Revamp to reflection.

Changes in brief:
1. Descriptor is now the entry point for all reflection.
2. IReflectedMessage has gone; there's now a Descriptor property in IMessage, which is explicitly implemented (due to the static property).
3. FieldAccessorTable has gone away
4. IFieldAccessor and OneofFieldAccessor still exist; we *could* put the functionality straight into FieldDescriptor and OneofDescriptor... I'm unsure about that.
5. There's a temporary property MessageDescriptor.FieldAccessorsByFieldNumber to make the test changes small - we probably want this to go away
6. Discovery for delegates is now via attributes applied to properties and the Clear method of a oneof

I'm happy with 1-3.
4 I'm unsure about - feedback welcome.
5 will go away
6 I'm unsure about, both in design and implementation. Should we have a ProtobufMessageAttribute too? Should we find all the relevant attributes in MessageDescriptor and pass them down, to avoid an O(N^2) scenario?

Generated code changes coming in the next commit.

1 files changed, 20 insertions, 0 deletions

diff --git a/csharp/src/Google.Protobuf/Reflection/ReflectionUtil.cs b/csharp/src/Google.Protobuf/Reflection/ReflectionUtil.cs
index d0dc3e8b..ec222dc1 100644
--- a/csharp/src/Google.Protobuf/Reflection/ReflectionUtil.cs
+++ b/csharp/src/Google.Protobuf/Reflection/ReflectionUtil.cs
@@ -31,6 +31,7 @@
 #endregion
 
 using System;
+using System.Collections.Generic;
 using System.Linq.Expressions;
 using System.Reflection;
 
@@ -102,5 +103,24 @@ namespace Google.Protobuf.Reflection
             Expression call = Expression.Call(castTarget, method);
             return Expression.Lambda<Action<object>>(call, targetParameter).Compile();
         }
+
+        /// <summary>
+        /// Returns the next type from an iterator of types, unless the iterator is a null reference,
+        /// in which case null is returned.
+        /// </summary>
+        internal static Type GetNextType(IEnumerator<Type> generatedTypeIterator)
+        {
+            if (generatedTypeIterator == null)
+            {
+                return null;
+            }
+            if (!generatedTypeIterator.MoveNext())
+            {
+                // This parameter name corresponds to any public method supplying the generated types to start with.
+                throw new ArgumentException("More generated types left over after consuming all expected ones", "generatedTypes");
+            }
+            return generatedTypeIterator.Current;
+        }
+
     }
 }
\ No newline at end of file