Implement freezing for messages and repeated fields.

Fixes issue #523.

25 files changed, 1668 insertions, 292 deletions

diff --git a/csharp/src/AddressBook/Addressbook.cs b/csharp/src/AddressBook/Addressbook.cs
index cd1f6231..2fb6be83 100644
--- a/csharp/src/AddressBook/Addressbook.cs
+++ b/csharp/src/AddressBook/Addressbook.cs
@@ -76,6 +76,9 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
       get { return global::Google.ProtocolBuffers.Examples.AddressBook.Addressbook.internal__static_tutorial_Person__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public Person() { }
 
     public Person(Person other) {
@@ -89,30 +92,44 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
       return new Person(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      phone_.Freeze();
+    }
+
     public const int NameFieldNumber = 1;
     private string name_ = "";
     public string Name {
       get { return name_; }
-      set { name_ = value ?? ""; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        name_ = value ?? "";
+      }
     }
 
-
     public const int IdFieldNumber = 2;
     private int id_;
     public int Id {
       get { return id_; }
-      set { id_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        id_ = value;
+      }
     }
 
-
     public const int EmailFieldNumber = 3;
     private string email_ = "";
     public string Email {
       get { return email_; }
-      set { email_ = value ?? ""; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        email_ = value ?? "";
+      }
     }
 
-
     public const int PhoneFieldNumber = 4;
     private readonly pbc::RepeatedField<global::Google.ProtocolBuffers.Examples.AddressBook.Person.Types.PhoneNumber> phone_ = new pbc::RepeatedField<global::Google.ProtocolBuffers.Examples.AddressBook.Person.Types.PhoneNumber>();
     public pbc::RepeatedField<global::Google.ProtocolBuffers.Examples.AddressBook.Person.Types.PhoneNumber> Phone {
@@ -254,6 +271,9 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
           get { return global::Google.ProtocolBuffers.Examples.AddressBook.Addressbook.internal__static_tutorial_Person_PhoneNumber__FieldAccessorTable; }
         }
 
+        private bool _frozen = false;
+        public bool IsFrozen { get { return _frozen; } }
+
         public PhoneNumber() { }
 
         public PhoneNumber(PhoneNumber other) {
@@ -265,22 +285,33 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
           return new PhoneNumber(this);
         }
 
+        public void Freeze() {
+          if (IsFrozen) {
+            return;
+          }
+          _frozen = true;
+        }
+
         public const int NumberFieldNumber = 1;
         private string number_ = "";
         public string Number {
           get { return number_; }
-          set { number_ = value ?? ""; }
+          set {
+            pb::Freezable.CheckMutable(this);
+            number_ = value ?? "";
+          }
         }
 
-
         public const int TypeFieldNumber = 2;
         private global::Google.ProtocolBuffers.Examples.AddressBook.Person.Types.PhoneType type_ = global::Google.ProtocolBuffers.Examples.AddressBook.Person.Types.PhoneType.HOME;
         public global::Google.ProtocolBuffers.Examples.AddressBook.Person.Types.PhoneType Type {
           get { return type_; }
-          set { type_ = value; }
+          set {
+            pb::Freezable.CheckMutable(this);
+            type_ = value;
+          }
         }
 
-
         public override bool Equals(object other) {
           return Equals(other as PhoneNumber);
         }
@@ -382,6 +413,9 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
       get { return global::Google.ProtocolBuffers.Examples.AddressBook.Addressbook.internal__static_tutorial_AddressBook__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public AddressBook() { }
 
     public AddressBook(AddressBook other) {
@@ -392,6 +426,14 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
       return new AddressBook(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      person_.Freeze();
+    }
+
     public const int PersonFieldNumber = 1;
     private readonly pbc::RepeatedField<global::Google.ProtocolBuffers.Examples.AddressBook.Person> person_ = new pbc::RepeatedField<global::Google.ProtocolBuffers.Examples.AddressBook.Person>();
     public pbc::RepeatedField<global::Google.ProtocolBuffers.Examples.AddressBook.Person> Person {
diff --git a/csharp/src/ProtocolBuffers.Test/GeneratedMessageTest.cs b/csharp/src/ProtocolBuffers.Test/GeneratedMessageTest.cs
index e21d904d..26165428 100644
--- a/csharp/src/ProtocolBuffers.Test/GeneratedMessageTest.cs
+++ b/csharp/src/ProtocolBuffers.Test/GeneratedMessageTest.cs
@@ -1,4 +1,5 @@
-using Google.Protobuf.TestProtos;

+using System;

+using Google.Protobuf.TestProtos;

 using NUnit.Framework;

 

 namespace Google.Protobuf

@@ -257,5 +258,22 @@ namespace Google.Protobuf
             original.OneofNestedMessage.Bb = 30;

             Assert.AreNotEqual(original, clone);

         }

+

+        [Test]

+        public void Freeze()

+        {

+            var frozen = new TestAllTypes();

+            frozen.Freeze();

+            Assert.IsTrue(frozen.IsFrozen);

+

+            Assert.Throws<InvalidOperationException>(() => frozen.ClearOneofField());

+            Assert.Throws<InvalidOperationException>(() => frozen.SingleInt32 = 0);

+            Assert.Throws<InvalidOperationException>(() => frozen.SingleNestedMessage = null);

+            Assert.Throws<InvalidOperationException>(() => frozen.SingleNestedEnum = 0);

+            Assert.Throws<InvalidOperationException>(() => frozen.OneofString = null);

+            Assert.Throws<InvalidOperationException>(() => frozen.OneofUint32 = 0U);

+            Assert.Throws<InvalidOperationException>(() => frozen.RepeatedDouble.Add(0.0));

+            Assert.Throws<InvalidOperationException>(() => frozen.RepeatedNestedMessage.Add(new TestAllTypes.Types.NestedMessage()));

+        }

     }

 }

diff --git a/csharp/src/ProtocolBuffers.Test/RepeatedFieldTest.cs b/csharp/src/ProtocolBuffers.Test/RepeatedFieldTest.cs
index cbe79294..c01cd8ff 100644
--- a/csharp/src/ProtocolBuffers.Test/RepeatedFieldTest.cs
+++ b/csharp/src/ProtocolBuffers.Test/RepeatedFieldTest.cs
@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using Google.Protobuf.Collections;
+using Google.Protobuf.TestProtos;
 using NUnit.Framework;
 
 namespace Google.Protobuf
@@ -11,8 +12,8 @@ namespace Google.Protobuf
         public void NullValuesRejected()
         {
             var list = new RepeatedField<string>();
-            Assert.Throws<ArgumentNullException>(() => list.Add((string) null));
-            Assert.Throws<ArgumentNullException>(() => list.Add((IEnumerable<string>) null));
+            Assert.Throws<ArgumentNullException>(() => list.Add((string)null));
+            Assert.Throws<ArgumentNullException>(() => list.Add((IEnumerable<string>)null));
             Assert.Throws<ArgumentNullException>(() => list.Add((RepeatedField<string>)null));
             Assert.Throws<ArgumentNullException>(() => list.Contains(null));
             Assert.Throws<ArgumentNullException>(() => list.IndexOf(null));
@@ -47,5 +48,47 @@ namespace Google.Protobuf
             Assert.AreEqual("foo", list[1]);
             Assert.AreEqual("bar", list[2]);
         }
+
+        [Test]
+        public void Freeze_FreezesElements()
+        {
+            var list = new RepeatedField<TestAllTypes> { new TestAllTypes() };
+            Assert.IsFalse(list[0].IsFrozen);
+            list.Freeze();
+            Assert.IsTrue(list[0].IsFrozen);
+        }
+
+        [Test]
+        public void Freeze_PreventsMutations()
+        {
+            var list = new RepeatedField<int> { 0 };
+            list.Freeze();
+            Assert.Throws<InvalidOperationException>(() => list.Add(1));
+            Assert.Throws<InvalidOperationException>(() => list[0] = 1);
+            Assert.Throws<InvalidOperationException>(() => list.Clear());
+            Assert.Throws<InvalidOperationException>(() => list.RemoveAt(0));
+            Assert.Throws<InvalidOperationException>(() => list.Remove(0));
+            Assert.Throws<InvalidOperationException>(() => list.Insert(0, 0));
+        }
+
+        [Test]
+        public void Freeze_ReportsFrozen()
+        {
+            var list = new RepeatedField<int> { 0 };
+            Assert.IsFalse(list.IsFrozen);
+            Assert.IsFalse(list.IsReadOnly);
+            list.Freeze();
+            Assert.IsTrue(list.IsFrozen);
+            Assert.IsTrue(list.IsReadOnly);
+        }
+
+        [Test]
+        public void Clone_ReturnsMutable()
+        {
+            var list = new RepeatedField<int> { 0 };
+            list.Freeze();
+            var clone = list.Clone();
+            clone[0] = 1;
+        }
     }
 }
diff --git a/csharp/src/ProtocolBuffers.Test/TestProtos/UnittestImportProto3.cs b/csharp/src/ProtocolBuffers.Test/TestProtos/UnittestImportProto3.cs
index 30256972..a32d19c2 100644
--- a/csharp/src/ProtocolBuffers.Test/TestProtos/UnittestImportProto3.cs
+++ b/csharp/src/ProtocolBuffers.Test/TestProtos/UnittestImportProto3.cs
@@ -74,6 +74,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestImportProto3.internal__static_protobuf_unittest_import_ImportMessage__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public ImportMessage() { }
 
     public ImportMessage(ImportMessage other) {
@@ -84,14 +87,23 @@ namespace Google.Protobuf.TestProtos {
       return new ImportMessage(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+    }
+
     public const int DFieldNumber = 1;
     private int d_;
     public int D {
       get { return d_; }
-      set { d_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        d_ = value;
+      }
     }
 
-
     public override bool Equals(object other) {
       return Equals(other as ImportMessage);
     }
diff --git a/csharp/src/ProtocolBuffers.Test/TestProtos/UnittestImportPublicProto3.cs b/csharp/src/ProtocolBuffers.Test/TestProtos/UnittestImportPublicProto3.cs
index cb7292f3..2c8b0a31 100644
--- a/csharp/src/ProtocolBuffers.Test/TestProtos/UnittestImportPublicProto3.cs
+++ b/csharp/src/ProtocolBuffers.Test/TestProtos/UnittestImportPublicProto3.cs
@@ -59,6 +59,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestImportPublicProto3.internal__static_protobuf_unittest_import_PublicImportMessage__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public PublicImportMessage() { }
 
     public PublicImportMessage(PublicImportMessage other) {
@@ -69,14 +72,23 @@ namespace Google.Protobuf.TestProtos {
       return new PublicImportMessage(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+    }
+
     public const int EFieldNumber = 1;
     private int e_;
     public int E {
       get { return e_; }
-      set { e_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        e_ = value;
+      }
     }
 
-
     public override bool Equals(object other) {
       return Equals(other as PublicImportMessage);
     }
diff --git a/csharp/src/ProtocolBuffers.Test/TestProtos/UnittestIssues.cs b/csharp/src/ProtocolBuffers.Test/TestProtos/UnittestIssues.cs
index d32718d5..28508a3b 100644
--- a/csharp/src/ProtocolBuffers.Test/TestProtos/UnittestIssues.cs
+++ b/csharp/src/ProtocolBuffers.Test/TestProtos/UnittestIssues.cs
@@ -104,6 +104,9 @@ namespace UnitTest.Issues.TestProtos {
       get { return global::UnitTest.Issues.TestProtos.UnittestIssues.internal__static_unittest_issues_NegativeEnumMessage__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public NegativeEnumMessage() { }
 
     public NegativeEnumMessage(NegativeEnumMessage other) {
@@ -116,14 +119,25 @@ namespace UnitTest.Issues.TestProtos {
       return new NegativeEnumMessage(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      values_.Freeze();
+      packedValues_.Freeze();
+    }
+
     public const int ValueFieldNumber = 1;
     private global::UnitTest.Issues.TestProtos.NegativeEnum value_ = global::UnitTest.Issues.TestProtos.NegativeEnum.NEGATIVE_ENUM_ZERO;
     public global::UnitTest.Issues.TestProtos.NegativeEnum Value {
       get { return value_; }
-      set { value_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        value_ = value;
+      }
     }
 
-
     public const int ValuesFieldNumber = 2;
     private readonly pbc::RepeatedField<global::UnitTest.Issues.TestProtos.NegativeEnum> values_ = new pbc::RepeatedField<global::UnitTest.Issues.TestProtos.NegativeEnum>();
     public pbc::RepeatedField<global::UnitTest.Issues.TestProtos.NegativeEnum> Values {
@@ -255,6 +269,9 @@ namespace UnitTest.Issues.TestProtos {
       get { return global::UnitTest.Issues.TestProtos.UnittestIssues.internal__static_unittest_issues_DeprecatedChild__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public DeprecatedChild() { }
 
     public DeprecatedChild(DeprecatedChild other) {
@@ -264,6 +281,13 @@ namespace UnitTest.Issues.TestProtos {
       return new DeprecatedChild(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+    }
+
     public override bool Equals(object other) {
       return Equals(other as DeprecatedChild);
     }
@@ -328,6 +352,9 @@ namespace UnitTest.Issues.TestProtos {
       get { return global::UnitTest.Issues.TestProtos.UnittestIssues.internal__static_unittest_issues_DeprecatedFieldsMessage__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public DeprecatedFieldsMessage() { }
 
     public DeprecatedFieldsMessage(DeprecatedFieldsMessage other) {
@@ -343,15 +370,28 @@ namespace UnitTest.Issues.TestProtos {
       return new DeprecatedFieldsMessage(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      primitiveArray_.Freeze();
+      if (messageValue_ != null) MessageValue.Freeze();
+      messageArray_.Freeze();
+      enumArray_.Freeze();
+    }
+
     public const int PrimitiveValueFieldNumber = 1;
     private int primitiveValue_;
     [global::System.ObsoleteAttribute()]
     public int PrimitiveValue {
       get { return primitiveValue_; }
-      set { primitiveValue_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        primitiveValue_ = value;
+      }
     }
 
-
     public const int PrimitiveArrayFieldNumber = 2;
     private readonly pbc::RepeatedField<int> primitiveArray_ = new pbc::RepeatedField<int>();
     [global::System.ObsoleteAttribute()]
@@ -364,7 +404,10 @@ namespace UnitTest.Issues.TestProtos {
     [global::System.ObsoleteAttribute()]
     public global::UnitTest.Issues.TestProtos.DeprecatedChild MessageValue {
       get { return messageValue_; }
-      set { messageValue_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        messageValue_ = value;
+      }
     }
 
     public const int MessageArrayFieldNumber = 4;
@@ -379,10 +422,12 @@ namespace UnitTest.Issues.TestProtos {
     [global::System.ObsoleteAttribute()]
     public global::UnitTest.Issues.TestProtos.DeprecatedEnum EnumValue {
       get { return enumValue_; }
-      set { enumValue_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        enumValue_ = value;
+      }
     }
 
-
     public const int EnumArrayFieldNumber = 6;
     private readonly pbc::RepeatedField<global::UnitTest.Issues.TestProtos.DeprecatedEnum> enumArray_ = new pbc::RepeatedField<global::UnitTest.Issues.TestProtos.DeprecatedEnum>();
     [global::System.ObsoleteAttribute()]
@@ -403,7 +448,8 @@ namespace UnitTest.Issues.TestProtos {
       }
       if (PrimitiveValue != other.PrimitiveValue) return false;
       if(!primitiveArray_.Equals(other.primitiveArray_)) return false;
-      if (!object.Equals(MessageValue, other.MessageValue)) return false;if(!messageArray_.Equals(other.messageArray_)) return false;
+      if (!object.Equals(MessageValue, other.MessageValue)) return false;
+      if(!messageArray_.Equals(other.messageArray_)) return false;
       if (EnumValue != other.EnumValue) return false;
       if(!enumArray_.Equals(other.enumArray_)) return false;
       return true;
@@ -563,6 +609,9 @@ namespace UnitTest.Issues.TestProtos {
       get { return global::UnitTest.Issues.TestProtos.UnittestIssues.internal__static_unittest_issues_ItemField__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public ItemField() { }
 
     public ItemField(ItemField other) {
@@ -573,14 +622,23 @@ namespace UnitTest.Issues.TestProtos {
       return new ItemField(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+    }
+
     public const int ItemFieldNumber = 1;
     private int item_;
     public int Item {
       get { return item_; }
-      set { item_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        item_ = value;
+      }
     }
 
