Added DynamicMessage and ExtendableBuilder, along with the first supporting tests.

28 files changed, 2494 insertions, 111 deletions

diff --git a/csharp/ProtocolBuffers.Test/AbstractMessageTest.cs b/csharp/ProtocolBuffers.Test/AbstractMessageTest.cs
new file mode 100644
index 00000000..2c16b5b4
--- /dev/null
+++ b/csharp/ProtocolBuffers.Test/AbstractMessageTest.cs
@@ -0,0 +1,342 @@
+using System;
+using System.Collections.Generic;
+using Google.ProtocolBuffers.Descriptors;
+using NUnit.Framework;
+using Google.ProtocolBuffers.TestProtos;
+
+namespace Google.ProtocolBuffers {
+  [TestFixture]
+  public class AbstractMessageTest {
+
+    [Test]
+    public void Clear() {
+      AbstractMessageWrapper message = (AbstractMessageWrapper)
+        new AbstractMessageWrapper.Builder(TestAllTypes.CreateBuilder(TestUtil.GetAllSet())).Clear().Build();
+      TestUtil.AssertClear((TestAllTypes) message.WrappedMessage);
+    }
+
+    [Test]
+    public void Copy() {
+      AbstractMessageWrapper message = (AbstractMessageWrapper)
+        new AbstractMessageWrapper.Builder(TestAllTypes.CreateBuilder()).MergeFrom(TestUtil.GetAllSet()).Build();
+      TestUtil.AssertAllFieldsSet((TestAllTypes) message.WrappedMessage);
+    }
+
+    [Test]
+    public void SerializedSize() {
+      TestAllTypes message = TestUtil.GetAllSet();
+      IMessage abstractMessage = new AbstractMessageWrapper(TestUtil.GetAllSet());
+
+      Assert.AreEqual(message.SerializedSize, abstractMessage.SerializedSize);
+    }
+
+    [Test]
+    public void Serialization() {
+      IMessage abstractMessage = new AbstractMessageWrapper(TestUtil.GetAllSet());
+      TestUtil.AssertAllFieldsSet(TestAllTypes.ParseFrom(abstractMessage.ToByteString()));
+      Assert.AreEqual(TestUtil.GetAllSet().ToByteString(), abstractMessage.ToByteString());
+    }
+
+    [Test]
+    public void Parsing() {
+      IBuilder builder = new AbstractMessageWrapper.Builder(TestAllTypes.CreateBuilder());
+      AbstractMessageWrapper message = (AbstractMessageWrapper) builder.MergeFrom(TestUtil.GetAllSet().ToByteString()).Build();
+      TestUtil.AssertAllFieldsSet((TestAllTypes) message.WrappedMessage);
+    }
+
+    [Test]
+    public void OptimizedForSize() {
+      // We're mostly only Checking that this class was compiled successfully.
+      TestOptimizedForSize message = TestOptimizedForSize.CreateBuilder().SetI(1).Build();
+      message = TestOptimizedForSize.ParseFrom(message.ToByteString());
+      Assert.AreEqual(2, message.SerializedSize);
+    }
+
+    // -----------------------------------------------------------------
+    // Tests for isInitialized().
+
+    private static readonly TestRequired TestRequiredUninitialized = TestRequired.DefaultInstance;
+    private static readonly TestRequired TestRequiredInitialized = TestRequired.CreateBuilder().SetA(1).SetB(2).SetC(3).Build();
+
+    [Test]
+    public void IsInitialized() {
+      TestRequired.Builder builder = TestRequired.CreateBuilder();
+      AbstractMessageWrapper.Builder abstractBuilder = new AbstractMessageWrapper.Builder(builder);
+
+      Assert.IsFalse(abstractBuilder.Initialized);
+      builder.A = 1;
+      Assert.IsFalse(abstractBuilder.Initialized);
+      builder.B = 1;
+      Assert.IsFalse(abstractBuilder.Initialized);
+      builder.C = 1;
+      Assert.IsTrue(abstractBuilder.Initialized);
+    }
+
+    [Test]
+    public void ForeignIsInitialized() {
+      TestRequiredForeign.Builder builder = TestRequiredForeign.CreateBuilder();
+      AbstractMessageWrapper.Builder abstractBuilder = new AbstractMessageWrapper.Builder(builder);
+
+      Assert.IsTrue(abstractBuilder.Initialized);
+
+      builder.SetOptionalMessage(TestRequiredUninitialized);
+      Assert.IsFalse(abstractBuilder.Initialized);
+
+      builder.SetOptionalMessage(TestRequiredInitialized);
+      Assert.IsTrue(abstractBuilder.Initialized);
+
+      builder.AddRepeatedMessage(TestRequiredUninitialized);
+      Assert.IsFalse(abstractBuilder.Initialized);
+
+      builder.SetRepeatedMessage(0, TestRequiredInitialized);
+      Assert.IsTrue(abstractBuilder.Initialized);
+    }
+
+    // -----------------------------------------------------------------
+    // Tests for mergeFrom
+
+    static readonly TestAllTypes MergeSource = TestAllTypes.CreateBuilder()
+        .SetOptionalInt32(1)
+        .SetOptionalString("foo")
+        .SetOptionalForeignMessage(ForeignMessage.DefaultInstance)
+        .AddRepeatedString("bar")
+        .Build();
+
+    static readonly TestAllTypes MergeDest = TestAllTypes.CreateBuilder()
+        .SetOptionalInt64(2)
+        .SetOptionalString("baz")
+        .SetOptionalForeignMessage(ForeignMessage.CreateBuilder().SetC(3).Build())
+        .AddRepeatedString("qux")
+        .Build();
+
+    const string MergeResultText = "optional_int32: 1\n" +
+        "optional_int64: 2\n" +
+        "optional_string: \"foo\"\n" +
+        "optional_foreign_message {\n" +
+        "  c: 3\n" +
+        "}\n" +
+        "repeated_string: \"qux\"\n" +
+        "repeated_string: \"bar\"\n";
+
+    [Test]
+    public void MergeFrom() {
+      AbstractMessageWrapper result = (AbstractMessageWrapper) 
+        new AbstractMessageWrapper.Builder(TestAllTypes.CreateBuilder(MergeDest))
+            .MergeFrom(MergeSource)
+            .Build();
+
+      Assert.AreEqual(MergeResultText, result.ToString());
+    }
+
+    // -----------------------------------------------------------------
+    // Tests for equals and hashCode
+    
+    [Test]
+    public void EqualsAndHashCode() {
+      TestAllTypes a = TestUtil.GetAllSet();
+      TestAllTypes b = TestAllTypes.CreateBuilder().Build();
+      TestAllTypes c = TestAllTypes.CreateBuilder(b).AddRepeatedString("x").Build();
+      TestAllTypes d = TestAllTypes.CreateBuilder(c).AddRepeatedString("y").Build();
+      TestAllExtensions e = TestUtil.GetAllExtensionsSet();
+      TestAllExtensions f = TestAllExtensions.CreateBuilder(e)
+          .AddExtension(UnitTestProtoFile.RepeatedInt32Extension, 999).Build();
+        
+      CheckEqualsIsConsistent(a);
+      CheckEqualsIsConsistent(b);
+      CheckEqualsIsConsistent(c);
+      CheckEqualsIsConsistent(d);
+      CheckEqualsIsConsistent(e);
+      CheckEqualsIsConsistent(f);
+      
+      CheckNotEqual(a, b);
+      CheckNotEqual(a, c);
+      CheckNotEqual(a, d);
+      CheckNotEqual(a, e);
+      CheckNotEqual(a, f);
+
+      CheckNotEqual(b, c);
+      CheckNotEqual(b, d);
+      CheckNotEqual(b, e);
+      CheckNotEqual(b, f);
+
+      CheckNotEqual(c, d);
+      CheckNotEqual(c, e);
+      CheckNotEqual(c, f);
+
+      CheckNotEqual(d, e);
+      CheckNotEqual(d, f);
+
+      CheckNotEqual(e, f);
+    }
+    
+    /// <summary>
+    /// Asserts that the given protos are equal and have the same hash code.
+    /// </summary>
+    private static void CheckEqualsIsConsistent(IMessage message) {
+      // Object should be equal to itself.
+      Assert.AreEqual(message, message);
+      
+      // Object should be equal to a dynamic copy of itself.
+      DynamicMessage dynamic = (DynamicMessage) ((IBuilder) DynamicMessage.CreateBuilder(message)).Build();
+      Assert.AreEqual(message, dynamic);
+      Assert.AreEqual(dynamic, message);
+      Assert.AreEqual(dynamic.GetHashCode(), message.GetHashCode());
+    }
+
+    /// <summary>
+    /// Asserts that the given protos are not equal and have different hash codes.
+    /// </summary>
+    /// <remarks>
+    /// It's valid for non-equal objects to have the same hash code, so
+    /// this test is stricter than it needs to be. However, this should happen
+    /// relatively rarely. (If this test fails, it's probably still due to a bug.)
+    /// </remarks>
+    private static void CheckNotEqual(IMessage m1, IMessage m2) {
+      String equalsError = string.Format("{0} should not be equal to {1}", m1, m2);
+      Assert.IsFalse(m1.Equals(m2), equalsError);
+      Assert.IsFalse(m2.Equals(m1), equalsError);
+
+      Assert.IsFalse(m1.GetHashCode() == m2.GetHashCode(),
+        string.Format("{0} should have a different hash code from {1}", m1, m2));
+    }
+
+    /// <summary>
+    /// Extends AbstractMessage and wraps some other message object.  The methods
+    /// of the Message interface which aren't explicitly implemented by
+    /// AbstractMessage are forwarded to the wrapped object.  This allows us to
+    /// test that AbstractMessage's implementations work even if the wrapped
+    /// object does not use them.
+    /// </summary>
+    private class AbstractMessageWrapper : AbstractMessage {
+      private readonly IMessage wrappedMessage;
+
+      public IMessage WrappedMessage {
+        get { return wrappedMessage; }
+      }
+
+      public AbstractMessageWrapper(IMessage wrappedMessage) {
+        this.wrappedMessage = wrappedMessage;
+      }
+
+      public override MessageDescriptor DescriptorForType {
+        get { return wrappedMessage.DescriptorForType; }
+      }
+
+      protected override IMessage DefaultInstanceForTypeImpl {
+        get { return new AbstractMessageWrapper(wrappedMessage.DefaultInstanceForType); }
+      }
+
+      public override IDictionary<FieldDescriptor, object> AllFields {
+        get { return wrappedMessage.AllFields; }
+      }
+
+      public override bool HasField(FieldDescriptor field) {
+        return wrappedMessage.HasField(field);
+      }
+    
+      public override object this[FieldDescriptor field] {
+        get { return wrappedMessage[field]; }
+      }
+
+      public override object this[FieldDescriptor field, int index] {
+        get { return wrappedMessage[field, index]; }
+      }
+
+      public override int GetRepeatedFieldCount(FieldDescriptor field) {
+        return wrappedMessage.GetRepeatedFieldCount(field);
+      }
+      
+      public override UnknownFieldSet UnknownFields {
+        get { return wrappedMessage.UnknownFields; }
+      }
+
+      protected override IBuilder CreateBuilderForTypeImpl() {
+        return new Builder(wrappedMessage.CreateBuilderForType());
+      }
+
+      internal class Builder : AbstractBuilder {
+        private readonly IBuilder wrappedBuilder;
+
+        internal Builder(IBuilder wrappedBuilder) {
+          this.wrappedBuilder = wrappedBuilder;
+        }
+
+        public override bool Initialized {
+          get { return wrappedBuilder.Initialized; }
+        }
+
+        public override IDictionary<FieldDescriptor, object> AllFields {
+          get { return wrappedBuilder.AllFields; }
+        }
+
+        public override object this[FieldDescriptor field] {
+          get { return wrappedBuilder[field]; }
+          set { wrappedBuilder[field] = value; }
+        }
+
+        public override MessageDescriptor DescriptorForType {
+          get { return wrappedBuilder.DescriptorForType; }
+        }
+
+        public override int GetRepeatedFieldCount(FieldDescriptor field) {
+          return wrappedBuilder.GetRepeatedFieldCount(field);
+        }
+
+        public override object this[FieldDescriptor field, int index] {
+          get { return wrappedBuilder[field, index]; }
+          set { wrappedBuilder[field, index] = value; }
+        }
+
+        public override bool HasField(FieldDescriptor field) {
+          return wrappedBuilder.HasField(field);
+        }
+
+        public override UnknownFieldSet UnknownFields {
+          get { return wrappedBuilder.UnknownFields; }
+          set { wrappedBuilder.UnknownFields = value; }
+        }
+
+        protected override IMessage BuildImpl() {
+          return new AbstractMessageWrapper(wrappedBuilder.Build());
+        }
+
+        protected override IMessage BuildPartialImpl() {
+          return new AbstractMessageWrapper(wrappedBuilder.BuildPartial());
+        }
+
+        protected override IBuilder CloneImpl() {
+          return new Builder(wrappedBuilder.Clone());
+        }
+
+        protected override IMessage DefaultInstanceForTypeImpl {
+          get { return wrappedBuilder.DefaultInstanceForType; }
+        }
+
+        protected override IBuilder ClearFieldImpl(FieldDescriptor field) {
+          wrappedBuilder.ClearField(field);
+          return this;
+        }
+
+        protected override IBuilder AddRepeatedFieldImpl(FieldDescriptor field, object value) {
+          wrappedBuilder.AddRepeatedField(field, value);
+          return this;
+        }
+
+        public override IBuilder CreateBuilderForField(FieldDescriptor field) {
+          wrappedBuilder.CreateBuilderForField(field);
+          return this;
+        }
+
+        public override IBuilder MergeFrom(IMessage other) {
+          wrappedBuilder.MergeFrom(other);
+          return this;
+        }
+
+        protected override IBuilder MergeFromImpl(CodedInputStream input, ExtensionRegistry extensionRegistry) {
+          wrappedBuilder.MergeFrom(input, extensionRegistry);
+          return this;
+        }
+      }
+    }
+  }
+}
diff --git a/csharp/ProtocolBuffers.Test/CodedInputStreamTest.cs b/csharp/ProtocolBuffers.Test/CodedInputStreamTest.cs
index 3be8041c..9dc34ca7 100644
--- a/csharp/ProtocolBuffers.Test/CodedInputStreamTest.cs
+++ b/csharp/ProtocolBuffers.Test/CodedInputStreamTest.cs
@@ -274,65 +274,65 @@ namespace Google.ProtocolBuffers {
         // success.
       }
     }
-
     
-    /* TODO(jonskeet): Reinstate this when protoc is ready
-    private TestRecursiveMessage makeRecursiveMessage(int depth) {
+    private static TestRecursiveMessage MakeRecursiveMessage(int depth) {
       if (depth == 0) {
-        return TestRecursiveMessage.newBuilder().setI(5).build();
+        return TestRecursiveMessage.CreateBuilder().SetI(5).Build();
       } else {
-        return TestRecursiveMessage.newBuilder()
-          .setA(makeRecursiveMessage(depth - 1)).build();
+        return TestRecursiveMessage.CreateBuilder()
+          .SetA(MakeRecursiveMessage(depth - 1)).Build();
       }
     }
 
-    private void assertMessageDepth(TestRecursiveMessage message, int depth) {
+    private static void AssertMessageDepth(TestRecursiveMessage message, int depth) {
       if (depth == 0) {
-        assertFalse(message.hasA());
-        assertEquals(5, message.getI());
+        Assert.IsFalse(message.HasA);
+        Assert.AreEqual(5, message.I);
       } else {
-        assertTrue(message.hasA());
-        assertMessageDepth(message.getA(), depth - 1);
+        Assert.IsTrue(message.HasA);
+        AssertMessageDepth(message.A, depth - 1);
       }
     }
 
-    public void testMaliciousRecursion() {
-      ByteString data64 = makeRecursiveMessage(64).toByteString();
-      ByteString data65 = makeRecursiveMessage(65).toByteString();
+    [Test]
+    public void MaliciousRecursion() {
+      ByteString data64 = MakeRecursiveMessage(64).ToByteString();
+      ByteString data65 = MakeRecursiveMessage(65).ToByteString();
 
-      assertMessageDepth(TestRecursiveMessage.parseFrom(data64), 64);
+      AssertMessageDepth(TestRecursiveMessage.ParseFrom(data64), 64);
 
       try {
-        TestRecursiveMessage.parseFrom(data65);
-        fail("Should have thrown an exception!");
-      } catch (InvalidProtocolBufferException e) {
+        TestRecursiveMessage.ParseFrom(data65);
+        Assert.Fail("Should have thrown an exception!");
+      } catch (InvalidProtocolBufferException) {
         // success.
       }
 
