessageHasBits.Types.NestedMessage> CreateBuilderForType() { return new Builder(); }
+        public override Builder CreateBuilderForType() { return new Builder(); }
         public static Builder CreateBuilder(self::TestNestedMessageHasBits.Types.NestedMessage prototype) {
           return (Builder) new Builder().MergeFrom(prototype);
         }
         
         public sealed partial class Builder : pb::GeneratedBuilder<self::TestNestedMessageHasBits.Types.NestedMessage, Builder> {
+          protected override Builder ThisBuilder {
+            get { return this; }
+          }
+          
           // Construct using self::TestNestedMessageHasBits.Types.NestedMessage.CreateBuilder()
           internal Builder() {}
           
@@ -10477,12 +10481,12 @@ namespace Google.ProtocolBuffers.TestProtos {
             get { return result; }
           }
           
-          public override IBuilder<self::TestNestedMessageHasBits.Types.NestedMessage> Clear() {
+          public override Builder Clear() {
             result = new self::TestNestedMessageHasBits.Types.NestedMessage();
             return this;
           }
           
-          public override IBuilder<self::TestNestedMessageHasBits.Types.NestedMessage> Clone() {
+          public override Builder Clone() {
             return new Builder().MergeFrom(result);
           }
           
@@ -10504,11 +10508,7 @@ namespace Google.ProtocolBuffers.TestProtos {
             return returnMe;
           }
           
-          protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-            return MergeFrom(data, extensionRegistry);
-          }
-          
-          public override IBuilder MergeFrom(pb::IMessage other) {
+          public override Builder MergeFrom(pb::IMessage other) {
             if (other is self::TestNestedMessageHasBits.Types.NestedMessage) {
               return MergeFrom((self::TestNestedMessageHasBits.Types.NestedMessage) other);
             } else {
@@ -10517,7 +10517,7 @@ namespace Google.ProtocolBuffers.TestProtos {
             }
           }
           
-          public override IBuilder<self::TestNestedMessageHasBits.Types.NestedMessage> MergeFrom(self::TestNestedMessageHasBits.Types.NestedMessage other) {
+          public override Builder MergeFrom(self::TestNestedMessageHasBits.Types.NestedMessage other) {
             if (other == self::TestNestedMessageHasBits.Types.NestedMessage.DefaultInstance) return this;
             if (other.nestedmessageRepeatedInt32_.Count != 0) {
               if (result.nestedmessageRepeatedInt32_.Count == 0) {
@@ -10535,11 +10535,11 @@ namespace Google.ProtocolBuffers.TestProtos {
             return this;
           }
           
-          public override IBuilder<self::TestNestedMessageHasBits.Types.NestedMessage> MergeFrom(pb::CodedInputStream input) {
+          public override Builder MergeFrom(pb::CodedInputStream input) {
             return MergeFrom(input, pb::ExtensionRegistry.Empty);
           }
           
-          public override IBuilder<self::TestNestedMessageHasBits.Types.NestedMessage> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+          public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
             pb::UnknownFieldSet.Builder unknownFields =
               pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
             while (true) {
@@ -10727,12 +10727,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::TestNestedMessageHasBits> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::TestNestedMessageHasBits prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::TestNestedMessageHasBits, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::TestNestedMessageHasBits.CreateBuilder()
       internal Builder() {}
       
@@ -10742,12 +10746,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::TestNestedMessageHasBits> Clear() {
+      public override Builder Clear() {
         result = new self::TestNestedMessageHasBits();
         return this;
       }
       
-      public override IBuilder<self::TestNestedMessageHasBits> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -10765,11 +10769,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::TestNestedMessageHasBits) {
           return MergeFrom((self::TestNestedMessageHasBits) other);
         } else {
@@ -10778,7 +10778,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
       }
       
-      public override IBuilder<self::TestNestedMessageHasBits> MergeFrom(self::TestNestedMessageHasBits other) {
+      public override Builder MergeFrom(self::TestNestedMessageHasBits other) {
         if (other == self::TestNestedMessageHasBits.DefaultInstance) return this;
         if (other.HasOptionalNestedMessage) {
           MergeOptionalNestedMessage(other.OptionalNestedMessage);
@@ -10787,11 +10787,11 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       
-      public override IBuilder<self::TestNestedMessageHasBits> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::TestNestedMessageHasBits> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -11143,12 +11143,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::TestCamelCaseFieldNames> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::TestCamelCaseFieldNames prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::TestCamelCaseFieldNames, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::TestCamelCaseFieldNames.CreateBuilder()
       internal Builder() {}
       
@@ -11158,12 +11162,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::TestCamelCaseFieldNames> Clear() {
+      public override Builder Clear() {
         result = new self::TestCamelCaseFieldNames();
         return this;
       }
       
-      public override IBuilder<self::TestCamelCaseFieldNames> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -11189,11 +11193,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::TestCamelCaseFieldNames) {
           return MergeFrom((self::TestCamelCaseFieldNames) other);
         } else {
@@ -11202,7 +11202,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
       }
       
-      public override IBuilder<self::TestCamelCaseFieldNames> MergeFrom(self::TestCamelCaseFieldNames other) {
+      public override Builder MergeFrom(self::TestCamelCaseFieldNames other) {
         if (other == self::TestCamelCaseFieldNames.DefaultInstance) return this;
         if (other.HasPrimitiveField) {
           PrimitiveField = other.PrimitiveField;
@@ -11262,11 +11262,11 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       
-      public override IBuilder<self::TestCamelCaseFieldNames> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::TestCamelCaseFieldNames> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -11824,12 +11824,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::TestFieldOrderings> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::TestFieldOrderings prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::ExtendableBuilder<self::TestFieldOrderings, self::TestFieldOrderings.Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::TestFieldOrderings.CreateBuilder()
       internal Builder() {}
       
@@ -11839,12 +11843,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::TestFieldOrderings> Clear() {
+      public override Builder Clear() {
         result = new self::TestFieldOrderings();
         return this;
       }
       
-      public override IBuilder<self::TestFieldOrderings> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -11862,11 +11866,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::TestFieldOrderings) {
           return MergeFrom((self::TestFieldOrderings) other);
         } else {
@@ -11875,7 +11875,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
       }
       
-      public override IBuilder<self::TestFieldOrderings> MergeFrom(self::TestFieldOrderings other) {
+      public override Builder MergeFrom(self::TestFieldOrderings other) {
         if (other == self::TestFieldOrderings.DefaultInstance) return this;
         if (other.HasMyString) {
           MyString = other.MyString;
@@ -11890,11 +11890,11 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       
-      public override IBuilder<self::TestFieldOrderings> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::TestFieldOrderings> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -12159,12 +12159,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::TestExtremeDefaultValues> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::TestExtremeDefaultValues prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::TestExtremeDefaultValues, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::TestExtremeDefaultValues.CreateBuilder()
       internal Builder() {}
       
@@ -12174,12 +12178,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::TestExtremeDefaultValues> Clear() {
+      public override Builder Clear() {
         result = new self::TestExtremeDefaultValues();
         return this;
       }
       
-      public override IBuilder<self::TestExtremeDefaultValues> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -12197,11 +12201,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::TestExtremeDefaultValues) {
           return MergeFrom((self::TestExtremeDefaultValues) other);
         } else {
@@ -12210,7 +12210,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
       }
       
-      public override IBuilder<self::TestExtremeDefaultValues> MergeFrom(self::TestExtremeDefaultValues other) {
+      public override Builder MergeFrom(self::TestExtremeDefaultValues other) {
         if (other == self::TestExtremeDefaultValues.DefaultInstance) return this;
         if (other.HasEscapedBytes) {
           EscapedBytes = other.EscapedBytes;
@@ -12234,11 +12234,11 @@ namespace Google.ProtocolBuffers.TestProtos {
         return this;
       }
       
-      public override IBuilder<self::TestExtremeDefaultValues> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::TestExtremeDefaultValues> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -12476,12 +12476,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::FooRequest> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::FooRequest prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::FooRequest, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::FooRequest.CreateBuilder()
       internal Builder() {}
       
@@ -12491,12 +12495,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::FooRequest> Clear() {
+      public override Builder Clear() {
         result = new self::FooRequest();
         return this;
       }
       
-      public override IBuilder<self::FooRequest> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -12514,11 +12518,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::FooRequest) {
           return MergeFrom((self::FooRequest) other);
         } else {
@@ -12527,17 +12527,17 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
       }
       
-      public override IBuilder<self::FooRequest> MergeFrom(self::FooRequest other) {
+      public override Builder MergeFrom(self::FooRequest other) {
         if (other == self::FooRequest.DefaultInstance) return this;
         this.MergeUnknownFields(other.UnknownFields);
         return this;
       }
       
-      public override IBuilder<self::FooRequest> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::FooRequest> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -12637,12 +12637,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::FooResponse> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::FooResponse prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::FooResponse, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::FooResponse.CreateBuilder()
       internal Builder() {}
       
@@ -12652,12 +12656,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::FooResponse> Clear() {
+      public override Builder Clear() {
         result = new self::FooResponse();
         return this;
       }
       
-      public override IBuilder<self::FooResponse> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -12675,11 +12679,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::FooResponse) {
           return MergeFrom((self::FooResponse) other);
         } else {
@@ -12688,17 +12688,17 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
       }
       
-      public override IBuilder<self::FooResponse> MergeFrom(self::FooResponse other) {
+      public override Builder MergeFrom(self::FooResponse other) {
         if (other == self::FooResponse.DefaultInstance) return this;
         this.MergeUnknownFields(other.UnknownFields);
         return this;
       }
       
-      public override IBuilder<self::FooResponse> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::FooResponse> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -12798,12 +12798,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::BarRequest> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::BarRequest prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::BarRequest, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::BarRequest.CreateBuilder()
       internal Builder() {}
       
@@ -12813,12 +12817,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::BarRequest> Clear() {
+      public override Builder Clear() {
         result = new self::BarRequest();
         return this;
       }
       
-      public override IBuilder<self::BarRequest> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -12836,11 +12840,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::BarRequest) {
           return MergeFrom((self::BarRequest) other);
         } else {
@@ -12849,17 +12849,17 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
       }
       
-      public override IBuilder<self::BarRequest> MergeFrom(self::BarRequest other) {
+      public override Builder MergeFrom(self::BarRequest other) {
         if (other == self::BarRequest.DefaultInstance) return this;
         this.MergeUnknownFields(other.UnknownFields);
         return this;
       }
       
-      public override IBuilder<self::BarRequest> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::BarRequest> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -12959,12 +12959,16 @@ namespace Google.ProtocolBuffers.TestProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::BarResponse> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::BarResponse prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::BarResponse, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::BarResponse.CreateBuilder()
       internal Builder() {}
       
@@ -12974,12 +12978,12 @@ namespace Google.ProtocolBuffers.TestProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::BarResponse> Clear() {
+      public override Builder Clear() {
         result = new self::BarResponse();
         return this;
       }
       
-      public override IBuilder<self::BarResponse> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -12997,11 +13001,7 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::BarResponse) {
           return MergeFrom((self::BarResponse) other);
         } else {
@@ -13010,17 +13010,17 @@ namespace Google.ProtocolBuffers.TestProtos {
         }
       }
       
-      public override IBuilder<self::BarResponse> MergeFrom(self::BarResponse other) {
+      public override Builder MergeFrom(self::BarResponse other) {
         if (other == self::BarResponse.DefaultInstance) return this;
         this.MergeUnknownFields(other.UnknownFields);
         return this;
       }
       
-      public override IBuilder<self::BarResponse> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::BarResponse> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -13147,7 +13147,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           controller,
           request,
           self::FooResponse.DefaultInstance,
-          pb::RpcUtil.GeneralizeCallback(done, self::FooResponse.DefaultInstance));
+          pb::RpcUtil.GeneralizeCallback<self::FooResponse, self::FooResponse.Builder>(done, self::FooResponse.DefaultInstance));
       }
       
       public override void Bar(
@@ -13159,7 +13159,7 @@ namespace Google.ProtocolBuffers.TestProtos {
           controller,
           request,
           self::BarResponse.DefaultInstance,
-          pb::RpcUtil.GeneralizeCallback(done, self::BarResponse.DefaultInstance));
+          pb::RpcUtil.GeneralizeCallback<self::BarResponse, self::BarResponse.Builder>(done, self::BarResponse.DefaultInstance));
       }
     }
   }
diff --git a/csharp/ProtocolBuffers/AbstractBuilder.cs b/csharp/ProtocolBuffers/AbstractBuilder.cs
index 94077d4f..261bbcf3 100644
--- a/csharp/ProtocolBuffers/AbstractBuilder.cs
+++ b/csharp/ProtocolBuffers/AbstractBuilder.cs
@@ -8,10 +8,16 @@ using System.IO;
 namespace Google.ProtocolBuffers {
   /// <summary>
   /// Implementation of the non-generic IMessage interface as far as possible.
-  /// TODO(jonskeet): Make this generic, to avoid so much casting in DynamicMessage.
   /// </summary>
-  public abstract class AbstractBuilder : IBuilder {
+  public abstract class AbstractBuilder<TMessage, TBuilder> : IBuilder<TMessage, TBuilder> 
+      where TMessage : AbstractMessage<TMessage, TBuilder>
+      where TBuilder : AbstractBuilder<TMessage, TBuilder> {
+
+    protected abstract TBuilder ThisBuilder { get; }
+    
     #region Unimplemented members of IBuilder
+    public abstract UnknownFieldSet UnknownFields { get; set; }
+    public abstract TBuilder MergeFrom(TMessage other);
     public abstract bool IsInitialized { get; }
     public abstract IDictionary<FieldDescriptor, object> AllFields { get; }
     public abstract object this[FieldDescriptor field] { get; set; }
@@ -19,55 +25,75 @@ namespace Google.ProtocolBuffers {
     public abstract int GetRepeatedFieldCount(FieldDescriptor field);
     public abstract object this[FieldDescriptor field, int index] { get; set; }
     public abstract bool HasField(FieldDescriptor field);
+    public abstract TMessage Build();
+    public abstract TMessage BuildPartial();
+    public abstract TBuilder Clone();
+    public abstract TMessage DefaultInstanceForType { get; }
+    public abstract IBuilder CreateBuilderForField(FieldDescriptor field);
+    public abstract TBuilder ClearField(FieldDescriptor field);
+    public abstract TBuilder AddRepeatedField(FieldDescriptor field, object value);
     #endregion
 