-
     public override bool Equals(object other) {
       return Equals(other as ItemField);
     }
diff --git a/csharp/src/ProtocolBuffers.Test/TestProtos/UnittestProto3.cs b/csharp/src/ProtocolBuffers.Test/TestProtos/UnittestProto3.cs
index d9d33b10..d758ef5c 100644
--- a/csharp/src/ProtocolBuffers.Test/TestProtos/UnittestProto3.cs
+++ b/csharp/src/ProtocolBuffers.Test/TestProtos/UnittestProto3.cs
@@ -416,6 +416,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_TestAllTypes__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public TestAllTypes() { }
 
     public TestAllTypes(TestAllTypes other) {
@@ -484,176 +487,258 @@ namespace Google.Protobuf.TestProtos {
       return new TestAllTypes(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      if (singleNestedMessage_ != null) SingleNestedMessage.Freeze();
+      if (singleForeignMessage_ != null) SingleForeignMessage.Freeze();
+      if (singleImportMessage_ != null) SingleImportMessage.Freeze();
+      if (singlePublicImportMessage_ != null) SinglePublicImportMessage.Freeze();
+      repeatedInt32_.Freeze();
+      repeatedInt64_.Freeze();
+      repeatedUint32_.Freeze();
+      repeatedUint64_.Freeze();
+      repeatedSint32_.Freeze();
+      repeatedSint64_.Freeze();
+      repeatedFixed32_.Freeze();
+      repeatedFixed64_.Freeze();
+      repeatedSfixed32_.Freeze();
+      repeatedSfixed64_.Freeze();
+      repeatedFloat_.Freeze();
+      repeatedDouble_.Freeze();
+      repeatedBool_.Freeze();
+      repeatedString_.Freeze();
+      repeatedBytes_.Freeze();
+      repeatedNestedMessage_.Freeze();
+      repeatedForeignMessage_.Freeze();
+      repeatedImportMessage_.Freeze();
+      repeatedNestedEnum_.Freeze();
+      repeatedForeignEnum_.Freeze();
+      repeatedImportEnum_.Freeze();
+      repeatedPublicImportMessage_.Freeze();
+      if (oneofField_ is IFreezable) ((IFreezable) oneofField_).Freeze();
+    }
+
     public const int SingleInt32FieldNumber = 1;
     private int singleInt32_;
     public int SingleInt32 {
       get { return singleInt32_; }
-      set { singleInt32_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        singleInt32_ = value;
+      }
     }
 
-
     public const int SingleInt64FieldNumber = 2;
     private long singleInt64_;
     public long SingleInt64 {
       get { return singleInt64_; }
-      set { singleInt64_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        singleInt64_ = value;
+      }
     }
 
-
     public const int SingleUint32FieldNumber = 3;
     private uint singleUint32_;
     public uint SingleUint32 {
       get { return singleUint32_; }
-      set { singleUint32_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        singleUint32_ = value;
+      }
     }
 
-
     public const int SingleUint64FieldNumber = 4;
     private ulong singleUint64_;
     public ulong SingleUint64 {
       get { return singleUint64_; }
-      set { singleUint64_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        singleUint64_ = value;
+      }
     }
 
-
     public const int SingleSint32FieldNumber = 5;
     private int singleSint32_;
     public int SingleSint32 {
       get { return singleSint32_; }
-      set { singleSint32_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        singleSint32_ = value;
+      }
     }
 
-
     public const int SingleSint64FieldNumber = 6;
     private long singleSint64_;
     public long SingleSint64 {
       get { return singleSint64_; }
-      set { singleSint64_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        singleSint64_ = value;
+      }
     }
 
-
     public const int SingleFixed32FieldNumber = 7;
     private uint singleFixed32_;
     public uint SingleFixed32 {
       get { return singleFixed32_; }
-      set { singleFixed32_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        singleFixed32_ = value;
+      }
     }
 
-
     public const int SingleFixed64FieldNumber = 8;
     private ulong singleFixed64_;
     public ulong SingleFixed64 {
       get { return singleFixed64_; }
-      set { singleFixed64_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        singleFixed64_ = value;
+      }
     }
 
-
     public const int SingleSfixed32FieldNumber = 9;
     private int singleSfixed32_;
     public int SingleSfixed32 {
       get { return singleSfixed32_; }
-      set { singleSfixed32_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        singleSfixed32_ = value;
+      }
     }
 
-
     public const int SingleSfixed64FieldNumber = 10;
     private long singleSfixed64_;
     public long SingleSfixed64 {
       get { return singleSfixed64_; }
-      set { singleSfixed64_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        singleSfixed64_ = value;
+      }
     }
 
-
     public const int SingleFloatFieldNumber = 11;
     private float singleFloat_;
     public float SingleFloat {
       get { return singleFloat_; }
-      set { singleFloat_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        singleFloat_ = value;
+      }
     }
 
-
     public const int SingleDoubleFieldNumber = 12;
     private double singleDouble_;
     public double SingleDouble {
       get { return singleDouble_; }
-      set { singleDouble_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        singleDouble_ = value;
+      }
     }
 
-
     public const int SingleBoolFieldNumber = 13;
     private bool singleBool_;
     public bool SingleBool {
       get { return singleBool_; }
-      set { singleBool_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        singleBool_ = value;
+      }
     }
 
-
     public const int SingleStringFieldNumber = 14;
     private string singleString_ = "";
     public string SingleString {
       get { return singleString_; }
-      set { singleString_ = value ?? ""; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        singleString_ = value ?? "";
+      }
     }
 
-
     public const int SingleBytesFieldNumber = 15;
     private pb::ByteString singleBytes_ = pb::ByteString.Empty;
     public pb::ByteString SingleBytes {
       get { return singleBytes_; }
-      set { singleBytes_ = value ?? pb::ByteString.Empty; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        singleBytes_ = value ?? pb::ByteString.Empty;
+      }
     }
 
-
     public const int SingleNestedMessageFieldNumber = 18;
     private global::Google.Protobuf.TestProtos.TestAllTypes.Types.NestedMessage singleNestedMessage_;
     public global::Google.Protobuf.TestProtos.TestAllTypes.Types.NestedMessage SingleNestedMessage {
       get { return singleNestedMessage_; }
-      set { singleNestedMessage_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        singleNestedMessage_ = value;
+      }
     }
 
     public const int SingleForeignMessageFieldNumber = 19;
     private global::Google.Protobuf.TestProtos.ForeignMessage singleForeignMessage_;
     public global::Google.Protobuf.TestProtos.ForeignMessage SingleForeignMessage {
       get { return singleForeignMessage_; }
-      set { singleForeignMessage_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        singleForeignMessage_ = value;
+      }
     }
 
     public const int SingleImportMessageFieldNumber = 20;
     private global::Google.Protobuf.TestProtos.ImportMessage singleImportMessage_;
     public global::Google.Protobuf.TestProtos.ImportMessage SingleImportMessage {
       get { return singleImportMessage_; }
-      set { singleImportMessage_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        singleImportMessage_ = value;
+      }
     }
 
     public const int SingleNestedEnumFieldNumber = 21;
     private global::Google.Protobuf.TestProtos.TestAllTypes.Types.NestedEnum singleNestedEnum_ = global::Google.Protobuf.TestProtos.TestAllTypes.Types.NestedEnum.NESTED_ENUM_UNSPECIFIED;
     public global::Google.Protobuf.TestProtos.TestAllTypes.Types.NestedEnum SingleNestedEnum {
       get { return singleNestedEnum_; }
-      set { singleNestedEnum_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        singleNestedEnum_ = value;
+      }
     }
 
-
     public const int SingleForeignEnumFieldNumber = 22;
     private global::Google.Protobuf.TestProtos.ForeignEnum singleForeignEnum_ = global::Google.Protobuf.TestProtos.ForeignEnum.FOREIGN_UNSPECIFIED;
     public global::Google.Protobuf.TestProtos.ForeignEnum SingleForeignEnum {
       get { return singleForeignEnum_; }
-      set { singleForeignEnum_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        singleForeignEnum_ = value;
+      }
     }
 
-
     public const int SingleImportEnumFieldNumber = 23;
     private global::Google.Protobuf.TestProtos.ImportEnum singleImportEnum_ = global::Google.Protobuf.TestProtos.ImportEnum.IMPORT_ENUM_UNSPECIFIED;
     public global::Google.Protobuf.TestProtos.ImportEnum SingleImportEnum {
       get { return singleImportEnum_; }
-      set { singleImportEnum_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        singleImportEnum_ = value;
+      }
     }
 
-
     public const int SinglePublicImportMessageFieldNumber = 26;
     private global::Google.Protobuf.TestProtos.PublicImportMessage singlePublicImportMessage_;
     public global::Google.Protobuf.TestProtos.PublicImportMessage SinglePublicImportMessage {
       get { return singlePublicImportMessage_; }
-      set { singlePublicImportMessage_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        singlePublicImportMessage_ = value;
+      }
     }
 
     public const int RepeatedInt32FieldNumber = 31;
@@ -792,6 +877,7 @@ namespace Google.Protobuf.TestProtos {
     public uint OneofUint32 {
       get { return oneofFieldCase_ == OneofFieldOneofCase.OneofUint32 ? (uint) oneofField_ : 0; }
       set {
+        pb::Freezable.CheckMutable(this);
         oneofField_ = value;
         oneofFieldCase_ = OneofFieldOneofCase.OneofUint32;
       }
@@ -801,6 +887,7 @@ namespace Google.Protobuf.TestProtos {
     public global::Google.Protobuf.TestProtos.TestAllTypes.Types.NestedMessage OneofNestedMessage {
       get { return oneofFieldCase_ == OneofFieldOneofCase.OneofNestedMessage ? (global::Google.Protobuf.TestProtos.TestAllTypes.Types.NestedMessage) oneofField_ : null; }
       set {
+        pb::Freezable.CheckMutable(this);
         oneofField_ = value;
         oneofFieldCase_ = value == null ? OneofFieldOneofCase.None : OneofFieldOneofCase.OneofNestedMessage;
       }
@@ -810,6 +897,7 @@ namespace Google.Protobuf.TestProtos {
     public string OneofString {
       get { return oneofFieldCase_ == OneofFieldOneofCase.OneofString ? (string) oneofField_ : ""; }
       set {
+        pb::Freezable.CheckMutable(this);
         oneofField_ = value ?? "";
         oneofFieldCase_ = OneofFieldOneofCase.OneofString;
       }
@@ -819,6 +907,7 @@ namespace Google.Protobuf.TestProtos {
     public pb::ByteString OneofBytes {
       get { return oneofFieldCase_ == OneofFieldOneofCase.OneofBytes ? (pb::ByteString) oneofField_ : pb::ByteString.Empty; }
       set {
+        pb::Freezable.CheckMutable(this);
         oneofField_ = value ?? pb::ByteString.Empty;
         oneofFieldCase_ = OneofFieldOneofCase.OneofBytes;
       }
@@ -838,6 +927,7 @@ namespace Google.Protobuf.TestProtos {
     }
 
     public void ClearOneofField() {
+      pb::Freezable.CheckMutable(this);
       oneofFieldCase_ = OneofFieldOneofCase.None;
       oneofField_ = null;
     }
@@ -868,10 +958,14 @@ namespace Google.Protobuf.TestProtos {
       if (SingleBool != other.SingleBool) return false;
       if (SingleString != other.SingleString) return false;
       if (SingleBytes != other.SingleBytes) return false;
-      if (!object.Equals(SingleNestedMessage, other.SingleNestedMessage)) return false;if (!object.Equals(SingleForeignMessage, other.SingleForeignMessage)) return false;if (!object.Equals(SingleImportMessage, other.SingleImportMessage)) return false;if (SingleNestedEnum != other.SingleNestedEnum) return false;
+      if (!object.Equals(SingleNestedMessage, other.SingleNestedMessage)) return false;
+      if (!object.Equals(SingleForeignMessage, other.SingleForeignMessage)) return false;
+      if (!object.Equals(SingleImportMessage, other.SingleImportMessage)) return false;
+      if (SingleNestedEnum != other.SingleNestedEnum) return false;
       if (SingleForeignEnum != other.SingleForeignEnum) return false;
       if (SingleImportEnum != other.SingleImportEnum) return false;
-      if (!object.Equals(SinglePublicImportMessage, other.SinglePublicImportMessage)) return false;if(!repeatedInt32_.Equals(other.repeatedInt32_)) return false;
+      if (!object.Equals(SinglePublicImportMessage, other.SinglePublicImportMessage)) return false;
+      if(!repeatedInt32_.Equals(other.repeatedInt32_)) return false;
       if(!repeatedInt64_.Equals(other.repeatedInt64_)) return false;
       if(!repeatedUint32_.Equals(other.repeatedUint32_)) return false;
       if(!repeatedUint64_.Equals(other.repeatedUint64_)) return false;
@@ -894,7 +988,8 @@ namespace Google.Protobuf.TestProtos {
       if(!repeatedImportEnum_.Equals(other.repeatedImportEnum_)) return false;
       if(!repeatedPublicImportMessage_.Equals(other.repeatedPublicImportMessage_)) return false;
       if (OneofUint32 != other.OneofUint32) return false;
-      if (!object.Equals(OneofNestedMessage, other.OneofNestedMessage)) return false;if (OneofString != other.OneofString) return false;
+      if (!object.Equals(OneofNestedMessage, other.OneofNestedMessage)) return false;
+      if (OneofString != other.OneofString) return false;
       if (OneofBytes != other.OneofBytes) return false;
       return true;
     }
@@ -1764,6 +1859,9 @@ namespace Google.Protobuf.TestProtos {
           get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_TestAllTypes_NestedMessage__FieldAccessorTable; }
         }
 
+        private bool _frozen = false;
+        public bool IsFrozen { get { return _frozen; } }
+
         public NestedMessage() { }
 
         public NestedMessage(NestedMessage other) {
@@ -1774,14 +1872,23 @@ namespace Google.Protobuf.TestProtos {
           return new NestedMessage(this);
         }
 
+        public void Freeze() {
+          if (IsFrozen) {
+            return;
+          }
+          _frozen = true;
+        }
+
         public const int BbFieldNumber = 1;
         private int bb_;
         public int Bb {
           get { return bb_; }
-          set { bb_ = value; }
+          set {
+            pb::Freezable.CheckMutable(this);
+            bb_ = value;
+          }
         }
 