-      CodedInputStream input = data64.newCodedInput();
-      input.setRecursionLimit(8);
+      CodedInputStream input = data64.CreateCodedInput();
+      input.SetRecursionLimit(8);
       try {
-        TestRecursiveMessage.parseFrom(input);
-        fail("Should have thrown an exception!");
-      } catch (InvalidProtocolBufferException e) {
+        TestRecursiveMessage.ParseFrom(input);
+        Assert.Fail("Should have thrown an exception!");
+      } catch (InvalidProtocolBufferException) {
         // success.
       }
     }
-     */
 
-     /* TODO(jonskeet): Reinstate this when protoc is ready
-    public void testSizeLimit() throws Exception {
-      CodedInputStream input = CodedInputStream.newInstance(
-        TestUtil.getAllSet().toByteString().newInput());
-      input.setSizeLimit(16);
+    [Test]
+    public void SizeLimit() {
+      // Have to use a Stream rather than ByteString.CreateCodedInput as SizeLimit doesn't
+      // apply to the latter case.
+      MemoryStream ms = new MemoryStream(TestUtil.GetAllSet().ToByteString().ToByteArray());
+      CodedInputStream input = CodedInputStream.CreateInstance(ms);
+      input.SetSizeLimit(16);
 
       try {
-        TestAllTypes.parseFrom(input);
-        fail("Should have thrown an exception!");
-      } catch (InvalidProtocolBufferException e) {
+        TestAllTypes.ParseFrom(input);
+        Assert.Fail("Should have thrown an exception!");
+      } catch (InvalidProtocolBufferException) {
         // success.
       }
-    }*/
+    }
 
     /// <summary>
     /// Tests that if we read an string that contains invalid UTF-8, no exception
diff --git a/csharp/ProtocolBuffers.Test/CodedOutputStreamTest.cs b/csharp/ProtocolBuffers.Test/CodedOutputStreamTest.cs
index f2f00dfe..60f7db87 100644
--- a/csharp/ProtocolBuffers.Test/CodedOutputStreamTest.cs
+++ b/csharp/ProtocolBuffers.Test/CodedOutputStreamTest.cs
@@ -14,6 +14,7 @@
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
+using Google.ProtocolBuffers.TestProtos;
 using NUnit.Framework;
 
 namespace Google.ProtocolBuffers {
@@ -33,6 +34,10 @@ namespace Google.ProtocolBuffers {
       return bytes;
     }
 
+    private static void AssertEqualBytes(byte[] a, byte[] b) {
+      Assert.AreEqual(ByteString.CopyFrom(a), ByteString.CopyFrom(b));
+    }
+
     /// <summary>
     /// Writes the given value using WriteRawVarint32() and WriteRawVarint64() and
     /// checks that the result matches the given bytes
@@ -174,24 +179,23 @@ namespace Google.ProtocolBuffers {
         0x9abcdef012345678UL);
     }
 
-    /* TODO(jonskeet): Put this back when we've got the rest working!
     [Test]
-    public void testWriteWholeMessage() throws Exception {
-      TestAllTypes message = TestUtil.getAllSet();
+    public void WriteWholeMessage() {
+      TestAllTypes message = TestUtil.GetAllSet();
 
-      byte[] rawBytes = message.toByteArray();
-      assertEqualBytes(TestUtil.getGoldenMessage().toByteArray(), rawBytes);
+      byte[] rawBytes = message.ToByteArray();
+      AssertEqualBytes(TestUtil.GoldenMessage.ToByteArray(), rawBytes);
 
       // Try different block sizes.
       for (int blockSize = 1; blockSize < 256; blockSize *= 2) {
         MemoryStream rawOutput = new MemoryStream();
         CodedOutputStream output =
-          CodedOutputStream.newInstance(rawOutput, blockSize);
-        message.writeTo(output);
-        output.flush();
-        assertEqualBytes(rawBytes, rawOutput.toByteArray());
+          CodedOutputStream.CreateInstance(rawOutput, blockSize);
+        message.WriteTo(output);
+        output.Flush();
+        AssertEqualBytes(rawBytes, rawOutput.ToArray());
       }
-    } */
+    }
 