-    #region New abstract methods to be overridden by implementations, allow explicit interface implementation
-    protected abstract IMessage BuildImpl();
-    protected abstract IMessage BuildPartialImpl();
-    protected abstract IBuilder CloneImpl();
-    protected abstract IMessage DefaultInstanceForTypeImpl { get; }
-    protected abstract IBuilder ClearFieldImpl(FieldDescriptor field);
-    protected abstract IBuilder AddRepeatedFieldImpl(FieldDescriptor field, object value);
-    #endregion
+    #region Implementation of methods which don't require type parameter information
+    public IMessage WeakBuild() {
+      return Build();
+    }
 
-    #region Methods simply proxying to the "Impl" methods, explicitly implementing IBuilder
-    IMessage IBuilder.Build() {
-      return BuildImpl();
+    public IBuilder WeakAddRepeatedField(FieldDescriptor field, object value) {
+      return AddRepeatedField(field, value);
     }
 
-    IMessage IBuilder.BuildPartial() {
-      return BuildPartialImpl();
+    public IBuilder WeakClear() {
+      return Clear();
     }
 
-    IBuilder IBuilder.Clone() {
-      return CloneImpl();
+    public IBuilder WeakMergeFrom(IMessage message) {
+      return MergeFrom(message);
     }
-    
-    IMessage IBuilder.DefaultInstanceForType {
-      get { return DefaultInstanceForTypeImpl; }
+
+    public IBuilder WeakMergeFrom(CodedInputStream input) {
+      return MergeFrom(input);
     }
 
-    public abstract IBuilder CreateBuilderForField(FieldDescriptor field);
+    public IBuilder WeakMergeFrom(CodedInputStream input, ExtensionRegistry registry) {
+      return MergeFrom(input, registry);
+    }
+
+    public IBuilder WeakMergeFrom(ByteString data) {
+      return MergeFrom(data);
+    }
+
+    public IBuilder WeakMergeFrom(ByteString data, ExtensionRegistry registry) {
+      return MergeFrom(data, registry);
+    }
 
-    IBuilder IBuilder.ClearField(FieldDescriptor field) {
-      return ClearFieldImpl(field);
+    public IMessage WeakBuildPartial() {
+      return BuildPartial();
     }
 
-    IBuilder IBuilder.AddRepeatedField(FieldDescriptor field, object value) {
-      return AddRepeatedFieldImpl(field, value);
+    public IBuilder WeakClone() {
+      return Clone();
+    }
+
+    public IMessage WeakDefaultInstanceForType {
+      get { return DefaultInstanceForType; } 
+    }
+
+    public IBuilder WeakClearField(FieldDescriptor field) {
+      return ClearField(field);
     }
     #endregion
 
-    public virtual IBuilder Clear() {
+    public virtual TBuilder Clear() {
       foreach(FieldDescriptor field in AllFields.Keys) {
-        ClearFieldImpl(field);
+        ClearField(field);
       }
-      return this;
+      return ThisBuilder;
     }
 
-    public virtual IBuilder MergeFrom(IMessage other) {
+    public virtual TBuilder MergeFrom(IMessage other) {
       if (other.DescriptorForType != DescriptorForType) {
-        throw new ArgumentException("MergeFrom(Message) can only merge messages of the same type.");
+        throw new ArgumentException("MergeFrom(IMessage) can only merge messages of the same type.");
       }
 
       // Note:  We don't attempt to verify that other's fields have valid
@@ -83,101 +109,95 @@ namespace Google.ProtocolBuffers {
         if (field.IsRepeated) {
           // Concatenate repeated fields
           foreach (object element in (IEnumerable) entry.Value) {
-            AddRepeatedFieldImpl(field, element);
+            AddRepeatedField(field, element);
           }
         } else if (field.MappedType == MappedType.Message) {
           // Merge singular messages
           IMessage existingValue = (IMessage) this[field];
-          if (existingValue == existingValue.DefaultInstanceForType) {
+          if (existingValue == existingValue.WeakDefaultInstanceForType) {
             this[field] = entry.Value;
           } else {
-            this[field] = existingValue.CreateBuilderForType()
-                                       .MergeFrom(existingValue)
-                                       .MergeFrom((IMessage) entry.Value)
-                                       .Build();
+            this[field] = existingValue.WeakCreateBuilderForType()
+                                       .WeakMergeFrom(existingValue)
+                                       .WeakMergeFrom((IMessage) entry.Value)
+                                       .WeakBuild();
           }
         } else {
           // Overwrite simple values
           this[field] = entry.Value;
         }
       }
-      return this;
+      return ThisBuilder;
     }
 
-    IBuilder IBuilder.MergeFrom(CodedInputStream input) {
-      return MergeFromImpl(input, ExtensionRegistry.Empty);
+    public virtual TBuilder MergeFrom(CodedInputStream input) {
+      return MergeFrom(input, ExtensionRegistry.Empty);
     }
 
-    protected virtual IBuilder MergeFromImpl(CodedInputStream input, ExtensionRegistry extensionRegistry) {
+    public virtual TBuilder MergeFrom(CodedInputStream input, ExtensionRegistry extensionRegistry) {
       UnknownFieldSet.Builder unknownFields = UnknownFieldSet.CreateBuilder(UnknownFields);
       FieldSet.MergeFrom(input, unknownFields, extensionRegistry, this);
       UnknownFields = unknownFields.Build();
-      return this;
-    }
-
-    IBuilder IBuilder.MergeFrom(CodedInputStream input, ExtensionRegistry extensionRegistry) {
-      return MergeFromImpl(input, extensionRegistry);
+      return ThisBuilder;
     }
 
-    IBuilder IBuilder.MergeUnknownFields(UnknownFieldSet unknownFields) {
+    public virtual TBuilder MergeUnknownFields(UnknownFieldSet unknownFields) {
       UnknownFields = UnknownFieldSet.CreateBuilder(UnknownFields)
           .MergeFrom(unknownFields)
           .Build();
-      return this;
+      return ThisBuilder;
     }
 
-    IBuilder IBuilder.MergeFrom(ByteString data) {
+    public virtual TBuilder MergeFrom(ByteString data) {
       CodedInputStream input = data.CreateCodedInput();
-      ((IBuilder)this).MergeFrom(input);
+      MergeFrom(input);
       input.CheckLastTagWas(0);
-      return this;
+      return ThisBuilder;
     }
 
-    IBuilder IBuilder.MergeFrom(ByteString data, ExtensionRegistry extensionRegistry) {
+    public virtual TBuilder MergeFrom(ByteString data, ExtensionRegistry extensionRegistry) {
       CodedInputStream input = data.CreateCodedInput();
-      ((IBuilder)this).MergeFrom(input, extensionRegistry);
+      MergeFrom(input, extensionRegistry);
       input.CheckLastTagWas(0);
-      return this;
+      return ThisBuilder;
     }
 
-    IBuilder IBuilder.MergeFrom(byte[] data) {
+    public virtual TBuilder MergeFrom(byte[] data) {
       CodedInputStream input = CodedInputStream.CreateInstance(data);
-      ((IBuilder)this).MergeFrom(input);
+      MergeFrom(input);
       input.CheckLastTagWas(0);
-      return this;
+      return ThisBuilder;
     }
 
-    IBuilder IBuilder.MergeFrom(byte[] data, ExtensionRegistry extensionRegistry) {
+    public virtual TBuilder MergeFrom(byte[] data, ExtensionRegistry extensionRegistry) {
       CodedInputStream input = CodedInputStream.CreateInstance(data);
-      ((IBuilder)this).MergeFrom(input, extensionRegistry);
+      MergeFrom(input, extensionRegistry);
       input.CheckLastTagWas(0);
-      return this;
+      return ThisBuilder;
     }
 
-    IBuilder IBuilder.MergeFrom(Stream input) {
+    public virtual TBuilder MergeFrom(Stream input) {
       CodedInputStream codedInput = CodedInputStream.CreateInstance(input);
-      ((IBuilder)this).MergeFrom(codedInput);
+      MergeFrom(codedInput);
       codedInput.CheckLastTagWas(0);
-      return this;
+      return ThisBuilder;
     }
 
-    IBuilder IBuilder.MergeFrom(Stream input, ExtensionRegistry extensionRegistry) {
+    public virtual TBuilder MergeFrom(Stream input, ExtensionRegistry extensionRegistry) {
       CodedInputStream codedInput = CodedInputStream.CreateInstance(input);
-      ((IBuilder)this).MergeFrom(codedInput, extensionRegistry);
+      MergeFrom(codedInput, extensionRegistry);
       codedInput.CheckLastTagWas(0);
-      return this;
+      return ThisBuilder;
     }
 
-    public abstract UnknownFieldSet UnknownFields { get; set; }
-    
-    public IBuilder SetField(FieldDescriptor field, object value) {
+    public virtual IBuilder SetField(FieldDescriptor field, object value) {
       this[field] = value;
-      return this;
+      return ThisBuilder;
     }
 
-    public IBuilder SetRepeatedField(FieldDescriptor field, int index, object value) {
+    public virtual IBuilder SetRepeatedField(FieldDescriptor field, int index, object value) {
       this[field, index] = value;
-      return this;
+      return ThisBuilder;
     }
   }
 }
diff --git a/csharp/ProtocolBuffers/AbstractMessage.cs b/csharp/ProtocolBuffers/AbstractMessage.cs
index 6dfcc46d..87172932 100644
--- a/csharp/ProtocolBuffers/AbstractMessage.cs
+++ b/csharp/ProtocolBuffers/AbstractMessage.cs
@@ -23,7 +23,9 @@ namespace Google.ProtocolBuffers {
   /// <summary>
   /// Implementation of the non-generic IMessage interface as far as possible.
   /// </summary>
-  public abstract class AbstractMessage : IMessage {
+  public abstract class AbstractMessage<TMessage, TBuilder> : IMessage<TMessage, TBuilder> 
+      where TMessage : AbstractMessage<TMessage, TBuilder> 
+      where TBuilder : AbstractBuilder<TMessage, TBuilder> {
     // TODO(jonskeet): Cleaner to use a Nullable<int>?
     /// <summary>
     /// The serialized size if it's already been computed, or -1
@@ -39,21 +41,17 @@ namespace Google.ProtocolBuffers {
     public abstract int GetRepeatedFieldCount(FieldDescriptor field);
     public abstract object this[FieldDescriptor field, int index] { get; }
     public abstract UnknownFieldSet UnknownFields { get; }
+    public abstract TMessage DefaultInstanceForType { get; }
+    public abstract TBuilder CreateBuilderForType();
     #endregion
-
-    #region New abstract methods to be overridden by implementations, allow explicit interface implementation
-    protected abstract IMessage DefaultInstanceForTypeImpl { get; }
-    protected abstract IBuilder CreateBuilderForTypeImpl();
-    #endregion
-
-    #region Methods simply proxying to the "Impl" methods, explicitly implementing IMessage
-    IMessage IMessage.DefaultInstanceForType { 
-      get { return DefaultInstanceForTypeImpl; }
+    
+    public IBuilder WeakCreateBuilderForType() {
+      return CreateBuilderForType();
     }
-    IBuilder IMessage.CreateBuilderForType() { 
-      return CreateBuilderForTypeImpl(); 
+
+    public IMessage WeakDefaultInstanceForType {
+      get { return DefaultInstanceForType; }
     }
-    #endregion
 