-
         public override bool Equals(object other) {
           return Equals(other as NestedMessage);
         }
@@ -1867,6 +1974,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_NestedTestAllTypes__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public NestedTestAllTypes() { }
 
     public NestedTestAllTypes(NestedTestAllTypes other) {
@@ -1879,18 +1989,34 @@ namespace Google.Protobuf.TestProtos {
       return new NestedTestAllTypes(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      if (child_ != null) Child.Freeze();
+      if (payload_ != null) Payload.Freeze();
+      repeatedChild_.Freeze();
+    }
+
     public const int ChildFieldNumber = 1;
     private global::Google.Protobuf.TestProtos.NestedTestAllTypes child_;
     public global::Google.Protobuf.TestProtos.NestedTestAllTypes Child {
       get { return child_; }
-      set { child_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        child_ = value;
+      }
     }
 
     public const int PayloadFieldNumber = 2;
     private global::Google.Protobuf.TestProtos.TestAllTypes payload_;
     public global::Google.Protobuf.TestProtos.TestAllTypes Payload {
       get { return payload_; }
-      set { payload_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        payload_ = value;
+      }
     }
 
     public const int RepeatedChildFieldNumber = 3;
@@ -1910,7 +2036,9 @@ namespace Google.Protobuf.TestProtos {
       if (ReferenceEquals(other, this)) {
         return true;
       }
-      if (!object.Equals(Child, other.Child)) return false;if (!object.Equals(Payload, other.Payload)) return false;if(!repeatedChild_.Equals(other.repeatedChild_)) return false;
+      if (!object.Equals(Child, other.Child)) return false;
+      if (!object.Equals(Payload, other.Payload)) return false;
+      if(!repeatedChild_.Equals(other.repeatedChild_)) return false;
       return true;
     }
 
@@ -2021,6 +2149,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_TestDeprecatedFields__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public TestDeprecatedFields() { }
 
     public TestDeprecatedFields(TestDeprecatedFields other) {
@@ -2031,15 +2162,24 @@ namespace Google.Protobuf.TestProtos {
       return new TestDeprecatedFields(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+    }
+
     public const int DeprecatedInt32FieldNumber = 1;
     private int deprecatedInt32_;
     [global::System.ObsoleteAttribute()]
     public int DeprecatedInt32 {
       get { return deprecatedInt32_; }
-      set { deprecatedInt32_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        deprecatedInt32_ = value;
+      }
     }
 
-
     public override bool Equals(object other) {
       return Equals(other as TestDeprecatedFields);
     }
@@ -2120,6 +2260,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_ForeignMessage__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public ForeignMessage() { }
 
     public ForeignMessage(ForeignMessage other) {
@@ -2130,14 +2273,23 @@ namespace Google.Protobuf.TestProtos {
       return new ForeignMessage(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+    }
+
     public const int CFieldNumber = 1;
     private int c_;
     public int C {
       get { return c_; }
-      set { c_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        c_ = value;
+      }
     }
 
-
     public override bool Equals(object other) {
       return Equals(other as ForeignMessage);
     }
@@ -2218,6 +2370,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_TestReservedFields__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public TestReservedFields() { }
 
     public TestReservedFields(TestReservedFields other) {
@@ -2227,6 +2382,13 @@ namespace Google.Protobuf.TestProtos {
       return new TestReservedFields(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+    }
+
     public override bool Equals(object other) {
       return Equals(other as TestReservedFields);
     }
@@ -2291,6 +2453,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_TestForeignNested__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public TestForeignNested() { }
 
     public TestForeignNested(TestForeignNested other) {
@@ -2301,11 +2466,22 @@ namespace Google.Protobuf.TestProtos {
       return new TestForeignNested(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      if (foreignNested_ != null) ForeignNested.Freeze();
+    }
+
     public const int ForeignNestedFieldNumber = 1;
     private global::Google.Protobuf.TestProtos.TestAllTypes.Types.NestedMessage foreignNested_;
     public global::Google.Protobuf.TestProtos.TestAllTypes.Types.NestedMessage ForeignNested {
       get { return foreignNested_; }
-      set { foreignNested_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        foreignNested_ = value;
+      }
     }
 
     public override bool Equals(object other) {
@@ -2319,7 +2495,8 @@ namespace Google.Protobuf.TestProtos {
       if (ReferenceEquals(other, this)) {
         return true;
       }
-      if (!object.Equals(ForeignNested, other.ForeignNested)) return false;  return true;
+      if (!object.Equals(ForeignNested, other.ForeignNested)) return false;
+      return true;
     }
 
     public override int GetHashCode() {
@@ -2393,6 +2570,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_TestReallyLargeTagNumber__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public TestReallyLargeTagNumber() { }
 
     public TestReallyLargeTagNumber(TestReallyLargeTagNumber other) {
@@ -2404,22 +2584,33 @@ namespace Google.Protobuf.TestProtos {
       return new TestReallyLargeTagNumber(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+    }
+
     public const int AFieldNumber = 1;
     private int a_;
     public int A {
       get { return a_; }
-      set { a_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        a_ = value;
+      }
     }
 
-
     public const int BbFieldNumber = 268435455;
     private int bb_;
     public int Bb {
       get { return bb_; }
-      set { bb_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        bb_ = value;
+      }
     }
 
-
     public override bool Equals(object other) {
       return Equals(other as TestReallyLargeTagNumber);
     }
@@ -2516,6 +2707,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_TestRecursiveMessage__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public TestRecursiveMessage() { }
 
     public TestRecursiveMessage(TestRecursiveMessage other) {
@@ -2527,21 +2721,34 @@ namespace Google.Protobuf.TestProtos {
       return new TestRecursiveMessage(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      if (a_ != null) A.Freeze();
+    }
+
     public const int AFieldNumber = 1;
     private global::Google.Protobuf.TestProtos.TestRecursiveMessage a_;
     public global::Google.Protobuf.TestProtos.TestRecursiveMessage A {
       get { return a_; }
-      set { a_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        a_ = value;
+      }
     }
 
     public const int IFieldNumber = 2;
     private int i_;
     public int I {
       get { return i_; }
-      set { i_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        i_ = value;
+      }
     }
 
-
     public override bool Equals(object other) {
       return Equals(other as TestRecursiveMessage);
     }
@@ -2553,7 +2760,8 @@ namespace Google.Protobuf.TestProtos {
       if (ReferenceEquals(other, this)) {
         return true;
       }
-      if (!object.Equals(A, other.A)) return false;if (I != other.I) return false;
+      if (!object.Equals(A, other.A)) return false;
+      if (I != other.I) return false;
       return true;
     }
 
@@ -2643,6 +2851,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_TestMutualRecursionA__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public TestMutualRecursionA() { }
 
     public TestMutualRecursionA(TestMutualRecursionA other) {
@@ -2653,11 +2864,22 @@ namespace Google.Protobuf.TestProtos {
       return new TestMutualRecursionA(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      if (bb_ != null) Bb.Freeze();
+    }
+
     public const int BbFieldNumber = 1;
     private global::Google.Protobuf.TestProtos.TestMutualRecursionB bb_;
     public global::Google.Protobuf.TestProtos.TestMutualRecursionB Bb {
       get { return bb_; }
-      set { bb_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        bb_ = value;
+      }
     }
 
     public override bool Equals(object other) {
@@ -2671,7 +2893,8 @@ namespace Google.Protobuf.TestProtos {
       if (ReferenceEquals(other, this)) {
         return true;
       }
-      if (!object.Equals(Bb, other.Bb)) return false;  return true;
+      if (!object.Equals(Bb, other.Bb)) return false;
+      return true;
     }
 
     public override int GetHashCode() {
@@ -2745,6 +2968,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_TestMutualRecursionB__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public TestMutualRecursionB() { }
 
     public TestMutualRecursionB(TestMutualRecursionB other) {
@@ -2756,21 +2982,34 @@ namespace Google.Protobuf.TestProtos {
       return new TestMutualRecursionB(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      if (a_ != null) A.Freeze();
+    }
+
     public const int AFieldNumber = 1;
     private global::Google.Protobuf.TestProtos.TestMutualRecursionA a_;
     public global::Google.Protobuf.TestProtos.TestMutualRecursionA A {
       get { return a_; }
-      set { a_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        a_ = value;
+      }
     }
 
     public const int OptionalInt32FieldNumber = 2;
     private int optionalInt32_;
     public int OptionalInt32 {
       get { return optionalInt32_; }
-      set { optionalInt32_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        optionalInt32_ = value;
+      }
     }
 
-
     public override bool Equals(object other) {
       return Equals(other as TestMutualRecursionB);
     }
@@ -2782,7 +3021,8 @@ namespace Google.Protobuf.TestProtos {
       if (ReferenceEquals(other, this)) {
         return true;
       }
-      if (!object.Equals(A, other.A)) return false;if (OptionalInt32 != other.OptionalInt32) return false;
+      if (!object.Equals(A, other.A)) return false;
+      if (OptionalInt32 != other.OptionalInt32) return false;
       return true;
     }
 
@@ -2872,6 +3112,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_TestCamelCaseFieldNames__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public TestCamelCaseFieldNames() { }
 
     public TestCamelCaseFieldNames(TestCamelCaseFieldNames other) {
@@ -2889,35 +3132,56 @@ namespace Google.Protobuf.TestProtos {
       return new TestCamelCaseFieldNames(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      if (messageField_ != null) MessageField.Freeze();
+      repeatedPrimitiveField_.Freeze();
+      repeatedStringField_.Freeze();
+      repeatedEnumField_.Freeze();
+      repeatedMessageField_.Freeze();
+    }
+
     public const int PrimitiveFieldFieldNumber = 1;
     private int primitiveField_;
     public int PrimitiveField {
       get { return primitiveField_; }
-      set { primitiveField_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        primitiveField_ = value;
+      }
     }
 
-
     public const int StringFieldFieldNumber = 2;
     private string stringField_ = "";
     public string StringField {
       get { return stringField_; }
-      set { stringField_ = value ?? ""; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        stringField_ = value ?? "";
+      }
     }
 
-
     public const int EnumFieldFieldNumber = 3;
     private global::Google.Protobuf.TestProtos.ForeignEnum enumField_ = global::Google.Protobuf.TestProtos.ForeignEnum.FOREIGN_UNSPECIFIED;
     public global::Google.Protobuf.TestProtos.ForeignEnum EnumField {
       get { return enumField_; }
-      set { enumField_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        enumField_ = value;
+      }
     }
 
-
     public const int MessageFieldFieldNumber = 4;
     private global::Google.Protobuf.TestProtos.ForeignMessage messageField_;
     public global::Google.Protobuf.TestProtos.ForeignMessage MessageField {
       get { return messageField_; }
-      set { messageField_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        messageField_ = value;
+      }
     }
 
     public const int RepeatedPrimitiveFieldFieldNumber = 7;
@@ -2958,7 +3222,8 @@ namespace Google.Protobuf.TestProtos {
       if (PrimitiveField != other.PrimitiveField) return false;
       if (StringField != other.StringField) return false;
       if (EnumField != other.EnumField) return false;
-      if (!object.Equals(MessageField, other.MessageField)) return false;if(!repeatedPrimitiveField_.Equals(other.repeatedPrimitiveField_)) return false;
+      if (!object.Equals(MessageField, other.MessageField)) return false;
+      if(!repeatedPrimitiveField_.Equals(other.repeatedPrimitiveField_)) return false;
       if(!repeatedStringField_.Equals(other.repeatedStringField_)) return false;
       if(!repeatedEnumField_.Equals(other.repeatedEnumField_)) return false;
       if(!repeatedMessageField_.Equals(other.repeatedMessageField_)) return false;
@@ -3151,6 +3416,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_TestFieldOrderings__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public TestFieldOrderings() { }
 
     public TestFieldOrderings(TestFieldOrderings other) {
@@ -3164,35 +3432,52 @@ namespace Google.Protobuf.TestProtos {
       return new TestFieldOrderings(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      if (singleNestedMessage_ != null) SingleNestedMessage.Freeze();
+    }
+
     public const int MyStringFieldNumber = 11;
     private string myString_ = "";
     public string MyString {
       get { return myString_; }
-      set { myString_ = value ?? ""; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        myString_ = value ?? "";
+      }
     }
 
-
     public const int MyIntFieldNumber = 1;
     private long myInt_;
     public long MyInt {
       get { return myInt_; }
-      set { myInt_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        myInt_ = value;
+      }
     }
 
-
     public const int MyFloatFieldNumber = 101;
     private float myFloat_;
     public float MyFloat {
       get { return myFloat_; }
-      set { myFloat_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        myFloat_ = value;
+      }
     }
 
-
     public const int SingleNestedMessageFieldNumber = 200;
     private global::Google.Protobuf.TestProtos.TestFieldOrderings.Types.NestedMessage singleNestedMessage_;
     public global::Google.Protobuf.TestProtos.TestFieldOrderings.Types.NestedMessage SingleNestedMessage {
       get { return singleNestedMessage_; }
-      set { singleNestedMessage_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        singleNestedMessage_ = value;
+      }
     }
 
     public override bool Equals(object other) {
@@ -3209,7 +3494,8 @@ namespace Google.Protobuf.TestProtos {
       if (MyString != other.MyString) return false;
       if (MyInt != other.MyInt) return false;
       if (MyFloat != other.MyFloat) return false;
-      if (!object.Equals(SingleNestedMessage, other.SingleNestedMessage)) return false;  return true;
+      if (!object.Equals(SingleNestedMessage, other.SingleNestedMessage)) return false;
+      return true;
     }
 
     public override int GetHashCode() {
@@ -3329,6 +3615,9 @@ namespace Google.Protobuf.TestProtos {
           get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_TestFieldOrderings_NestedMessage__FieldAccessorTable; }
         }
 
+        private bool _frozen = false;
+        public bool IsFrozen { get { return _frozen; } }
+
         public NestedMessage() { }
 
         public NestedMessage(NestedMessage other) {
@@ -3340,22 +3629,33 @@ namespace Google.Protobuf.TestProtos {
           return new NestedMessage(this);
         }
 
+        public void Freeze() {
+          if (IsFrozen) {
+            return;
+          }
+          _frozen = true;
+        }
+
         public const int OoFieldNumber = 2;
         private long oo_;
         public long Oo {
           get { return oo_; }
-          set { oo_ = value; }
+          set {
+            pb::Freezable.CheckMutable(this);
+            oo_ = value;
+          }
         }
 
-
         public const int BbFieldNumber = 1;
         private int bb_;
         public int Bb {
           get { return bb_; }
-          set { bb_ = value; }
+          set {
+            pb::Freezable.CheckMutable(this);
+            bb_ = value;
+          }
         }
 
-
         public override bool Equals(object other) {
           return Equals(other as NestedMessage);
         }
@@ -3457,6 +3757,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_SparseEnumMessage__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public SparseEnumMessage() { }
 
     public SparseEnumMessage(SparseEnumMessage other) {
@@ -3467,14 +3770,23 @@ namespace Google.Protobuf.TestProtos {
       return new SparseEnumMessage(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+    }
+
     public const int SparseEnumFieldNumber = 1;
     private global::Google.Protobuf.TestProtos.TestSparseEnum sparseEnum_ = global::Google.Protobuf.TestProtos.TestSparseEnum.TEST_SPARSE_ENUM_UNSPECIFIED;
     public global::Google.Protobuf.TestProtos.TestSparseEnum SparseEnum {
       get { return sparseEnum_; }
-      set { sparseEnum_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        sparseEnum_ = value;
+      }
     }
 
-
     public override bool Equals(object other) {
       return Equals(other as SparseEnumMessage);
     }
@@ -3555,6 +3867,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_OneString__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public OneString() { }
 
     public OneString(OneString other) {
@@ -3565,14 +3880,23 @@ namespace Google.Protobuf.TestProtos {
       return new OneString(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+    }
+
     public const int DataFieldNumber = 1;
     private string data_ = "";
     public string Data {
       get { return data_; }
-      set { data_ = value ?? ""; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        data_ = value ?? "";
+      }
     }
 