 
     [Test]
diff --git a/csharp/ProtocolBuffers.Test/ProtocolBuffers.Test.csproj b/csharp/ProtocolBuffers.Test/ProtocolBuffers.Test.csproj
index bbb93a1f..87c5bedb 100644
--- a/csharp/ProtocolBuffers.Test/ProtocolBuffers.Test.csproj
+++ b/csharp/ProtocolBuffers.Test/ProtocolBuffers.Test.csproj
@@ -44,10 +44,12 @@
     <Reference Include="System.Xml" />
   </ItemGroup>
   <ItemGroup>
+    <Compile Include="AbstractMessageTest.cs" />
     <Compile Include="ByteStringTest.cs" />
     <Compile Include="CodedInputStreamTest.cs" />
     <Compile Include="CodedOutputStreamTest.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
+    <Compile Include="ReflectionTester.cs" />
     <Compile Include="TestProtos\UnitTestEmbedOptimizeForProtoFile.cs" />
     <Compile Include="TestProtos\UnitTestImportProtoFile.cs" />
     <Compile Include="TestProtos\UnitTestMessageSetProtoFile.cs" />
diff --git a/csharp/ProtocolBuffers.Test/ReflectionTester.cs b/csharp/ProtocolBuffers.Test/ReflectionTester.cs
new file mode 100644
index 00000000..c7767724
--- /dev/null
+++ b/csharp/ProtocolBuffers.Test/ReflectionTester.cs
@@ -0,0 +1,782 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using Google.ProtocolBuffers.Descriptors;
+using NUnit.Framework;
+
+namespace Google.ProtocolBuffers {
+  /// <summary>
+  /// Performs the same things that the methods of TestUtil do, but
+  /// via the reflection interface.  This is its own class because it needs
+  /// to know what descriptor to use.
+  /// </summary>
+  internal class ReflectionTester {
+    private readonly MessageDescriptor baseDescriptor;
+    private readonly ExtensionRegistry extensionRegistry;
+
+    private readonly FileDescriptor file;
+    private readonly FileDescriptor importFile;
+
+    private readonly MessageDescriptor optionalGroup;
+    private readonly MessageDescriptor repeatedGroup;
+    private readonly MessageDescriptor nestedMessage;
+    private readonly MessageDescriptor foreignMessage;
+    private readonly MessageDescriptor importMessage;
+
+    private readonly FieldDescriptor groupA;
+    private readonly FieldDescriptor repeatedGroupA;
+    private readonly FieldDescriptor nestedB;
+    private readonly FieldDescriptor foreignC;
+    private readonly FieldDescriptor importD;
+
+    private readonly EnumDescriptor nestedEnum;
+    private readonly EnumDescriptor foreignEnum;
+    private readonly EnumDescriptor importEnum;
+
+    private readonly EnumValueDescriptor nestedFoo;
+    private readonly EnumValueDescriptor nestedBar;
+    private readonly EnumValueDescriptor nestedBaz;
+    private readonly EnumValueDescriptor foreignFoo;
+    private readonly EnumValueDescriptor foreignBar;
+    private readonly EnumValueDescriptor foreignBaz;
+    private readonly EnumValueDescriptor importFoo;
+    private readonly EnumValueDescriptor importBar;
+    private readonly EnumValueDescriptor importBaz;
+
+    /// <summary>
+    /// Constructs an instance that will expect messages using the given
+    /// descriptor. Normally <paramref name="baseDescriptor"/> should be
+    /// a descriptor for TestAllTypes. However, if extensionRegistry is non-null,
+    /// then baseDescriptor should be for TestAllExtensions instead, and instead of
+    /// reading and writing normal fields, the tester will read and write extensions.
+    /// All of the TestAllExtensions extensions must be registered in the registry.
+    /// TODO(jonskeet): Enforce all of these with two factory methods.
+    /// </summary>
+    public ReflectionTester(MessageDescriptor baseDescriptor,
+                            ExtensionRegistry extensionRegistry) {
+      this.baseDescriptor = baseDescriptor;
+      this.extensionRegistry = extensionRegistry;
+
+      this.file = baseDescriptor.File;
+      Assert.AreEqual(1, file.Dependencies.Count);
+      this.importFile = file.Dependencies[0];
+
+      MessageDescriptor testAllTypes;
+      if (extensionRegistry == null) {
+        testAllTypes = baseDescriptor;
+      } else {
+        testAllTypes = file.FindTypeByName<MessageDescriptor>("TestAllTypes");
+        Assert.IsNotNull(testAllTypes);
+      }
+
+      if (extensionRegistry == null) {
+        this.optionalGroup =
+          baseDescriptor.FindDescriptor<MessageDescriptor>("OptionalGroup");
+        this.repeatedGroup =
+          baseDescriptor.FindDescriptor<MessageDescriptor>("RepeatedGroup");
+      } else {
+        this.optionalGroup =
+          file.FindTypeByName<MessageDescriptor>("OptionalGroup_extension");
+        this.repeatedGroup =
+          file.FindTypeByName<MessageDescriptor>("RepeatedGroup_extension");
+      }
+      this.nestedMessage = testAllTypes.FindDescriptor<MessageDescriptor>("NestedMessage");
+      this.foreignMessage = file.FindTypeByName<MessageDescriptor>("ForeignMessage");
+      this.importMessage = importFile.FindTypeByName<MessageDescriptor>("ImportMessage");
+
+      this.nestedEnum = testAllTypes.FindDescriptor<EnumDescriptor>("NestedEnum");
+      this.foreignEnum = file.FindTypeByName<EnumDescriptor>("ForeignEnum");
+      this.importEnum = importFile.FindTypeByName<EnumDescriptor>("ImportEnum");
+
+      Assert.IsNotNull(optionalGroup );
+      Assert.IsNotNull(repeatedGroup );
+      Assert.IsNotNull(nestedMessage );
+      Assert.IsNotNull(foreignMessage);
+      Assert.IsNotNull(importMessage );
+      Assert.IsNotNull(nestedEnum    );
+      Assert.IsNotNull(foreignEnum   );
+      Assert.IsNotNull(importEnum    );
+
+      this.nestedB  = nestedMessage.FindDescriptor<FieldDescriptor>("bb");
+      this.foreignC = foreignMessage.FindDescriptor<FieldDescriptor>("c");
+      this.importD  = importMessage .FindDescriptor<FieldDescriptor>("d");
+      this.nestedFoo = nestedEnum.FindValueByName("FOO");
+      this.nestedBar = nestedEnum.FindValueByName("BAR");
+      this.nestedBaz = nestedEnum.FindValueByName("BAZ");
+      this.foreignFoo = foreignEnum.FindValueByName("FOREIGN_FOO");
+      this.foreignBar = foreignEnum.FindValueByName("FOREIGN_BAR");
+      this.foreignBaz = foreignEnum.FindValueByName("FOREIGN_BAZ");
+      this.importFoo = importEnum.FindValueByName("IMPORT_FOO");
+      this.importBar = importEnum.FindValueByName("IMPORT_BAR");
+      this.importBaz = importEnum.FindValueByName("IMPORT_BAZ");
+
+      this.groupA = optionalGroup.FindDescriptor<FieldDescriptor>("a");
+      this.repeatedGroupA = repeatedGroup.FindDescriptor<FieldDescriptor>("a");
+
+      Assert.IsNotNull(groupA        );
+      Assert.IsNotNull(repeatedGroupA);
+      Assert.IsNotNull(nestedB       );
+      Assert.IsNotNull(foreignC      );
+      Assert.IsNotNull(importD       );
+      Assert.IsNotNull(nestedFoo     );
+      Assert.IsNotNull(nestedBar     );
+      Assert.IsNotNull(nestedBaz     );
+      Assert.IsNotNull(foreignFoo    );
+      Assert.IsNotNull(foreignBar    );
+      Assert.IsNotNull(foreignBaz    );
+      Assert.IsNotNull(importFoo     );
+      Assert.IsNotNull(importBar     );
+      Assert.IsNotNull(importBaz     );
+    }
+
+    /**
+     * Shorthand to get a FieldDescriptor for a field of unittest::TestAllTypes.
+     */
+    private FieldDescriptor f(String name) {
+      FieldDescriptor result;
+      if (extensionRegistry == null) {
+        result = baseDescriptor.FindDescriptor<FieldDescriptor>(name);
+      } else {
+        result = file.FindTypeByName<FieldDescriptor>(name + "_extension");
+      }
+      Assert.IsNotNull(result);
+      return result;
+    }
+
+    /**
+     * Calls {@code parent.CreateBuilderForField()} or uses the
+     * {@code ExtensionRegistry} to find an appropriateIBuilder, depending
+     * on what type is being tested.
+     */
+    private IBuilder CreateBuilderForField(IBuilder parent, FieldDescriptor field) {
+      if (extensionRegistry == null) {
+        return parent.CreateBuilderForField(field);
+      } else {
+        ExtensionInfo extension = extensionRegistry[field.ContainingType, field.FieldNumber];
+        Assert.IsNotNull(extension);
+        Assert.IsNotNull(extension.DefaultInstance);
+        return extension.DefaultInstance.CreateBuilderForType();
+      }
+    }
+
+    // -------------------------------------------------------------------
+
+    /**
+     * Set every field of {@code message} to the values expected by
+     * {@code assertAllFieldsSet()}, using the {@link MessageIBuilder}
+     * reflection interface.
+     */
+    internal void SetAllFieldsViaReflection(IBuilder message) {
+      message[f("optional_int32"   )] = 101 ;
+      message[f("optional_int64"   )] = 102L;
+      message[f("optional_uint32"  )] = 103 ;
+      message[f("optional_uint64"  )] = 104L;
+      message[f("optional_sint32"  )] = 105 ;
+      message[f("optional_sint64"  )] = 106L;
+      message[f("optional_fixed32" )] = 107 ;
+      message[f("optional_fixed64" )] = 108L;
+      message[f("optional_sfixed32")] = 109 ;
+      message[f("optional_sfixed64")] = 110L;
+      message[f("optional_float"   )] = 111F;
+      message[f("optional_double"  )] = 112D;
+      message[f("optional_bool"    )] = true;
+      message[f("optional_string"  )] = "115";
+      message[f("optional_bytes")] = TestUtil.ToBytes("116");
+
+      message[f("optionalgroup")] = CreateBuilderForField(message, f("optionalgroup")).SetField(groupA, 117).Build();
+      message[f("optional_nested_message")] = CreateBuilderForField(message, f("optional_nested_message")).SetField(nestedB, 118).Build();
+      message[f("optional_foreign_message")] = CreateBuilderForField(message, f("optional_foreign_message")).SetField(foreignC, 119).Build();
+      message[f("optional_import_message")] = CreateBuilderForField(message, f("optional_import_message")).SetField(importD, 120).Build();
+
+      message[f("optional_nested_enum" )] =  nestedBaz;
+      message[f("optional_foreign_enum")] = foreignBaz;
+      message[f("optional_import_enum" )] =  importBaz;
+
+      message[f("optional_string_piece" )] = "124";
+      message[f("optional_cord" )] = "125";
+
+      // -----------------------------------------------------------------
+
+      message.AddRepeatedField(f("repeated_int32"   ), 201 );
+      message.AddRepeatedField(f("repeated_int64"   ), 202L);
+      message.AddRepeatedField(f("repeated_uint32"  ), 203 );
+      message.AddRepeatedField(f("repeated_uint64"  ), 204L);
+      message.AddRepeatedField(f("repeated_sint32"  ), 205 );
+      message.AddRepeatedField(f("repeated_sint64"  ), 206L);
+      message.AddRepeatedField(f("repeated_fixed32" ), 207 );
+      message.AddRepeatedField(f("repeated_fixed64" ), 208L);
+      message.AddRepeatedField(f("repeated_sfixed32"), 209 );
+      message.AddRepeatedField(f("repeated_sfixed64"), 210L);
+      message.AddRepeatedField(f("repeated_float"   ), 211F);
+      message.AddRepeatedField(f("repeated_double"  ), 212D);
+      message.AddRepeatedField(f("repeated_bool"    ), true);
+      message.AddRepeatedField(f("repeated_string"  ), "215");
+      message.AddRepeatedField(f("repeated_bytes"   ), TestUtil.ToBytes("216"));
+
+
+      message.AddRepeatedField(f("repeatedgroup"), CreateBuilderForField(message, f("repeatedgroup")).SetField(repeatedGroupA, 217).Build());
+      message.AddRepeatedField(f("repeated_nested_message"), CreateBuilderForField(message, f("repeated_nested_message")).SetField(nestedB, 218).Build());
+      message.AddRepeatedField(f("repeated_foreign_message"), CreateBuilderForField(message, f("repeated_foreign_message")).SetField(foreignC, 219).Build());
+      message.AddRepeatedField(f("repeated_import_message"), CreateBuilderForField(message, f("repeated_import_message")).SetField(importD, 220).Build());
+
+      message.AddRepeatedField(f("repeated_nested_enum" ),  nestedBar);
+      message.AddRepeatedField(f("repeated_foreign_enum"), foreignBar);
+      message.AddRepeatedField(f("repeated_import_enum" ),  importBar);
+
+      message.AddRepeatedField(f("repeated_string_piece" ), "224");
+      message.AddRepeatedField(f("repeated_cord" ), "225");
+
+      // Add a second one of each field.
+      message.AddRepeatedField(f("repeated_int32"   ), 301 );
+      message.AddRepeatedField(f("repeated_int64"   ), 302L);
+      message.AddRepeatedField(f("repeated_uint32"  ), 303 );
+      message.AddRepeatedField(f("repeated_uint64"  ), 304L);
+      message.AddRepeatedField(f("repeated_sint32"  ), 305 );
+      message.AddRepeatedField(f("repeated_sint64"  ), 306L);
+      message.AddRepeatedField(f("repeated_fixed32" ), 307 );
+      message.AddRepeatedField(f("repeated_fixed64" ), 308L);
+      message.AddRepeatedField(f("repeated_sfixed32"), 309 );
+      message.AddRepeatedField(f("repeated_sfixed64"), 310L);
+      message.AddRepeatedField(f("repeated_float"   ), 311F);
+      message.AddRepeatedField(f("repeated_double"  ), 312D);
+      message.AddRepeatedField(f("repeated_bool"    ), false);
+      message.AddRepeatedField(f("repeated_string"  ), "315");
+      message.AddRepeatedField(f("repeated_bytes"   ), TestUtil.ToBytes("316"));
+
+      message.AddRepeatedField(f("repeatedgroup"),
+        CreateBuilderForField(message, f("repeatedgroup"))
+               .SetField(repeatedGroupA, 317).Build());
+      message.AddRepeatedField(f("repeated_nested_message"),
+        CreateBuilderForField(message, f("repeated_nested_message"))
+               .SetField(nestedB, 318).Build());
+      message.AddRepeatedField(f("repeated_foreign_message"),
+        CreateBuilderForField(message, f("repeated_foreign_message"))
+               .SetField(foreignC, 319).Build());
+      message.AddRepeatedField(f("repeated_import_message"),
+        CreateBuilderForField(message, f("repeated_import_message"))
+               .SetField(importD, 320).Build());
+
+      message.AddRepeatedField(f("repeated_nested_enum" ),  nestedBaz);
+      message.AddRepeatedField(f("repeated_foreign_enum"), foreignBaz);
+      message.AddRepeatedField(f("repeated_import_enum" ),  importBaz);
+
+      message.AddRepeatedField(f("repeated_string_piece" ), "324");
+      message.AddRepeatedField(f("repeated_cord" ), "325");
+
+      // -----------------------------------------------------------------
+
+      message[f("default_int32"   )] = 401 ;
+      message[f("default_int64"   )] = 402L;
+      message[f("default_uint32"  )] = 403 ;
+      message[f("default_uint64"  )] = 404L;
+      message[f("default_sint32"  )] = 405 ;
+      message[f("default_sint64"  )] = 406L;
+      message[f("default_fixed32" )] = 407 ;
+      message[f("default_fixed64" )] = 408L;
+      message[f("default_sfixed32")] = 409 ;
+      message[f("default_sfixed64")] = 410L;
+      message[f("default_float"   )] = 411F;
+      message[f("default_double"  )] = 412D;
+      message[f("default_bool"    )] = false;
+      message[f("default_string"  )] = "415";
+      message[f("default_bytes"   )] = TestUtil.ToBytes("416");
+
+      message[f("default_nested_enum" )] =  nestedFoo;
+      message[f("default_foreign_enum")] = foreignFoo;
+      message[f("default_import_enum" )] =  importFoo;
+
+      message[f("default_string_piece" )] = "424";
+      message[f("default_cord" )] = "425";
+    }
+
+    // -------------------------------------------------------------------
+
+    /// <summary>
+    /// Modify the repeated fields of the specified message to contain the
+    /// values expected by AssertRepeatedFieldsModified, using the IBuilder
+    /// reflection interface.
+    /// </summary>
+    internal void ModifyRepeatedFieldsViaReflection(IBuilder message) {
+      message[f("repeated_int32"   ), 1] = 501 ;
+      message[f("repeated_int64"   ), 1] = 502L;
+      message[f("repeated_uint32"  ), 1] = 503 ;
+      message[f("repeated_uint64"  ), 1] = 504L;
+      message[f("repeated_sint32"  ), 1] = 505 ;
+      message[f("repeated_sint64"  ), 1] = 506L;
+      message[f("repeated_fixed32" ), 1] = 507 ;
+      message[f("repeated_fixed64" ), 1] = 508L;
+      message[f("repeated_sfixed32"), 1] = 509 ;
+      message[f("repeated_sfixed64"), 1] = 510L;
+      message[f("repeated_float"   ), 1] = 511F;
+      message[f("repeated_double"  ), 1] = 512D;
+      message[f("repeated_bool"    ), 1] = true;
+      message[f("repeated_string"  ), 1] = "515";
+      message.SetRepeatedField(f("repeated_bytes"   ), 1, TestUtil.ToBytes("516"));
+
+      message.SetRepeatedField(f("repeatedgroup"), 1, CreateBuilderForField(message, f("repeatedgroup")).SetField(repeatedGroupA, 517).Build());
+      message.SetRepeatedField(f("repeated_nested_message"), 1, CreateBuilderForField(message, f("repeated_nested_message")).SetField(nestedB, 518).Build());
+      message.SetRepeatedField(f("repeated_foreign_message"), 1, CreateBuilderForField(message, f("repeated_foreign_message")).SetField(foreignC, 519).Build());
+      message.SetRepeatedField(f("repeated_import_message"), 1, CreateBuilderForField(message, f("repeated_import_message")).SetField(importD, 520).Build());
+
+      message[f("repeated_nested_enum" ), 1] =  nestedFoo;
+      message[f("repeated_foreign_enum"), 1] = foreignFoo;
+      message[f("repeated_import_enum" ), 1] =  importFoo;
+
+      message[f("repeated_string_piece"), 1] = "524";
+      message[f("repeated_cord"), 1] = "525";
+    }
+
+    // -------------------------------------------------------------------
+
+    /// <summary>
+    /// Asserts that all fields of the specified message are set to the values
+    /// assigned by SetAllFields, using the IMessage reflection interface.
+    /// </summary>
+    public void assertAllFieldsSetViaReflection(IMessage message) {
+      Assert.IsTrue(message.HasField(f("optional_int32"   )));
+      Assert.IsTrue(message.HasField(f("optional_int64"   )));
+      Assert.IsTrue(message.HasField(f("optional_uint32"  )));
+      Assert.IsTrue(message.HasField(f("optional_uint64"  )));
+      Assert.IsTrue(message.HasField(f("optional_sint32"  )));
+      Assert.IsTrue(message.HasField(f("optional_sint64"  )));
+      Assert.IsTrue(message.HasField(f("optional_fixed32" )));
+      Assert.IsTrue(message.HasField(f("optional_fixed64" )));
+      Assert.IsTrue(message.HasField(f("optional_sfixed32")));
+      Assert.IsTrue(message.HasField(f("optional_sfixed64")));
+      Assert.IsTrue(message.HasField(f("optional_float"   )));
+      Assert.IsTrue(message.HasField(f("optional_double"  )));
+      Assert.IsTrue(message.HasField(f("optional_bool"    )));
+      Assert.IsTrue(message.HasField(f("optional_string"  )));
+      Assert.IsTrue(message.HasField(f("optional_bytes"   )));
+
+      Assert.IsTrue(message.HasField(f("optionalgroup"           )));
+      Assert.IsTrue(message.HasField(f("optional_nested_message" )));
+      Assert.IsTrue(message.HasField(f("optional_foreign_message")));
+      Assert.IsTrue(message.HasField(f("optional_import_message" )));
+
+      Assert.IsTrue(((IMessage)message[f("optionalgroup")]).HasField(groupA));
+      Assert.IsTrue(((IMessage)message[f("optional_nested_message")]).HasField(nestedB));
+      Assert.IsTrue(((IMessage)message[f("optional_foreign_message")]).HasField(foreignC));
+      Assert.IsTrue(((IMessage)message[f("optional_import_message")]).HasField(importD));
+
+      Assert.IsTrue(message.HasField(f("optional_nested_enum" )));
+      Assert.IsTrue(message.HasField(f("optional_foreign_enum")));
+      Assert.IsTrue(message.HasField(f("optional_import_enum" )));
+
+      Assert.IsTrue(message.HasField(f("optional_string_piece")));
+      Assert.IsTrue(message.HasField(f("optional_cord")));
+
+      Assert.AreEqual(101  , message[f("optional_int32"   )]);
+      Assert.AreEqual(102L , message[f("optional_int64"   )]);
+      Assert.AreEqual(103  , message[f("optional_uint32"  )]);
+      Assert.AreEqual(104L , message[f("optional_uint64"  )]);
+      Assert.AreEqual(105  , message[f("optional_sint32"  )]);
+      Assert.AreEqual(106L , message[f("optional_sint64"  )]);
+      Assert.AreEqual(107  , message[f("optional_fixed32" )]);
+      Assert.AreEqual(108L , message[f("optional_fixed64" )]);
+      Assert.AreEqual(109  , message[f("optional_sfixed32")]);
+      Assert.AreEqual(110L , message[f("optional_sfixed64")]);
+      Assert.AreEqual(111F , message[f("optional_float"   )]);
+      Assert.AreEqual(112D , message[f("optional_double"  )]);
+      Assert.AreEqual(true , message[f("optional_bool"    )]);
+      Assert.AreEqual("115", message[f("optional_string"  )]);
+      Assert.AreEqual(TestUtil.ToBytes("116"), message[f("optional_bytes")]);
+
+      Assert.AreEqual(117,((IMessage)message[f("optionalgroup")])[groupA]);
+      Assert.AreEqual(118,((IMessage)message[f("optional_nested_message")])[nestedB]);
+      Assert.AreEqual(119,((IMessage)message[f("optional_foreign_message")])[foreignC]);
+      Assert.AreEqual(120,((IMessage)message[f("optional_import_message")])[importD]);
+
+      Assert.AreEqual( nestedBaz, message[f("optional_nested_enum" )]);
+      Assert.AreEqual(foreignBaz, message[f("optional_foreign_enum")]);
+      Assert.AreEqual( importBaz, message[f("optional_import_enum" )]);
+
+      Assert.AreEqual("124", message[f("optional_string_piece")]);
+      Assert.AreEqual("125", message[f("optional_cord")]);
+
+      // -----------------------------------------------------------------
+
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_int32"   )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_int64"   )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_uint32"  )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_uint64"  )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_sint32"  )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_sint64"  )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_fixed32" )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_fixed64" )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_sfixed32")));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_sfixed64")));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_float"   )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_double"  )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_bool"    )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_string"  )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_bytes"   )));