     public virtual bool IsInitialized {
       get {
@@ -71,7 +69,7 @@ namespace Google.ProtocolBuffers {
             if (field.IsRepeated) {
               // We know it's an IList<T>, but not the exact type - so
               // IEnumerable is the best we can do. (C# generics aren't covariant yet.)
-              foreach (IMessage element in (IEnumerable)entry.Value) {
+              foreach (IMessage element in (IEnumerable) entry.Value) {
                 if (!element.IsInitialized) {
                   return false;
                 }
@@ -124,7 +122,7 @@ namespace Google.ProtocolBuffers {
         foreach (KeyValuePair<FieldDescriptor, object> entry in AllFields) {
           FieldDescriptor field = entry.Key;
           if (field.IsRepeated) {
-            foreach (object element in (IEnumerable)entry.Value) {
+            foreach (object element in (IEnumerable) entry.Value) {
               size += CodedOutputStream.ComputeFieldSize(field.FieldType, field.FieldNumber, element);
             }
           } else {
diff --git a/csharp/ProtocolBuffers/CodedInputStream.cs b/csharp/ProtocolBuffers/CodedInputStream.cs
index 7fab7d21..d9dbc217 100644
--- a/csharp/ProtocolBuffers/CodedInputStream.cs
+++ b/csharp/ProtocolBuffers/CodedInputStream.cs
@@ -224,7 +224,7 @@ namespace Google.ProtocolBuffers {
         throw InvalidProtocolBufferException.RecursionLimitExceeded();
       }
       ++recursionDepth;
-      builder.MergeFrom(this, extensionRegistry);
+      builder.WeakMergeFrom(this, extensionRegistry);
       CheckLastTagWas(WireFormat.MakeTag(fieldNumber, WireFormat.WireType.EndGroup));
       --recursionDepth;
     }
@@ -253,7 +253,7 @@ namespace Google.ProtocolBuffers {
       }
       int oldLimit = PushLimit(length);
       ++recursionDepth;
-      builder.MergeFrom(this, extensionRegistry);
+      builder.WeakMergeFrom(this, extensionRegistry);
       CheckLastTagWas(0);
       --recursionDepth;
       PopLimit(oldLimit);
diff --git a/csharp/ProtocolBuffers/DescriptorProtos/DescriptorProtoFile.cs b/csharp/ProtocolBuffers/DescriptorProtos/DescriptorProtoFile.cs
index a7772cf8..fe8d0656 100644
--- a/csharp/ProtocolBuffers/DescriptorProtos/DescriptorProtoFile.cs
+++ b/csharp/ProtocolBuffers/DescriptorProtos/DescriptorProtoFile.cs
@@ -492,12 +492,16 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::FileDescriptorProto> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::FileDescriptorProto prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::FileDescriptorProto, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::FileDescriptorProto.CreateBuilder()
       internal Builder() {}
       
@@ -507,12 +511,12 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::FileDescriptorProto> Clear() {
+      public override Builder Clear() {
         result = new self::FileDescriptorProto();
         return this;
       }
       
-      public override IBuilder<self::FileDescriptorProto> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -543,11 +547,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::FileDescriptorProto) {
           return MergeFrom((self::FileDescriptorProto) other);
         } else {
@@ -556,7 +556,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         }
       }
       
-      public override IBuilder<self::FileDescriptorProto> MergeFrom(self::FileDescriptorProto other) {
+      public override Builder MergeFrom(self::FileDescriptorProto other) {
         if (other == self::FileDescriptorProto.DefaultInstance) return this;
         if (other.HasName) {
           Name = other.Name;
@@ -601,11 +601,11 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return this;
       }
       
-      public override IBuilder<self::FileDescriptorProto> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::FileDescriptorProto> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -1084,12 +1084,16 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         }
         
         public static Builder CreateBuilder() { return new Builder(); }
-        public override IBuilder<self::DescriptorProto.Types.ExtensionRange> CreateBuilderForType() { return new Builder(); }
+        public override Builder CreateBuilderForType() { return new Builder(); }
         public static Builder CreateBuilder(self::DescriptorProto.Types.ExtensionRange prototype) {
           return (Builder) new Builder().MergeFrom(prototype);
         }
         
         public sealed partial class Builder : pb::GeneratedBuilder<self::DescriptorProto.Types.ExtensionRange, Builder> {
+          protected override Builder ThisBuilder {
+            get { return this; }
+          }
+          
           // Construct using self::DescriptorProto.Types.ExtensionRange.CreateBuilder()
           internal Builder() {}
           
@@ -1099,12 +1103,12 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
             get { return result; }
           }
           
-          public override IBuilder<self::DescriptorProto.Types.ExtensionRange> Clear() {
+          public override Builder Clear() {
             result = new self::DescriptorProto.Types.ExtensionRange();
             return this;
           }
           
-          public override IBuilder<self::DescriptorProto.Types.ExtensionRange> Clone() {
+          public override Builder Clone() {
             return new Builder().MergeFrom(result);
           }
           
@@ -1122,11 +1126,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
             return returnMe;
           }
           
-          protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-            return MergeFrom(data, extensionRegistry);
-          }
-          
-          public override IBuilder MergeFrom(pb::IMessage other) {
+          public override Builder MergeFrom(pb::IMessage other) {
             if (other is self::DescriptorProto.Types.ExtensionRange) {
               return MergeFrom((self::DescriptorProto.Types.ExtensionRange) other);
             } else {
@@ -1135,7 +1135,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
             }
           }
           
-          public override IBuilder<self::DescriptorProto.Types.ExtensionRange> MergeFrom(self::DescriptorProto.Types.ExtensionRange other) {
+          public override Builder MergeFrom(self::DescriptorProto.Types.ExtensionRange other) {
             if (other == self::DescriptorProto.Types.ExtensionRange.DefaultInstance) return this;
             if (other.HasStart) {
               Start = other.Start;
@@ -1147,11 +1147,11 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
             return this;
           }
           
-          public override IBuilder<self::DescriptorProto.Types.ExtensionRange> MergeFrom(pb::CodedInputStream input) {
+          public override Builder MergeFrom(pb::CodedInputStream input) {
             return MergeFrom(input, pb::ExtensionRegistry.Empty);
           }
           
-          public override IBuilder<self::DescriptorProto.Types.ExtensionRange> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+          public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
             pb::UnknownFieldSet.Builder unknownFields =
               pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
             while (true) {
@@ -1404,12 +1404,16 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::DescriptorProto> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::DescriptorProto prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::DescriptorProto, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::DescriptorProto.CreateBuilder()
       internal Builder() {}
       
@@ -1419,12 +1423,12 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::DescriptorProto> Clear() {
+      public override Builder Clear() {
         result = new self::DescriptorProto();
         return this;
       }
       
-      public override IBuilder<self::DescriptorProto> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -1457,11 +1461,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::DescriptorProto) {
           return MergeFrom((self::DescriptorProto) other);
         } else {
@@ -1470,7 +1470,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         }
       }
       
-      public override IBuilder<self::DescriptorProto> MergeFrom(self::DescriptorProto other) {
+      public override Builder MergeFrom(self::DescriptorProto other) {
         if (other == self::DescriptorProto.DefaultInstance) return this;
         if (other.HasName) {
           Name = other.Name;
@@ -1512,11 +1512,11 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return this;
       }
       
-      public override IBuilder<self::DescriptorProto> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::DescriptorProto> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -2091,12 +2091,16 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::FieldDescriptorProto> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::FieldDescriptorProto prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::FieldDescriptorProto, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::FieldDescriptorProto.CreateBuilder()
       internal Builder() {}
       
@@ -2106,12 +2110,12 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::FieldDescriptorProto> Clear() {
+      public override Builder Clear() {
         result = new self::FieldDescriptorProto();
         return this;
       }
       
-      public override IBuilder<self::FieldDescriptorProto> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -2129,11 +2133,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::FieldDescriptorProto) {
           return MergeFrom((self::FieldDescriptorProto) other);
         } else {
@@ -2142,7 +2142,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         }
       }
       
-      public override IBuilder<self::FieldDescriptorProto> MergeFrom(self::FieldDescriptorProto other) {
+      public override Builder MergeFrom(self::FieldDescriptorProto other) {
         if (other == self::FieldDescriptorProto.DefaultInstance) return this;
         if (other.HasName) {
           Name = other.Name;
@@ -2172,11 +2172,11 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return this;
       }
       
-      public override IBuilder<self::FieldDescriptorProto> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::FieldDescriptorProto> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -2541,12 +2541,16 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::EnumDescriptorProto> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::EnumDescriptorProto prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::EnumDescriptorProto, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::EnumDescriptorProto.CreateBuilder()
       internal Builder() {}
       
@@ -2556,12 +2560,12 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::EnumDescriptorProto> Clear() {
+      public override Builder Clear() {
         result = new self::EnumDescriptorProto();
         return this;
       }
       
-      public override IBuilder<self::EnumDescriptorProto> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -2582,11 +2586,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::EnumDescriptorProto) {
           return MergeFrom((self::EnumDescriptorProto) other);
         } else {
@@ -2595,7 +2595,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         }
       }
       
-      public override IBuilder<self::EnumDescriptorProto> MergeFrom(self::EnumDescriptorProto other) {
+      public override Builder MergeFrom(self::EnumDescriptorProto other) {
         if (other == self::EnumDescriptorProto.DefaultInstance) return this;
         if (other.HasName) {
           Name = other.Name;
@@ -2613,11 +2613,11 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return this;
       }
       
-      public override IBuilder<self::EnumDescriptorProto> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::EnumDescriptorProto> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -2882,12 +2882,16 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::EnumValueDescriptorProto> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::EnumValueDescriptorProto prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::EnumValueDescriptorProto, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::EnumValueDescriptorProto.CreateBuilder()
       internal Builder() {}
       
@@ -2897,12 +2901,12 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::EnumValueDescriptorProto> Clear() {
+      public override Builder Clear() {
         result = new self::EnumValueDescriptorProto();
         return this;
       }
       
-      public override IBuilder<self::EnumValueDescriptorProto> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -2920,11 +2924,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::EnumValueDescriptorProto) {
           return MergeFrom((self::EnumValueDescriptorProto) other);
         } else {
@@ -2933,7 +2933,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         }
       }
       
-      public override IBuilder<self::EnumValueDescriptorProto> MergeFrom(self::EnumValueDescriptorProto other) {
+      public override Builder MergeFrom(self::EnumValueDescriptorProto other) {
         if (other == self::EnumValueDescriptorProto.DefaultInstance) return this;
         if (other.HasName) {
           Name = other.Name;
@@ -2948,11 +2948,11 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return this;
       }
       
-      public override IBuilder<self::EnumValueDescriptorProto> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::EnumValueDescriptorProto> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -3192,12 +3192,16 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::ServiceDescriptorProto> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::ServiceDescriptorProto prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::ServiceDescriptorProto, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::ServiceDescriptorProto.CreateBuilder()
       internal Builder() {}
       
@@ -3207,12 +3211,12 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::ServiceDescriptorProto> Clear() {
+      public override Builder Clear() {
         result = new self::ServiceDescriptorProto();
         return this;
       }
       
-      public override IBuilder<self::ServiceDescriptorProto> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -3233,11 +3237,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::ServiceDescriptorProto) {
           return MergeFrom((self::ServiceDescriptorProto) other);
         } else {
@@ -3246,7 +3246,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         }
       }
       
-      public override IBuilder<self::ServiceDescriptorProto> MergeFrom(self::ServiceDescriptorProto other) {
+      public override Builder MergeFrom(self::ServiceDescriptorProto other) {
         if (other == self::ServiceDescriptorProto.DefaultInstance) return this;
         if (other.HasName) {
           Name = other.Name;
@@ -3264,11 +3264,11 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return this;
       }
       
-      public override IBuilder<self::ServiceDescriptorProto> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::ServiceDescriptorProto> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -3549,12 +3549,16 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::MethodDescriptorProto> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::MethodDescriptorProto prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::MethodDescriptorProto, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::MethodDescriptorProto.CreateBuilder()
       internal Builder() {}
       
@@ -3564,12 +3568,12 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::MethodDescriptorProto> Clear() {
+      public override Builder Clear() {
         result = new self::MethodDescriptorProto();
         return this;
       }
       
-      public override IBuilder<self::MethodDescriptorProto> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -3587,11 +3591,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::MethodDescriptorProto) {
           return MergeFrom((self::MethodDescriptorProto) other);
         } else {
@@ -3600,7 +3600,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         }
       }
       
-      public override IBuilder<self::MethodDescriptorProto> MergeFrom(self::MethodDescriptorProto other) {
+      public override Builder MergeFrom(self::MethodDescriptorProto other) {
         if (other == self::MethodDescriptorProto.DefaultInstance) return this;
         if (other.HasName) {
           Name = other.Name;
@@ -3618,11 +3618,11 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return this;
       }
       
-      public override IBuilder<self::MethodDescriptorProto> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::MethodDescriptorProto> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -3988,12 +3988,16 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::FileOptions> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::FileOptions prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::FileOptions, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::FileOptions.CreateBuilder()
       internal Builder() {}
       
@@ -4003,12 +4007,12 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::FileOptions> Clear() {
+      public override Builder Clear() {
         result = new self::FileOptions();
         return this;
       }
       
-      public override IBuilder<self::FileOptions> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -4026,11 +4030,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::FileOptions) {
           return MergeFrom((self::FileOptions) other);
         } else {
@@ -4039,7 +4039,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         }
       }
       
-      public override IBuilder<self::FileOptions> MergeFrom(self::FileOptions other) {
+      public override Builder MergeFrom(self::FileOptions other) {
         if (other == self::FileOptions.DefaultInstance) return this;
         if (other.HasJavaPackage) {
           JavaPackage = other.JavaPackage;
@@ -4072,11 +4072,11 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return this;
       }
       