-
     public override bool Equals(object other) {
       return Equals(other as OneString);
     }
@@ -3653,6 +3977,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_MoreString__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public MoreString() { }
 
     public MoreString(MoreString other) {
@@ -3663,6 +3990,14 @@ namespace Google.Protobuf.TestProtos {
       return new MoreString(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      data_.Freeze();
+    }
+
     public const int DataFieldNumber = 1;
     private readonly pbc::RepeatedField<string> data_ = new pbc::RepeatedField<string>();
     public pbc::RepeatedField<string> Data {
@@ -3751,6 +4086,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_OneBytes__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public OneBytes() { }
 
     public OneBytes(OneBytes other) {
@@ -3761,14 +4099,23 @@ namespace Google.Protobuf.TestProtos {
       return new OneBytes(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+    }
+
     public const int DataFieldNumber = 1;
     private pb::ByteString data_ = pb::ByteString.Empty;
     public pb::ByteString Data {
       get { return data_; }
-      set { data_ = value ?? pb::ByteString.Empty; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        data_ = value ?? pb::ByteString.Empty;
+      }
     }
 
-
     public override bool Equals(object other) {
       return Equals(other as OneBytes);
     }
@@ -3849,6 +4196,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_MoreBytes__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public MoreBytes() { }
 
     public MoreBytes(MoreBytes other) {
@@ -3859,14 +4209,23 @@ namespace Google.Protobuf.TestProtos {
       return new MoreBytes(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+    }
+
     public const int DataFieldNumber = 1;
     private pb::ByteString data_ = pb::ByteString.Empty;
     public pb::ByteString Data {
       get { return data_; }
-      set { data_ = value ?? pb::ByteString.Empty; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        data_ = value ?? pb::ByteString.Empty;
+      }
     }
 
-
     public override bool Equals(object other) {
       return Equals(other as MoreBytes);
     }
@@ -3947,6 +4306,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_Int32Message__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public Int32Message() { }
 
     public Int32Message(Int32Message other) {
@@ -3957,14 +4319,23 @@ namespace Google.Protobuf.TestProtos {
       return new Int32Message(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+    }
+
     public const int DataFieldNumber = 1;
     private int data_;
     public int Data {
       get { return data_; }
-      set { data_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        data_ = value;
+      }
     }
 
-
     public override bool Equals(object other) {
       return Equals(other as Int32Message);
     }
@@ -4045,6 +4416,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_Uint32Message__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public Uint32Message() { }
 
     public Uint32Message(Uint32Message other) {
@@ -4055,14 +4429,23 @@ namespace Google.Protobuf.TestProtos {
       return new Uint32Message(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+    }
+
     public const int DataFieldNumber = 1;
     private uint data_;
     public uint Data {
       get { return data_; }
-      set { data_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        data_ = value;
+      }
     }
 
-
     public override bool Equals(object other) {
       return Equals(other as Uint32Message);
     }
@@ -4143,6 +4526,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_Int64Message__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public Int64Message() { }
 
     public Int64Message(Int64Message other) {
@@ -4153,14 +4539,23 @@ namespace Google.Protobuf.TestProtos {
       return new Int64Message(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+    }
+
     public const int DataFieldNumber = 1;
     private long data_;
     public long Data {
       get { return data_; }
-      set { data_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        data_ = value;
+      }
     }
 
-
     public override bool Equals(object other) {
       return Equals(other as Int64Message);
     }
@@ -4241,6 +4636,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_Uint64Message__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public Uint64Message() { }
 
     public Uint64Message(Uint64Message other) {
@@ -4251,14 +4649,23 @@ namespace Google.Protobuf.TestProtos {
       return new Uint64Message(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+    }
+
     public const int DataFieldNumber = 1;
     private ulong data_;
     public ulong Data {
       get { return data_; }
-      set { data_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        data_ = value;
+      }
     }
 
-
     public override bool Equals(object other) {
       return Equals(other as Uint64Message);
     }
@@ -4339,6 +4746,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_BoolMessage__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public BoolMessage() { }
 
     public BoolMessage(BoolMessage other) {
@@ -4349,14 +4759,23 @@ namespace Google.Protobuf.TestProtos {
       return new BoolMessage(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+    }
+
     public const int DataFieldNumber = 1;
     private bool data_;
     public bool Data {
       get { return data_; }
-      set { data_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        data_ = value;
+      }
     }
 
-
     public override bool Equals(object other) {
       return Equals(other as BoolMessage);
     }
@@ -4437,6 +4856,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_TestOneof__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public TestOneof() { }
 
     public TestOneof(TestOneof other) {
@@ -4458,10 +4880,19 @@ namespace Google.Protobuf.TestProtos {
       return new TestOneof(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      if (foo_ is IFreezable) ((IFreezable) foo_).Freeze();
+    }
+
     public const int FooIntFieldNumber = 1;
     public int FooInt {
       get { return fooCase_ == FooOneofCase.FooInt ? (int) foo_ : 0; }
       set {
+        pb::Freezable.CheckMutable(this);
         foo_ = value;
         fooCase_ = FooOneofCase.FooInt;
       }
@@ -4471,6 +4902,7 @@ namespace Google.Protobuf.TestProtos {
     public string FooString {
       get { return fooCase_ == FooOneofCase.FooString ? (string) foo_ : ""; }
       set {
+        pb::Freezable.CheckMutable(this);
         foo_ = value ?? "";
         fooCase_ = FooOneofCase.FooString;
       }
@@ -4480,6 +4912,7 @@ namespace Google.Protobuf.TestProtos {
     public global::Google.Protobuf.TestProtos.TestAllTypes FooMessage {
       get { return fooCase_ == FooOneofCase.FooMessage ? (global::Google.Protobuf.TestProtos.TestAllTypes) foo_ : null; }
       set {
+        pb::Freezable.CheckMutable(this);
         foo_ = value;
         fooCase_ = value == null ? FooOneofCase.None : FooOneofCase.FooMessage;
       }
@@ -4498,6 +4931,7 @@ namespace Google.Protobuf.TestProtos {
     }
 
     public void ClearFoo() {
+      pb::Freezable.CheckMutable(this);
       fooCase_ = FooOneofCase.None;
       foo_ = null;
     }
@@ -4515,7 +4949,8 @@ namespace Google.Protobuf.TestProtos {
       }
       if (FooInt != other.FooInt) return false;
       if (FooString != other.FooString) return false;
-      if (!object.Equals(FooMessage, other.FooMessage)) return false;  return true;
+      if (!object.Equals(FooMessage, other.FooMessage)) return false;
+      return true;
     }
 
     public override int GetHashCode() {
@@ -4621,6 +5056,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_TestPackedTypes__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public TestPackedTypes() { }
 
     public TestPackedTypes(TestPackedTypes other) {
@@ -4644,6 +5082,27 @@ namespace Google.Protobuf.TestProtos {
       return new TestPackedTypes(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      packedInt32_.Freeze();
+      packedInt64_.Freeze();
+      packedUint32_.Freeze();
+      packedUint64_.Freeze();
+      packedSint32_.Freeze();
+      packedSint64_.Freeze();
+      packedFixed32_.Freeze();
+      packedFixed64_.Freeze();
+      packedSfixed32_.Freeze();
+      packedSfixed64_.Freeze();
+      packedFloat_.Freeze();
+      packedDouble_.Freeze();
+      packedBool_.Freeze();
+      packedEnum_.Freeze();
+    }
+
     public const int PackedInt32FieldNumber = 90;
     private readonly pbc::RepeatedField<int> packedInt32_ = new pbc::RepeatedField<int>();
     public pbc::RepeatedField<int> PackedInt32 {
@@ -5058,6 +5517,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_TestUnpackedTypes__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public TestUnpackedTypes() { }
 
     public TestUnpackedTypes(TestUnpackedTypes other) {
@@ -5081,6 +5543,27 @@ namespace Google.Protobuf.TestProtos {
       return new TestUnpackedTypes(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      unpackedInt32_.Freeze();
+      unpackedInt64_.Freeze();
+      unpackedUint32_.Freeze();
+      unpackedUint64_.Freeze();
+      unpackedSint32_.Freeze();
+      unpackedSint64_.Freeze();
+      unpackedFixed32_.Freeze();
+      unpackedFixed64_.Freeze();
+      unpackedSfixed32_.Freeze();
+      unpackedSfixed64_.Freeze();
+      unpackedFloat_.Freeze();
+      unpackedDouble_.Freeze();
+      unpackedBool_.Freeze();
+      unpackedEnum_.Freeze();
+    }
+
     public const int UnpackedInt32FieldNumber = 90;
     private readonly pbc::RepeatedField<int> unpackedInt32_ = new pbc::RepeatedField<int>();
     public pbc::RepeatedField<int> UnpackedInt32 {
@@ -5481,6 +5964,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_TestRepeatedScalarDifferentTagSizes__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public TestRepeatedScalarDifferentTagSizes() { }
 
     public TestRepeatedScalarDifferentTagSizes(TestRepeatedScalarDifferentTagSizes other) {
@@ -5496,6 +5982,19 @@ namespace Google.Protobuf.TestProtos {
       return new TestRepeatedScalarDifferentTagSizes(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      repeatedFixed32_.Freeze();
+      repeatedInt32_.Freeze();
+      repeatedFixed64_.Freeze();
+      repeatedInt64_.Freeze();
+      repeatedFloat_.Freeze();
+      repeatedUint64_.Freeze();
+    }
+
     public const int RepeatedFixed32FieldNumber = 12;
     private readonly pbc::RepeatedField<uint> repeatedFixed32_ = new pbc::RepeatedField<uint>();
     public pbc::RepeatedField<uint> RepeatedFixed32 {
@@ -5710,6 +6209,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_TestCommentInjectionMessage__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public TestCommentInjectionMessage() { }
 
     public TestCommentInjectionMessage(TestCommentInjectionMessage other) {
@@ -5720,14 +6222,23 @@ namespace Google.Protobuf.TestProtos {
       return new TestCommentInjectionMessage(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+    }
+
     public const int AFieldNumber = 1;
     private string a_ = "";
     public string A {
       get { return a_; }
-      set { a_ = value ?? ""; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        a_ = value ?? "";
+      }
     }
 
-
     public override bool Equals(object other) {
       return Equals(other as TestCommentInjectionMessage);
     }
@@ -5808,6 +6319,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_FooRequest__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public FooRequest() { }
 
     public FooRequest(FooRequest other) {
@@ -5817,6 +6331,13 @@ namespace Google.Protobuf.TestProtos {
       return new FooRequest(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+    }
+
     public override bool Equals(object other) {
       return Equals(other as FooRequest);
     }
@@ -5881,6 +6402,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_FooResponse__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public FooResponse() { }
 
     public FooResponse(FooResponse other) {
@@ -5890,6 +6414,13 @@ namespace Google.Protobuf.TestProtos {
       return new FooResponse(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+    }
+
     public override bool Equals(object other) {
       return Equals(other as FooResponse);
     }
@@ -5954,6 +6485,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_FooClientMessage__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public FooClientMessage() { }
 
     public FooClientMessage(FooClientMessage other) {
@@ -5963,6 +6497,13 @@ namespace Google.Protobuf.TestProtos {
       return new FooClientMessage(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+    }
+
     public override bool Equals(object other) {
       return Equals(other as FooClientMessage);
     }
@@ -6027,6 +6568,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_FooServerMessage__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public FooServerMessage() { }
 
     public FooServerMessage(FooServerMessage other) {
@@ -6036,6 +6580,13 @@ namespace Google.Protobuf.TestProtos {
       return new FooServerMessage(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+    }
+
     public override bool Equals(object other) {
       return Equals(other as FooServerMessage);
     }
@@ -6100,6 +6651,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_BarRequest__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public BarRequest() { }
 
     public BarRequest(BarRequest other) {
@@ -6109,6 +6663,13 @@ namespace Google.Protobuf.TestProtos {
       return new BarRequest(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+    }
+
     public override bool Equals(object other) {
       return Equals(other as BarRequest);
     }
@@ -6173,6 +6734,9 @@ namespace Google.Protobuf.TestProtos {
       get { return global::Google.Protobuf.TestProtos.UnittestProto3.internal__static_protobuf_unittest_BarResponse__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public BarResponse() { }
 
     public BarResponse(BarResponse other) {
@@ -6182,6 +6746,13 @@ namespace Google.Protobuf.TestProtos {
       return new BarResponse(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+    }
+
     public override bool Equals(object other) {
       return Equals(other as BarResponse);
     }
diff --git a/csharp/src/ProtocolBuffers/Collections/RepeatedField.cs b/csharp/src/ProtocolBuffers/Collections/RepeatedField.cs
index 5100e4db..ebfc522f 100644
--- a/csharp/src/ProtocolBuffers/Collections/RepeatedField.cs
+++ b/csharp/src/ProtocolBuffers/Collections/RepeatedField.cs
@@ -4,10 +4,16 @@ using System.Collections.Generic;
 
 namespace Google.Protobuf.Collections
 {
-    public sealed class RepeatedField<T> : IList<T>, IEquatable<RepeatedField<T>>
+    /// <summary>
+    /// The contents of a repeated field: essentially, a collection with some extra
+    /// restrictions (no null values) and capabilities (deep cloning and freezing).
+    /// </summary>
+    /// <typeparam name="T">The element type of the repeated field.</typeparam>
+    public sealed class RepeatedField<T> : IList<T>, IDeepCloneable<RepeatedField<T>>, IEquatable<RepeatedField<T>>, IFreezable
     {
         private static readonly T[] EmptyArray = new T[0];
 
+        private bool frozen;
         private const int MinArraySize = 8;
         private T[] array = EmptyArray;
         private int count = 0;
@@ -26,6 +32,7 @@ namespace Google.Protobuf.Collections
         public RepeatedField<T> Clone()
         {
             RepeatedField<T> clone = new RepeatedField<T>();
+            // Clone is implicitly *not* frozen, even if this object is.
             if (array != EmptyArray)
             {
                 clone.array = (T[])array.Clone();
@@ -42,6 +49,21 @@ namespace Google.Protobuf.Collections
             return clone;
         }
 
+        public bool IsFrozen { get { return frozen; } }
+
+        public void Freeze()
+        {
+            frozen = true;
+            IFreezable[] freezableArray = array as IFreezable[];
+            if (freezableArray != null)
+            {
+                for (int i = 0; i < count; i++)
+                {
+                    freezableArray[i].Freeze();
+                }
+            }
+        }
+
         private void EnsureSize(int size)
         {
             size = Math.Max(size, MinArraySize);
@@ -60,6 +82,7 @@ namespace Google.Protobuf.Collections
             {
                 throw new ArgumentNullException("item");
             }
+            this.CheckMutable();
             EnsureSize(count + 1);
             array[count++] = item;
         }
@@ -70,6 +93,7 @@ namespace Google.Protobuf.Collections
         /// <param name="readEnum"></param>
         internal void AddInt32(int item)
         {
+            this.CheckMutable();
             EnsureSize(count + 1);
             int[] castArray = (int[]) (object) array;
             castArray[count++] = item;
@@ -77,6 +101,7 @@ namespace Google.Protobuf.Collections
 
         public void Clear()
         {
+            this.CheckMutable();
             array = EmptyArray;
             count = 0;
         }
@@ -93,6 +118,7 @@ namespace Google.Protobuf.Collections
 
         public bool Remove(T item)
         {
+            this.CheckMutable();
             int index = IndexOf(item);
             if (index == -1)
             {
@@ -107,7 +133,7 @@ namespace Google.Protobuf.Collections
         public int Count { get { return count; } }
 