+
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeatedgroup"           )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_nested_message" )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_foreign_message")));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_import_message" )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_nested_enum"    )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_foreign_enum"   )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_import_enum"    )));
+
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_string_piece")));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_cord")));
+
+      Assert.AreEqual(201  , message[f("repeated_int32"   ), 0]);
+      Assert.AreEqual(202L , message[f("repeated_int64"   ), 0]);
+      Assert.AreEqual(203  , message[f("repeated_uint32"  ), 0]);
+      Assert.AreEqual(204L , message[f("repeated_uint64"  ), 0]);
+      Assert.AreEqual(205  , message[f("repeated_sint32"  ), 0]);
+      Assert.AreEqual(206L , message[f("repeated_sint64"  ), 0]);
+      Assert.AreEqual(207  , message[f("repeated_fixed32" ), 0]);
+      Assert.AreEqual(208L , message[f("repeated_fixed64" ), 0]);
+      Assert.AreEqual(209  , message[f("repeated_sfixed32"), 0]);
+      Assert.AreEqual(210L , message[f("repeated_sfixed64"), 0]);
+      Assert.AreEqual(211F , message[f("repeated_float"   ), 0]);
+      Assert.AreEqual(212D , message[f("repeated_double"  ), 0]);
+      Assert.AreEqual(true , message[f("repeated_bool"    ), 0]);
+      Assert.AreEqual("215", message[f("repeated_string"  ), 0]);
+      Assert.AreEqual(TestUtil.ToBytes("216"), message[f("repeated_bytes"), 0]);
+
+      Assert.AreEqual(217,((IMessage)message[f("repeatedgroup"), 0])[repeatedGroupA]);
+      Assert.AreEqual(218,((IMessage)message[f("repeated_nested_message"), 0])[nestedB]);
+      Assert.AreEqual(219,((IMessage)message[f("repeated_foreign_message"), 0])[foreignC]);
+      Assert.AreEqual(220,((IMessage)message[f("repeated_import_message"), 0])[importD]);
+
+      Assert.AreEqual( nestedBar, message[f("repeated_nested_enum" ),0]);
+      Assert.AreEqual(foreignBar, message[f("repeated_foreign_enum"),0]);
+      Assert.AreEqual( importBar, message[f("repeated_import_enum" ),0]);
+
+      Assert.AreEqual("224", message[f("repeated_string_piece"), 0]);
+      Assert.AreEqual("225", message[f("repeated_cord"), 0]);
+
+      Assert.AreEqual(301  , message[f("repeated_int32"   ), 1]);
+      Assert.AreEqual(302L , message[f("repeated_int64"   ), 1]);
+      Assert.AreEqual(303  , message[f("repeated_uint32"  ), 1]);
+      Assert.AreEqual(304L , message[f("repeated_uint64"  ), 1]);
+      Assert.AreEqual(305  , message[f("repeated_sint32"  ), 1]);
+      Assert.AreEqual(306L , message[f("repeated_sint64"  ), 1]);
+      Assert.AreEqual(307  , message[f("repeated_fixed32" ), 1]);
+      Assert.AreEqual(308L , message[f("repeated_fixed64" ), 1]);
+      Assert.AreEqual(309  , message[f("repeated_sfixed32"), 1]);
+      Assert.AreEqual(310L , message[f("repeated_sfixed64"), 1]);
+      Assert.AreEqual(311F , message[f("repeated_float"   ), 1]);
+      Assert.AreEqual(312D , message[f("repeated_double"  ), 1]);
+      Assert.AreEqual(false, message[f("repeated_bool"    ), 1]);
+      Assert.AreEqual("315", message[f("repeated_string"  ), 1]);
+      Assert.AreEqual(TestUtil.ToBytes("316"), message[f("repeated_bytes"), 1]);
+
+      Assert.AreEqual(317,((IMessage)message[f("repeatedgroup"), 1])[repeatedGroupA]);
+      Assert.AreEqual(318,((IMessage)message[f("repeated_nested_message"), 1])[nestedB]);
+      Assert.AreEqual(319,
+        ((IMessage)message[f("repeated_foreign_message"), 1])
+                         [foreignC]);
+      Assert.AreEqual(320,
+        ((IMessage)message[f("repeated_import_message"), 1])
+                         [importD]);
+
+      Assert.AreEqual( nestedBaz, message[f("repeated_nested_enum" ),1]);
+      Assert.AreEqual(foreignBaz, message[f("repeated_foreign_enum"),1]);
+      Assert.AreEqual( importBaz, message[f("repeated_import_enum" ),1]);
+
+      Assert.AreEqual("324", message[f("repeated_string_piece"), 1]);
+      Assert.AreEqual("325", message[f("repeated_cord"), 1]);
+
+      // -----------------------------------------------------------------
+
+      Assert.IsTrue(message.HasField(f("default_int32"   )));
+      Assert.IsTrue(message.HasField(f("default_int64"   )));
+      Assert.IsTrue(message.HasField(f("default_uint32"  )));
+      Assert.IsTrue(message.HasField(f("default_uint64"  )));
+      Assert.IsTrue(message.HasField(f("default_sint32"  )));
+      Assert.IsTrue(message.HasField(f("default_sint64"  )));
+      Assert.IsTrue(message.HasField(f("default_fixed32" )));
+      Assert.IsTrue(message.HasField(f("default_fixed64" )));
+      Assert.IsTrue(message.HasField(f("default_sfixed32")));
+      Assert.IsTrue(message.HasField(f("default_sfixed64")));
+      Assert.IsTrue(message.HasField(f("default_float"   )));
+      Assert.IsTrue(message.HasField(f("default_double"  )));
+      Assert.IsTrue(message.HasField(f("default_bool"    )));
+      Assert.IsTrue(message.HasField(f("default_string"  )));
+      Assert.IsTrue(message.HasField(f("default_bytes"   )));
+
+      Assert.IsTrue(message.HasField(f("default_nested_enum" )));
+      Assert.IsTrue(message.HasField(f("default_foreign_enum")));
+      Assert.IsTrue(message.HasField(f("default_import_enum" )));
+
+      Assert.IsTrue(message.HasField(f("default_string_piece")));
+      Assert.IsTrue(message.HasField(f("default_cord")));
+
+      Assert.AreEqual(401  , message[f("default_int32"   )]);
+      Assert.AreEqual(402L , message[f("default_int64"   )]);
+      Assert.AreEqual(403  , message[f("default_uint32"  )]);
+      Assert.AreEqual(404L , message[f("default_uint64"  )]);
+      Assert.AreEqual(405  , message[f("default_sint32"  )]);
+      Assert.AreEqual(406L , message[f("default_sint64"  )]);
+      Assert.AreEqual(407  , message[f("default_fixed32" )]);
+      Assert.AreEqual(408L , message[f("default_fixed64" )]);
+      Assert.AreEqual(409  , message[f("default_sfixed32")]);
+      Assert.AreEqual(410L , message[f("default_sfixed64")]);
+      Assert.AreEqual(411F , message[f("default_float"   )]);
+      Assert.AreEqual(412D , message[f("default_double"  )]);
+      Assert.AreEqual(false, message[f("default_bool"    )]);
+      Assert.AreEqual("415", message[f("default_string"  )]);
+      Assert.AreEqual(TestUtil.ToBytes("416"), message[f("default_bytes")]);
+
+      Assert.AreEqual( nestedFoo, message[f("default_nested_enum" )]);
+      Assert.AreEqual(foreignFoo, message[f("default_foreign_enum")]);
+      Assert.AreEqual( importFoo, message[f("default_import_enum" )]);
+
+      Assert.AreEqual("424", message[f("default_string_piece")]);
+      Assert.AreEqual("425", message[f("default_cord")]);
+    }
+
+    // -------------------------------------------------------------------
+
+    /**
+     * Assert (using {@code junit.framework.Assert}} that all fields of
+     * {@code message} are cleared, and that getting the fields returns their
+     * default values, using the {@link Message} reflection interface.
+     */
+    public void assertClearViaReflection(IMessage message) {
+      // has_blah() should initially be false for all optional fields.
+      Assert.IsFalse(message.HasField(f("optional_int32"   )));
+      Assert.IsFalse(message.HasField(f("optional_int64"   )));
+      Assert.IsFalse(message.HasField(f("optional_uint32"  )));
+      Assert.IsFalse(message.HasField(f("optional_uint64"  )));
+      Assert.IsFalse(message.HasField(f("optional_sint32"  )));
+      Assert.IsFalse(message.HasField(f("optional_sint64"  )));
+      Assert.IsFalse(message.HasField(f("optional_fixed32" )));
+      Assert.IsFalse(message.HasField(f("optional_fixed64" )));
+      Assert.IsFalse(message.HasField(f("optional_sfixed32")));
+      Assert.IsFalse(message.HasField(f("optional_sfixed64")));
+      Assert.IsFalse(message.HasField(f("optional_float"   )));
+      Assert.IsFalse(message.HasField(f("optional_double"  )));
+      Assert.IsFalse(message.HasField(f("optional_bool"    )));
+      Assert.IsFalse(message.HasField(f("optional_string"  )));
+      Assert.IsFalse(message.HasField(f("optional_bytes"   )));
+
+      Assert.IsFalse(message.HasField(f("optionalgroup"           )));
+      Assert.IsFalse(message.HasField(f("optional_nested_message" )));
+      Assert.IsFalse(message.HasField(f("optional_foreign_message")));
+      Assert.IsFalse(message.HasField(f("optional_import_message" )));
+
+      Assert.IsFalse(message.HasField(f("optional_nested_enum" )));
+      Assert.IsFalse(message.HasField(f("optional_foreign_enum")));
+      Assert.IsFalse(message.HasField(f("optional_import_enum" )));
+
+      Assert.IsFalse(message.HasField(f("optional_string_piece")));
+      Assert.IsFalse(message.HasField(f("optional_cord")));
+
+      // Optional fields without defaults are set to zero or something like it.
+      Assert.AreEqual(0    , message[f("optional_int32"   )]);
+      Assert.AreEqual(0L   , message[f("optional_int64"   )]);
+      Assert.AreEqual(0    , message[f("optional_uint32"  )]);
+      Assert.AreEqual(0L   , message[f("optional_uint64"  )]);
+      Assert.AreEqual(0    , message[f("optional_sint32"  )]);
+      Assert.AreEqual(0L   , message[f("optional_sint64"  )]);
+      Assert.AreEqual(0    , message[f("optional_fixed32" )]);
+      Assert.AreEqual(0L   , message[f("optional_fixed64" )]);
+      Assert.AreEqual(0    , message[f("optional_sfixed32")]);
+      Assert.AreEqual(0L   , message[f("optional_sfixed64")]);
+      Assert.AreEqual(0F   , message[f("optional_float"   )]);
+      Assert.AreEqual(0D   , message[f("optional_double"  )]);
+      Assert.AreEqual(false, message[f("optional_bool"    )]);
+      Assert.AreEqual(""   , message[f("optional_string"  )]);
+      Assert.AreEqual(ByteString.Empty, message[f("optional_bytes")]);
+
+      // Embedded messages should also be clear.
+      Assert.IsFalse(
+        ((IMessage)message[f("optionalgroup")]).HasField(groupA));
+      Assert.IsFalse(
+        ((IMessage)message[f("optional_nested_message")])
+                         .HasField(nestedB));
+      Assert.IsFalse(
+        ((IMessage)message[f("optional_foreign_message")])
+                         .HasField(foreignC));
+      Assert.IsFalse(
+        ((IMessage)message[f("optional_import_message")])
+                         .HasField(importD));
+
+      Assert.AreEqual(0,((IMessage)message[f("optionalgroup")])[groupA]);
+      Assert.AreEqual(0,((IMessage)message[f("optional_nested_message")])[nestedB]);
+      Assert.AreEqual(0,((IMessage)message[f("optional_foreign_message")])[foreignC]);
+      Assert.AreEqual(0,((IMessage)message[f("optional_import_message")])[importD]);
+
+      // Enums without defaults are set to the first value in the enum.
+      Assert.AreEqual( nestedFoo, message[f("optional_nested_enum" )]);
+      Assert.AreEqual(foreignFoo, message[f("optional_foreign_enum")]);
+      Assert.AreEqual( importFoo, message[f("optional_import_enum" )]);
+
+      Assert.AreEqual("", message[f("optional_string_piece")]);
+      Assert.AreEqual("", message[f("optional_cord")]);
+
+      // Repeated fields are empty.
+      Assert.AreEqual(0, message.GetRepeatedFieldCount(f("repeated_int32"   )));
+      Assert.AreEqual(0, message.GetRepeatedFieldCount(f("repeated_int64"   )));
+      Assert.AreEqual(0, message.GetRepeatedFieldCount(f("repeated_uint32"  )));
+      Assert.AreEqual(0, message.GetRepeatedFieldCount(f("repeated_uint64"  )));
+      Assert.AreEqual(0, message.GetRepeatedFieldCount(f("repeated_sint32"  )));
+      Assert.AreEqual(0, message.GetRepeatedFieldCount(f("repeated_sint64"  )));
+      Assert.AreEqual(0, message.GetRepeatedFieldCount(f("repeated_fixed32" )));
+      Assert.AreEqual(0, message.GetRepeatedFieldCount(f("repeated_fixed64" )));
+      Assert.AreEqual(0, message.GetRepeatedFieldCount(f("repeated_sfixed32")));
+      Assert.AreEqual(0, message.GetRepeatedFieldCount(f("repeated_sfixed64")));
+      Assert.AreEqual(0, message.GetRepeatedFieldCount(f("repeated_float"   )));
+      Assert.AreEqual(0, message.GetRepeatedFieldCount(f("repeated_double"  )));
+      Assert.AreEqual(0, message.GetRepeatedFieldCount(f("repeated_bool"    )));
+      Assert.AreEqual(0, message.GetRepeatedFieldCount(f("repeated_string"  )));
+      Assert.AreEqual(0, message.GetRepeatedFieldCount(f("repeated_bytes"   )));
+
+      Assert.AreEqual(0, message.GetRepeatedFieldCount(f("repeatedgroup"           )));
+      Assert.AreEqual(0, message.GetRepeatedFieldCount(f("repeated_nested_message" )));
+      Assert.AreEqual(0, message.GetRepeatedFieldCount(f("repeated_foreign_message")));
+      Assert.AreEqual(0, message.GetRepeatedFieldCount(f("repeated_import_message" )));
+      Assert.AreEqual(0, message.GetRepeatedFieldCount(f("repeated_nested_enum"    )));
+      Assert.AreEqual(0, message.GetRepeatedFieldCount(f("repeated_foreign_enum"   )));
+      Assert.AreEqual(0, message.GetRepeatedFieldCount(f("repeated_import_enum"    )));
+
+      Assert.AreEqual(0, message.GetRepeatedFieldCount(f("repeated_string_piece")));
+      Assert.AreEqual(0, message.GetRepeatedFieldCount(f("repeated_cord")));
+
+      // has_blah() should also be false for all default fields.
+      Assert.IsFalse(message.HasField(f("default_int32"   )));
+      Assert.IsFalse(message.HasField(f("default_int64"   )));
+      Assert.IsFalse(message.HasField(f("default_uint32"  )));
+      Assert.IsFalse(message.HasField(f("default_uint64"  )));
+      Assert.IsFalse(message.HasField(f("default_sint32"  )));
+      Assert.IsFalse(message.HasField(f("default_sint64"  )));
+      Assert.IsFalse(message.HasField(f("default_fixed32" )));
+      Assert.IsFalse(message.HasField(f("default_fixed64" )));
+      Assert.IsFalse(message.HasField(f("default_sfixed32")));
+      Assert.IsFalse(message.HasField(f("default_sfixed64")));
+      Assert.IsFalse(message.HasField(f("default_float"   )));
+      Assert.IsFalse(message.HasField(f("default_double"  )));
+      Assert.IsFalse(message.HasField(f("default_bool"    )));
+      Assert.IsFalse(message.HasField(f("default_string"  )));
+      Assert.IsFalse(message.HasField(f("default_bytes"   )));
+
+      Assert.IsFalse(message.HasField(f("default_nested_enum" )));
+      Assert.IsFalse(message.HasField(f("default_foreign_enum")));
+      Assert.IsFalse(message.HasField(f("default_import_enum" )));
+
+      Assert.IsFalse(message.HasField(f("default_string_piece" )));
+      Assert.IsFalse(message.HasField(f("default_cord" )));
+
+      // Fields with defaults have their default values (duh).
+      Assert.AreEqual( 41    , message[f("default_int32"   )]);
+      Assert.AreEqual( 42L   , message[f("default_int64"   )]);
+      Assert.AreEqual( 43    , message[f("default_uint32"  )]);
+      Assert.AreEqual( 44L   , message[f("default_uint64"  )]);
+      Assert.AreEqual(-45    , message[f("default_sint32"  )]);
+      Assert.AreEqual( 46L   , message[f("default_sint64"  )]);
+      Assert.AreEqual( 47    , message[f("default_fixed32" )]);
+      Assert.AreEqual( 48L   , message[f("default_fixed64" )]);
+      Assert.AreEqual( 49    , message[f("default_sfixed32")]);
+      Assert.AreEqual(-50L   , message[f("default_sfixed64")]);
+      Assert.AreEqual( 51.5F , message[f("default_float"   )]);
+      Assert.AreEqual( 52e3D , message[f("default_double"  )]);
+      Assert.AreEqual(true   , message[f("default_bool"    )]);
+      Assert.AreEqual("hello", message[f("default_string"  )]);
+      Assert.AreEqual(TestUtil.ToBytes("world"), message[f("default_bytes")]);
+
+      Assert.AreEqual( nestedBar, message[f("default_nested_enum" )]);
+      Assert.AreEqual(foreignBar, message[f("default_foreign_enum")]);
+      Assert.AreEqual( importBar, message[f("default_import_enum" )]);
+
+      Assert.AreEqual("abc", message[f("default_string_piece")]);
+      Assert.AreEqual("123", message[f("default_cord")]);
+    }
+
+    // ---------------------------------------------------------------
+
+    internal void AssertRepeatedFieldsModifiedViaReflection(IMessage message) {
+      // ModifyRepeatedFields only sets the second repeated element of each
+      // field.  In addition to verifying this, we also verify that the first
+      // element and size were *not* modified.
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_int32"   )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_int64"   )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_uint32"  )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_uint64"  )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_sint32"  )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_sint64"  )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_fixed32" )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_fixed64" )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_sfixed32")));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_sfixed64")));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_float"   )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_double"  )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_bool"    )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_string"  )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_bytes"   )));
+
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeatedgroup"           )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_nested_message" )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_foreign_message")));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_import_message" )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_nested_enum"    )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_foreign_enum"   )));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_import_enum"    )));
+
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_string_piece")));
+      Assert.AreEqual(2, message.GetRepeatedFieldCount(f("repeated_cord")));
+
+      Assert.AreEqual(201  , message[f("repeated_int32"   ), 0]);
+      Assert.AreEqual(202L , message[f("repeated_int64"   ), 0]);
+      Assert.AreEqual(203  , message[f("repeated_uint32"  ), 0]);
+      Assert.AreEqual(204L , message[f("repeated_uint64"  ), 0]);
+      Assert.AreEqual(205  , message[f("repeated_sint32"  ), 0]);
+      Assert.AreEqual(206L , message[f("repeated_sint64"  ), 0]);
+      Assert.AreEqual(207  , message[f("repeated_fixed32" ), 0]);
+      Assert.AreEqual(208L , message[f("repeated_fixed64" ), 0]);
+      Assert.AreEqual(209  , message[f("repeated_sfixed32"), 0]);
+      Assert.AreEqual(210L , message[f("repeated_sfixed64"), 0]);
+      Assert.AreEqual(211F , message[f("repeated_float"   ), 0]);
+      Assert.AreEqual(212D , message[f("repeated_double"  ), 0]);
+      Assert.AreEqual(true , message[f("repeated_bool"    ), 0]);
+      Assert.AreEqual("215", message[f("repeated_string"  ), 0]);
+      Assert.AreEqual(TestUtil.ToBytes("216"), message[f("repeated_bytes"), 0]);
+
+      Assert.AreEqual(217,((IMessage)message[f("repeatedgroup"), 0])[repeatedGroupA]);
+      Assert.AreEqual(218,((IMessage)message[f("repeated_nested_message"), 0])[nestedB]);
+      Assert.AreEqual(219,((IMessage)message[f("repeated_foreign_message"), 0])[foreignC]);
+      Assert.AreEqual(220,((IMessage)message[f("repeated_import_message"), 0])[importD]);
+
+      Assert.AreEqual( nestedBar, message[f("repeated_nested_enum" ),0]);
+      Assert.AreEqual(foreignBar, message[f("repeated_foreign_enum"),0]);
+      Assert.AreEqual( importBar, message[f("repeated_import_enum" ),0]);
+
+      Assert.AreEqual("224", message[f("repeated_string_piece"), 0]);
+      Assert.AreEqual("225", message[f("repeated_cord"), 0]);
+
+      Assert.AreEqual(501  , message[f("repeated_int32"   ), 1]);
+      Assert.AreEqual(502L , message[f("repeated_int64"   ), 1]);
+      Assert.AreEqual(503  , message[f("repeated_uint32"  ), 1]);
+      Assert.AreEqual(504L , message[f("repeated_uint64"  ), 1]);
+      Assert.AreEqual(505  , message[f("repeated_sint32"  ), 1]);
+      Assert.AreEqual(506L , message[f("repeated_sint64"  ), 1]);
+      Assert.AreEqual(507  , message[f("repeated_fixed32" ), 1]);
+      Assert.AreEqual(508L , message[f("repeated_fixed64" ), 1]);
+      Assert.AreEqual(509  , message[f("repeated_sfixed32"), 1]);
+      Assert.AreEqual(510L , message[f("repeated_sfixed64"), 1]);
+      Assert.AreEqual(511F , message[f("repeated_float"   ), 1]);
+      Assert.AreEqual(512D , message[f("repeated_double"  ), 1]);
+      Assert.AreEqual(true , message[f("repeated_bool"    ), 1]);
+      Assert.AreEqual("515", message[f("repeated_string"  ), 1]);
+      Assert.AreEqual(TestUtil.ToBytes("516"), message[f("repeated_bytes"), 1]);
+
+      Assert.AreEqual(517,((IMessage)message[f("repeatedgroup"), 1])[repeatedGroupA]);
+      Assert.AreEqual(518,((IMessage)message[f("repeated_nested_message"), 1])[nestedB]);
+      Assert.AreEqual(519,((IMessage)message[f("repeated_foreign_message"), 1])[foreignC]);
+      Assert.AreEqual(520,((IMessage)message[f("repeated_import_message"), 1])[importD]);
+
+      Assert.AreEqual( nestedFoo, message[f("repeated_nested_enum" ),1]);
+      Assert.AreEqual(foreignFoo, message[f("repeated_foreign_enum"),1]);
+      Assert.AreEqual( importFoo, message[f("repeated_import_enum" ),1]);
+
+      Assert.AreEqual("524", message[f("repeated_string_piece"), 1]);
+      Assert.AreEqual("525", message[f("repeated_cord"), 1]);
+    }
+  }
+}
diff --git a/csharp/ProtocolBuffers.Test/TestProtos/UnitTestEmbedOptimizeForProtoFile.cs b/csharp/ProtocolBuffers.Test/TestProtos/UnitTestEmbedOptimizeForProtoFile.cs
index f3228fe8..dd07da89 100644
--- a/csharp/ProtocolBuffers.Test/TestProtos/UnitTestEmbedOptimizeForProtoFile.cs
+++ b/csharp/ProtocolBuffers.Test/TestProtos/UnitTestEmbedOptimizeForProtoFile.cs
@@ -40,7 +40,6 @@ namespace Google.ProtocolBuffers.TestProtos {
     #endregion
     