-      public override IBuilder<self::FileOptions> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::FileOptions> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -4404,12 +4404,16 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::MessageOptions> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::MessageOptions prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::MessageOptions, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::MessageOptions.CreateBuilder()
       internal Builder() {}
       
@@ -4419,12 +4423,12 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::MessageOptions> Clear() {
+      public override Builder Clear() {
         result = new self::MessageOptions();
         return this;
       }
       
-      public override IBuilder<self::MessageOptions> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -4442,11 +4446,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::MessageOptions) {
           return MergeFrom((self::MessageOptions) other);
         } else {
@@ -4455,7 +4455,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         }
       }
       
-      public override IBuilder<self::MessageOptions> MergeFrom(self::MessageOptions other) {
+      public override Builder MergeFrom(self::MessageOptions other) {
         if (other == self::MessageOptions.DefaultInstance) return this;
         if (other.HasMessageSetWireFormat) {
           MessageSetWireFormat = other.MessageSetWireFormat;
@@ -4464,11 +4464,11 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return this;
       }
       
-      public override IBuilder<self::MessageOptions> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::MessageOptions> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -4632,12 +4632,16 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::FieldOptions> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::FieldOptions prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::FieldOptions, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::FieldOptions.CreateBuilder()
       internal Builder() {}
       
@@ -4647,12 +4651,12 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::FieldOptions> Clear() {
+      public override Builder Clear() {
         result = new self::FieldOptions();
         return this;
       }
       
-      public override IBuilder<self::FieldOptions> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -4670,11 +4674,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::FieldOptions) {
           return MergeFrom((self::FieldOptions) other);
         } else {
@@ -4683,7 +4683,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         }
       }
       
-      public override IBuilder<self::FieldOptions> MergeFrom(self::FieldOptions other) {
+      public override Builder MergeFrom(self::FieldOptions other) {
         if (other == self::FieldOptions.DefaultInstance) return this;
         if (other.HasCtype) {
           Ctype = other.Ctype;
@@ -4695,11 +4695,11 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return this;
       }
       
-      public override IBuilder<self::FieldOptions> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::FieldOptions> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -4850,12 +4850,16 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::EnumOptions> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::EnumOptions prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::EnumOptions, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::EnumOptions.CreateBuilder()
       internal Builder() {}
       
@@ -4865,12 +4869,12 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::EnumOptions> Clear() {
+      public override Builder Clear() {
         result = new self::EnumOptions();
         return this;
       }
       
-      public override IBuilder<self::EnumOptions> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -4888,11 +4892,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::EnumOptions) {
           return MergeFrom((self::EnumOptions) other);
         } else {
@@ -4901,17 +4901,17 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         }
       }
       
-      public override IBuilder<self::EnumOptions> MergeFrom(self::EnumOptions other) {
+      public override Builder MergeFrom(self::EnumOptions other) {
         if (other == self::EnumOptions.DefaultInstance) return this;
         this.MergeUnknownFields(other.UnknownFields);
         return this;
       }
       
-      public override IBuilder<self::EnumOptions> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::EnumOptions> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -5011,12 +5011,16 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::EnumValueOptions> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::EnumValueOptions prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::EnumValueOptions, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::EnumValueOptions.CreateBuilder()
       internal Builder() {}
       
@@ -5026,12 +5030,12 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::EnumValueOptions> Clear() {
+      public override Builder Clear() {
         result = new self::EnumValueOptions();
         return this;
       }
       
-      public override IBuilder<self::EnumValueOptions> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -5049,11 +5053,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::EnumValueOptions) {
           return MergeFrom((self::EnumValueOptions) other);
         } else {
@@ -5062,17 +5062,17 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         }
       }
       
-      public override IBuilder<self::EnumValueOptions> MergeFrom(self::EnumValueOptions other) {
+      public override Builder MergeFrom(self::EnumValueOptions other) {
         if (other == self::EnumValueOptions.DefaultInstance) return this;
         this.MergeUnknownFields(other.UnknownFields);
         return this;
       }
       
-      public override IBuilder<self::EnumValueOptions> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::EnumValueOptions> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -5172,12 +5172,16 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::ServiceOptions> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::ServiceOptions prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::ServiceOptions, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::ServiceOptions.CreateBuilder()
       internal Builder() {}
       
@@ -5187,12 +5191,12 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::ServiceOptions> Clear() {
+      public override Builder Clear() {
         result = new self::ServiceOptions();
         return this;
       }
       
-      public override IBuilder<self::ServiceOptions> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -5210,11 +5214,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::ServiceOptions) {
           return MergeFrom((self::ServiceOptions) other);
         } else {
@@ -5223,17 +5223,17 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         }
       }
       
-      public override IBuilder<self::ServiceOptions> MergeFrom(self::ServiceOptions other) {
+      public override Builder MergeFrom(self::ServiceOptions other) {
         if (other == self::ServiceOptions.DefaultInstance) return this;
         this.MergeUnknownFields(other.UnknownFields);
         return this;
       }
       
-      public override IBuilder<self::ServiceOptions> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::ServiceOptions> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
@@ -5333,12 +5333,16 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     }
     
     public static Builder CreateBuilder() { return new Builder(); }
-    public override IBuilder<self::MethodOptions> CreateBuilderForType() { return new Builder(); }
+    public override Builder CreateBuilderForType() { return new Builder(); }
     public static Builder CreateBuilder(self::MethodOptions prototype) {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
     public sealed partial class Builder : pb::GeneratedBuilder<self::MethodOptions, Builder> {
+      protected override Builder ThisBuilder {
+        get { return this; }
+      }
+      
       // Construct using self::MethodOptions.CreateBuilder()
       internal Builder() {}
       
@@ -5348,12 +5352,12 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         get { return result; }
       }
       
-      public override IBuilder<self::MethodOptions> Clear() {
+      public override Builder Clear() {
         result = new self::MethodOptions();
         return this;
       }
       
-      public override IBuilder<self::MethodOptions> Clone() {
+      public override Builder Clone() {
         return new Builder().MergeFrom(result);
       }
       
@@ -5371,11 +5375,7 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return returnMe;
       }
       
-      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-        return MergeFrom(data, extensionRegistry);
-      }
-      
-      public override IBuilder MergeFrom(pb::IMessage other) {
+      public override Builder MergeFrom(pb::IMessage other) {
         if (other is self::MethodOptions) {
           return MergeFrom((self::MethodOptions) other);
         } else {
@@ -5384,17 +5384,17 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         }
       }
       
-      public override IBuilder<self::MethodOptions> MergeFrom(self::MethodOptions other) {
+      public override Builder MergeFrom(self::MethodOptions other) {
         if (other == self::MethodOptions.DefaultInstance) return this;
         this.MergeUnknownFields(other.UnknownFields);
         return this;
       }
       
-      public override IBuilder<self::MethodOptions> MergeFrom(pb::CodedInputStream input) {
+      public override Builder MergeFrom(pb::CodedInputStream input) {
         return MergeFrom(input, pb::ExtensionRegistry.Empty);
       }
       
-      public override IBuilder<self::MethodOptions> MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(pb::CodedInputStream input, pb::ExtensionRegistry extensionRegistry) {
         pb::UnknownFieldSet.Builder unknownFields =
           pb::UnknownFieldSet.CreateBuilder(this.UnknownFields);
         while (true) {
diff --git a/csharp/ProtocolBuffers/DynamicMessage.cs b/csharp/ProtocolBuffers/DynamicMessage.cs
index 675c4c18..9690981e 100644
--- a/csharp/ProtocolBuffers/DynamicMessage.cs
+++ b/csharp/ProtocolBuffers/DynamicMessage.cs
@@ -10,7 +10,7 @@ namespace Google.ProtocolBuffers {
   /// An implementation of IMessage that can represent arbitrary types, given a MessageaDescriptor.
   /// TODO: Implement appropriate generics.
   /// </summary>
-  public class DynamicMessage : AbstractMessage {
+  public class DynamicMessage : AbstractMessage<DynamicMessage, DynamicMessage.Builder> {
 
     private readonly MessageDescriptor type;
     private readonly FieldSet fields;
@@ -42,8 +42,8 @@ namespace Google.ProtocolBuffers {
     /// Parses a message of the given type from the given stream.
     /// </summary>
     public static DynamicMessage ParseFrom(MessageDescriptor type, CodedInputStream input) {
-      IBuilder builder = CreateBuilder(type);
-      Builder dynamicBuilder = (Builder)builder.MergeFrom(input);
+      Builder builder = CreateBuilder(type);
+      Builder dynamicBuilder = builder.MergeFrom(input);
       return dynamicBuilder.BuildParsed();
 
     }
@@ -56,8 +56,8 @@ namespace Google.ProtocolBuffers {
     /// <param name="extensionRegistry"></param>
     /// <returns></returns>
     public static DynamicMessage ParseFrom(MessageDescriptor type, CodedInputStream input, ExtensionRegistry extensionRegistry) {
-      IBuilder builder = CreateBuilder(type);
-      Builder dynamicBuilder = (Builder) builder.MergeFrom(input, extensionRegistry);
+      Builder builder = CreateBuilder(type);
+      Builder dynamicBuilder = builder.MergeFrom(input, extensionRegistry);
       return dynamicBuilder.BuildParsed();
     }
 
@@ -65,8 +65,8 @@ namespace Google.ProtocolBuffers {
     /// Parses a message of the given type from the given stream.
     /// </summary>
     public static DynamicMessage ParseFrom(MessageDescriptor type, Stream input) {
-      IBuilder builder = CreateBuilder(type);
-      Builder dynamicBuilder = (Builder)builder.MergeFrom(input);
+      Builder builder = CreateBuilder(type);
+      Builder dynamicBuilder = builder.MergeFrom(input);
       return dynamicBuilder.BuildParsed();
     }
 
@@ -78,8 +78,8 @@ namespace Google.ProtocolBuffers {
     /// <param name="extensionRegistry"></param>
     /// <returns></returns>
     public static DynamicMessage ParseFrom(MessageDescriptor type, Stream input, ExtensionRegistry extensionRegistry) {
-      IBuilder builder = CreateBuilder(type);
-      Builder dynamicBuilder = (Builder)builder.MergeFrom(input, extensionRegistry);
+      Builder builder = CreateBuilder(type);
+      Builder dynamicBuilder = builder.MergeFrom(input, extensionRegistry);
       return dynamicBuilder.BuildParsed();
     }
 
@@ -87,8 +87,8 @@ namespace Google.ProtocolBuffers {
     /// Parse <paramref name="data"/> as a message of the given type and return it.
     /// </summary>
     public static DynamicMessage ParseFrom(MessageDescriptor type, ByteString data) {
-      IBuilder builder = CreateBuilder(type);
-      Builder dynamicBuilder = (Builder)builder.MergeFrom(data);
+      Builder builder = CreateBuilder(type);
+      Builder dynamicBuilder = builder.MergeFrom(data);
       return dynamicBuilder.BuildParsed();
     }
 
@@ -96,8 +96,8 @@ namespace Google.ProtocolBuffers {
     /// Parse <paramref name="data"/> as a message of the given type and return it.
     /// </summary>
     public static DynamicMessage ParseFrom(MessageDescriptor type, ByteString data, ExtensionRegistry extensionRegistry) {
-      IBuilder builder = CreateBuilder(type);
-      Builder dynamicBuilder = (Builder)builder.MergeFrom(data, extensionRegistry);
+      Builder builder = CreateBuilder(type);
+      Builder dynamicBuilder = builder.MergeFrom(data, extensionRegistry);
       return dynamicBuilder.BuildParsed();
 
     }
@@ -106,8 +106,8 @@ namespace Google.ProtocolBuffers {
     /// Parse <paramref name="data"/> as a message of the given type and return it.
     /// </summary>
     public static DynamicMessage ParseFrom(MessageDescriptor type, byte[] data) {
-      IBuilder builder = CreateBuilder(type);
-      Builder dynamicBuilder = (Builder)builder.MergeFrom(data);
+      Builder builder = CreateBuilder(type);
+      Builder dynamicBuilder = builder.MergeFrom(data);
       return dynamicBuilder.BuildParsed();
     }
 
@@ -115,8 +115,8 @@ namespace Google.ProtocolBuffers {
     /// Parse <paramref name="data"/> as a message of the given type and return it.
     /// </summary>
     public static DynamicMessage ParseFrom(MessageDescriptor type, byte[] data, ExtensionRegistry extensionRegistry) {
-      IBuilder builder = CreateBuilder(type);
-      Builder dynamicBuilder = (Builder)builder.MergeFrom(data, extensionRegistry);
+      Builder builder = CreateBuilder(type);
+      Builder dynamicBuilder = builder.MergeFrom(data, extensionRegistry);
       return dynamicBuilder.BuildParsed();
     }
 
@@ -134,7 +134,7 @@ namespace Google.ProtocolBuffers {
     /// <param name="prototype"></param>
     /// <returns></returns>
     public static Builder CreateBuilder(IMessage prototype) {
-      return (Builder) new Builder(prototype.DescriptorForType).MergeFrom(prototype);
+      return new Builder(prototype.DescriptorForType).MergeFrom(prototype);
     }
 
     // -----------------------------------------------------------------
@@ -144,7 +144,7 @@ namespace Google.ProtocolBuffers {
       get { return type; }
     }
 