         // TODO(jonskeet): If we implement freezing, make this reflect it.
-        public bool IsReadOnly { get { return false; } }
+        public bool IsReadOnly { get { return IsFrozen; } }
 
         public void Add(RepeatedField<T> values)
         {
@@ -115,6 +141,7 @@ namespace Google.Protobuf.Collections
             {
                 throw new ArgumentNullException("values");
             }
+            this.CheckMutable();
             EnsureSize(count + values.count);
             // We know that all the values will be valid, because it's a RepeatedField.
             Array.Copy(values.array, 0, array, count, values.count);
@@ -127,6 +154,7 @@ namespace Google.Protobuf.Collections
             {
                 throw new ArgumentNullException("values");
             }
+            this.CheckMutable();
             // TODO: Check for ICollection and get the Count?
             foreach (T item in values)
             {
@@ -227,6 +255,7 @@ namespace Google.Protobuf.Collections
             {
                 throw new ArgumentOutOfRangeException("index");
             }
+            this.CheckMutable();
             EnsureSize(count + 1);
             Array.Copy(array, index, array, index + 1, count - index);
             count++;
@@ -238,6 +267,7 @@ namespace Google.Protobuf.Collections
             {
                 throw new ArgumentOutOfRangeException("index");
             }
+            this.CheckMutable();
             Array.Copy(array, index + 1, array, index, count - index - 1);
             count--;
             array[count] = default(T);
@@ -259,6 +289,7 @@ namespace Google.Protobuf.Collections
                 {
                     throw new ArgumentOutOfRangeException("index");
                 }
+                this.CheckMutable();
                 if (value == null)
                 {
                     throw new ArgumentNullException("value");
diff --git a/csharp/src/ProtocolBuffers/DescriptorProtos/DescriptorProtoFile.cs b/csharp/src/ProtocolBuffers/DescriptorProtos/DescriptorProtoFile.cs
index 23d5e964..eedb21fe 100644
--- a/csharp/src/ProtocolBuffers/DescriptorProtos/DescriptorProtoFile.cs
+++ b/csharp/src/ProtocolBuffers/DescriptorProtos/DescriptorProtoFile.cs
@@ -292,6 +292,9 @@ namespace Google.Protobuf.DescriptorProtos {
       get { return global::Google.Protobuf.DescriptorProtos.DescriptorProtoFile.internal__static_google_protobuf_FileDescriptorSet__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public FileDescriptorSet() { }
 
     public FileDescriptorSet(FileDescriptorSet other) {
@@ -302,6 +305,14 @@ namespace Google.Protobuf.DescriptorProtos {
       return new FileDescriptorSet(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      file_.Freeze();
+    }
+
     public const int FileFieldNumber = 1;
     private readonly pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.FileDescriptorProto> file_ = new pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.FileDescriptorProto>();
     public pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.FileDescriptorProto> File {
@@ -388,6 +399,9 @@ namespace Google.Protobuf.DescriptorProtos {
       get { return global::Google.Protobuf.DescriptorProtos.DescriptorProtoFile.internal__static_google_protobuf_FileDescriptorProto__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public FileDescriptorProto() { }
 
     public FileDescriptorProto(FileDescriptorProto other) {
@@ -409,22 +423,42 @@ namespace Google.Protobuf.DescriptorProtos {
       return new FileDescriptorProto(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      dependency_.Freeze();
+      publicDependency_.Freeze();
+      weakDependency_.Freeze();
+      messageType_.Freeze();
+      enumType_.Freeze();
+      service_.Freeze();
+      extension_.Freeze();
+      if (options_ != null) Options.Freeze();
+      if (sourceCodeInfo_ != null) SourceCodeInfo.Freeze();
+    }
+
     public const int NameFieldNumber = 1;
     private string name_ = "";
     public string Name {
       get { return name_; }
-      set { name_ = value ?? ""; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        name_ = value ?? "";
+      }
     }
 
-
     public const int PackageFieldNumber = 2;
     private string package_ = "";
     public string Package {
       get { return package_; }
-      set { package_ = value ?? ""; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        package_ = value ?? "";
+      }
     }
 
-
     public const int DependencyFieldNumber = 3;
     private readonly pbc::RepeatedField<string> dependency_ = new pbc::RepeatedField<string>();
     public pbc::RepeatedField<string> Dependency {
@@ -471,24 +505,32 @@ namespace Google.Protobuf.DescriptorProtos {
     private global::Google.Protobuf.DescriptorProtos.FileOptions options_;
     public global::Google.Protobuf.DescriptorProtos.FileOptions Options {
       get { return options_; }
-      set { options_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        options_ = value;
+      }
     }
 
     public const int SourceCodeInfoFieldNumber = 9;
     private global::Google.Protobuf.DescriptorProtos.SourceCodeInfo sourceCodeInfo_;
     public global::Google.Protobuf.DescriptorProtos.SourceCodeInfo SourceCodeInfo {
       get { return sourceCodeInfo_; }
-      set { sourceCodeInfo_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        sourceCodeInfo_ = value;
+      }
     }
 
     public const int SyntaxFieldNumber = 12;
     private string syntax_ = "";
     public string Syntax {
       get { return syntax_; }
-      set { syntax_ = value ?? ""; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        syntax_ = value ?? "";
+      }
     }
 
-
     public override bool Equals(object other) {
       return Equals(other as FileDescriptorProto);
     }
@@ -509,7 +551,9 @@ namespace Google.Protobuf.DescriptorProtos {
       if(!enumType_.Equals(other.enumType_)) return false;
       if(!service_.Equals(other.service_)) return false;
       if(!extension_.Equals(other.extension_)) return false;
-      if (!object.Equals(Options, other.Options)) return false;if (!object.Equals(SourceCodeInfo, other.SourceCodeInfo)) return false;if (Syntax != other.Syntax) return false;
+      if (!object.Equals(Options, other.Options)) return false;
+      if (!object.Equals(SourceCodeInfo, other.SourceCodeInfo)) return false;
+      if (Syntax != other.Syntax) return false;
       return true;
     }
 
@@ -763,6 +807,9 @@ namespace Google.Protobuf.DescriptorProtos {
       get { return global::Google.Protobuf.DescriptorProtos.DescriptorProtoFile.internal__static_google_protobuf_DescriptorProto__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public DescriptorProto() { }
 
     public DescriptorProto(DescriptorProto other) {
@@ -782,14 +829,32 @@ namespace Google.Protobuf.DescriptorProtos {
       return new DescriptorProto(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      field_.Freeze();
+      extension_.Freeze();
+      nestedType_.Freeze();
+      enumType_.Freeze();
+      extensionRange_.Freeze();
+      oneofDecl_.Freeze();
+      if (options_ != null) Options.Freeze();
+      reservedRange_.Freeze();
+      reservedName_.Freeze();
+    }
+
     public const int NameFieldNumber = 1;
     private string name_ = "";
     public string Name {
       get { return name_; }
-      set { name_ = value ?? ""; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        name_ = value ?? "";
+      }
     }
 
-
     public const int FieldFieldNumber = 2;
     private readonly pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.FieldDescriptorProto> field_ = new pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.FieldDescriptorProto>();
     public pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.FieldDescriptorProto> Field {
@@ -830,7 +895,10 @@ namespace Google.Protobuf.DescriptorProtos {
     private global::Google.Protobuf.DescriptorProtos.MessageOptions options_;
     public global::Google.Protobuf.DescriptorProtos.MessageOptions Options {
       get { return options_; }
-      set { options_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        options_ = value;
+      }
     }
 
     public const int ReservedRangeFieldNumber = 9;
@@ -863,7 +931,8 @@ namespace Google.Protobuf.DescriptorProtos {
       if(!enumType_.Equals(other.enumType_)) return false;
       if(!extensionRange_.Equals(other.extensionRange_)) return false;
       if(!oneofDecl_.Equals(other.oneofDecl_)) return false;
-      if (!object.Equals(Options, other.Options)) return false;if(!reservedRange_.Equals(other.reservedRange_)) return false;
+      if (!object.Equals(Options, other.Options)) return false;
+      if(!reservedRange_.Equals(other.reservedRange_)) return false;
       if(!reservedName_.Equals(other.reservedName_)) return false;
       return true;
     }
@@ -1077,6 +1146,9 @@ namespace Google.Protobuf.DescriptorProtos {
           get { return global::Google.Protobuf.DescriptorProtos.DescriptorProtoFile.internal__static_google_protobuf_DescriptorProto_ExtensionRange__FieldAccessorTable; }
         }
 
+        private bool _frozen = false;
+        public bool IsFrozen { get { return _frozen; } }
+
         public ExtensionRange() { }
 
         public ExtensionRange(ExtensionRange other) {
@@ -1088,22 +1160,33 @@ namespace Google.Protobuf.DescriptorProtos {
           return new ExtensionRange(this);
         }
 
+        public void Freeze() {
+          if (IsFrozen) {
+            return;
+          }
+          _frozen = true;
+        }
+
         public const int StartFieldNumber = 1;
         private int start_;
         public int Start {
           get { return start_; }
-          set { start_ = value; }
+          set {
+            pb::Freezable.CheckMutable(this);
+            start_ = value;
+          }
         }
 
-
         public const int EndFieldNumber = 2;
         private int end_;
         public int End {
           get { return end_; }
-          set { end_ = value; }
+          set {
+            pb::Freezable.CheckMutable(this);
+            end_ = value;
+          }
         }
 
-
         public override bool Equals(object other) {
           return Equals(other as ExtensionRange);
         }
@@ -1200,6 +1283,9 @@ namespace Google.Protobuf.DescriptorProtos {
           get { return global::Google.Protobuf.DescriptorProtos.DescriptorProtoFile.internal__static_google_protobuf_DescriptorProto_ReservedRange__FieldAccessorTable; }
         }
 
+        private bool _frozen = false;
+        public bool IsFrozen { get { return _frozen; } }
+
         public ReservedRange() { }
 
         public ReservedRange(ReservedRange other) {
@@ -1211,22 +1297,33 @@ namespace Google.Protobuf.DescriptorProtos {
           return new ReservedRange(this);
         }
 
+        public void Freeze() {
+          if (IsFrozen) {
+            return;
+          }
+          _frozen = true;
+        }
+
         public const int StartFieldNumber = 1;
         private int start_;
         public int Start {
           get { return start_; }
-          set { start_ = value; }
+          set {
+            pb::Freezable.CheckMutable(this);
+            start_ = value;
+          }
         }
 
-
         public const int EndFieldNumber = 2;
         private int end_;
         public int End {
           get { return end_; }
-          set { end_ = value; }
+          set {
+            pb::Freezable.CheckMutable(this);
+            end_ = value;
+          }
         }
 
-
         public override bool Equals(object other) {
           return Equals(other as ReservedRange);
         }
@@ -1328,6 +1425,9 @@ namespace Google.Protobuf.DescriptorProtos {
       get { return global::Google.Protobuf.DescriptorProtos.DescriptorProtoFile.internal__static_google_protobuf_FieldDescriptorProto__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public FieldDescriptorProto() { }
 
     public FieldDescriptorProto(FieldDescriptorProto other) {
@@ -1346,75 +1446,102 @@ namespace Google.Protobuf.DescriptorProtos {
       return new FieldDescriptorProto(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      if (options_ != null) Options.Freeze();
+    }
+
     public const int NameFieldNumber = 1;
     private string name_ = "";
     public string Name {
       get { return name_; }
-      set { name_ = value ?? ""; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        name_ = value ?? "";
+      }
     }
 
-
     public const int NumberFieldNumber = 3;
     private int number_;
     public int Number {
       get { return number_; }
-      set { number_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        number_ = value;
+      }
     }
 
-
     public const int LabelFieldNumber = 4;
     private global::Google.Protobuf.DescriptorProtos.FieldDescriptorProto.Types.Label label_ = global::Google.Protobuf.DescriptorProtos.FieldDescriptorProto.Types.Label.LABEL_OPTIONAL;
     public global::Google.Protobuf.DescriptorProtos.FieldDescriptorProto.Types.Label Label {
       get { return label_; }
-      set { label_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        label_ = value;
+      }
     }
 
-
     public const int TypeFieldNumber = 5;
     private global::Google.Protobuf.DescriptorProtos.FieldDescriptorProto.Types.Type type_ = global::Google.Protobuf.DescriptorProtos.FieldDescriptorProto.Types.Type.TYPE_DOUBLE;
     public global::Google.Protobuf.DescriptorProtos.FieldDescriptorProto.Types.Type Type {
       get { return type_; }
-      set { type_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        type_ = value;
+      }
     }
 
-
     public const int TypeNameFieldNumber = 6;
     private string typeName_ = "";
     public string TypeName {
       get { return typeName_; }
-      set { typeName_ = value ?? ""; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        typeName_ = value ?? "";
+      }
     }
 
-
     public const int ExtendeeFieldNumber = 2;
     private string extendee_ = "";
     public string Extendee {
       get { return extendee_; }
-      set { extendee_ = value ?? ""; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        extendee_ = value ?? "";
+      }
     }
 
-
     public const int DefaultValueFieldNumber = 7;
     private string defaultValue_ = "";
     public string DefaultValue {
       get { return defaultValue_; }
-      set { defaultValue_ = value ?? ""; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        defaultValue_ = value ?? "";
+      }
     }
 
-
     public const int OneofIndexFieldNumber = 9;
     private int oneofIndex_;
     public int OneofIndex {
       get { return oneofIndex_; }
-      set { oneofIndex_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        oneofIndex_ = value;
+      }
     }
 
-
     public const int OptionsFieldNumber = 8;
     private global::Google.Protobuf.DescriptorProtos.FieldOptions options_;
     public global::Google.Protobuf.DescriptorProtos.FieldOptions Options {
       get { return options_; }
-      set { options_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        options_ = value;
+      }
     }
 
     public override bool Equals(object other) {
@@ -1436,7 +1563,8 @@ namespace Google.Protobuf.DescriptorProtos {
       if (Extendee != other.Extendee) return false;
       if (DefaultValue != other.DefaultValue) return false;
       if (OneofIndex != other.OneofIndex) return false;
-      if (!object.Equals(Options, other.Options)) return false;  return true;
+      if (!object.Equals(Options, other.Options)) return false;
+      return true;
     }
 
     public override int GetHashCode() {
@@ -1663,6 +1791,9 @@ namespace Google.Protobuf.DescriptorProtos {
       get { return global::Google.Protobuf.DescriptorProtos.DescriptorProtoFile.internal__static_google_protobuf_OneofDescriptorProto__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public OneofDescriptorProto() { }
 
     public OneofDescriptorProto(OneofDescriptorProto other) {
@@ -1673,14 +1804,23 @@ namespace Google.Protobuf.DescriptorProtos {
       return new OneofDescriptorProto(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+    }
+
     public const int NameFieldNumber = 1;
     private string name_ = "";
     public string Name {
       get { return name_; }
-      set { name_ = value ?? ""; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        name_ = value ?? "";
+      }
     }
 
-
     public override bool Equals(object other) {
       return Equals(other as OneofDescriptorProto);
     }
@@ -1761,6 +1901,9 @@ namespace Google.Protobuf.DescriptorProtos {
       get { return global::Google.Protobuf.DescriptorProtos.DescriptorProtoFile.internal__static_google_protobuf_EnumDescriptorProto__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public EnumDescriptorProto() { }
 
     public EnumDescriptorProto(EnumDescriptorProto other) {
@@ -1773,14 +1916,25 @@ namespace Google.Protobuf.DescriptorProtos {
       return new EnumDescriptorProto(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      value_.Freeze();
+      if (options_ != null) Options.Freeze();
+    }
+
     public const int NameFieldNumber = 1;
     private string name_ = "";
     public string Name {
       get { return name_; }
-      set { name_ = value ?? ""; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        name_ = value ?? "";
+      }
     }
 