     #region Extensions
-    /**/
     #endregion
     
     #region Static variables
@@ -219,6 +218,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::TestEmbedOptimizedForSize) {
           return MergeFrom((self::TestEmbedOptimizedForSize) other);
diff --git a/csharp/ProtocolBuffers.Test/TestProtos/UnitTestImportProtoFile.cs b/csharp/ProtocolBuffers.Test/TestProtos/UnitTestImportProtoFile.cs
index e0f35000..c7e68878 100644
--- a/csharp/ProtocolBuffers.Test/TestProtos/UnitTestImportProtoFile.cs
+++ b/csharp/ProtocolBuffers.Test/TestProtos/UnitTestImportProtoFile.cs
@@ -34,7 +34,6 @@ namespace Google.ProtocolBuffers.TestProtos {
     #endregion
     
     #region Extensions
-    /**/
     #endregion
     
     #region Static variables
@@ -192,6 +191,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::ImportMessage) {
           return MergeFrom((self::ImportMessage) other);
diff --git a/csharp/ProtocolBuffers.Test/TestProtos/UnitTestMessageSetProtoFile.cs b/csharp/ProtocolBuffers.Test/TestProtos/UnitTestMessageSetProtoFile.cs
index 77b43d2a..4a8fc794 100644
--- a/csharp/ProtocolBuffers.Test/TestProtos/UnitTestMessageSetProtoFile.cs
+++ b/csharp/ProtocolBuffers.Test/TestProtos/UnitTestMessageSetProtoFile.cs
@@ -55,7 +55,6 @@ namespace Google.ProtocolBuffers.TestProtos {
     #endregion
     
     #region Extensions
-    /**/
     #endregion
     
     #region Static variables
@@ -197,7 +196,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
-    public sealed partial class Builder : pb::GeneratedBuilder<self::TestMessageSet, self::TestMessageSet.Builder>.ExtendableBuilder {
+    public sealed partial class Builder : pb::ExtendableBuilder<self::TestMessageSet, self::TestMessageSet.Builder> {
       // Construct using self::TestMessageSet.CreateBuilder()
       internal Builder() {}
       
@@ -230,6 +229,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::TestMessageSet) {
           return MergeFrom((self::TestMessageSet) other);
@@ -409,6 +412,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::TestMessageSetContainer) {
           return MergeFrom((self::TestMessageSetContainer) other);
@@ -639,6 +646,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::TestMessageSetExtension1) {
           return MergeFrom((self::TestMessageSetExtension1) other);
@@ -848,6 +859,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::TestMessageSetExtension2) {
           return MergeFrom((self::TestMessageSetExtension2) other);
@@ -1091,6 +1106,10 @@ namespace Google.ProtocolBuffers.TestProtos {
             return returnMe;
           }
           
+          protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+            return MergeFrom(data, extensionRegistry);
+          }
+          
           public override IBuilder MergeFrom(pb::IMessage other) {
             if (other is self::RawMessageSet.Types.Item) {
               return MergeFrom((self::RawMessageSet.Types.Item) other);
@@ -1309,6 +1328,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::RawMessageSet) {
           return MergeFrom((self::RawMessageSet) other);
diff --git a/csharp/ProtocolBuffers.Test/TestProtos/UnitTestOptimizeForProtoFile.cs b/csharp/ProtocolBuffers.Test/TestProtos/UnitTestOptimizeForProtoFile.cs
index ead26b3a..f950d8f6 100644
--- a/csharp/ProtocolBuffers.Test/TestProtos/UnitTestOptimizeForProtoFile.cs
+++ b/csharp/ProtocolBuffers.Test/TestProtos/UnitTestOptimizeForProtoFile.cs
@@ -39,7 +39,6 @@ namespace Google.ProtocolBuffers.TestProtos {
     #endregion
     
     #region Extensions
-    /**/
     #endregion
     
     #region Static variables
@@ -146,7 +145,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
-    public sealed partial class Builder : pb::GeneratedBuilder<self::TestOptimizedForSize, self::TestOptimizedForSize.Builder>.ExtendableBuilder {
+    public sealed partial class Builder : pb::ExtendableBuilder<self::TestOptimizedForSize, self::TestOptimizedForSize.Builder> {
       // Construct using self::TestOptimizedForSize.CreateBuilder()
       internal Builder() {}
       
diff --git a/csharp/ProtocolBuffers.Test/TestProtos/UnitTestProtoFile.cs b/csharp/ProtocolBuffers.Test/TestProtos/UnitTestProtoFile.cs
index 7868649f..e5099ce8 100644
--- a/csharp/ProtocolBuffers.Test/TestProtos/UnitTestProtoFile.cs
+++ b/csharp/ProtocolBuffers.Test/TestProtos/UnitTestProtoFile.cs
@@ -632,7 +632,7 @@ namespace Google.ProtocolBuffers.TestProtos {
     #endregion
     
     #region Extensions
-    /*public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, int> OptionalInt32Extension =
+    public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, int> OptionalInt32Extension =
           pb::GeneratedSingleExtension<self::TestAllExtensions, int>.CreateInstance(Descriptor.Extensions[0]);
     public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, long> OptionalInt64Extension =
           pb::GeneratedSingleExtension<self::TestAllExtensions, long>.CreateInstance(Descriptor.Extensions[1]);
@@ -681,76 +681,76 @@ namespace Google.ProtocolBuffers.TestProtos {
     public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, string> OptionalCordExtension =
           pb::GeneratedSingleExtension<self::TestAllExtensions, string>.CreateInstance(Descriptor.Extensions[23]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<int>> name =
+      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<int>> RepeatedInt32Extension =
           pb::GeneratedRepeatExtension<self::TestAllExtensions, int>.CreateInstance(Descriptor.Extensions[24]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<long>> name =
+      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<long>> RepeatedInt64Extension =
           pb::GeneratedRepeatExtension<self::TestAllExtensions, long>.CreateInstance(Descriptor.Extensions[25]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<uint>> name =
+      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<uint>> RepeatedUint32Extension =
           pb::GeneratedRepeatExtension<self::TestAllExtensions, uint>.CreateInstance(Descriptor.Extensions[26]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<ulong>> name =
+      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<ulong>> RepeatedUint64Extension =
           pb::GeneratedRepeatExtension<self::TestAllExtensions, ulong>.CreateInstance(Descriptor.Extensions[27]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<int>> name =
+      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<int>> RepeatedSint32Extension =
           pb::GeneratedRepeatExtension<self::TestAllExtensions, int>.CreateInstance(Descriptor.Extensions[28]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<long>> name =
+      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<long>> RepeatedSint64Extension =
           pb::GeneratedRepeatExtension<self::TestAllExtensions, long>.CreateInstance(Descriptor.Extensions[29]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<uint>> name =
+      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<uint>> RepeatedFixed32Extension =
           pb::GeneratedRepeatExtension<self::TestAllExtensions, uint>.CreateInstance(Descriptor.Extensions[30]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<ulong>> name =
+      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<ulong>> RepeatedFixed64Extension =
           pb::GeneratedRepeatExtension<self::TestAllExtensions, ulong>.CreateInstance(Descriptor.Extensions[31]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<int>> name =
+      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<int>> RepeatedSfixed32Extension =
           pb::GeneratedRepeatExtension<self::TestAllExtensions, int>.CreateInstance(Descriptor.Extensions[32]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<long>> name =
+      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<long>> RepeatedSfixed64Extension =
           pb::GeneratedRepeatExtension<self::TestAllExtensions, long>.CreateInstance(Descriptor.Extensions[33]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<float>> name =
+      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<float>> RepeatedFloatExtension =
           pb::GeneratedRepeatExtension<self::TestAllExtensions, float>.CreateInstance(Descriptor.Extensions[34]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<double>> name =
+      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<double>> RepeatedDoubleExtension =
           pb::GeneratedRepeatExtension<self::TestAllExtensions, double>.CreateInstance(Descriptor.Extensions[35]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<bool>> name =
+      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<bool>> RepeatedBoolExtension =
           pb::GeneratedRepeatExtension<self::TestAllExtensions, bool>.CreateInstance(Descriptor.Extensions[36]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<string>> name =
+      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<string>> RepeatedStringExtension =
           pb::GeneratedRepeatExtension<self::TestAllExtensions, string>.CreateInstance(Descriptor.Extensions[37]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<pb::ByteString>> name =
+      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<pb::ByteString>> RepeatedBytesExtension =
           pb::GeneratedRepeatExtension<self::TestAllExtensions, pb::ByteString>.CreateInstance(Descriptor.Extensions[38]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<self::RepeatedGroup_extension>> name =
+      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<self::RepeatedGroup_extension>> RepeatedGroupExtension =
           pb::GeneratedRepeatExtension<self::TestAllExtensions, self::RepeatedGroup_extension>.CreateInstance(Descriptor.Extensions[39]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<self::TestAllTypes.Types.NestedMessage>> name =
+      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<self::TestAllTypes.Types.NestedMessage>> RepeatedNestedMessageExtension =
           pb::GeneratedRepeatExtension<self::TestAllExtensions, self::TestAllTypes.Types.NestedMessage>.CreateInstance(Descriptor.Extensions[40]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<self::ForeignMessage>> name =
+      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<self::ForeignMessage>> RepeatedForeignMessageExtension =
           pb::GeneratedRepeatExtension<self::TestAllExtensions, self::ForeignMessage>.CreateInstance(Descriptor.Extensions[41]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<self::ImportMessage>> name =
+      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<self::ImportMessage>> RepeatedImportMessageExtension =
           pb::GeneratedRepeatExtension<self::TestAllExtensions, self::ImportMessage>.CreateInstance(Descriptor.Extensions[42]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<self::TestAllTypes.Types.NestedEnum>> name =
+      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<self::TestAllTypes.Types.NestedEnum>> RepeatedNestedEnumExtension =
           pb::GeneratedRepeatExtension<self::TestAllExtensions, self::TestAllTypes.Types.NestedEnum>.CreateInstance(Descriptor.Extensions[43]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<self::ForeignEnum>> name =
+      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<self::ForeignEnum>> RepeatedForeignEnumExtension =
           pb::GeneratedRepeatExtension<self::TestAllExtensions, self::ForeignEnum>.CreateInstance(Descriptor.Extensions[44]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<self::ImportEnum>> name =
+      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<self::ImportEnum>> RepeatedImportEnumExtension =
           pb::GeneratedRepeatExtension<self::TestAllExtensions, self::ImportEnum>.CreateInstance(Descriptor.Extensions[45]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<string>> name =
+      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<string>> RepeatedStringPieceExtension =
           pb::GeneratedRepeatExtension<self::TestAllExtensions, string>.CreateInstance(Descriptor.Extensions[46]);
     public static readonly
-      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<string>> name =
+      pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<string>> RepeatedCordExtension =
           pb::GeneratedRepeatExtension<self::TestAllExtensions, string>.CreateInstance(Descriptor.Extensions[47]);
     public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, int> DefaultInt32Extension =
           pb::GeneratedSingleExtension<self::TestAllExtensions, int>.CreateInstance(Descriptor.Extensions[48]);
@@ -796,7 +796,6 @@ namespace Google.ProtocolBuffers.TestProtos {
           pb::GeneratedSingleExtension<self::TestFieldOrderings, string>.CreateInstance(Descriptor.Extensions[68]);
     public static readonly pb::GeneratedExtensionBase<self::TestFieldOrderings, int> MyExtensionInt =
           pb::GeneratedSingleExtension<self::TestFieldOrderings, int>.CreateInstance(Descriptor.Extensions[69]);
-    */
     #endregion
     
     #region Static variables
@@ -1195,6 +1194,10 @@ namespace Google.ProtocolBuffers.TestProtos {
             return returnMe;
           }
           
+          protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+            return MergeFrom(data, extensionRegistry);
+          }
+          
           public override IBuilder MergeFrom(pb::IMessage other) {
             if (other is self::TestAllTypes.Types.NestedMessage) {
               return MergeFrom((self::TestAllTypes.Types.NestedMessage) other);
@@ -1397,6 +1400,10 @@ namespace Google.ProtocolBuffers.TestProtos {
             return returnMe;
           }
           
+          protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+            return MergeFrom(data, extensionRegistry);
+          }
+          
           public override IBuilder MergeFrom(pb::IMessage other) {
             if (other is self::TestAllTypes.Types.OptionalGroup) {
               return MergeFrom((self::TestAllTypes.Types.OptionalGroup) other);
@@ -1599,6 +1606,10 @@ namespace Google.ProtocolBuffers.TestProtos {
             return returnMe;
           }
           
+          protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+            return MergeFrom(data, extensionRegistry);
+          }
+          
           public override IBuilder MergeFrom(pb::IMessage other) {
             if (other is self::TestAllTypes.Types.RepeatedGroup) {
               return MergeFrom((self::TestAllTypes.Types.RepeatedGroup) other);
@@ -2949,6 +2960,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::TestAllTypes) {
           return MergeFrom((self::TestAllTypes) other);
@@ -5485,6 +5500,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::ForeignMessage) {
           return MergeFrom((self::ForeignMessage) other);
@@ -5642,7 +5661,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
-    public sealed partial class Builder : pb::GeneratedBuilder<self::TestAllExtensions, self::TestAllExtensions.Builder>.ExtendableBuilder {
+    public sealed partial class Builder : pb::ExtendableBuilder<self::TestAllExtensions, self::TestAllExtensions.Builder> {
       // Construct using self::TestAllExtensions.CreateBuilder()
       internal Builder() {}
       
@@ -5675,6 +5694,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::TestAllExtensions) {
           return MergeFrom((self::TestAllExtensions) other);
@@ -5851,6 +5874,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::OptionalGroup_extension) {
           return MergeFrom((self::OptionalGroup_extension) other);
@@ -6053,6 +6080,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::RepeatedGroup_extension) {
           return MergeFrom((self::RepeatedGroup_extension) other);
@@ -6148,7 +6179,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       public static readonly pb::GeneratedExtensionBase<self::TestAllExtensions, self::TestRequired> Single =
             pb::GeneratedSingleExtension<self::TestAllExtensions, self::TestRequired>.CreateInstance(Descriptor.Extensions[0]);
       public static readonly
-        pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<self::TestRequired>> name =
+        pb::GeneratedExtensionBase<self::TestAllExtensions, scg::IList<self::TestRequired>> Multi =
             pb::GeneratedRepeatExtension<self::TestAllExtensions, self::TestRequired>.CreateInstance(Descriptor.Extensions[1]);
     }
     #endregion
@@ -6780,6 +6811,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::TestRequired) {
           return MergeFrom((self::TestRequired) other);
@@ -7857,6 +7892,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::TestRequiredForeign) {
           return MergeFrom((self::TestRequiredForeign) other);
@@ -8162,6 +8201,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::TestForeignNested) {
           return MergeFrom((self::TestForeignNested) other);
@@ -8369,6 +8412,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::TestEmptyMessage) {
           return MergeFrom((self::TestEmptyMessage) other);
@@ -8500,7 +8547,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
-    public sealed partial class Builder : pb::GeneratedBuilder<self::TestEmptyMessageWithExtensions, self::TestEmptyMessageWithExtensions.Builder>.ExtendableBuilder {
+    public sealed partial class Builder : pb::ExtendableBuilder<self::TestEmptyMessageWithExtensions, self::TestEmptyMessageWithExtensions.Builder> {
       // Construct using self::TestEmptyMessageWithExtensions.CreateBuilder()
       internal Builder() {}
       