-    protected override IMessage DefaultInstanceForTypeImpl {
+    public override DynamicMessage DefaultInstanceForType {
       get { return GetDefaultInstance(type); }
     }
 
@@ -214,7 +214,7 @@ namespace Google.ProtocolBuffers {
       }
     }
 
-    protected override IBuilder CreateBuilderForTypeImpl() {
+    public override Builder CreateBuilderForType() {
       return new Builder(type);
     }
 
@@ -227,7 +227,7 @@ namespace Google.ProtocolBuffers {
       }
     }
 
-    public class Builder : AbstractBuilder {
+    public class Builder : AbstractBuilder<DynamicMessage, DynamicMessage.Builder> {
       private readonly MessageDescriptor type;
       private FieldSet fields;
       private UnknownFieldSet unknownFields;
@@ -238,16 +238,16 @@ namespace Google.ProtocolBuffers {
         this.unknownFields = UnknownFieldSet.DefaultInstance;
       }
 
-      public DynamicMessage Build() {
-        return (DynamicMessage)((IBuilder)this).Build();
+      protected override Builder ThisBuilder {
+        get { return this; }
       }
 
-      public override IBuilder Clear() {
+      public override Builder Clear() {
         fields.Clear();
         return this;
       }
 
-      public override IBuilder MergeFrom(IMessage other) {
+      public override Builder MergeFrom(IMessage other) {
         if (other.DescriptorForType != type) {
           throw new ArgumentException("MergeFrom(IMessage) can only merge messages of the same type.");
         }
@@ -255,11 +255,19 @@ namespace Google.ProtocolBuffers {
         return this;
       }
 
-      protected override IMessage BuildImpl() {
+      public override Builder MergeFrom(DynamicMessage other) {
+        if (other.DescriptorForType != type) {
+          throw new ArgumentException("MergeFrom(IMessage) can only merge messages of the same type.");
+        }
+        fields.MergeFrom(other);
+        return this;
+      }
+
+      public override DynamicMessage Build() {
    	    if (!IsInitialized) {
           throw new UninitializedMessageException(new DynamicMessage(type, fields, unknownFields));
         }
-        return BuildPartialImpl();
+        return BuildPartial();
       }
 
       /// <summary>
@@ -271,10 +279,10 @@ namespace Google.ProtocolBuffers {
         if (!IsInitialized) {
           throw new UninitializedMessageException(new DynamicMessage(type, fields, unknownFields)).AsInvalidProtocolBufferException();
         }
-        return (DynamicMessage) BuildPartialImpl();
+        return BuildPartial();
       }
 
-      protected override IMessage BuildPartialImpl() {
+      public override DynamicMessage BuildPartial() {
         fields.MakeImmutable();
         DynamicMessage result = new DynamicMessage(type, fields, unknownFields);
         fields = null;
@@ -282,7 +290,7 @@ namespace Google.ProtocolBuffers {
         return result;
       }
 
-      protected override IBuilder CloneImpl() {
+      public override Builder Clone() {
         Builder result = new Builder(type);
         result.fields.MergeFrom(fields);
         return result;
@@ -292,7 +300,7 @@ namespace Google.ProtocolBuffers {
       	get { return fields.IsInitializedWithRespectTo(type); }
       }
 
-      protected override IBuilder MergeFromImpl(CodedInputStream input, ExtensionRegistry extensionRegistry) {
+      public override Builder MergeFrom(CodedInputStream input, ExtensionRegistry extensionRegistry) {
         UnknownFieldSet.Builder unknownFieldsBuilder = UnknownFieldSet.CreateBuilder(unknownFields);
         FieldSet.MergeFrom(input, unknownFieldsBuilder, extensionRegistry, this);
         unknownFields = unknownFieldsBuilder.Build();
@@ -303,7 +311,7 @@ namespace Google.ProtocolBuffers {
         get { return type; }
       }
 
-      protected override IMessage DefaultInstanceForTypeImpl {
+      public override DynamicMessage DefaultInstanceForType {
         get { return GetDefaultInstance(type); }
       }
 
@@ -316,7 +324,7 @@ namespace Google.ProtocolBuffers {
         if (field.MappedType != MappedType.Message) {
           throw new ArgumentException("CreateBuilderForField is only valid for fields with message type.");
         }
-        return new Builder(field.MessageType);        
+        return new Builder(field.MessageType);     
       }
 
       public override bool HasField(FieldDescriptor field) {
@@ -350,7 +358,7 @@ namespace Google.ProtocolBuffers {
         }
       }
 
-      protected override IBuilder ClearFieldImpl(FieldDescriptor field) {
+      public override Builder ClearField(FieldDescriptor field) {
         VerifyContainingType(field);
         fields.ClearField(field);
         return this;
@@ -361,7 +369,7 @@ namespace Google.ProtocolBuffers {
         return fields.GetRepeatedFieldCount(field);
       }
 
-      protected override IBuilder AddRepeatedFieldImpl(FieldDescriptor field, object value) {
+      public override Builder AddRepeatedField(FieldDescriptor field, object value) {
         VerifyContainingType(field);
         fields.AddRepeatedField(field, value);
         return this;
diff --git a/csharp/ProtocolBuffers/ExtendableBuilder.cs b/csharp/ProtocolBuffers/ExtendableBuilder.cs
index 0c96ace6..b55d4b99 100644
--- a/csharp/ProtocolBuffers/ExtendableBuilder.cs
+++ b/csharp/ProtocolBuffers/ExtendableBuilder.cs
@@ -13,57 +13,55 @@ namespace Google.ProtocolBuffers {
     /// <summary>
     /// Checks if a singular extension is present
     /// </summary>
-    public bool HasExtension<TExtension>(GeneratedExtensionBase<TMessage, TExtension> extension) {
+    public bool HasExtension<TExtension>(GeneratedExtensionBase<TExtension> extension) {
       return MessageBeingBuilt.HasExtension(extension);
     }
 
     /// <summary>
     /// Returns the number of elements in a repeated extension.
     /// </summary>
-    public int GetExtensionCount<TExtension>(GeneratedExtensionBase<TMessage, IList<TExtension>> extension) {
+    public int GetExtensionCount<TExtension>(GeneratedExtensionBase<IList<TExtension>> extension) {
       return MessageBeingBuilt.GetExtensionCount(extension);
     }
 
     /// <summary>
     /// Returns the value of an extension.
     /// </summary>
-    public TExtension GetExtension<TExtension>(GeneratedExtensionBase<TMessage, TExtension> extension) {
+    public TExtension GetExtension<TExtension>(GeneratedExtensionBase<TExtension> extension) {
       return MessageBeingBuilt.GetExtension(extension);
     }
 
     /// <summary>
     /// Returns one element of a repeated extension.
     /// </summary>
-    public TExtension GetExtension<TExtension>(GeneratedExtensionBase<TMessage, IList<TExtension>> extension, int index) {
+    public TExtension GetExtension<TExtension>(GeneratedExtensionBase<IList<TExtension>> extension, int index) {
       return MessageBeingBuilt.GetExtension(extension, index);
     }
 
     /// <summary>
     /// Sets the value of an extension.
     /// </summary>
-    public ExtendableBuilder<TMessage, TBuilder> SetExtension<TExtension>(GeneratedExtensionBase<TMessage, TExtension> extension, TExtension value) {
+    public TBuilder SetExtension<TExtension>(GeneratedExtensionBase<TExtension> extension, TExtension value) {
       ExtendableMessage<TMessage, TBuilder> message = MessageBeingBuilt;
       message.VerifyExtensionContainingType(extension);
       message.Extensions[extension.Descriptor] = extension.ToReflectionType(value);
-      return this;
+      return ThisBuilder;
     }
 
     /// <summary>
     /// Sets the value of one element of a repeated extension.
     /// </summary>
-    public ExtendableBuilder<TMessage, TBuilder> SetExtension<TExtension>(
-        GeneratedExtensionBase<TMessage, IList<TExtension>> extension, int index, TExtension value) {
+    public TBuilder SetExtension<TExtension>(GeneratedExtensionBase<IList<TExtension>> extension, int index, TExtension value) {
       ExtendableMessage<TMessage, TBuilder> message = MessageBeingBuilt;
       message.VerifyExtensionContainingType(extension);
       message.Extensions[extension.Descriptor, index] = extension.SingularToReflectionType(value);
-      return this;
+      return ThisBuilder;
     }
 
     /// <summary>
     /// Appends a value to a repeated extension.
     /// </summary>
-    public ExtendableBuilder<TMessage, TBuilder> AddExtension<TExtension>(
-        GeneratedExtensionBase<TMessage, IList<TExtension>> extension, TExtension value) {
+    public ExtendableBuilder<TMessage, TBuilder> AddExtension<TExtension>(GeneratedExtensionBase<IList<TExtension>> extension, TExtension value) {
       ExtendableMessage<TMessage, TBuilder> message = MessageBeingBuilt;
       message.VerifyExtensionContainingType(extension);
       message.Extensions.AddRepeatedField(extension.Descriptor, extension.SingularToReflectionType(value));
@@ -73,8 +71,7 @@ namespace Google.ProtocolBuffers {
     /// <summary>
     /// Clears an extension.
     /// </summary>
-    public ExtendableBuilder<TMessage, TBuilder> ClearExtension<TExtension>(
-        GeneratedExtensionBase<TMessage, TExtension> extension) {
+    public ExtendableBuilder<TMessage, TBuilder> ClearExtension<TExtension>(GeneratedExtensionBase<TExtension> extension) {
       ExtendableMessage<TMessage, TBuilder> message = MessageBeingBuilt;
       message.VerifyExtensionContainingType(extension);
       message.Extensions.ClearField(extension.Descriptor);
@@ -121,23 +118,23 @@ namespace Google.ProtocolBuffers {
       }
     }
 
-    public override IBuilder<TMessage> ClearField(FieldDescriptor field) {
+    public override TBuilder ClearField(FieldDescriptor field) {
       if (field.IsExtension) {
         ExtendableMessage<TMessage, TBuilder> message = MessageBeingBuilt;
         message.VerifyContainingType(field);
         message.Extensions.ClearField(field);
-        return this;
+        return ThisBuilder;
       } else {
         return base.ClearField(field);
       }
     }
 
-    public override IBuilder<TMessage> AddRepeatedField(FieldDescriptor field, object value) {
+    public override TBuilder AddRepeatedField(FieldDescriptor field, object value) {
       if (field.IsExtension) {
         ExtendableMessage<TMessage, TBuilder> message = MessageBeingBuilt;
         message.VerifyContainingType(field); 
         message.Extensions.AddRepeatedField(field, value);
-        return this;
+        return ThisBuilder;
       } else {
         return base.AddRepeatedField(field, value);
       }
diff --git a/csharp/ProtocolBuffers/ExtendableMessage.cs b/csharp/ProtocolBuffers/ExtendableMessage.cs
index 0a2d0317..60d0d583 100644
--- a/csharp/ProtocolBuffers/ExtendableMessage.cs
+++ b/csharp/ProtocolBuffers/ExtendableMessage.cs
@@ -5,9 +5,9 @@ using Google.ProtocolBuffers.Descriptors;
 using Google.ProtocolBuffers.Collections;
 
 namespace Google.ProtocolBuffers {
-  public abstract class ExtendableMessage<TMessage,TBuilder> : GeneratedMessage<TMessage,TBuilder>
+  public abstract class ExtendableMessage<TMessage, TBuilder> : GeneratedMessage<TMessage, TBuilder>
     where TMessage : GeneratedMessage<TMessage, TBuilder>
-    where TBuilder : IBuilder<TMessage> {
+    where TBuilder : GeneratedBuilder<TMessage, TBuilder> {
 
     protected ExtendableMessage() {}
     private readonly FieldSet extensions = FieldSet.CreateFieldSet();
@@ -22,21 +22,21 @@ namespace Google.ProtocolBuffers {
     /// <summary>
     /// Checks if a singular extension is present.
     /// </summary>
-    public bool HasExtension<TExtension>(GeneratedExtensionBase<TMessage, TExtension> extension) {
+    public bool HasExtension<TExtension>(GeneratedExtensionBase<TExtension> extension) {
       return extensions.HasField(extension.Descriptor);
     }
 
     /// <summary>
     /// Returns the number of elements in a repeated extension.
     /// </summary>
-    public int GetExtensionCount<TExtension>(GeneratedExtensionBase<TMessage, IList<TExtension>> extension) {
+    public int GetExtensionCount<TExtension>(GeneratedExtensionBase<IList<TExtension>> extension) {
       return extensions.GetRepeatedFieldCount(extension.Descriptor);
     }
 
     /// <summary>
     /// Returns the value of an extension.
     /// </summary>
-    public TExtension GetExtension<TExtension>(GeneratedExtensionBase<TMessage, TExtension> extension) {
+    public TExtension GetExtension<TExtension>(GeneratedExtensionBase<TExtension> extension) {
       object value = extensions[extension.Descriptor];
       if (value == null) {
         return (TExtension) extension.MessageDefaultInstance;
@@ -48,7 +48,7 @@ namespace Google.ProtocolBuffers {
     /// <summary>
     /// Returns one element of a repeated extension.
     /// </summary>
-    public TExtension GetExtension<TExtension>(GeneratedExtensionBase<TMessage, IList<TExtension>> extension, int index) {
+    public TExtension GetExtension<TExtension>(GeneratedExtensionBase<IList<TExtension>> extension, int index) {
       return (TExtension) extension.SingularFromReflectionType(extensions[extension.Descriptor, index]);
     }
 