-
     public const int ValueFieldNumber = 2;
     private readonly pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.EnumValueDescriptorProto> value_ = new pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.EnumValueDescriptorProto>();
     public pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.EnumValueDescriptorProto> Value {
@@ -1791,7 +1945,10 @@ namespace Google.Protobuf.DescriptorProtos {
     private global::Google.Protobuf.DescriptorProtos.EnumOptions options_;
     public global::Google.Protobuf.DescriptorProtos.EnumOptions Options {
       get { return options_; }
-      set { options_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        options_ = value;
+      }
     }
 
     public override bool Equals(object other) {
@@ -1807,7 +1964,8 @@ namespace Google.Protobuf.DescriptorProtos {
       }
       if (Name != other.Name) return false;
       if(!value_.Equals(other.value_)) return false;
-      if (!object.Equals(Options, other.Options)) return false;  return true;
+      if (!object.Equals(Options, other.Options)) return false;
+      return true;
     }
 
     public override int GetHashCode() {
@@ -1911,6 +2069,9 @@ namespace Google.Protobuf.DescriptorProtos {
       get { return global::Google.Protobuf.DescriptorProtos.DescriptorProtoFile.internal__static_google_protobuf_EnumValueDescriptorProto__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public EnumValueDescriptorProto() { }
 
     public EnumValueDescriptorProto(EnumValueDescriptorProto other) {
@@ -1923,27 +2084,42 @@ namespace Google.Protobuf.DescriptorProtos {
       return new EnumValueDescriptorProto(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      if (options_ != null) Options.Freeze();
+    }
+
     public const int NameFieldNumber = 1;
     private string name_ = "";
     public string Name {
       get { return name_; }
-      set { name_ = value ?? ""; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        name_ = value ?? "";
+      }
     }
 
-
     public const int NumberFieldNumber = 2;
     private int number_;
     public int Number {
       get { return number_; }
-      set { number_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        number_ = value;
+      }
     }
 
-
     public const int OptionsFieldNumber = 3;
     private global::Google.Protobuf.DescriptorProtos.EnumValueOptions options_;
     public global::Google.Protobuf.DescriptorProtos.EnumValueOptions Options {
       get { return options_; }
-      set { options_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        options_ = value;
+      }
     }
 
     public override bool Equals(object other) {
@@ -1959,7 +2135,8 @@ namespace Google.Protobuf.DescriptorProtos {
       }
       if (Name != other.Name) return false;
       if (Number != other.Number) return false;
-      if (!object.Equals(Options, other.Options)) return false;  return true;
+      if (!object.Equals(Options, other.Options)) return false;
+      return true;
     }
 
     public override int GetHashCode() {
@@ -2063,6 +2240,9 @@ namespace Google.Protobuf.DescriptorProtos {
       get { return global::Google.Protobuf.DescriptorProtos.DescriptorProtoFile.internal__static_google_protobuf_ServiceDescriptorProto__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public ServiceDescriptorProto() { }
 
     public ServiceDescriptorProto(ServiceDescriptorProto other) {
@@ -2075,14 +2255,25 @@ namespace Google.Protobuf.DescriptorProtos {
       return new ServiceDescriptorProto(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      method_.Freeze();
+      if (options_ != null) Options.Freeze();
+    }
+
     public const int NameFieldNumber = 1;
     private string name_ = "";
     public string Name {
       get { return name_; }
-      set { name_ = value ?? ""; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        name_ = value ?? "";
+      }
     }
 
-
     public const int MethodFieldNumber = 2;
     private readonly pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.MethodDescriptorProto> method_ = new pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.MethodDescriptorProto>();
     public pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.MethodDescriptorProto> Method {
@@ -2093,7 +2284,10 @@ namespace Google.Protobuf.DescriptorProtos {
     private global::Google.Protobuf.DescriptorProtos.ServiceOptions options_;
     public global::Google.Protobuf.DescriptorProtos.ServiceOptions Options {
       get { return options_; }
-      set { options_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        options_ = value;
+      }
     }
 
     public override bool Equals(object other) {
@@ -2109,7 +2303,8 @@ namespace Google.Protobuf.DescriptorProtos {
       }
       if (Name != other.Name) return false;
       if(!method_.Equals(other.method_)) return false;
-      if (!object.Equals(Options, other.Options)) return false;  return true;
+      if (!object.Equals(Options, other.Options)) return false;
+      return true;
     }
 
     public override int GetHashCode() {
@@ -2213,6 +2408,9 @@ namespace Google.Protobuf.DescriptorProtos {
       get { return global::Google.Protobuf.DescriptorProtos.DescriptorProtoFile.internal__static_google_protobuf_MethodDescriptorProto__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public MethodDescriptorProto() { }
 
     public MethodDescriptorProto(MethodDescriptorProto other) {
@@ -2228,53 +2426,74 @@ namespace Google.Protobuf.DescriptorProtos {
       return new MethodDescriptorProto(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      if (options_ != null) Options.Freeze();
+    }
+
     public const int NameFieldNumber = 1;
     private string name_ = "";
     public string Name {
       get { return name_; }
-      set { name_ = value ?? ""; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        name_ = value ?? "";
+      }
     }
 
-
     public const int InputTypeFieldNumber = 2;
     private string inputType_ = "";
     public string InputType {
       get { return inputType_; }
-      set { inputType_ = value ?? ""; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        inputType_ = value ?? "";
+      }
     }
 
-
     public const int OutputTypeFieldNumber = 3;
     private string outputType_ = "";
     public string OutputType {
       get { return outputType_; }
-      set { outputType_ = value ?? ""; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        outputType_ = value ?? "";
+      }
     }
 
-
     public const int OptionsFieldNumber = 4;
     private global::Google.Protobuf.DescriptorProtos.MethodOptions options_;
     public global::Google.Protobuf.DescriptorProtos.MethodOptions Options {
       get { return options_; }
-      set { options_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        options_ = value;
+      }
     }
 
     public const int ClientStreamingFieldNumber = 5;
     private bool clientStreaming_;
     public bool ClientStreaming {
       get { return clientStreaming_; }
-      set { clientStreaming_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        clientStreaming_ = value;
+      }
     }
 
-
     public const int ServerStreamingFieldNumber = 6;
     private bool serverStreaming_;
     public bool ServerStreaming {
       get { return serverStreaming_; }
-      set { serverStreaming_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        serverStreaming_ = value;
+      }
     }
 
-
     public override bool Equals(object other) {
       return Equals(other as MethodDescriptorProto);
     }
@@ -2289,7 +2508,8 @@ namespace Google.Protobuf.DescriptorProtos {
       if (Name != other.Name) return false;
       if (InputType != other.InputType) return false;
       if (OutputType != other.OutputType) return false;
-      if (!object.Equals(Options, other.Options)) return false;if (ClientStreaming != other.ClientStreaming) return false;
+      if (!object.Equals(Options, other.Options)) return false;
+      if (ClientStreaming != other.ClientStreaming) return false;
       if (ServerStreaming != other.ServerStreaming) return false;
       return true;
     }
@@ -2440,6 +2660,9 @@ namespace Google.Protobuf.DescriptorProtos {
       get { return global::Google.Protobuf.DescriptorProtos.DescriptorProtoFile.internal__static_google_protobuf_FileOptions__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public FileOptions() { }
 
     public FileOptions(FileOptions other) {
@@ -2464,118 +2687,154 @@ namespace Google.Protobuf.DescriptorProtos {
       return new FileOptions(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      uninterpretedOption_.Freeze();
+    }
+
     public const int JavaPackageFieldNumber = 1;
     private string javaPackage_ = "";
     public string JavaPackage {
       get { return javaPackage_; }
-      set { javaPackage_ = value ?? ""; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        javaPackage_ = value ?? "";
+      }
     }
 
-
     public const int JavaOuterClassnameFieldNumber = 8;
     private string javaOuterClassname_ = "";
     public string JavaOuterClassname {
       get { return javaOuterClassname_; }
-      set { javaOuterClassname_ = value ?? ""; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        javaOuterClassname_ = value ?? "";
+      }
     }
 
-
     public const int JavaMultipleFilesFieldNumber = 10;
     private bool javaMultipleFiles_;
     public bool JavaMultipleFiles {
       get { return javaMultipleFiles_; }
-      set { javaMultipleFiles_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        javaMultipleFiles_ = value;
+      }
     }
 
-
     public const int JavaGenerateEqualsAndHashFieldNumber = 20;
     private bool javaGenerateEqualsAndHash_;
     public bool JavaGenerateEqualsAndHash {
       get { return javaGenerateEqualsAndHash_; }
-      set { javaGenerateEqualsAndHash_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        javaGenerateEqualsAndHash_ = value;
+      }
     }
 
-
     public const int JavaStringCheckUtf8FieldNumber = 27;
     private bool javaStringCheckUtf8_;
     public bool JavaStringCheckUtf8 {
       get { return javaStringCheckUtf8_; }
-      set { javaStringCheckUtf8_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        javaStringCheckUtf8_ = value;
+      }
     }
 
-
     public const int OptimizeForFieldNumber = 9;
     private global::Google.Protobuf.DescriptorProtos.FileOptions.Types.OptimizeMode optimizeFor_ = global::Google.Protobuf.DescriptorProtos.FileOptions.Types.OptimizeMode.SPEED;
     public global::Google.Protobuf.DescriptorProtos.FileOptions.Types.OptimizeMode OptimizeFor {
       get { return optimizeFor_; }
-      set { optimizeFor_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        optimizeFor_ = value;
+      }
     }
 
-
     public const int GoPackageFieldNumber = 11;
     private string goPackage_ = "";
     public string GoPackage {
       get { return goPackage_; }
-      set { goPackage_ = value ?? ""; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        goPackage_ = value ?? "";
+      }
     }
 
-
     public const int CcGenericServicesFieldNumber = 16;
     private bool ccGenericServices_;
     public bool CcGenericServices {
       get { return ccGenericServices_; }
-      set { ccGenericServices_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        ccGenericServices_ = value;
+      }
     }
 
-
     public const int JavaGenericServicesFieldNumber = 17;
     private bool javaGenericServices_;
     public bool JavaGenericServices {
       get { return javaGenericServices_; }
-      set { javaGenericServices_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        javaGenericServices_ = value;
+      }
     }
 
-
     public const int PyGenericServicesFieldNumber = 18;
     private bool pyGenericServices_;
     public bool PyGenericServices {
       get { return pyGenericServices_; }
-      set { pyGenericServices_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        pyGenericServices_ = value;
+      }
     }
 
-
     public const int DeprecatedFieldNumber = 23;
     private bool deprecated_;
     public bool Deprecated {
       get { return deprecated_; }
-      set { deprecated_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        deprecated_ = value;
+      }
     }
 
-
     public const int CcEnableArenasFieldNumber = 31;
     private bool ccEnableArenas_;
     public bool CcEnableArenas {
       get { return ccEnableArenas_; }
-      set { ccEnableArenas_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        ccEnableArenas_ = value;
+      }
     }
 
-
     public const int ObjcClassPrefixFieldNumber = 36;
     private string objcClassPrefix_ = "";
     public string ObjcClassPrefix {
       get { return objcClassPrefix_; }
-      set { objcClassPrefix_ = value ?? ""; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        objcClassPrefix_ = value ?? "";
+      }
     }
 
-
     public const int CsharpNamespaceFieldNumber = 37;
     private string csharpNamespace_ = "";
     public string CsharpNamespace {
       get { return csharpNamespace_; }
-      set { csharpNamespace_ = value ?? ""; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        csharpNamespace_ = value ?? "";
+      }
     }
 
-
     public const int UninterpretedOptionFieldNumber = 999;
     private readonly pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.UninterpretedOption> uninterpretedOption_ = new pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.UninterpretedOption>();
     public pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.UninterpretedOption> UninterpretedOption {
@@ -2898,6 +3157,9 @@ namespace Google.Protobuf.DescriptorProtos {
       get { return global::Google.Protobuf.DescriptorProtos.DescriptorProtoFile.internal__static_google_protobuf_MessageOptions__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public MessageOptions() { }
 
     public MessageOptions(MessageOptions other) {
@@ -2912,38 +3174,54 @@ namespace Google.Protobuf.DescriptorProtos {
       return new MessageOptions(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      uninterpretedOption_.Freeze();
+    }
+
     public const int MessageSetWireFormatFieldNumber = 1;
     private bool messageSetWireFormat_;
     public bool MessageSetWireFormat {
       get { return messageSetWireFormat_; }
-      set { messageSetWireFormat_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        messageSetWireFormat_ = value;
+      }
     }
 
-
     public const int NoStandardDescriptorAccessorFieldNumber = 2;
     private bool noStandardDescriptorAccessor_;
     public bool NoStandardDescriptorAccessor {
       get { return noStandardDescriptorAccessor_; }
-      set { noStandardDescriptorAccessor_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        noStandardDescriptorAccessor_ = value;
+      }
     }
 
-
     public const int DeprecatedFieldNumber = 3;
     private bool deprecated_;
     public bool Deprecated {
       get { return deprecated_; }
-      set { deprecated_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        deprecated_ = value;
+      }
     }
 
-
     public const int MapEntryFieldNumber = 7;
     private bool mapEntry_;
     public bool MapEntry {
       get { return mapEntry_; }
-      set { mapEntry_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        mapEntry_ = value;
+      }
     }
 
-
     public const int UninterpretedOptionFieldNumber = 999;
     private readonly pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.UninterpretedOption> uninterpretedOption_ = new pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.UninterpretedOption>();
     public pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.UninterpretedOption> UninterpretedOption {
@@ -3094,6 +3372,9 @@ namespace Google.Protobuf.DescriptorProtos {
       get { return global::Google.Protobuf.DescriptorProtos.DescriptorProtoFile.internal__static_google_protobuf_FieldOptions__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public FieldOptions() { }
 
     public FieldOptions(FieldOptions other) {
@@ -3110,54 +3391,74 @@ namespace Google.Protobuf.DescriptorProtos {
       return new FieldOptions(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      uninterpretedOption_.Freeze();
+    }
+
     public const int CtypeFieldNumber = 1;
     private global::Google.Protobuf.DescriptorProtos.FieldOptions.Types.CType ctype_ = global::Google.Protobuf.DescriptorProtos.FieldOptions.Types.CType.STRING;
     public global::Google.Protobuf.DescriptorProtos.FieldOptions.Types.CType Ctype {
       get { return ctype_; }
-      set { ctype_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        ctype_ = value;
+      }
     }
 
-
     public const int PackedFieldNumber = 2;
     private bool packed_;
     public bool Packed {
       get { return packed_; }
-      set { packed_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        packed_ = value;
+      }
     }
 
-
     public const int JstypeFieldNumber = 6;
     private global::Google.Protobuf.DescriptorProtos.FieldOptions.Types.JSType jstype_ = global::Google.Protobuf.DescriptorProtos.FieldOptions.Types.JSType.JS_NORMAL;
     public global::Google.Protobuf.DescriptorProtos.FieldOptions.Types.JSType Jstype {
       get { return jstype_; }
-      set { jstype_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        jstype_ = value;
+      }
     }
 
-
     public const int LazyFieldNumber = 5;
     private bool lazy_;
     public bool Lazy {
       get { return lazy_; }
-      set { lazy_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        lazy_ = value;
+      }
     }
 
-
     public const int DeprecatedFieldNumber = 3;
     private bool deprecated_;
     public bool Deprecated {
       get { return deprecated_; }
-      set { deprecated_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        deprecated_ = value;
+      }
     }
 
-
     public const int WeakFieldNumber = 10;
     private bool weak_;
     public bool Weak {
       get { return weak_; }
-      set { weak_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        weak_ = value;
+      }
     }
 
-
     public const int UninterpretedOptionFieldNumber = 999;
     private readonly pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.UninterpretedOption> uninterpretedOption_ = new pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.UninterpretedOption>();
     public pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.UninterpretedOption> UninterpretedOption {
@@ -3358,6 +3659,9 @@ namespace Google.Protobuf.DescriptorProtos {
       get { return global::Google.Protobuf.DescriptorProtos.DescriptorProtoFile.internal__static_google_protobuf_EnumOptions__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public EnumOptions() { }
 
     public EnumOptions(EnumOptions other) {
@@ -3370,22 +3674,34 @@ namespace Google.Protobuf.DescriptorProtos {
       return new EnumOptions(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      uninterpretedOption_.Freeze();
+    }
+
     public const int AllowAliasFieldNumber = 2;
     private bool allowAlias_;
     public bool AllowAlias {
       get { return allowAlias_; }
-      set { allowAlias_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        allowAlias_ = value;
+      }
     }
 