@@ -8533,6 +8580,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::TestEmptyMessageWithExtensions) {
           return MergeFrom((self::TestEmptyMessageWithExtensions) other);
@@ -8725,6 +8776,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::TestReallyLargeTagNumber) {
           return MergeFrom((self::TestReallyLargeTagNumber) other);
@@ -8969,6 +9024,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::TestRecursiveMessage) {
           return MergeFrom((self::TestRecursiveMessage) other);
@@ -9218,6 +9277,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::TestMutualRecursionA) {
           return MergeFrom((self::TestMutualRecursionA) other);
@@ -9457,6 +9520,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::TestMutualRecursionB) {
           return MergeFrom((self::TestMutualRecursionB) other);
@@ -9729,6 +9796,10 @@ namespace Google.ProtocolBuffers.TestProtos {
             return returnMe;
           }
           
+          protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+            return MergeFrom(data, extensionRegistry);
+          }
+          
           public override IBuilder MergeFrom(pb::IMessage other) {
             if (other is self::TestDupFieldNumber.Types.Foo) {
               return MergeFrom((self::TestDupFieldNumber.Types.Foo) other);
@@ -9931,6 +10002,10 @@ namespace Google.ProtocolBuffers.TestProtos {
             return returnMe;
           }
           
+          protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+            return MergeFrom(data, extensionRegistry);
+          }
+          
           public override IBuilder MergeFrom(pb::IMessage other) {
             if (other is self::TestDupFieldNumber.Types.Bar) {
               return MergeFrom((self::TestDupFieldNumber.Types.Bar) other);
@@ -10147,6 +10222,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::TestDupFieldNumber) {
           return MergeFrom((self::TestDupFieldNumber) other);
@@ -10491,6 +10570,10 @@ namespace Google.ProtocolBuffers.TestProtos {
             return returnMe;
           }
           
+          protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+            return MergeFrom(data, extensionRegistry);
+          }
+          
           public override IBuilder MergeFrom(pb::IMessage other) {
             if (other is self::TestNestedMessageHasBits.Types.NestedMessage) {
               return MergeFrom((self::TestNestedMessageHasBits.Types.NestedMessage) other);
@@ -10748,6 +10831,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::TestNestedMessageHasBits) {
           return MergeFrom((self::TestNestedMessageHasBits) other);
@@ -11171,6 +11258,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::TestCamelCaseFieldNames) {
           return MergeFrom((self::TestCamelCaseFieldNames) other);
@@ -11810,7 +11901,7 @@ namespace Google.ProtocolBuffers.TestProtos {
       return (Builder) new Builder().MergeFrom(prototype);
     }
     
-    public sealed partial class Builder : pb::GeneratedBuilder<self::TestFieldOrderings, self::TestFieldOrderings.Builder>.ExtendableBuilder {
+    public sealed partial class Builder : pb::ExtendableBuilder<self::TestFieldOrderings, self::TestFieldOrderings.Builder> {
       // Construct using self::TestFieldOrderings.CreateBuilder()
       internal Builder() {}
       
@@ -11843,6 +11934,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::TestFieldOrderings) {
           return MergeFrom((self::TestFieldOrderings) other);
@@ -12177,6 +12272,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::TestExtremeDefaultValues) {
           return MergeFrom((self::TestExtremeDefaultValues) other);
@@ -12493,6 +12592,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::FooRequest) {
           return MergeFrom((self::FooRequest) other);
@@ -12653,6 +12756,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::FooResponse) {
           return MergeFrom((self::FooResponse) other);
@@ -12813,6 +12920,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::BarRequest) {
           return MergeFrom((self::BarRequest) other);
@@ -12973,6 +13084,10 @@ namespace Google.ProtocolBuffers.TestProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::BarResponse) {
           return MergeFrom((self::BarResponse) other);
diff --git a/csharp/ProtocolBuffers.Test/TestUtil.cs b/csharp/ProtocolBuffers.Test/TestUtil.cs
index 190e8f75..2cc1b5a2 100644
--- a/csharp/ProtocolBuffers.Test/TestUtil.cs
+++ b/csharp/ProtocolBuffers.Test/TestUtil.cs
@@ -8,9 +8,10 @@ using NUnit.Framework;
 namespace Google.ProtocolBuffers {
   internal static class TestUtil {
 
-    private static DirectoryInfo testDataDirectory;
+    private static string testDataDirectory;
+    private static ByteString goldenMessage = null;
 
-    internal static DirectoryInfo TestDataDirectory {
+    internal static string TestDataDirectory {
       get {
         if (testDataDirectory != null) {
           return testDataDirectory;
@@ -21,7 +22,7 @@ namespace Google.ProtocolBuffers {
         while (ancestor != null) {
           string candidate = Path.Combine(ancestor.FullName, "src/google/protobuf");
           if (Directory.Exists(candidate)) {
-            testDataDirectory = new DirectoryInfo(candidate);
+            testDataDirectory = Path.Combine(ancestor.FullName, "src/google/protobuf/testdata");
             return testDataDirectory;
           }
           ancestor = ancestor.Parent;
@@ -31,10 +32,113 @@ namespace Google.ProtocolBuffers {
       }
     }
 
+    internal static ByteString GoldenMessage {
+      get {
+        if (goldenMessage == null) {
+          goldenMessage = ReadBytesFromFile("golden_message");
+        }
+        return goldenMessage;
+      }
+    }
+
+    /// <summary>
+    /// Creates an unmodifiable ExtensionRegistry containing all the extensions
+    /// of TestAllExtensions.
+    /// </summary>
+    /// <returns></returns>
+    internal static ExtensionRegistry CreateExtensionRegistry() {
+      ExtensionRegistry registry = ExtensionRegistry.CreateInstance();
+      RegisterAllExtensions(registry);
+      return registry.AsReadOnly();
+    }
+
+    /// <summary>
+    /// Registers all of the extensions in TestAllExtensions with the given
+    /// ExtensionRegistry.
+    /// </summary>
+    internal static void RegisterAllExtensions(ExtensionRegistry registry) {
+      registry.Add(UnitTestProtoFile.OptionalInt32Extension);
+      registry.Add(UnitTestProtoFile.OptionalInt64Extension);
+      registry.Add(UnitTestProtoFile.OptionalUint32Extension);
+      registry.Add(UnitTestProtoFile.OptionalUint64Extension);
+      registry.Add(UnitTestProtoFile.OptionalSint32Extension);
+      registry.Add(UnitTestProtoFile.OptionalSint64Extension);
+      registry.Add(UnitTestProtoFile.OptionalFixed32Extension);
+      registry.Add(UnitTestProtoFile.OptionalFixed64Extension);
+      registry.Add(UnitTestProtoFile.OptionalSfixed32Extension);
+      registry.Add(UnitTestProtoFile.OptionalSfixed64Extension);
+      registry.Add(UnitTestProtoFile.OptionalFloatExtension);
+      registry.Add(UnitTestProtoFile.OptionalDoubleExtension);
+      registry.Add(UnitTestProtoFile.OptionalBoolExtension);
+      registry.Add(UnitTestProtoFile.OptionalStringExtension);
+      registry.Add(UnitTestProtoFile.OptionalBytesExtension);
+      registry.Add(UnitTestProtoFile.OptionalGroupExtension);
+      registry.Add(UnitTestProtoFile.OptionalNestedMessageExtension);
+      registry.Add(UnitTestProtoFile.OptionalForeignMessageExtension);
+      registry.Add(UnitTestProtoFile.OptionalImportMessageExtension);
+      registry.Add(UnitTestProtoFile.OptionalNestedEnumExtension);
+      registry.Add(UnitTestProtoFile.OptionalForeignEnumExtension);
+      registry.Add(UnitTestProtoFile.OptionalImportEnumExtension);
+      registry.Add(UnitTestProtoFile.OptionalStringPieceExtension);
+      registry.Add(UnitTestProtoFile.OptionalCordExtension);
+
+      registry.Add(UnitTestProtoFile.RepeatedInt32Extension);
+      registry.Add(UnitTestProtoFile.RepeatedInt64Extension);
+      registry.Add(UnitTestProtoFile.RepeatedUint32Extension);
+      registry.Add(UnitTestProtoFile.RepeatedUint64Extension);
+      registry.Add(UnitTestProtoFile.RepeatedSint32Extension);
+      registry.Add(UnitTestProtoFile.RepeatedSint64Extension);
+      registry.Add(UnitTestProtoFile.RepeatedFixed32Extension);
+      registry.Add(UnitTestProtoFile.RepeatedFixed64Extension);
+      registry.Add(UnitTestProtoFile.RepeatedSfixed32Extension);
+      registry.Add(UnitTestProtoFile.RepeatedSfixed64Extension);
+      registry.Add(UnitTestProtoFile.RepeatedFloatExtension);
+      registry.Add(UnitTestProtoFile.RepeatedDoubleExtension);
+      registry.Add(UnitTestProtoFile.RepeatedBoolExtension);
+      registry.Add(UnitTestProtoFile.RepeatedStringExtension);
+      registry.Add(UnitTestProtoFile.RepeatedBytesExtension);
+      registry.Add(UnitTestProtoFile.RepeatedGroupExtension);
+      registry.Add(UnitTestProtoFile.RepeatedNestedMessageExtension);
+      registry.Add(UnitTestProtoFile.RepeatedForeignMessageExtension);
+      registry.Add(UnitTestProtoFile.RepeatedImportMessageExtension);
+      registry.Add(UnitTestProtoFile.RepeatedNestedEnumExtension);
+      registry.Add(UnitTestProtoFile.RepeatedForeignEnumExtension);
+      registry.Add(UnitTestProtoFile.RepeatedImportEnumExtension);
+      registry.Add(UnitTestProtoFile.RepeatedStringPieceExtension);
+      registry.Add(UnitTestProtoFile.RepeatedCordExtension);
+
+      registry.Add(UnitTestProtoFile.DefaultInt32Extension);
+      registry.Add(UnitTestProtoFile.DefaultInt64Extension);
+      registry.Add(UnitTestProtoFile.DefaultUint32Extension);
+      registry.Add(UnitTestProtoFile.DefaultUint64Extension);
+      registry.Add(UnitTestProtoFile.DefaultSint32Extension);
+      registry.Add(UnitTestProtoFile.DefaultSint64Extension);
+      registry.Add(UnitTestProtoFile.DefaultFixed32Extension);
+      registry.Add(UnitTestProtoFile.DefaultFixed64Extension);
+      registry.Add(UnitTestProtoFile.DefaultSfixed32Extension);
+      registry.Add(UnitTestProtoFile.DefaultSfixed64Extension);
+      registry.Add(UnitTestProtoFile.DefaultFloatExtension);
+      registry.Add(UnitTestProtoFile.DefaultDoubleExtension);
+      registry.Add(UnitTestProtoFile.DefaultBoolExtension);
+      registry.Add(UnitTestProtoFile.DefaultStringExtension);
+      registry.Add(UnitTestProtoFile.DefaultBytesExtension);
+      registry.Add(UnitTestProtoFile.DefaultNestedEnumExtension);
+      registry.Add(UnitTestProtoFile.DefaultForeignEnumExtension);
+      registry.Add(UnitTestProtoFile.DefaultImportEnumExtension);
+      registry.Add(UnitTestProtoFile.DefaultStringPieceExtension);
+      registry.Add(UnitTestProtoFile.DefaultCordExtension);
+    }
+
+
+    internal static ByteString ReadBytesFromFile(String filename) {
+      byte[] data = File.ReadAllBytes(Path.Combine(TestDataDirectory, filename));
+      return ByteString.CopyFrom(data);
+    }
+
     /// <summary>
     /// Helper to convert a String to ByteString.
     /// </summary>
-    private static ByteString ToBytes(String str) {
+    internal static ByteString ToBytes(String str) {
       return ByteString.CopyFrom(Encoding.UTF8.GetBytes(str));
     }
 
@@ -362,5 +466,275 @@ namespace Google.ProtocolBuffers {
       Assert.AreEqual("425", message.DefaultCord);
     }
 