@@ -169,7 +169,7 @@ namespace Google.ProtocolBuffers {
       get { return extensions.SerializedSize; }
     }
 
-    internal void VerifyExtensionContainingType<TExtension>(GeneratedExtensionBase<TMessage, TExtension> extension) {
+    internal void VerifyExtensionContainingType<TExtension>(GeneratedExtensionBase<TExtension> extension) {
       if (extension.Descriptor.ContainingType != DescriptorForType) {
         // This can only happen if someone uses unchecked operations.
         throw new ArgumentException("Extension is for type \"" + extension.Descriptor.ContainingType.FullName
diff --git a/csharp/ProtocolBuffers/ExtensionRegistry.cs b/csharp/ProtocolBuffers/ExtensionRegistry.cs
index c8f31d37..c9e05308 100644
--- a/csharp/ProtocolBuffers/ExtensionRegistry.cs
+++ b/csharp/ProtocolBuffers/ExtensionRegistry.cs
@@ -88,8 +88,7 @@ namespace Google.ProtocolBuffers {
     /// <summary>
     /// Add an extension from a generated file to the registry.
     /// </summary>
-    public void Add<TContainer, TExtension> (GeneratedExtensionBase<TContainer, TExtension> extension) 
-        where TContainer : IMessage<TContainer> {
+    public void Add<TExtension> (GeneratedExtensionBase<TExtension> extension) {
       if (extension.Descriptor.MappedType == MappedType.Message) {
         Add(new ExtensionInfo(extension.Descriptor, extension.MessageDefaultInstance));
       } else {
diff --git a/csharp/ProtocolBuffers/FieldAccess/RepeatedMessageAccessor.cs b/csharp/ProtocolBuffers/FieldAccess/RepeatedMessageAccessor.cs
index 18da75c4..92cc2c94 100644
--- a/csharp/ProtocolBuffers/FieldAccess/RepeatedMessageAccessor.cs
+++ b/csharp/ProtocolBuffers/FieldAccess/RepeatedMessageAccessor.cs
@@ -40,7 +40,7 @@ namespace Google.ProtocolBuffers.FieldAccess {
 
       // No... so let's create a builder of the right type, and merge the value in.
       IMessage message = (IMessage) value;
-      return CreateBuilder().MergeFrom(message).Build();
+      return CreateBuilder().WeakMergeFrom(message).WeakBuild();
     }
 
     public override void SetRepeated(IBuilder builder, int index, object value) {
diff --git a/csharp/ProtocolBuffers/FieldAccess/SingleMessageAccessor.cs b/csharp/ProtocolBuffers/FieldAccess/SingleMessageAccessor.cs
index 20e1ba13..8bdf95d1 100644
--- a/csharp/ProtocolBuffers/FieldAccess/SingleMessageAccessor.cs
+++ b/csharp/ProtocolBuffers/FieldAccess/SingleMessageAccessor.cs
@@ -38,7 +38,7 @@ namespace Google.ProtocolBuffers.FieldAccess {
       
       // No... so let's create a builder of the right type, and merge the value in.
       IMessage message = (IMessage) value;
-      return CreateBuilder().MergeFrom(message).Build();
+      return CreateBuilder().WeakMergeFrom(message).WeakBuild();
     }
 
     public override void SetValue(IBuilder builder, object value) {
diff --git a/csharp/ProtocolBuffers/FieldSet.cs b/csharp/ProtocolBuffers/FieldSet.cs
index 4f660533..79394ca4 100644
--- a/csharp/ProtocolBuffers/FieldSet.cs
+++ b/csharp/ProtocolBuffers/FieldSet.cs
@@ -154,19 +154,19 @@ namespace Google.ProtocolBuffers {
         case FieldType.Message: {
             IBuilder subBuilder;
             if (defaultFieldInstance != null) {
-              subBuilder = defaultFieldInstance.CreateBuilderForType();
+              subBuilder = defaultFieldInstance.WeakCreateBuilderForType();
             } else {
               subBuilder = builder.CreateBuilderForField(field);
             }
             if (!field.IsRepeated) {
-              subBuilder.MergeFrom((IMessage) builder[field]);
+              subBuilder.WeakMergeFrom((IMessage) builder[field]);
             }
             if (field.FieldType == FieldType.Group) {
               input.ReadGroup(field.FieldNumber, subBuilder, extensionRegistry);
             } else {
               input.ReadMessage(subBuilder, extensionRegistry);
             }
-            value = subBuilder.Build();
+            value = subBuilder.WeakBuild();
             break;
           }
         case FieldType.Enum: {
@@ -185,7 +185,7 @@ namespace Google.ProtocolBuffers {
           break;
       }
       if (field.IsRepeated) {
-        builder.AddRepeatedField(field, value);
+        builder.WeakAddRepeatedField(field, value);
       } else {
         builder[field] = value;
       } 
@@ -236,16 +236,16 @@ namespace Google.ProtocolBuffers {
             ExtensionInfo extension = extensionRegistry[type, typeId];
             if (extension != null) {
               field = extension.Descriptor;
-              subBuilder = extension.DefaultInstance.CreateBuilderForType();
+              subBuilder = extension.DefaultInstance.WeakCreateBuilderForType();
               IMessage originalMessage = (IMessage) builder[field];
               if (originalMessage != null) {
-                subBuilder.MergeFrom(originalMessage);
+                subBuilder.WeakMergeFrom(originalMessage);
               }
               if (rawBytes != null) {
                 // We already encountered the message.  Parse it now.
                 // TODO(jonskeet): Check this is okay. It's subtly different from the Java, as it doesn't create an input stream from rawBytes.
                 // In fact, why don't we just call MergeFrom(rawBytes)? And what about the extension registry?
-                subBuilder.MergeFrom(rawBytes.CreateCodedInput());
+                subBuilder.WeakMergeFrom(rawBytes.CreateCodedInput());
                 rawBytes = null;
               }
             } else {
@@ -286,7 +286,7 @@ namespace Google.ProtocolBuffers {
       input.CheckLastTagWas(WireFormat.MessageSetTag.ItemEnd);
 
       if (subBuilder != null) {
-        builder[field] = subBuilder.Build();
+        builder[field] = subBuilder.WeakBuild();
       }
     }
 
@@ -381,7 +381,7 @@ namespace Google.ProtocolBuffers {
     }
 
     /// <summary>
-    /// See <see cref="IBuilder.AddRepeatedField" />
+    /// See <see cref="IBuilder{TMessage, TBuilder}.AddRepeatedField" />
     /// </summary>
     internal void AddRepeatedField(FieldDescriptor field, object value) {
       if (!field.IsRepeated) {
@@ -449,7 +449,7 @@ namespace Google.ProtocolBuffers {
     }
 
     /// <summary>
-    /// See <see cref="IBuilder.ClearField" />
+    /// See <see cref="IBuilder{TMessage, TBuilder}.ClearField" />
     /// </summary>
     public void ClearField(FieldDescriptor field) {
       fields.Remove(field);
@@ -495,10 +495,10 @@ namespace Google.ProtocolBuffers {
           }
         } else if (field.MappedType == MappedType.Message && existingValue != null) {
           IMessage existingMessage = (IMessage)existingValue;
-          IMessage merged = existingMessage.CreateBuilderForType()
-              .MergeFrom(existingMessage)
-              .MergeFrom((IMessage)entry.Value)
-              .Build();
+          IMessage merged = existingMessage.WeakCreateBuilderForType()
+              .WeakMergeFrom(existingMessage)
+              .WeakMergeFrom((IMessage) entry.Value)
+              .WeakBuild();
           this[field] = merged;
         } else {
           this[field] = entry.Value;
diff --git a/csharp/ProtocolBuffers/GeneratedBuilder.cs b/csharp/ProtocolBuffers/GeneratedBuilder.cs
index a4114b5d..72ecfd40 100644
--- a/csharp/ProtocolBuffers/GeneratedBuilder.cs
+++ b/csharp/ProtocolBuffers/GeneratedBuilder.cs
@@ -13,9 +13,9 @@ namespace Google.ProtocolBuffers {
   /// most of the IBuilder interface using reflection. Users can ignore this class
   /// as an implementation detail.
   /// </summary>
-  public abstract class GeneratedBuilder<TMessage, TBuilder> : AbstractBuilder, IBuilder<TMessage>
+  public abstract class GeneratedBuilder<TMessage, TBuilder> : AbstractBuilder<TMessage, TBuilder>
       where TMessage : GeneratedMessage <TMessage, TBuilder>
-      where TBuilder : GeneratedBuilder<TMessage, TBuilder>, IBuilder<TMessage> {
+      where TBuilder : GeneratedBuilder<TMessage, TBuilder> {
 
     /// <summary>
     /// Returns the message being built at the moment.
@@ -43,7 +43,7 @@ namespace Google.ProtocolBuffers {
           : MessageBeingBuilt[field];
       }
       set {
-        InternalFieldAccessors[field].SetValue(this, value);
+        InternalFieldAccessors[field].SetValue(ThisBuilder, value);
       }
     }
 
@@ -87,40 +87,16 @@ namespace Google.ProtocolBuffers {
       return MessageBeingBuilt.HasField(field);
     }
 
-    protected override IMessage BuildImpl() {
-      return Build();
-    }
-
-    protected override IMessage BuildPartialImpl() {
-      return BuildPartial();
-    }
-
-    protected override IBuilder CloneImpl() {
-      return Clone();
-    }
-
-    protected override IMessage DefaultInstanceForTypeImpl {
-      get { return DefaultInstanceForType; }
-    }
-
     public override IBuilder CreateBuilderForField(FieldDescriptor field) {
       return InternalFieldAccessors[field].CreateBuilder();
     }
 
-    protected override IBuilder ClearFieldImpl(FieldDescriptor field) {
-      return ClearField(field);
-    }
-
-    protected override IBuilder AddRepeatedFieldImpl(FieldDescriptor field, object value) {
-      return AddRepeatedField(field, value);
-    }
-
-    public virtual IBuilder<TMessage> ClearField(FieldDescriptor field) {
+    public override TBuilder ClearField(FieldDescriptor field) {
       InternalFieldAccessors[field].Clear(this);
-      return this;
+      return ThisBuilder;
     }
 
-    public virtual IBuilder<TMessage> MergeFrom(TMessage other) {
+    public override TBuilder MergeFrom(TMessage other) {
       if (other.DescriptorForType != InternalFieldAccessors.Descriptor) {
         throw new ArgumentException("Message type mismatch");
       }
@@ -135,78 +111,32 @@ namespace Google.ProtocolBuffers {
         } else if (field.MappedType == MappedType.Message && HasField(field)) {
           // Merge singular embedded messages
           IMessage oldValue = (IMessage)this[field];
-          this[field] = oldValue.CreateBuilderForType()
-              .MergeFrom(oldValue)
-              .MergeFrom((IMessage)entry.Value)
-              .BuildPartial();
+          this[field] = oldValue.WeakCreateBuilderForType()
+              .WeakMergeFrom(oldValue)
+              .WeakMergeFrom((IMessage)entry.Value)
+              .WeakBuildPartial();
         } else {
           // Just overwrite
           this[field] = entry.Value;
         }
       }
-      return this;
+      return ThisBuilder;
     }
 
-    public virtual IBuilder<TMessage> MergeUnknownFields(UnknownFieldSet unknownFields) {
+    public override TBuilder MergeUnknownFields(UnknownFieldSet unknownFields) {
       TMessage result = MessageBeingBuilt;
       result.SetUnknownFields(UnknownFieldSet.CreateBuilder(result.UnknownFields)
           .MergeFrom(unknownFields)
           .Build());
-      return this;
+      return ThisBuilder;
     }
 
-    public virtual IBuilder<TMessage> AddRepeatedField(FieldDescriptor field, object value) {
+    public override TBuilder AddRepeatedField(FieldDescriptor field, object value) {
       InternalFieldAccessors[field].AddRepeated(this, value);
-      return this;
-    }
-
-    public IBuilder<TMessage> MergeFrom(ByteString data) {
-      ((IBuilder) this).MergeFrom(data);
-      return this;
-    }
-
-    public IBuilder<TMessage> MergeFrom(ByteString data, ExtensionRegistry extensionRegistry) {
-      ((IBuilder) this).MergeFrom(data, extensionRegistry);
-      return this;
-    }
-
-    public IBuilder<TMessage> MergeFrom(byte[] data) {
-      ((IBuilder) this).MergeFrom(data);
-      return this;
-    }
-
-    public IBuilder<TMessage> MergeFrom(byte[] data, ExtensionRegistry extensionRegistry) {
-      ((IBuilder) this).MergeFrom(data, extensionRegistry);
-      return this;
-    }
-
-    public IBuilder<TMessage> MergeFrom(Stream input) {
-      ((IBuilder) this).MergeFrom(input);
-      return this;
-    }
-
-    public IBuilder<TMessage> MergeFrom(Stream input, ExtensionRegistry extensionRegistry) {
-      ((IBuilder) this).MergeFrom(input, extensionRegistry);
-      return this;
+      return ThisBuilder;
     }
 