-
     public const int DeprecatedFieldNumber = 3;
     private bool deprecated_;
     public bool Deprecated {
       get { return deprecated_; }
-      set { deprecated_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        deprecated_ = value;
+      }
     }
 
-
     public const int UninterpretedOptionFieldNumber = 999;
     private readonly pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.UninterpretedOption> uninterpretedOption_ = new pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.UninterpretedOption>();
     public pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.UninterpretedOption> UninterpretedOption {
@@ -3504,6 +3820,9 @@ namespace Google.Protobuf.DescriptorProtos {
       get { return global::Google.Protobuf.DescriptorProtos.DescriptorProtoFile.internal__static_google_protobuf_EnumValueOptions__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public EnumValueOptions() { }
 
     public EnumValueOptions(EnumValueOptions other) {
@@ -3515,14 +3834,24 @@ namespace Google.Protobuf.DescriptorProtos {
       return new EnumValueOptions(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      uninterpretedOption_.Freeze();
+    }
+
     public const int DeprecatedFieldNumber = 1;
     private bool deprecated_;
     public bool Deprecated {
       get { return deprecated_; }
-      set { deprecated_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        deprecated_ = value;
+      }
     }
 
-
     public const int UninterpretedOptionFieldNumber = 999;
     private readonly pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.UninterpretedOption> uninterpretedOption_ = new pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.UninterpretedOption>();
     public pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.UninterpretedOption> UninterpretedOption {
@@ -3625,6 +3954,9 @@ namespace Google.Protobuf.DescriptorProtos {
       get { return global::Google.Protobuf.DescriptorProtos.DescriptorProtoFile.internal__static_google_protobuf_ServiceOptions__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public ServiceOptions() { }
 
     public ServiceOptions(ServiceOptions other) {
@@ -3636,14 +3968,24 @@ namespace Google.Protobuf.DescriptorProtos {
       return new ServiceOptions(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      uninterpretedOption_.Freeze();
+    }
+
     public const int DeprecatedFieldNumber = 33;
     private bool deprecated_;
     public bool Deprecated {
       get { return deprecated_; }
-      set { deprecated_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        deprecated_ = value;
+      }
     }
 
-
     public const int UninterpretedOptionFieldNumber = 999;
     private readonly pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.UninterpretedOption> uninterpretedOption_ = new pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.UninterpretedOption>();
     public pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.UninterpretedOption> UninterpretedOption {
@@ -3746,6 +4088,9 @@ namespace Google.Protobuf.DescriptorProtos {
       get { return global::Google.Protobuf.DescriptorProtos.DescriptorProtoFile.internal__static_google_protobuf_MethodOptions__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public MethodOptions() { }
 
     public MethodOptions(MethodOptions other) {
@@ -3757,14 +4102,24 @@ namespace Google.Protobuf.DescriptorProtos {
       return new MethodOptions(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      uninterpretedOption_.Freeze();
+    }
+
     public const int DeprecatedFieldNumber = 33;
     private bool deprecated_;
     public bool Deprecated {
       get { return deprecated_; }
-      set { deprecated_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        deprecated_ = value;
+      }
     }
 
-
     public const int UninterpretedOptionFieldNumber = 999;
     private readonly pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.UninterpretedOption> uninterpretedOption_ = new pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.UninterpretedOption>();
     public pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.UninterpretedOption> UninterpretedOption {
@@ -3867,6 +4222,9 @@ namespace Google.Protobuf.DescriptorProtos {
       get { return global::Google.Protobuf.DescriptorProtos.DescriptorProtoFile.internal__static_google_protobuf_UninterpretedOption__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public UninterpretedOption() { }
 
     public UninterpretedOption(UninterpretedOption other) {
@@ -3883,6 +4241,14 @@ namespace Google.Protobuf.DescriptorProtos {
       return new UninterpretedOption(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      name_.Freeze();
+    }
+
     public const int NameFieldNumber = 2;
     private readonly pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.UninterpretedOption.Types.NamePart> name_ = new pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.UninterpretedOption.Types.NamePart>();
     public pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.UninterpretedOption.Types.NamePart> Name {
@@ -3893,50 +4259,62 @@ namespace Google.Protobuf.DescriptorProtos {
     private string identifierValue_ = "";
     public string IdentifierValue {
       get { return identifierValue_; }
-      set { identifierValue_ = value ?? ""; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        identifierValue_ = value ?? "";
+      }
     }
 
-
     public const int PositiveIntValueFieldNumber = 4;
     private ulong positiveIntValue_;
     public ulong PositiveIntValue {
       get { return positiveIntValue_; }
-      set { positiveIntValue_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        positiveIntValue_ = value;
+      }
     }
 
-
     public const int NegativeIntValueFieldNumber = 5;
     private long negativeIntValue_;
     public long NegativeIntValue {
       get { return negativeIntValue_; }
-      set { negativeIntValue_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        negativeIntValue_ = value;
+      }
     }
 
-
     public const int DoubleValueFieldNumber = 6;
     private double doubleValue_;
     public double DoubleValue {
       get { return doubleValue_; }
-      set { doubleValue_ = value; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        doubleValue_ = value;
+      }
     }
 
-
     public const int StringValueFieldNumber = 7;
     private pb::ByteString stringValue_ = pb::ByteString.Empty;
     public pb::ByteString StringValue {
       get { return stringValue_; }
-      set { stringValue_ = value ?? pb::ByteString.Empty; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        stringValue_ = value ?? pb::ByteString.Empty;
+      }
     }
 
-
     public const int AggregateValueFieldNumber = 8;
     private string aggregateValue_ = "";
     public string AggregateValue {
       get { return aggregateValue_; }
-      set { aggregateValue_ = value ?? ""; }
+      set {
+        pb::Freezable.CheckMutable(this);
+        aggregateValue_ = value ?? "";
+      }
     }
 
-
     public override bool Equals(object other) {
       return Equals(other as UninterpretedOption);
     }
@@ -4114,6 +4492,9 @@ namespace Google.Protobuf.DescriptorProtos {
           get { return global::Google.Protobuf.DescriptorProtos.DescriptorProtoFile.internal__static_google_protobuf_UninterpretedOption_NamePart__FieldAccessorTable; }
         }
 
+        private bool _frozen = false;
+        public bool IsFrozen { get { return _frozen; } }
+
         public NamePart() { }
 
         public NamePart(NamePart other) {
@@ -4125,22 +4506,33 @@ namespace Google.Protobuf.DescriptorProtos {
           return new NamePart(this);
         }
 
+        public void Freeze() {
+          if (IsFrozen) {
+            return;
+          }
+          _frozen = true;
+        }
+
         public const int NamePart_FieldNumber = 1;
         private string namePart_ = "";
         public string NamePart_ {
           get { return namePart_; }
-          set { namePart_ = value ?? ""; }
+          set {
+            pb::Freezable.CheckMutable(this);
+            namePart_ = value ?? "";
+          }
         }
 
-
         public const int IsExtensionFieldNumber = 2;
         private bool isExtension_;
         public bool IsExtension {
           get { return isExtension_; }
-          set { isExtension_ = value; }
+          set {
+            pb::Freezable.CheckMutable(this);
+            isExtension_ = value;
+          }
         }
 
-
         public override bool Equals(object other) {
           return Equals(other as NamePart);
         }
@@ -4242,6 +4634,9 @@ namespace Google.Protobuf.DescriptorProtos {
       get { return global::Google.Protobuf.DescriptorProtos.DescriptorProtoFile.internal__static_google_protobuf_SourceCodeInfo__FieldAccessorTable; }
     }
 
+    private bool _frozen = false;
+    public bool IsFrozen { get { return _frozen; } }
+
     public SourceCodeInfo() { }
 
     public SourceCodeInfo(SourceCodeInfo other) {
@@ -4252,6 +4647,14 @@ namespace Google.Protobuf.DescriptorProtos {
       return new SourceCodeInfo(this);
     }
 
+    public void Freeze() {
+      if (IsFrozen) {
+        return;
+      }
+      _frozen = true;
+      location_.Freeze();
+    }
+
     public const int LocationFieldNumber = 1;
     private readonly pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.SourceCodeInfo.Types.Location> location_ = new pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.SourceCodeInfo.Types.Location>();
     public pbc::RepeatedField<global::Google.Protobuf.DescriptorProtos.SourceCodeInfo.Types.Location> Location {
@@ -4339,6 +4742,9 @@ namespace Google.Protobuf.DescriptorProtos {
           get { return global::Google.Protobuf.DescriptorProtos.DescriptorProtoFile.internal__static_google_protobuf_SourceCodeInfo_Location__FieldAccessorTable; }
         }
 
+        private bool _frozen = false;
+        public bool IsFrozen { get { return _frozen; } }
+
         public Location() { }
 
         public Location(Location other) {
@@ -4353,6 +4759,16 @@ namespace Google.Protobuf.DescriptorProtos {
           return new Location(this);
         }
 
+        public void Freeze() {
+          if (IsFrozen) {
+            return;
+          }
+          _frozen = true;
+          path_.Freeze();
+          span_.Freeze();
+          leadingDetachedComments_.Freeze();
+        }
+
         public const int PathFieldNumber = 1;
         private readonly pbc::RepeatedField<int> path_ = new pbc::RepeatedField<int>();
         public pbc::RepeatedField<int> Path {
@@ -4369,18 +4785,22 @@ namespace Google.Protobuf.DescriptorProtos {
         private string leadingComments_ = "";
         public string LeadingComments {
           get { return leadingComments_; }
-          set { leadingComments_ = value ?? ""; }
+          set {
+            pb::Freezable.CheckMutable(this);
+            leadingComments_ = value ?? "";
+          }
         }
 
-
         public const int TrailingCommentsFieldNumber = 4;
         private string trailingComments_ = "";
         public string TrailingComments {
           get { return trailingComments_; }
-          set { trailingComments_ = value ?? ""; }
+          set {
+            pb::Freezable.CheckMutable(this);
+            trailingComments_ = value ?? "";
+          }
         }
 
-
         public const int LeadingDetachedCommentsFieldNumber = 6;
         private readonly pbc::RepeatedField<string> leadingDetachedComments_ = new pbc::RepeatedField<string>();
         public pbc::RepeatedField<string> LeadingDetachedComments {
diff --git a/csharp/src/ProtocolBuffers/Freezable.cs b/csharp/src/ProtocolBuffers/Freezable.cs
new file mode 100644
index 00000000..40b4398a
--- /dev/null
+++ b/csharp/src/ProtocolBuffers/Freezable.cs
@@ -0,0 +1,60 @@
+#region Copyright notice and license
+
+// Protocol Buffers - Google's data interchange format
+// Copyright 2015 Google Inc.  All rights reserved.
+// http://github.com/google/protobuf
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#endregion
+
+using System;
+
+namespace Google.Protobuf
+{
+    /// <summary>
+    /// Extension methods for <see cref="IFreezable"/> types.
+    /// </summary>
+    public static class Freezable
+    {
+        /// <summary>
+        /// Throws an <see cref="InvalidOperationException"/> if <paramref name="target"/>
+        /// is frozen.
+        /// </summary>
+        /// <remarks>
+        /// This is a convenience methods that freezable types can call before all
+        /// mutations, to protect frozen objects.
+        /// </remarks>
+        public static void CheckMutable(this IFreezable target)
+        {
+            if (target.IsFrozen)
+            {
+                throw new InvalidOperationException("Attempt to mutate frozen object");
+            }
+        }
+    }
+}
diff --git a/csharp/src/ProtocolBuffers/IMessage.cs b/csharp/src/ProtocolBuffers/IMessage.cs
index 5d662cfd..d606aee1 100644
--- a/csharp/src/ProtocolBuffers/IMessage.cs
+++ b/csharp/src/ProtocolBuffers/IMessage.cs
@@ -41,6 +41,7 @@ namespace Google.Protobuf
 {

 

     // TODO(jonskeet): Do we want a "weak" (non-generic) version of IReflectedMessage?

+    // TODO(jonskeet): Split these interfaces into separate files when we're happy with them.

 

     /// <summary>

     /// Reflection support for a specific message type. message

@@ -85,7 +86,7 @@ namespace Google.Protobuf
     /// the implementation class.

     /// </summary>

     /// <typeparam name="T">The message type.</typeparam>

-    public interface IMessage<T> : IMessage, IEquatable<T>, IDeepCloneable<T> where T : IMessage<T>

+    public interface IMessage<T> : IMessage, IEquatable<T>, IDeepCloneable<T>, IFreezable where T : IMessage<T>

     {

         /// <summary>

         /// Merges the given message into this one.

@@ -102,6 +103,11 @@ namespace Google.Protobuf
     /// All generated messages implement this interface, but so do some non-message types.

     /// Additionally, due to the type constraint on <c>T</c> in <see cref="IMessage{T}"/>,

     /// it is simpler to keep this as a separate interface.

+    /// </para>

+    /// <para>

+    /// Freezable types which implement this interface should always return a mutable clone,

+    /// even if the original object is frozen.

+    /// </para>

     /// </remarks>

     /// <typeparam name="T">The type itself, returned by the <see cref="Clone"/> method.</typeparam>

     public interface IDeepCloneable<T>

@@ -112,4 +118,32 @@ namespace Google.Protobuf
         /// <returns>A deep clone of this object.</returns>

         T Clone();

     }

+

+    /// <summary>

+    /// Provides a mechanism for freezing a message (or repeated field collection)

+    /// to make it immutable.

+    /// </summary>

+    /// <remarks>

+    /// Implementations are under no obligation to make this thread-safe: if a freezable

+    /// type instance is shared between threads before being frozen, and one thread then

+    /// freezes it, it is possible for other threads to make changes during the freezing

+    /// operation and also to observe stale values for mutated fields. Objects should be

+    /// frozen before being made available to other threads.

+    /// </remarks>

+    public interface IFreezable

+    {

+        /// <summary>

+        /// Freezes this object.

+        /// </summary>

+        /// <remarks>

+        /// If the object is already frozen, this method has no effect.

+        /// </remarks>

+        void Freeze();

+

+        /// <summary>

+        /// Returns whether or not this object is frozen (and therefore immutable).