+    internal static void AssertClear(TestAllTypes message) {
+      // HasBlah() should initially be false for all optional fields.
+      Assert.IsFalse(message.HasOptionalInt32);
+      Assert.IsFalse(message.HasOptionalInt64);
+      Assert.IsFalse(message.HasOptionalUint32);
+      Assert.IsFalse(message.HasOptionalUint64);
+      Assert.IsFalse(message.HasOptionalSint32);
+      Assert.IsFalse(message.HasOptionalSint64);
+      Assert.IsFalse(message.HasOptionalFixed32);
+      Assert.IsFalse(message.HasOptionalFixed64);
+      Assert.IsFalse(message.HasOptionalSfixed32);
+      Assert.IsFalse(message.HasOptionalSfixed64);
+      Assert.IsFalse(message.HasOptionalFloat);
+      Assert.IsFalse(message.HasOptionalDouble);
+      Assert.IsFalse(message.HasOptionalBool);
+      Assert.IsFalse(message.HasOptionalString);
+      Assert.IsFalse(message.HasOptionalBytes);
+
+      Assert.IsFalse(message.HasOptionalGroup);
+      Assert.IsFalse(message.HasOptionalNestedMessage);
+      Assert.IsFalse(message.HasOptionalForeignMessage);
+      Assert.IsFalse(message.HasOptionalImportMessage);
+
+      Assert.IsFalse(message.HasOptionalNestedEnum);
+      Assert.IsFalse(message.HasOptionalForeignEnum);
+      Assert.IsFalse(message.HasOptionalImportEnum);
+
+      Assert.IsFalse(message.HasOptionalStringPiece);
+      Assert.IsFalse(message.HasOptionalCord);
+
+      // Optional fields without defaults are set to zero or something like it.
+      Assert.AreEqual(0, message.OptionalInt32);
+      Assert.AreEqual(0, message.OptionalInt64);
+      Assert.AreEqual(0, message.OptionalUint32);
+      Assert.AreEqual(0, message.OptionalUint64);
+      Assert.AreEqual(0, message.OptionalSint32);
+      Assert.AreEqual(0, message.OptionalSint64);
+      Assert.AreEqual(0, message.OptionalFixed32);
+      Assert.AreEqual(0, message.OptionalFixed64);
+      Assert.AreEqual(0, message.OptionalSfixed32);
+      Assert.AreEqual(0, message.OptionalSfixed64);
+      Assert.AreEqual(0, message.OptionalFloat);
+      Assert.AreEqual(0, message.OptionalDouble);
+      Assert.AreEqual(false, message.OptionalBool);
+      Assert.AreEqual("", message.OptionalString);
+      Assert.AreEqual(ByteString.Empty, message.OptionalBytes);
+
+      // Embedded messages should also be clear.
+      Assert.IsFalse(message.OptionalGroup.HasA);
+      Assert.IsFalse(message.OptionalNestedMessage.HasBb);
+      Assert.IsFalse(message.OptionalForeignMessage.HasC);
+      Assert.IsFalse(message.OptionalImportMessage.HasD);
+
+      Assert.AreEqual(0, message.OptionalGroup.A);
+      Assert.AreEqual(0, message.OptionalNestedMessage.Bb);
+      Assert.AreEqual(0, message.OptionalForeignMessage.C);
+      Assert.AreEqual(0, message.OptionalImportMessage.D);
+
+      // Enums without defaults are set to the first value in the enum.
+      Assert.AreEqual(TestAllTypes.Types.NestedEnum.FOO, message.OptionalNestedEnum);
+      Assert.AreEqual(ForeignEnum.FOREIGN_FOO, message.OptionalForeignEnum);
+      Assert.AreEqual(ImportEnum.IMPORT_FOO, message.OptionalImportEnum);
+
+      Assert.AreEqual("", message.OptionalStringPiece);
+      Assert.AreEqual("", message.OptionalCord);
+
+      // Repeated fields are empty.
+      Assert.AreEqual(0, message.RepeatedInt32Count);
+      Assert.AreEqual(0, message.RepeatedInt64Count);
+      Assert.AreEqual(0, message.RepeatedUint32Count);
+      Assert.AreEqual(0, message.RepeatedUint64Count);
+      Assert.AreEqual(0, message.RepeatedSint32Count);
+      Assert.AreEqual(0, message.RepeatedSint64Count);
+      Assert.AreEqual(0, message.RepeatedFixed32Count);
+      Assert.AreEqual(0, message.RepeatedFixed64Count);
+      Assert.AreEqual(0, message.RepeatedSfixed32Count);
+      Assert.AreEqual(0, message.RepeatedSfixed64Count);
+      Assert.AreEqual(0, message.RepeatedFloatCount);
+      Assert.AreEqual(0, message.RepeatedDoubleCount);
+      Assert.AreEqual(0, message.RepeatedBoolCount);
+      Assert.AreEqual(0, message.RepeatedStringCount);
+      Assert.AreEqual(0, message.RepeatedBytesCount);
+
+      Assert.AreEqual(0, message.RepeatedGroupCount);
+      Assert.AreEqual(0, message.RepeatedNestedMessageCount);
+      Assert.AreEqual(0, message.RepeatedForeignMessageCount);
+      Assert.AreEqual(0, message.RepeatedImportMessageCount);
+      Assert.AreEqual(0, message.RepeatedNestedEnumCount);
+      Assert.AreEqual(0, message.RepeatedForeignEnumCount);
+      Assert.AreEqual(0, message.RepeatedImportEnumCount);
+
+      Assert.AreEqual(0, message.RepeatedStringPieceCount);
+      Assert.AreEqual(0, message.RepeatedCordCount);
+
+      // HasBlah() should also be false for all default fields.
+      Assert.IsFalse(message.HasDefaultInt32);
+      Assert.IsFalse(message.HasDefaultInt64);
+      Assert.IsFalse(message.HasDefaultUint32);
+      Assert.IsFalse(message.HasDefaultUint64);
+      Assert.IsFalse(message.HasDefaultSint32);
+      Assert.IsFalse(message.HasDefaultSint64);
+      Assert.IsFalse(message.HasDefaultFixed32);
+      Assert.IsFalse(message.HasDefaultFixed64);
+      Assert.IsFalse(message.HasDefaultSfixed32);
+      Assert.IsFalse(message.HasDefaultSfixed64);
+      Assert.IsFalse(message.HasDefaultFloat);
+      Assert.IsFalse(message.HasDefaultDouble);
+      Assert.IsFalse(message.HasDefaultBool);
+      Assert.IsFalse(message.HasDefaultString);
+      Assert.IsFalse(message.HasDefaultBytes);
+
+      Assert.IsFalse(message.HasDefaultNestedEnum);
+      Assert.IsFalse(message.HasDefaultForeignEnum);
+      Assert.IsFalse(message.HasDefaultImportEnum);
+
+      Assert.IsFalse(message.HasDefaultStringPiece);
+      Assert.IsFalse(message.HasDefaultCord);
+
+      // Fields with defaults have their default values (duh).
+      Assert.AreEqual(41, message.DefaultInt32);
+      Assert.AreEqual(42, message.DefaultInt64);
+      Assert.AreEqual(43, message.DefaultUint32);
+      Assert.AreEqual(44, message.DefaultUint64);
+      Assert.AreEqual(-45, message.DefaultSint32);
+      Assert.AreEqual(46, message.DefaultSint64);
+      Assert.AreEqual(47, message.DefaultFixed32);
+      Assert.AreEqual(48, message.DefaultFixed64);
+      Assert.AreEqual(49, message.DefaultSfixed32);
+      Assert.AreEqual(-50, message.DefaultSfixed64);
+      Assert.AreEqual(51.5, message.DefaultFloat, 0.0);
+      Assert.AreEqual(52e3, message.DefaultDouble, 0.0);
+      Assert.AreEqual(true, message.DefaultBool);
+      Assert.AreEqual("hello", message.DefaultString);
+      Assert.AreEqual(ToBytes("world"), message.DefaultBytes);
+
+      Assert.AreEqual(TestAllTypes.Types.NestedEnum.BAR, message.DefaultNestedEnum);
+      Assert.AreEqual(ForeignEnum.FOREIGN_BAR, message.DefaultForeignEnum);
+      Assert.AreEqual(ImportEnum.IMPORT_BAR, message.DefaultImportEnum);
+
+      Assert.AreEqual("abc", message.DefaultStringPiece);
+      Assert.AreEqual("123", message.DefaultCord);
+    }
+
+    /// <summary>
+    /// Get a TestAllExtensions with all fields set as they would be by
+    /// SetAllExtensions(TestAllExtensions.Builder).
+    /// </summary>
+    internal static TestAllExtensions GetAllExtensionsSet() {
+      TestAllExtensions.Builder builder = TestAllExtensions.CreateBuilder();
+      SetAllExtensions(builder);
+      return builder.Build();
+    }
+
+    /// <summary>
+    /// Sets every field of the specified builder to the values expected by
+    /// AssertAllExtensionsSet.
+    /// </summary>
+    internal static void SetAllExtensions(TestAllExtensions.Builder message) {
+      message.SetExtension(UnitTestProtoFile.OptionalInt32Extension, 101);
+      message.SetExtension(UnitTestProtoFile.OptionalInt64Extension, 102L);
+      message.SetExtension(UnitTestProtoFile.OptionalUint32Extension, 103U);
+      message.SetExtension(UnitTestProtoFile.OptionalUint64Extension, 104UL);
+      message.SetExtension(UnitTestProtoFile.OptionalSint32Extension, 105);
+      message.SetExtension(UnitTestProtoFile.OptionalSint64Extension, 106L);
+      message.SetExtension(UnitTestProtoFile.OptionalFixed32Extension, 107U);
+      message.SetExtension(UnitTestProtoFile.OptionalFixed64Extension, 108UL);
+      message.SetExtension(UnitTestProtoFile.OptionalSfixed32Extension, 109);
+      message.SetExtension(UnitTestProtoFile.OptionalSfixed64Extension, 110L);
+      message.SetExtension(UnitTestProtoFile.OptionalFloatExtension, 111F);
+      message.SetExtension(UnitTestProtoFile.OptionalDoubleExtension, 112D);
+      message.SetExtension(UnitTestProtoFile.OptionalBoolExtension, true);
+      message.SetExtension(UnitTestProtoFile.OptionalStringExtension, "115");
+      message.SetExtension(UnitTestProtoFile.OptionalBytesExtension, ToBytes("116"));
+
+      message.SetExtension(UnitTestProtoFile.OptionalGroupExtension, OptionalGroup_extension.CreateBuilder().SetA(117).Build());
+      message.SetExtension(UnitTestProtoFile.OptionalNestedMessageExtension, TestAllTypes.Types.NestedMessage.CreateBuilder().SetBb(118).Build());
+      message.SetExtension(UnitTestProtoFile.OptionalForeignMessageExtension, ForeignMessage.CreateBuilder().SetC(119).Build());
+      message.SetExtension(UnitTestProtoFile.OptionalImportMessageExtension, ImportMessage.CreateBuilder().SetD(120).Build());
+
+      message.SetExtension(UnitTestProtoFile.OptionalNestedEnumExtension, TestAllTypes.Types.NestedEnum.BAZ);
+      message.SetExtension(UnitTestProtoFile.OptionalForeignEnumExtension, ForeignEnum.FOREIGN_BAZ);
+      message.SetExtension(UnitTestProtoFile.OptionalImportEnumExtension, ImportEnum.IMPORT_BAZ);
+
+      message.SetExtension(UnitTestProtoFile.OptionalStringPieceExtension, "124");
+      message.SetExtension(UnitTestProtoFile.OptionalCordExtension, "125");
+
+      // -----------------------------------------------------------------
+
+      message.AddExtension(UnitTestProtoFile.RepeatedInt32Extension, 201);
+      message.AddExtension(UnitTestProtoFile.RepeatedInt64Extension, 202L);
+      message.AddExtension(UnitTestProtoFile.RepeatedUint32Extension, 203U);
+      message.AddExtension(UnitTestProtoFile.RepeatedUint64Extension, 204UL);
+      message.AddExtension(UnitTestProtoFile.RepeatedSint32Extension, 205);
+      message.AddExtension(UnitTestProtoFile.RepeatedSint64Extension, 206L);
+      message.AddExtension(UnitTestProtoFile.RepeatedFixed32Extension, 207U);
+      message.AddExtension(UnitTestProtoFile.RepeatedFixed64Extension, 208UL);
+      message.AddExtension(UnitTestProtoFile.RepeatedSfixed32Extension, 209);
+      message.AddExtension(UnitTestProtoFile.RepeatedSfixed64Extension, 210L);
+      message.AddExtension(UnitTestProtoFile.RepeatedFloatExtension, 211F);
+      message.AddExtension(UnitTestProtoFile.RepeatedDoubleExtension, 212D);
+      message.AddExtension(UnitTestProtoFile.RepeatedBoolExtension, true);
+      message.AddExtension(UnitTestProtoFile.RepeatedStringExtension, "215");
+      message.AddExtension(UnitTestProtoFile.RepeatedBytesExtension, ToBytes("216"));
+
+      message.AddExtension(UnitTestProtoFile.RepeatedGroupExtension, RepeatedGroup_extension.CreateBuilder().SetA(217).Build());
+      message.AddExtension(UnitTestProtoFile.RepeatedNestedMessageExtension, TestAllTypes.Types.NestedMessage.CreateBuilder().SetBb(218).Build());
+      message.AddExtension(UnitTestProtoFile.RepeatedForeignMessageExtension, ForeignMessage.CreateBuilder().SetC(219).Build());
+      message.AddExtension(UnitTestProtoFile.RepeatedImportMessageExtension, ImportMessage.CreateBuilder().SetD(220).Build());
+
+      message.AddExtension(UnitTestProtoFile.RepeatedNestedEnumExtension, TestAllTypes.Types.NestedEnum.BAR);
+      message.AddExtension(UnitTestProtoFile.RepeatedForeignEnumExtension, ForeignEnum.FOREIGN_BAR);
+      message.AddExtension(UnitTestProtoFile.RepeatedImportEnumExtension, ImportEnum.IMPORT_BAR);
+
+      message.AddExtension(UnitTestProtoFile.RepeatedStringPieceExtension, "224");
+      message.AddExtension(UnitTestProtoFile.RepeatedCordExtension, "225");
+
+      // Add a second one of each field.
+      message.AddExtension(UnitTestProtoFile.RepeatedInt32Extension, 301);
+      message.AddExtension(UnitTestProtoFile.RepeatedInt64Extension, 302L);
+      message.AddExtension(UnitTestProtoFile.RepeatedUint32Extension, 303U);
+      message.AddExtension(UnitTestProtoFile.RepeatedUint64Extension, 304UL);
+      message.AddExtension(UnitTestProtoFile.RepeatedSint32Extension, 305);
+      message.AddExtension(UnitTestProtoFile.RepeatedSint64Extension, 306L);
+      message.AddExtension(UnitTestProtoFile.RepeatedFixed32Extension, 307U);
+      message.AddExtension(UnitTestProtoFile.RepeatedFixed64Extension, 308UL);
+      message.AddExtension(UnitTestProtoFile.RepeatedSfixed32Extension, 309);
+      message.AddExtension(UnitTestProtoFile.RepeatedSfixed64Extension, 310L);
+      message.AddExtension(UnitTestProtoFile.RepeatedFloatExtension, 311F);
+      message.AddExtension(UnitTestProtoFile.RepeatedDoubleExtension, 312D);
+      message.AddExtension(UnitTestProtoFile.RepeatedBoolExtension, false);
+      message.AddExtension(UnitTestProtoFile.RepeatedStringExtension, "315");
+      message.AddExtension(UnitTestProtoFile.RepeatedBytesExtension, ToBytes("316"));
+
+      message.AddExtension(UnitTestProtoFile.RepeatedGroupExtension, RepeatedGroup_extension.CreateBuilder().SetA(317).Build());
+      message.AddExtension(UnitTestProtoFile.RepeatedNestedMessageExtension, TestAllTypes.Types.NestedMessage.CreateBuilder().SetBb(318).Build());
+      message.AddExtension(UnitTestProtoFile.RepeatedForeignMessageExtension, ForeignMessage.CreateBuilder().SetC(319).Build());
+      message.AddExtension(UnitTestProtoFile.RepeatedImportMessageExtension, ImportMessage.CreateBuilder().SetD(320).Build());
+
+      message.AddExtension(UnitTestProtoFile.RepeatedNestedEnumExtension, TestAllTypes.Types.NestedEnum.BAZ);
+      message.AddExtension(UnitTestProtoFile.RepeatedForeignEnumExtension, ForeignEnum.FOREIGN_BAZ);
+      message.AddExtension(UnitTestProtoFile.RepeatedImportEnumExtension, ImportEnum.IMPORT_BAZ);
+
+      message.AddExtension(UnitTestProtoFile.RepeatedStringPieceExtension, "324");
+      message.AddExtension(UnitTestProtoFile.RepeatedCordExtension, "325");
+
+      // -----------------------------------------------------------------
+
+      message.SetExtension(UnitTestProtoFile.DefaultInt32Extension, 401);
+      message.SetExtension(UnitTestProtoFile.DefaultInt64Extension, 402L);
+      message.SetExtension(UnitTestProtoFile.DefaultUint32Extension, 403U);
+      message.SetExtension(UnitTestProtoFile.DefaultUint64Extension, 404UL);
+      message.SetExtension(UnitTestProtoFile.DefaultSint32Extension, 405);
+      message.SetExtension(UnitTestProtoFile.DefaultSint64Extension, 406L);
+      message.SetExtension(UnitTestProtoFile.DefaultFixed32Extension, 407U);
+      message.SetExtension(UnitTestProtoFile.DefaultFixed64Extension, 408UL);
+      message.SetExtension(UnitTestProtoFile.DefaultSfixed32Extension, 409);
+      message.SetExtension(UnitTestProtoFile.DefaultSfixed64Extension, 410L);
+      message.SetExtension(UnitTestProtoFile.DefaultFloatExtension, 411F);
+      message.SetExtension(UnitTestProtoFile.DefaultDoubleExtension, 412D);
+      message.SetExtension(UnitTestProtoFile.DefaultBoolExtension, false);
+      message.SetExtension(UnitTestProtoFile.DefaultStringExtension, "415");
+      message.SetExtension(UnitTestProtoFile.DefaultBytesExtension, ToBytes("416"));
+
+      message.SetExtension(UnitTestProtoFile.DefaultNestedEnumExtension, TestAllTypes.Types.NestedEnum.FOO);
+      message.SetExtension(UnitTestProtoFile.DefaultForeignEnumExtension, ForeignEnum.FOREIGN_FOO);
+      message.SetExtension(UnitTestProtoFile.DefaultImportEnumExtension, ImportEnum.IMPORT_FOO);
+
+      message.SetExtension(UnitTestProtoFile.DefaultStringPieceExtension, "424");
+      message.SetExtension(UnitTestProtoFile.DefaultCordExtension, "425");
+    }
   }
 }
diff --git a/csharp/ProtocolBuffers/AbstractBuilder.cs b/csharp/ProtocolBuffers/AbstractBuilder.cs
index 256975e9..d65c0911 100644
--- a/csharp/ProtocolBuffers/AbstractBuilder.cs
+++ b/csharp/ProtocolBuffers/AbstractBuilder.cs
@@ -8,6 +8,7 @@ using System.IO;
 namespace Google.ProtocolBuffers {
   /// <summary>
   /// Implementation of the non-generic IMessage interface as far as possible.
+  /// TODO(jonskeet): Make this generic, to avoid so much casting in DynamicMessage.
   /// </summary>
   public abstract class AbstractBuilder : IBuilder {
     #region Unimplemented members of IBuilder
@@ -57,7 +58,7 @@ namespace Google.ProtocolBuffers {
     }
     #endregion
 