     /// <summary>
-    /// Overridden when optimized for speed.
-    /// </summary>
-    public virtual IBuilder<TMessage> MergeFrom(CodedInputStream input) {
-      ((IBuilder)this).MergeFrom(input);
-      return this;
-    }
-
-    /// <summary>
-    /// Overridden when optimized for speed.
-    /// </summary>
-    public virtual IBuilder<TMessage> MergeFrom(CodedInputStream input, ExtensionRegistry extensionRegistry) {
-      ((IBuilder)this).MergeFrom(input, extensionRegistry);
-      return this;
-    }
-    
-    /// <summary>
     /// Like Build(), but will wrap UninitializedMessageException in
     /// InvalidProtocolBufferException.
     /// TODO(jonskeet): This used to be generated for each class. Find out why.
@@ -219,10 +149,10 @@ namespace Google.ProtocolBuffers {
     }
 
     /// <summary>
-    /// Implementation of <see cref="IBuilder{T}.Build" />.
+    /// Implementation of <see cref="IBuilder{TMessage, TBuilder}.Build" />.
     /// TODO(jonskeet): This used to be generated for each class. Find out why.
     /// </summary>
-    public TMessage Build() {
+    public override TMessage Build() {
       if (!IsInitialized) {
         throw new UninitializedMessageException(MessageBeingBuilt);
       }
@@ -233,13 +163,5 @@ namespace Google.ProtocolBuffers {
       get { return MessageBeingBuilt.UnknownFields; }
       set { MessageBeingBuilt.SetUnknownFields(value); }
     }
-    
-    public abstract TMessage BuildPartial();
-    public abstract IBuilder<TMessage> Clone();
-    public abstract new IBuilder<TMessage> Clear();
-    public abstract TMessage DefaultInstanceForType { get; }
-    
-    public abstract class ExtendableBuilder : GeneratedBuilder<TMessage, TBuilder> {
-    }
   }
 }
diff --git a/csharp/ProtocolBuffers/GeneratedExtensionBase.cs b/csharp/ProtocolBuffers/GeneratedExtensionBase.cs
index 2ab6d7a6..028dc76a 100644
--- a/csharp/ProtocolBuffers/GeneratedExtensionBase.cs
+++ b/csharp/ProtocolBuffers/GeneratedExtensionBase.cs
@@ -29,7 +29,7 @@ namespace Google.ProtocolBuffers {
   /// The interface implemented by both GeneratedException and GeneratedRepeatException,
   /// to make it easier to cope with repeats separately.
   /// </remarks>
-  public abstract class GeneratedExtensionBase<TContainer, TExtension> {
+  public abstract class GeneratedExtensionBase<TExtension> {
 
     private readonly FieldDescriptor descriptor;
     private readonly IMessage messageDefaultInstance;
@@ -73,8 +73,8 @@ namespace Google.ProtocolBuffers {
             // GeneratedExtension manually and gives it a different type.
             // This should not happen in normal use.  But, to be nice, we'll
             // copy the message to whatever type the caller was expecting.
-            return MessageDefaultInstance.CreateBuilderForType()
-                           .MergeFrom((IMessage)value).Build();
+            return MessageDefaultInstance.WeakCreateBuilderForType()
+                           .WeakMergeFrom((IMessage)value).WeakBuild();
           }
         case MappedType.Enum:
           // Just return a boxed int - that can be unboxed to the enum
diff --git a/csharp/ProtocolBuffers/GeneratedMessage.cs b/csharp/ProtocolBuffers/GeneratedMessage.cs
index 37fd2e6b..0bdf0e3f 100644
--- a/csharp/ProtocolBuffers/GeneratedMessage.cs
+++ b/csharp/ProtocolBuffers/GeneratedMessage.cs
@@ -13,9 +13,9 @@ namespace Google.ProtocolBuffers {
   /// most of the IMessage interface using reflection. Users
   /// can ignore this class as an implementation detail.
   /// </summary>
-  public abstract class GeneratedMessage<TMessage, TBuilder> : AbstractMessage, IMessage<TMessage>
+  public abstract class GeneratedMessage<TMessage, TBuilder> : AbstractMessage<TMessage, TBuilder>
       where TMessage : GeneratedMessage<TMessage, TBuilder> 
-      where TBuilder : IBuilder<TMessage> {
+      where TBuilder : GeneratedBuilder<TMessage, TBuilder> {
 
     private UnknownFieldSet unknownFields = UnknownFieldSet.DefaultInstance;
 
@@ -29,18 +29,6 @@ namespace Google.ProtocolBuffers {
       get { return InternalFieldAccessors.Descriptor; }
     }
 
-    protected override IMessage DefaultInstanceForTypeImpl {
-      get { return DefaultInstanceForType; }
-    }
-
-    protected override IBuilder CreateBuilderForTypeImpl() {
-      return CreateBuilderForType();
-    }
-
-    public abstract TMessage DefaultInstanceForType { get; }
-
-    public abstract IBuilder<TMessage> CreateBuilderForType();
-
     internal IDictionary<FieldDescriptor, Object> GetMutableFieldMap() {
 
       // Use a SortedList so we'll end up serializing fields in order
diff --git a/csharp/ProtocolBuffers/GeneratedRepeatException.cs b/csharp/ProtocolBuffers/GeneratedRepeatException.cs
index a38f5c1b..f7dee511 100644
--- a/csharp/ProtocolBuffers/GeneratedRepeatException.cs
+++ b/csharp/ProtocolBuffers/GeneratedRepeatException.cs
@@ -7,15 +7,15 @@ namespace Google.ProtocolBuffers {
   /// <summary>
   /// Class used to represent repeat extensions in generated classes.
   /// </summary>
-  public class GeneratedRepeatExtension<TContainer, TExtensionElement> : GeneratedExtensionBase<TContainer, IList<TExtensionElement>> {
+  public class GeneratedRepeatExtension<TExtensionElement> : GeneratedExtensionBase<IList<TExtensionElement>> {
     private GeneratedRepeatExtension(FieldDescriptor field) : base(field, typeof(TExtensionElement)) {
     }
 
-    public static GeneratedExtensionBase<TContainer, IList<TExtensionElement>> CreateInstance(FieldDescriptor descriptor) {
+    public static GeneratedExtensionBase<IList<TExtensionElement>> CreateInstance(FieldDescriptor descriptor) {
       if (!descriptor.IsRepeated) {
         throw new ArgumentException("Must call GeneratedRepeatExtension.CreateInstance() for repeated types.");
       }
-      return new GeneratedRepeatExtension<TContainer, TExtensionElement>(descriptor);
+      return new GeneratedRepeatExtension<TExtensionElement>(descriptor);
     }
 
     /// <summary>
diff --git a/csharp/ProtocolBuffers/GeneratedSingleExtension.cs b/csharp/ProtocolBuffers/GeneratedSingleExtension.cs
index 0adcd7ef..d9a0adcf 100644
--- a/csharp/ProtocolBuffers/GeneratedSingleExtension.cs
+++ b/csharp/ProtocolBuffers/GeneratedSingleExtension.cs
@@ -6,17 +6,15 @@ namespace Google.ProtocolBuffers {
   /// <summary>
   /// Generated extension for a singular field.
   /// </remarks>
-  public class GeneratedSingleExtension<TContainer, TExtension> : GeneratedExtensionBase<TContainer, TExtension>    
-      where TContainer : IMessage<TContainer> {
-
+  public class GeneratedSingleExtension<TExtension> : GeneratedExtensionBase<TExtension>  {
     internal GeneratedSingleExtension(FieldDescriptor descriptor) : base(descriptor, typeof(TExtension)) {
     }
 
-    public static GeneratedSingleExtension<TContainer, TExtension> CreateInstance(FieldDescriptor descriptor) {
+    public static GeneratedSingleExtension<TExtension> CreateInstance(FieldDescriptor descriptor) {
       if (descriptor.IsRepeated) {
         throw new ArgumentException("Must call GeneratedRepeateExtension.CreateInstance() for repeated types.");
       }
-      return new GeneratedSingleExtension<TContainer, TExtension>(descriptor);
+      return new GeneratedSingleExtension<TExtension>(descriptor);
     }
 
     public override object FromReflectionType(object value) {
diff --git a/csharp/ProtocolBuffers/IBuilder.cs b/csharp/ProtocolBuffers/IBuilder.cs
index dcb3d272..1671c84e 100644
--- a/csharp/ProtocolBuffers/IBuilder.cs
+++ b/csharp/ProtocolBuffers/IBuilder.cs
@@ -44,13 +44,19 @@ namespace Google.ProtocolBuffers {
 
     /// <summary>
     /// Allows getting and setting of a field.
-    /// <see cref="IMessage{T}.Item(FieldDescriptor)"/>
+    /// <see cref="IMessage{TMessage, TBuilder}.Item(FieldDescriptor)"/>
     /// </summary>
     /// <param name="field"></param>
     /// <returns></returns>
     object this[FieldDescriptor field] { get; set; }
 
     /// <summary>
+    /// Get the message's type's descriptor.
+    /// <see cref="IMessage{TMessage, TBuilder}.DescriptorForType"/>
+    /// </summary>
+    MessageDescriptor DescriptorForType { get; }
+
+    /// <summary>
     /// Only present in the nongeneric interface - useful for tests, but
     /// not as much in real life.
     /// </summary>
@@ -63,13 +69,7 @@ namespace Google.ProtocolBuffers {
     IBuilder SetRepeatedField(FieldDescriptor field, int index, object value);
 
     /// <summary>
-    /// Get the message's type's descriptor.
-    /// <see cref="IMessage{T}.DescriptorForType"/>
-    /// </summary>
-    MessageDescriptor DescriptorForType { get; }
-
-    /// <summary>
-    /// <see cref="IMessage{T}.GetRepeatedFieldCount"/>
+    /// <see cref="IMessage{TMessage, TBuilder}.GetRepeatedFieldCount"/>
     /// </summary>
     /// <param name="field"></param>
     /// <returns></returns>
@@ -77,39 +77,40 @@ namespace Google.ProtocolBuffers {
 
     /// <summary>
     /// Allows getting and setting of a repeated field value.
-    /// <see cref="IMessage{T}.Item(FieldDescriptor, int)"/>
+    /// <see cref="IMessage{TMessage, TBuilder}.Item(FieldDescriptor, int)"/>
     /// </summary>
     object this[FieldDescriptor field, int index] { get; set; }
 
     /// <summary>
-    /// <see cref="IMessage{T}.HasField"/>
+    /// <see cref="IMessage{TMessage, TBuilder}.HasField"/>
     /// </summary>
     bool HasField(FieldDescriptor field);
 
     /// <summary>
-    /// <see cref="IMessage{T}.UnknownFields"/>
+    /// <see cref="IMessage{TMessage, TBuilder}.UnknownFields"/>
     /// </summary>
     UnknownFieldSet UnknownFields { get; set; }
 
-    #region Non-generic versions of generic methods in IBuilder<T>
-    IBuilder Clear();
-    IBuilder MergeFrom(IMessage other);
-    IMessage Build();
-    IMessage BuildPartial();
-    IBuilder Clone();
-    IBuilder MergeFrom(CodedInputStream input);
-    IBuilder MergeFrom(CodedInputStream codedInputStream, ExtensionRegistry extensionRegistry);
-    IMessage DefaultInstanceForType { get; }
+    /// <summary>
+    /// Create a builder for messages of the appropriate type for the given field.
+    /// Messages built with this can then be passed to the various mutation properties
+    /// and methods.
+    /// </summary>
     IBuilder CreateBuilderForField(FieldDescriptor field);
-    IBuilder ClearField(FieldDescriptor field);
-    IBuilder AddRepeatedField(FieldDescriptor field, object value);
-    IBuilder MergeUnknownFields(UnknownFieldSet unknownFields);
-    IBuilder MergeFrom(ByteString data);
-    IBuilder MergeFrom(ByteString data, ExtensionRegistry extensionRegistry);
-    IBuilder MergeFrom(byte[] data);
-    IBuilder MergeFrom(byte[] data, ExtensionRegistry extensionRegistry);
-    IBuilder MergeFrom(Stream input);
-    IBuilder MergeFrom(Stream input, ExtensionRegistry extensionRegistry);
+
+    #region Methods which are like those of the generic form, but without any knowledge of the type parameters
+    IBuilder WeakAddRepeatedField(FieldDescriptor field, object value);
+    IBuilder WeakClear();
+    IBuilder WeakClearField(FieldDescriptor field);
+    IBuilder WeakMergeFrom(IMessage message);
+    IBuilder WeakMergeFrom(ByteString data);
+    IBuilder WeakMergeFrom(ByteString data, ExtensionRegistry registry);
+    IBuilder WeakMergeFrom(CodedInputStream input);
+    IBuilder WeakMergeFrom(CodedInputStream input, ExtensionRegistry registry);
+    IMessage WeakBuild();
+    IMessage WeakBuildPartial();
+    IBuilder WeakClone();
+    IMessage WeakDefaultInstanceForType { get; }
     #endregion
   }
 