+        /// </summary>

+        /// <value><c>true</c> if this object is frozen; <c>false</c> otherwise.</value>

+        bool IsFrozen { get; }

+    }

 }

diff --git a/csharp/src/ProtocolBuffers/ProtocolBuffers.csproj b/csharp/src/ProtocolBuffers/ProtocolBuffers.csproj
index 33a32ff2..d1551148 100644
--- a/csharp/src/ProtocolBuffers/ProtocolBuffers.csproj
+++ b/csharp/src/ProtocolBuffers/ProtocolBuffers.csproj
@@ -85,6 +85,7 @@
     <Compile Include="Descriptors\PackageDescriptor.cs" />

     <Compile Include="Descriptors\ServiceDescriptor.cs" />

     <Compile Include="FrameworkPortability.cs" />

+    <Compile Include="Freezable.cs" />

     <Compile Include="MessageExtensions.cs" />

     <Compile Include="FieldAccess\FieldAccessorBase.cs" />

     <Compile Include="FieldAccess\ReflectionUtil.cs" />

diff --git a/src/google/protobuf/compiler/csharp/csharp_field_base.cc b/src/google/protobuf/compiler/csharp/csharp_field_base.cc
index 54f281ee..0bfbc70e 100644
--- a/src/google/protobuf/compiler/csharp/csharp_field_base.cc
+++ b/src/google/protobuf/compiler/csharp/csharp_field_base.cc
@@ -107,6 +107,11 @@ FieldGeneratorBase::FieldGeneratorBase(const FieldDescriptor* descriptor,
 FieldGeneratorBase::~FieldGeneratorBase() {
 }
 
+void FieldGeneratorBase::GenerateFreezingCode(io::Printer* printer) {
+  // No-op: only message fields and repeated fields need
+  // special handling for freezing, so default to not generating any code.
+}
+
 void FieldGeneratorBase::AddDeprecatedFlag(io::Printer* printer) {
   if (descriptor_->options().deprecated())
   {
diff --git a/src/google/protobuf/compiler/csharp/csharp_field_base.h b/src/google/protobuf/compiler/csharp/csharp_field_base.h
index 91ae3ba1..abf9254b 100644
--- a/src/google/protobuf/compiler/csharp/csharp_field_base.h
+++ b/src/google/protobuf/compiler/csharp/csharp_field_base.h
@@ -48,6 +48,7 @@ class FieldGeneratorBase : public SourceGeneratorBase {
   ~FieldGeneratorBase();
 
   virtual void GenerateCloningCode(io::Printer* printer) = 0;
+  virtual void GenerateFreezingCode(io::Printer* printer);
   virtual void GenerateMembers(io::Printer* printer) = 0;
   virtual void GenerateMergingCode(io::Printer* printer) = 0;
   virtual void GenerateParsingCode(io::Printer* printer) = 0;
diff --git a/src/google/protobuf/compiler/csharp/csharp_message.cc b/src/google/protobuf/compiler/csharp/csharp_message.cc
index 39938fa3..9580c167 100644
--- a/src/google/protobuf/compiler/csharp/csharp_message.cc
+++ b/src/google/protobuf/compiler/csharp/csharp_message.cc
@@ -211,7 +211,9 @@ void MessageGenerator::Generate(io::Printer* printer) {
     "public pb::FieldAccess.FieldAccessorTable<$class_name$> Fields {\n"
     "  get { return $umbrella_class_name$.internal__$identifier$__FieldAccessorTable; }\n"
     "}\n"
-    "\n");
+    "\n"
+    "private bool _frozen = false;\n"
+    "public bool IsFrozen { get { return _frozen; } }\n\n");
 
   // Parameterless constructor
   printer->Print(
@@ -219,6 +221,7 @@ void MessageGenerator::Generate(io::Printer* printer) {
     "public $class_name$() { }\n\n");
 
   GenerateCloningCode(printer);
+  GenerateFreezingCode(printer);
 
   // Fields/properties
   for (int i = 0; i < descriptor_->field_count(); i++) {
@@ -260,6 +263,7 @@ void MessageGenerator::Generate(io::Printer* printer) {
       "  get { return $name$Case_; }\n"
       "}\n\n"
       "public void Clear$property_name$() {\n"
+      "  pb::Freezable.CheckMutable(this);\n"
       "  $name$Case_ = $property_name$OneofCase.None;\n"
       "  $name$_ = null;\n"
       "}\n\n");
@@ -346,6 +350,36 @@ void MessageGenerator::GenerateCloningCode(io::Printer* printer) {
     "}\n\n");
 }
 
+void MessageGenerator::GenerateFreezingCode(io::Printer* printer) {
+    map<string, string> vars;
+    vars["class_name"] = class_name();
+    printer->Print(
+      "public void Freeze() {\n"
+      "  if (IsFrozen) {\n"
+      "    return;\n"
+      "  }\n"
+      "  _frozen = true;\n");
+    printer->Indent();
+    // Freeze non-oneof fields first (only messages and repeated fields will actually generate any code)
+    for (int i = 0; i < descriptor_->field_count(); i++) {
+        if (!descriptor_->field(i)->containing_oneof()) {
+            scoped_ptr<FieldGeneratorBase> generator(
+                CreateFieldGeneratorInternal(descriptor_->field(i)));
+            generator->GenerateFreezingCode(printer);
+        }
+    }
+
+    // For each oneof, if the value is freezable, freeze it. We don't actually need to know which type it was.
+    for (int i = 0; i < descriptor_->oneof_decl_count(); ++i) {
+        vars["name"] = UnderscoresToCamelCase(descriptor_->oneof_decl(i)->name(), false);
+        printer->Print(vars,
+            "if ($name$_ is IFreezable) ((IFreezable) $name$_).Freeze();\n");
+    }
+
+    printer->Outdent();
+    printer->Print("}\n\n");
+}
+
 void MessageGenerator::GenerateFrameworkMethods(io::Printer* printer) {
     map<string, string> vars;
     vars["class_name"] = class_name();
diff --git a/src/google/protobuf/compiler/csharp/csharp_message.h b/src/google/protobuf/compiler/csharp/csharp_message.h
index c3a37a0e..6c7153aa 100644
--- a/src/google/protobuf/compiler/csharp/csharp_message.h
+++ b/src/google/protobuf/compiler/csharp/csharp_message.h
@@ -51,6 +51,7 @@ class MessageGenerator : public SourceGeneratorBase {
   ~MessageGenerator();
 
   void GenerateCloningCode(io::Printer* printer);
+  void GenerateFreezingCode(io::Printer* printer);
   void GenerateFrameworkMethods(io::Printer* printer);
   void GenerateStaticVariables(io::Printer* printer);
   void GenerateStaticVariableInitializers(io::Printer* printer);
diff --git a/src/google/protobuf/compiler/csharp/csharp_message_field.cc b/src/google/protobuf/compiler/csharp/csharp_message_field.cc
index 82deef54..cbf182d2 100644
--- a/src/google/protobuf/compiler/csharp/csharp_message_field.cc
+++ b/src/google/protobuf/compiler/csharp/csharp_message_field.cc
@@ -66,7 +66,10 @@ void MessageFieldGenerator::GenerateMembers(io::Printer* printer) {
     variables_,
     "public $type_name$ $property_name$ {\n"
     "  get { return $name$_; }\n"
-    "  set { $name$_ = value; }\n"
+    "  set {\n"
+    "    pb::Freezable.CheckMutable(this);\n"
+    "    $name$_ = value;\n"
+    "  }\n"
     "}\n");
 }
 
@@ -116,7 +119,7 @@ void MessageFieldGenerator::WriteHash(io::Printer* printer) {
 void MessageFieldGenerator::WriteEquals(io::Printer* printer) {
   printer->Print(
     variables_,
-    "if (!object.Equals($property_name$, other.$property_name$)) return false;");
+    "if (!object.Equals($property_name$, other.$property_name$)) return false;\n");
 }
 void MessageFieldGenerator::WriteToString(io::Printer* printer) {
   variables_["field_name"] = GetFieldName(descriptor_);
@@ -130,6 +133,11 @@ void MessageFieldGenerator::GenerateCloningCode(io::Printer* printer) {
     "$property_name$ = other.$has_property_check$ ? other.$property_name$.Clone() : null;\n");
 }
 
+void MessageFieldGenerator::GenerateFreezingCode(io::Printer* printer) {
+  printer->Print(variables_,
+    "if ($has_property_check$) $property_name$.Freeze();\n");
+}
+
 MessageOneofFieldGenerator::MessageOneofFieldGenerator(const FieldDescriptor* descriptor,
 						       int fieldOrdinal)
     : MessageFieldGenerator(descriptor, fieldOrdinal) {
@@ -147,6 +155,7 @@ void MessageOneofFieldGenerator::GenerateMembers(io::Printer* printer) {
     "public $type_name$ $property_name$ {\n"
     "  get { return $has_property_check$ ? ($type_name$) $oneof_name$_ : null; }\n"
     "  set {\n"
+    "    pb::Freezable.CheckMutable(this);\n"
     "    $oneof_name$_ = value;\n"
     "    $oneof_name$Case_ = value == null ? $oneof_property_name$OneofCase.None : $oneof_property_name$OneofCase.$property_name$;\n"
     "  }\n"
diff --git a/src/google/protobuf/compiler/csharp/csharp_message_field.h b/src/google/protobuf/compiler/csharp/csharp_message_field.h
index f15e8e7e..3e17f92a 100644
--- a/src/google/protobuf/compiler/csharp/csharp_message_field.h
+++ b/src/google/protobuf/compiler/csharp/csharp_message_field.h
@@ -47,6 +47,7 @@ class MessageFieldGenerator : public FieldGeneratorBase {
   ~MessageFieldGenerator();
 
   virtual void GenerateCloningCode(io::Printer* printer);
+  virtual void GenerateFreezingCode(io::Printer* printer);
   virtual void GenerateMembers(io::Printer* printer);
   virtual void GenerateMergingCode(io::Printer* printer);
   virtual void GenerateParsingCode(io::Printer* printer);
diff --git a/src/google/protobuf/compiler/csharp/csharp_primitive_field.cc b/src/google/protobuf/compiler/csharp/csharp_primitive_field.cc
index c426c37a..d5542f57 100644
--- a/src/google/protobuf/compiler/csharp/csharp_primitive_field.cc
+++ b/src/google/protobuf/compiler/csharp/csharp_primitive_field.cc
@@ -72,17 +72,21 @@ void PrimitiveFieldGenerator::GenerateMembers(io::Printer* printer) {
   printer->Print(
     variables_,
     "public $type_name$ $property_name$ {\n"
-    "  get { return $name$_; }\n");
+    "  get { return $name$_; }\n"
+    "  set {\n"
+    "    pb::Freezable.CheckMutable(this);\n");
   if (is_value_type) {
     printer->Print(
       variables_,
-      "  set { $name$_ = value; }\n");
+      "    $name$_ = value;\n");
   } else {
     printer->Print(
       variables_,
-      "  set { $name$_ = value ?? $default_value$; }\n");
+      "    $name$_ = value ?? $default_value$;\n");
   }
-  printer->Print("}\n\n");
+  printer->Print(
+    "  }\n"
+    "}\n");
 }
 
 void PrimitiveFieldGenerator::GenerateMergingCode(io::Printer* printer) {
@@ -166,7 +170,8 @@ void PrimitiveOneofFieldGenerator::GenerateMembers(io::Printer* printer) {
     variables_,
     "public $type_name$ $property_name$ {\n"
     "  get { return $has_property_check$ ? ($type_name$) $oneof_name$_ : $default_value$; }\n"
-    "  set {\n");
+    "  set {\n"
+    "    pb::Freezable.CheckMutable(this);\n");
     if (is_value_type) {
       printer->Print(
         variables_,
diff --git a/src/google/protobuf/compiler/csharp/csharp_repeated_enum_field.cc b/src/google/protobuf/compiler/csharp/csharp_repeated_enum_field.cc
index ce526b37..d223273c 100644
--- a/src/google/protobuf/compiler/csharp/csharp_repeated_enum_field.cc
+++ b/src/google/protobuf/compiler/csharp/csharp_repeated_enum_field.cc
@@ -147,6 +147,11 @@ void RepeatedEnumFieldGenerator::GenerateCloningCode(io::Printer* printer) {
     "$name$_ = other.$name$_.Clone();\n");
 }
 
+void RepeatedEnumFieldGenerator::GenerateFreezingCode(io::Printer* printer) {
+  printer->Print(variables_,
+    "$name$_.Freeze();\n");
+}
+
 }  // namespace csharp
 }  // namespace compiler
 }  // namespace protobuf
diff --git a/src/google/protobuf/compiler/csharp/csharp_repeated_enum_field.h b/src/google/protobuf/compiler/csharp/csharp_repeated_enum_field.h
index c7846a61..ee50eef0 100644
--- a/src/google/protobuf/compiler/csharp/csharp_repeated_enum_field.h
+++ b/src/google/protobuf/compiler/csharp/csharp_repeated_enum_field.h
@@ -49,6 +49,7 @@ class RepeatedEnumFieldGenerator : public FieldGeneratorBase {
   ~RepeatedEnumFieldGenerator();
 
   virtual void GenerateCloningCode(io::Printer* printer);
+  virtual void GenerateFreezingCode(io::Printer* printer);
   virtual void GenerateMembers(io::Printer* printer);
   virtual void GenerateMergingCode(io::Printer* printer);
   virtual void GenerateParsingCode(io::Printer* printer);
diff --git a/src/google/protobuf/compiler/csharp/csharp_repeated_message_field.cc b/src/google/protobuf/compiler/csharp/csharp_repeated_message_field.cc
index edfb98b4..400f0e4f 100644
--- a/src/google/protobuf/compiler/csharp/csharp_repeated_message_field.cc
+++ b/src/google/protobuf/compiler/csharp/csharp_repeated_message_field.cc
@@ -123,6 +123,11 @@ void RepeatedMessageFieldGenerator::GenerateCloningCode(io::Printer* printer) {
     "$name$_ = other.$name$_.Clone();\n");
 }
 
+void RepeatedMessageFieldGenerator::GenerateFreezingCode(io::Printer* printer) {
+  printer->Print(variables_,
+    "$name$_.Freeze();\n");
+}
+
 }  // namespace csharp
 }  // namespace compiler
 }  // namespace protobuf
diff --git a/src/google/protobuf/compiler/csharp/csharp_repeated_message_field.h b/src/google/protobuf/compiler/csharp/csharp_repeated_message_field.h
index 38006731..cf601c7e 100644
--- a/src/google/protobuf/compiler/csharp/csharp_repeated_message_field.h
+++ b/src/google/protobuf/compiler/csharp/csharp_repeated_message_field.h
@@ -47,6 +47,7 @@ class RepeatedMessageFieldGenerator : public FieldGeneratorBase {
   ~RepeatedMessageFieldGenerator();
 
   virtual void GenerateCloningCode(io::Printer* printer);
+  virtual void GenerateFreezingCode(io::Printer* printer);
   virtual void GenerateMembers(io::Printer* printer);
   virtual void GenerateMergingCode(io::Printer* printer);
   virtual void GenerateParsingCode(io::Printer* printer);
diff --git a/src/google/protobuf/compiler/csharp/csharp_repeated_primitive_field.cc b/src/google/protobuf/compiler/csharp/csharp_repeated_primitive_field.cc
index 49a29c55..a78a74c0 100644
--- a/src/google/protobuf/compiler/csharp/csharp_repeated_primitive_field.cc
+++ b/src/google/protobuf/compiler/csharp/csharp_repeated_primitive_field.cc
@@ -153,6 +153,11 @@ void RepeatedPrimitiveFieldGenerator::GenerateCloningCode(io::Printer* printer)
     "$name$_ = other.$name$_.Clone();\n");
 }
 
+void RepeatedPrimitiveFieldGenerator::GenerateFreezingCode(io::Printer* printer) {
+  printer->Print(variables_,
+    "$name$_.Freeze();\n");
+}
+
 }  // namespace csharp
 }  // namespace compiler
 }  // namespace protobuf
diff --git a/src/google/protobuf/compiler/csharp/csharp_repeated_primitive_field.h b/src/google/protobuf/compiler/csharp/csharp_repeated_primitive_field.h
index 7f8f17a8..f1ceeb50 100644
--- a/src/google/protobuf/compiler/csharp/csharp_repeated_primitive_field.h
+++ b/src/google/protobuf/compiler/csharp/csharp_repeated_primitive_field.h
@@ -47,6 +47,7 @@ class RepeatedPrimitiveFieldGenerator : public FieldGeneratorBase {
   ~RepeatedPrimitiveFieldGenerator();
 
   virtual void GenerateCloningCode(io::Printer* printer);
+  virtual void GenerateFreezingCode(io::Printer* printer);
   virtual void GenerateMembers(io::Printer* printer);
   virtual void GenerateMergingCode(io::Printer* printer);
   virtual void GenerateParsingCode(io::Printer* printer);