@@ -117,12 +118,15 @@ namespace Google.ProtocolBuffers {
   /// Interface implemented by Protocol Message builders.
   /// TODO(jonskeet): Consider "SetXXX" methods returning the builder, as well as the properties.
   /// </summary>
-  /// <typeparam name="T">Type of message</typeparam>
-  public interface IBuilder<T> : IBuilder where T : IMessage<T> {
+  /// <typeparam name="TMessage">Type of message</typeparam>
+  /// <typeparam name="TBuilder">Type of builder</typeparam>
+  public interface IBuilder<TMessage, TBuilder> : IBuilder
+      where TMessage : IMessage<TMessage, TBuilder> 
+      where TBuilder : IBuilder<TMessage, TBuilder> {
     /// <summary>
     /// Resets all fields to their default values.
     /// </summary>
-    new IBuilder<T> Clear();
+    TBuilder Clear();
 
     /// <summary>
     /// Merge the specified other message into the message being
@@ -137,7 +141,13 @@ namespace Google.ProtocolBuffers {
     /// </summary>
     /// <param name="other"></param>
     /// <returns></returns>
-    IBuilder<T> MergeFrom(T other);
+    TBuilder MergeFrom(TMessage other);
+
+    /// <summary>
+    /// Merge the specified other message which may be a different implementation of
+    /// the same message descriptor.
+    /// </summary>
+    TBuilder MergeFrom(IMessage other);
 
     /// <summary>
     /// Constructs the final message. Once this is called, this Builder instance
@@ -148,19 +158,19 @@ namespace Google.ProtocolBuffers {
     /// <exception cref="UninitializedMessageException">the message
     /// is missing one or more required fields; use BuildPartial to bypass
     /// this check</exception>
-    new T Build();
+    TMessage Build();
 
     /// <summary>
     /// Like Build(), but does not throw an exception if the message is missing
     /// required fields. Instead, a partial message is returned.
     /// </summary>
-    new T BuildPartial();
+    TMessage BuildPartial();
 
     /// <summary>
     /// Clones this builder.
     /// TODO(jonskeet): Explain depth of clone.
     /// </summary>
-    new IBuilder<T> Clone();
+    TBuilder Clone();
 
     /// <summary>
     /// Parses a message of this type from the input and merges it with this
@@ -181,7 +191,7 @@ namespace Google.ProtocolBuffers {
     /// Use BuildPartial to build, which ignores missing required fields.
     /// </list>
     /// </remarks>
-    new IBuilder<T> MergeFrom(CodedInputStream input);
+    TBuilder MergeFrom(CodedInputStream input);
 
     /// <summary>
     /// Like MergeFrom(CodedInputStream), but also parses extensions.
@@ -189,20 +199,13 @@ namespace Google.ProtocolBuffers {
     /// in <paramref name="extensionRegistry"/>. Extensions not in the registry
     /// will be treated as unknown fields.
     /// </summary>
-    new IBuilder<T> MergeFrom(CodedInputStream input, ExtensionRegistry extensionRegistry);
+    TBuilder MergeFrom(CodedInputStream input, ExtensionRegistry extensionRegistry);
 
     /// <summary>
     /// Get's the message's type's default instance.
-    /// <see cref="IMessage{T}.DefaultInstanceForType" />
-    /// </summary>
-    new T DefaultInstanceForType { get; }
-
-    /// <summary>
-    /// Create a builder for messages of the appropriate type for the given field.
-    /// Messages built with this can then be passed to the various mutation properties
-    /// and methods.
+    /// <see cref="IMessage{TMessage}.DefaultInstanceForType" />
     /// </summary>
-    //new IBuilder<TField> NewBuilderForField<TField>(FieldDescriptor field) where TField : IMessage<TField>;
+    TMessage DefaultInstanceForType { get; }
 
     /// <summary>
     /// Clears the field. This is exactly equivalent to calling the generated
@@ -210,7 +213,7 @@ namespace Google.ProtocolBuffers {
     /// </summary>
     /// <param name="field"></param>
     /// <returns></returns>
-    new IBuilder<T> ClearField(FieldDescriptor field);
+    TBuilder ClearField(FieldDescriptor field);
 
     /// <summary>
     /// Appends the given value as a new element for the specified repeated field.
@@ -219,12 +222,12 @@ namespace Google.ProtocolBuffers {
     /// the field does not belong to this builder's type, or the value is
     /// of the incorrect type
     /// </exception>
-    new IBuilder<T> AddRepeatedField(FieldDescriptor field, object value);
+    TBuilder AddRepeatedField(FieldDescriptor field, object value);
 
     /// <summary>
     /// Merge some unknown fields into the set for this message.
     /// </summary>
-    new IBuilder<T> MergeUnknownFields(UnknownFieldSet unknownFields);
+    TBuilder MergeUnknownFields(UnknownFieldSet unknownFields);
 
     #region Convenience methods
     // TODO(jonskeet): Implement these as extension methods?
@@ -233,28 +236,28 @@ namespace Google.ProtocolBuffers {
     /// it with the message being built. This is just a small wrapper around
     /// MergeFrom(CodedInputStream).
     /// </summary>
-    new IBuilder<T> MergeFrom(ByteString data);
+    TBuilder MergeFrom(ByteString data);
 
     /// <summary>
     /// Parse <paramref name="data"/> as a message of this type and merge
     /// it with the message being built. This is just a small wrapper around
     /// MergeFrom(CodedInputStream, ExtensionRegistry).
     /// </summary>
-    new IBuilder<T> MergeFrom(ByteString data, ExtensionRegistry extensionRegistry);
+    TBuilder MergeFrom(ByteString data, ExtensionRegistry extensionRegistry);
 
     /// <summary>
     /// Parse <paramref name="data"/> as a message of this type and merge
     /// it with the message being built. This is just a small wrapper around
     /// MergeFrom(CodedInputStream).
     /// </summary>
-    new IBuilder<T> MergeFrom(byte[] data);
+    TBuilder MergeFrom(byte[] data);
 
     /// <summary>
     /// Parse <paramref name="data"/> as a message of this type and merge
     /// it with the message being built. This is just a small wrapper around
     /// MergeFrom(CodedInputStream, ExtensionRegistry).
     /// </summary>
-    new IBuilder<T> MergeFrom(byte[] data, ExtensionRegistry extensionRegistry);
+    TBuilder MergeFrom(byte[] data, ExtensionRegistry extensionRegistry);
 
     /// <summary>
     /// Parse <paramref name="input"/> as a message of this type and merge
@@ -265,14 +268,14 @@ namespace Google.ProtocolBuffers {
     /// stream which limits reading. Despite usually reading the entire
     /// stream, this method never closes the stream.
     /// </summary>
-    new IBuilder<T> MergeFrom(Stream input);
+    TBuilder MergeFrom(Stream input);
 
     /// <summary>
     /// Parse <paramref name="input"/> as a message of this type and merge
     /// it with the message being built. This is just a small wrapper around
     /// MergeFrom(CodedInputStream, ExtensionRegistry).
     /// </summary>
-    new IBuilder<T> MergeFrom(Stream input, ExtensionRegistry extensionRegistry);
+    TBuilder MergeFrom(Stream input, ExtensionRegistry extensionRegistry);
     #endregion
   }
 }
diff --git a/csharp/ProtocolBuffers/IMessage.cs b/csharp/ProtocolBuffers/IMessage.cs
index abb29f72..1ce18a5c 100644
--- a/csharp/ProtocolBuffers/IMessage.cs
+++ b/csharp/ProtocolBuffers/IMessage.cs
@@ -21,11 +21,8 @@ using Google.ProtocolBuffers.Descriptors;
 namespace Google.ProtocolBuffers {
 
   /// <summary>
-  /// Non-generic interface implemented by all Protocol Buffers messages.
-  /// Some members are repeated in the generic interface but with a
-  /// type-specific signature. Type-safe implementations
-  /// are encouraged to implement these non-generic members explicitly,
-  /// and the generic members implicitly.
+  /// Non-generic interface used for all parts of the API which don't require
+  /// any type knowledge.
   /// </summary>
   public interface IMessage {
     /// <summary>
@@ -152,27 +149,17 @@ namespace Google.ProtocolBuffers {
     void WriteTo(Stream output);
     #endregion
 
-    #region Weakly typed members
     /// <summary>
-    /// Returns an instance of this message type with all fields set to
-    /// their default values. This may or may not be a singleton. This differs
-    /// from the DefaultInstance property of each generated message class in that this
-    /// method is an abstract method of IMessage whereas DefaultInstance is
-    /// a static property of a specific class. They return the same thing.
+    /// Creates a builder for the type, but in a weakly typed manner. This
+    /// is typically implemented by strongly typed builders by just returning
+    /// the result of CreateBuilderForType.
     /// </summary>
-    IMessage DefaultInstanceForType { get; }
+    IBuilder WeakCreateBuilderForType();
 
-    /// <summary>
-    /// Constructs a new builder for a message of the same type as this message.
-    /// </summary>
-    IBuilder CreateBuilderForType();
-    #endregion
+    IMessage WeakDefaultInstanceForType { get; }
   }
 
-  /// <summary>
-  /// Type-safe interface for all generated messages to implement.
-  /// </summary>
-  public interface IMessage<T> : IMessage where T : IMessage<T> {
+  public interface IMessage<TMessage> : IMessage {
     /// <summary>
     /// Returns an instance of this message type with all fields set to
     /// their default values. This may or may not be a singleton. This differs
@@ -180,13 +167,20 @@ namespace Google.ProtocolBuffers {
     /// method is an abstract method of IMessage whereas DefaultInstance is
     /// a static property of a specific class. They return the same thing.
     /// </summary>
-    new T DefaultInstanceForType { get; }
+    TMessage DefaultInstanceForType { get; }
+  }
 
+  /// <summary>
+  /// Type-safe interface for all generated messages to implement.
+  /// </summary>
+  public interface IMessage<TMessage, TBuilder> : IMessage<TMessage>
+      where TMessage : IMessage<TMessage, TBuilder> 
+      where TBuilder : IBuilder<TMessage, TBuilder> {
     #region Builders
     /// <summary>
     /// Constructs a new builder for a message of the same type as this message.
     /// </summary>
-    new IBuilder<T> CreateBuilderForType();
+    TBuilder CreateBuilderForType();
     #endregion
   }
 }
diff --git a/csharp/ProtocolBuffers/InvalidProtocolBufferException.cs b/csharp/ProtocolBuffers/InvalidProtocolBufferException.cs
index ba6950cf..48e86cc3 100644
--- a/csharp/ProtocolBuffers/InvalidProtocolBufferException.cs
+++ b/csharp/ProtocolBuffers/InvalidProtocolBufferException.cs
@@ -67,13 +67,13 @@ namespace Google.ProtocolBuffers {
     internal static InvalidProtocolBufferException RecursionLimitExceeded() {
       return new InvalidProtocolBufferException(
         "Protocol message had too many levels of nesting.  May be malicious.  " +
-        "Use CodedInputStream.setRecursionLimit() to increase the depth limit.");
+        "Use CodedInputStream.SetRecursionLimit() to increase the depth limit.");
     }
 
     internal static InvalidProtocolBufferException SizeLimitExceeded() {
       return new InvalidProtocolBufferException(
         "Protocol message was too large.  May be malicious.  " +
-        "Use CodedInputStream.setSizeLimit() to increase the size limit.");
+        "Use CodedInputStream.SetSizeLimit() to increase the size limit.");
     }
   }
 }
diff --git a/csharp/ProtocolBuffers/RpcUtil.cs b/csharp/ProtocolBuffers/RpcUtil.cs
index 75e6f34b..ebd3f47f 100644
--- a/csharp/ProtocolBuffers/RpcUtil.cs
+++ b/csharp/ProtocolBuffers/RpcUtil.cs
@@ -21,12 +21,13 @@ namespace Google.ProtocolBuffers {
     /// callback is given a message with a different descriptor, an
     /// exception will be thrown.
     /// </summary>
-    public static Action<IMessage> GeneralizeCallback<T>(Action<T> action, T defaultInstance)
-        where T : class, IMessage<T> {
+    public static Action<IMessage> GeneralizeCallback<TMessage, TBuilder>(Action<TMessage> action, TMessage defaultInstance)
+        where TMessage : class, IMessage<TMessage, TBuilder> 
+        where TBuilder : IBuilder<TMessage, TBuilder> {
       return message => {
-        T castMessage = message as T;
+        TMessage castMessage = message as TMessage;
         if (castMessage == null) {
-          castMessage = (T) defaultInstance.CreateBuilderForType().MergeFrom(message).Build();
+          castMessage = defaultInstance.CreateBuilderForType().MergeFrom(message).Build();
         }
         action(castMessage);
       };
diff --git a/csharp/ProtocolBuffers/TextFormat.cs b/csharp/ProtocolBuffers/TextFormat.cs
index a9a4e1b8..46d19801 100644
--- a/csharp/ProtocolBuffers/TextFormat.cs
+++ b/csharp/ProtocolBuffers/TextFormat.cs
@@ -44,6 +44,7 @@ namespace Google.ProtocolBuffers {
     }
 
     private static void Print(IMessage message, TextGenerator generator) {
+      // TODO(jonskeet): Check why descriptor is never used.
       MessageDescriptor descriptor = message.DescriptorForType;
       foreach (KeyValuePair<FieldDescriptor, object> entry in message.AllFields) {
         PrintField(entry.Key, entry.Value, generator);