-    public IBuilder Clear() {
+    public virtual IBuilder Clear() {
       foreach(FieldDescriptor field in AllFields.Keys) {
         ClearFieldImpl(field);
       }
@@ -168,5 +169,15 @@ namespace Google.ProtocolBuffers {
     }
 
     public abstract UnknownFieldSet UnknownFields { get; set; }
+    
+    public IBuilder SetField(FieldDescriptor field, object value) {
+      this[field] = value;
+      return this;
+    }
+
+    public IBuilder SetRepeatedField(FieldDescriptor field, int index, object value) {
+      this[field, index] = value;
+      return this;
+    }
   }
 }
diff --git a/csharp/ProtocolBuffers/AbstractMessage.cs b/csharp/ProtocolBuffers/AbstractMessage.cs
index 9f855a45..6dfcc46d 100644
--- a/csharp/ProtocolBuffers/AbstractMessage.cs
+++ b/csharp/ProtocolBuffers/AbstractMessage.cs
@@ -16,6 +16,7 @@
 using System.Collections;
 using System.Collections.Generic;
 using System.IO;
+using Google.ProtocolBuffers.Collections;
 using Google.ProtocolBuffers.Descriptors;
 
 namespace Google.ProtocolBuffers {
@@ -171,15 +172,13 @@ namespace Google.ProtocolBuffers {
       if (otherMessage == null || otherMessage.DescriptorForType != DescriptorForType) {
         return false;
       }
-      // TODO(jonskeet): Check that dictionaries support equality appropriately
-      // (I suspect they don't!)
-      return AllFields.Equals(otherMessage.AllFields);
+      return Dictionaries.Equals(AllFields, otherMessage.AllFields);
     }
 
     public override int GetHashCode() {
       int hash = 41;
       hash = (19 * hash) + DescriptorForType.GetHashCode();
-      hash = (53 * hash) + AllFields.GetHashCode();
+      hash = (53 * hash) + Dictionaries.GetHashCode(AllFields);
       return hash;
     }
   }
diff --git a/csharp/ProtocolBuffers/Collections/Dictionaries.cs b/csharp/ProtocolBuffers/Collections/Dictionaries.cs
index fb0ebdd2..640b6597 100644
--- a/csharp/ProtocolBuffers/Collections/Dictionaries.cs
+++ b/csharp/ProtocolBuffers/Collections/Dictionaries.cs
@@ -1,6 +1,8 @@
 using System;
 using System.Collections.Generic;
 using System.Text;
+using System.Collections;
+using Google.ProtocolBuffers.Descriptors;
 
 namespace Google.ProtocolBuffers.Collections {
 
@@ -9,8 +11,85 @@ namespace Google.ProtocolBuffers.Collections {
   /// in the generic class.
   /// </summary>
   public static class Dictionaries {
+
+    /// <summary>
+    /// Compares two dictionaries for equality. Each value is compared with equality using Equals
+    /// for non-IEnumerable implementations, and using EnumerableEquals otherwise.
+    /// TODO(jonskeet): This is clearly pretty slow, and involves lots of boxing/unboxing...
+    /// </summary>
+    public static bool Equals<TKey, TValue>(IDictionary<TKey, TValue> left, IDictionary<TKey, TValue> right) {
+      if (left.Count != right.Count) {
+        return false;
+      }
+      foreach (KeyValuePair<TKey,TValue> leftEntry in left)
+      {
+        TValue rightValue;
+        if (!right.TryGetValue(leftEntry.Key, out rightValue)) {
+          return false;
+        }
+
+        IEnumerable leftEnumerable = leftEntry.Value as IEnumerable;
+        IEnumerable rightEnumerable = rightValue as IEnumerable;
+        if (leftEnumerable == null || rightEnumerable == null) {
+          if (!object.Equals(leftEntry.Value, rightValue)) {
+            return false;
+          }
+        } else {
+          IEnumerator leftEnumerator = leftEnumerable.GetEnumerator();
+          try {
+            foreach (object rightObject in rightEnumerable) {
+              if (!leftEnumerator.MoveNext()) {
+                return false;
+              }
+              if (!object.Equals(leftEnumerator.Current, rightObject)) {
+                return false;
+              }
+            }
+            if (leftEnumerator.MoveNext()) {
+              return false;
+            }
+          } finally {
+            if (leftEnumerator is IDisposable) {
+              ((IDisposable)leftEnumerator).Dispose();
+            }
+          }
+        }
+      }
+      return true;
+    }
+
     public static IDictionary<TKey, TValue> AsReadOnly<TKey, TValue> (IDictionary<TKey, TValue> dictionary) {
       return dictionary.IsReadOnly ? dictionary : new ReadOnlyDictionary<TKey, TValue>(dictionary);
     }
+
+    /// <summary>
+    /// Creates a hashcode for a dictionary by XORing the hashcodes of all the fields
+    /// and values. (By XORing, we avoid ordering issues.)
+    /// TODO(jonskeet): Currently XORs other stuff too, and assumes non-null values.
+    /// </summary>
+    public static int GetHashCode<TKey, TValue>(IDictionary<TKey, TValue> dictionary) {
+      int ret = 31;
+      foreach (KeyValuePair<TKey, TValue> entry in dictionary) {
+        int hash = entry.Key.GetHashCode() ^ GetDeepHashCode(entry.Value);
+        ret ^= hash;
+      }
+      return ret;
+    }
+
+    /// <summary>
+    /// Determines the hash of a value by either taking it directly or hashing all the elements
+    /// for IEnumerable implementations.
+    /// </summary>
+    private static int GetDeepHashCode(object value) {
+      IEnumerable iterable = value as IEnumerable;
+      if (iterable == null) {
+        return value.GetHashCode();
+      }
+      int hash = 29;
+      foreach (object element in iterable) {
+        hash = hash * 37 + element.GetHashCode();
+      }
+      return hash;
+    }
   }
 }
diff --git a/csharp/ProtocolBuffers/DescriptorProtos/DescriptorProtoFile.cs b/csharp/ProtocolBuffers/DescriptorProtos/DescriptorProtoFile.cs
index ed159229..14e1f177 100644
--- a/csharp/ProtocolBuffers/DescriptorProtos/DescriptorProtoFile.cs
+++ b/csharp/ProtocolBuffers/DescriptorProtos/DescriptorProtoFile.cs
@@ -161,7 +161,6 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
     #endregion
     
     #region Extensions
-    /**/
     #endregion
     
     #region Static variables
@@ -547,6 +546,10 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::FileDescriptorProto) {
           return MergeFrom((self::FileDescriptorProto) other);
@@ -1128,6 +1131,10 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
             return returnMe;
           }
           
+          protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+            return MergeFrom(data, extensionRegistry);
+          }
+          
           public override IBuilder MergeFrom(pb::IMessage other) {
             if (other is self::DescriptorProto.Types.ExtensionRange) {
               return MergeFrom((self::DescriptorProto.Types.ExtensionRange) other);
@@ -1459,6 +1466,10 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::DescriptorProto) {
           return MergeFrom((self::DescriptorProto) other);
@@ -2130,6 +2141,10 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::FieldDescriptorProto) {
           return MergeFrom((self::FieldDescriptorProto) other);
@@ -2582,6 +2597,10 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::EnumDescriptorProto) {
           return MergeFrom((self::EnumDescriptorProto) other);
@@ -2919,6 +2938,10 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::EnumValueDescriptorProto) {
           return MergeFrom((self::EnumValueDescriptorProto) other);
@@ -3231,6 +3254,10 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::ServiceDescriptorProto) {
           return MergeFrom((self::ServiceDescriptorProto) other);
@@ -3584,6 +3611,10 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::MethodDescriptorProto) {
           return MergeFrom((self::MethodDescriptorProto) other);
@@ -4022,6 +4053,10 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::FileOptions) {
           return MergeFrom((self::FileOptions) other);
@@ -4437,6 +4472,10 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::MessageOptions) {
           return MergeFrom((self::MessageOptions) other);
@@ -4664,6 +4703,10 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::FieldOptions) {
           return MergeFrom((self::FieldOptions) other);
@@ -4881,6 +4924,10 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::EnumOptions) {
           return MergeFrom((self::EnumOptions) other);
@@ -5041,6 +5088,10 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::EnumValueOptions) {
           return MergeFrom((self::EnumValueOptions) other);
@@ -5201,6 +5252,10 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::ServiceOptions) {
           return MergeFrom((self::ServiceOptions) other);
@@ -5361,6 +5416,10 @@ namespace Google.ProtocolBuffers.DescriptorProtos {
         return returnMe;
       }
       
+      protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
+        return MergeFrom(data, extensionRegistry);
+      }
+      
       public override IBuilder MergeFrom(pb::IMessage other) {
         if (other is self::MethodOptions) {
           return MergeFrom((self::MethodOptions) other);
diff --git a/csharp/ProtocolBuffers/Descriptors/EnumDescriptor.cs b/csharp/ProtocolBuffers/Descriptors/EnumDescriptor.cs
index 83807582..a28efc5f 100644
--- a/csharp/ProtocolBuffers/Descriptors/EnumDescriptor.cs
+++ b/csharp/ProtocolBuffers/Descriptors/EnumDescriptor.cs
@@ -43,7 +43,8 @@ namespace Google.ProtocolBuffers.Descriptors {
     /// Finds an enum value by number. If multiple enum values have the
     /// same number, this returns the first defined value with that number.
     /// </summary>
-    internal EnumValueDescriptor FindValueByNumber(int number) {
+    // TODO(jonskeet): Make internal and use InternalsVisibleTo?
+    public EnumValueDescriptor FindValueByNumber(int number) {
       return File.DescriptorPool.FindEnumValueByNumber(this, number);
     }
 
@@ -52,7 +53,8 @@ namespace Google.ProtocolBuffers.Descriptors {
     /// </summary>
     /// <param name="name">The unqualified name of the value (e.g. "FOO").</param>
     /// <returns>The value's descriptor, or null if not found.</returns>
-    internal EnumValueDescriptor FindValueByName(string name) {
+    // TODO(jonskeet): Make internal and use InternalsVisibleTo?
+    public EnumValueDescriptor FindValueByName(string name) {
       return File.DescriptorPool.FindSymbol<EnumValueDescriptor>(FullName + "." + name);
     }
   }
diff --git a/csharp/ProtocolBuffers/DynamicMessage.cs b/csharp/ProtocolBuffers/DynamicMessage.cs
index 8a18375c..5b22d38b 100644
--- a/csharp/ProtocolBuffers/DynamicMessage.cs
+++ b/csharp/ProtocolBuffers/DynamicMessage.cs
@@ -1,11 +1,381 @@
 using System;
 using System.Collections.Generic;
+using System.IO;
 using System.Text;
+using Google.ProtocolBuffers.Descriptors;
 
 namespace Google.ProtocolBuffers {
-  public class DynamicMessage {
-    internal static object GetDefaultInstance(Google.ProtocolBuffers.Descriptors.MessageDescriptor messageDescriptor) {
-      throw new NotImplementedException();
+  public class DynamicMessage : AbstractMessage {
+
+    private readonly MessageDescriptor type;
+    private readonly FieldSet fields;
+    private readonly UnknownFieldSet unknownFields;
+    private int memoizedSize = -1;
+
+    /// <summary>
+    /// Creates a DynamicMessage with the given FieldSet.
+    /// </summary>
+    /// <param name="type"></param>
+    /// <param name="fields"></param>
+    /// <param name="unknownFields"></param>
+    private DynamicMessage(MessageDescriptor type, FieldSet fields, UnknownFieldSet unknownFields) {
+      this.type = type;
+      this.fields = fields;
+      this.unknownFields = unknownFields;
+    }
+
+    /// <summary>
+    /// Returns a DynamicMessage representing the default instance of the given type.
+    /// </summary>
+    /// <param name="type"></param>
+    /// <returns></returns>
+    public static DynamicMessage GetDefaultInstance(MessageDescriptor type) {
+      return new DynamicMessage(type, FieldSet.DefaultInstance, UnknownFieldSet.DefaultInstance);
+    }
+
+    /// <summary>
+    /// Parses a message of the given type from the given stream.
+    /// </summary>
+    public static DynamicMessage ParseFrom(MessageDescriptor type, CodedInputStream input) {
+      IBuilder builder = CreateBuilder(type);
+      Builder dynamicBuilder = (Builder)builder.MergeFrom(input);
+      return dynamicBuilder.BuildParsed();
+
+    }
+
+    /// <summary>
+    /// Parse a message of the given type from the given stream and extension registry.
+    /// </summary>
+    /// <param name="type"></param>
+    /// <param name="input"></param>
+    /// <param name="extensionRegistry"></param>
+    /// <returns></returns>
+    public static DynamicMessage ParseFrom(MessageDescriptor type, CodedInputStream input, ExtensionRegistry extensionRegistry) {
+      IBuilder builder = CreateBuilder(type);
+      Builder dynamicBuilder = (Builder) builder.MergeFrom(input, extensionRegistry);
+      return dynamicBuilder.BuildParsed();
+    }
+
+    /// <summary>
+    /// Parses a message of the given type from the given stream.
+    /// </summary>
+    public static DynamicMessage ParseFrom(MessageDescriptor type, Stream input) {
+      IBuilder builder = CreateBuilder(type);
+      Builder dynamicBuilder = (Builder)builder.MergeFrom(input);
+      return dynamicBuilder.BuildParsed();
+    }
+
+    /// <summary>
+    /// Parse a message of the given type from the given stream and extension registry.
+    /// </summary>
+    /// <param name="type"></param>
+    /// <param name="input"></param>
+    /// <param name="extensionRegistry"></param>
+    /// <returns></returns>
+    public static DynamicMessage ParseFrom(MessageDescriptor type, Stream input, ExtensionRegistry extensionRegistry) {
+      IBuilder builder = CreateBuilder(type);
+      Builder dynamicBuilder = (Builder)builder.MergeFrom(input, extensionRegistry);
+      return dynamicBuilder.BuildParsed();
+    }
+
+    /// <summary>
+    /// Parse <paramref name="data"/> as a message of the given type and return it.
+    /// </summary>
+    public static DynamicMessage ParseFrom(MessageDescriptor type, ByteString data) {
+      IBuilder builder = CreateBuilder(type);
+      Builder dynamicBuilder = (Builder)builder.MergeFrom(data);
+      return dynamicBuilder.BuildParsed();
+    }
+
+    /// <summary>
+    /// Parse <paramref name="data"/> as a message of the given type and return it.
+    /// </summary>
+    public static DynamicMessage ParseFrom(MessageDescriptor type, ByteString data, ExtensionRegistry extensionRegistry) {
+      IBuilder builder = CreateBuilder(type);
+      Builder dynamicBuilder = (Builder)builder.MergeFrom(data, extensionRegistry);
+      return dynamicBuilder.BuildParsed();
+
+    }
+
+    /// <summary>
+    /// Parse <paramref name="data"/> as a message of the given type and return it.
+    /// </summary>
+    public static DynamicMessage ParseFrom(MessageDescriptor type, byte[] data) {
+      IBuilder builder = CreateBuilder(type);
+      Builder dynamicBuilder = (Builder)builder.MergeFrom(data);
+      return dynamicBuilder.BuildParsed();
+    }
+
+    /// <summary>
+    /// Parse <paramref name="data"/> as a message of the given type and return it.
+    /// </summary>
+    public static DynamicMessage ParseFrom(MessageDescriptor type, byte[] data, ExtensionRegistry extensionRegistry) {
+      IBuilder builder = CreateBuilder(type);
+      Builder dynamicBuilder = (Builder)builder.MergeFrom(data, extensionRegistry);
+      return dynamicBuilder.BuildParsed();
+    }
+
+    /// <summary>
+    /// Constructs a builder for the given type.
+    /// </summary>
+    public static Builder CreateBuilder(MessageDescriptor type) {
+      return new Builder(type);
+    }
+
+    /// <summary>
+    /// Constructs a builder for a message of the same type as <paramref name="prototype"/>,
+    /// and initializes it with the same contents.
+    /// </summary>
+    /// <param name="prototype"></param>
+    /// <returns></returns>
+    public static Builder CreateBuilder(IMessage prototype) {
+      return (Builder) new Builder(prototype.DescriptorForType).MergeFrom(prototype);
+    }
+
+    // -----------------------------------------------------------------
+    // Implementation of IMessage interface.
+
+    public override MessageDescriptor DescriptorForType {
+      get { return type; }
+    }
+
+    protected override IMessage DefaultInstanceForTypeImpl {
+      get { return GetDefaultInstance(type); }
+    }
+
+    public override IDictionary<FieldDescriptor, object> AllFields {
+      get { return fields.AllFields; }
+    }
+
+    public override bool HasField(FieldDescriptor field) {
+      VerifyContainingType(field);
+      return fields.HasField(field);
+    }
+
+    public override object this[FieldDescriptor field] {
+      get {
+        VerifyContainingType(field);
+        object result = fields[field];
+        if (result == null) {
+          result = GetDefaultInstance(field.MessageType);
+        }
+        return result;
+      }
+    }
+
+    public override int GetRepeatedFieldCount(FieldDescriptor field) {
+      VerifyContainingType(field);
+      return fields.GetRepeatedFieldCount(field);
+    }
+
+    public override object this[FieldDescriptor field, int index] {
+      get {
+        VerifyContainingType(field);
+        return fields[field, index];
+      }
+    }
+
+    public override UnknownFieldSet UnknownFields {
+      get { return unknownFields; }
+    }
+
+    public bool Initialized {
+      get { return fields.IsInitializedWithRespectTo(type); }
+    }
+
+    public override void WriteTo(CodedOutputStream output) {
+      fields.WriteTo(output);
+      if (type.Options.MessageSetWireFormat) {
+        unknownFields.WriteAsMessageSetTo(output);
+      } else {
+        unknownFields.WriteTo(output);
+      }
+    }
+
+    public override int SerializedSize {
+      get {
+        int size = memoizedSize;
+        if (size != -1) return size;
+
+        size = fields.SerializedSize;
+        if (type.Options.MessageSetWireFormat) {
+          size += unknownFields.SerializedSizeAsMessageSet;
+        } else {
+          size += unknownFields.SerializedSize;
+        }
+
+        memoizedSize = size;
+        return size;
+      }
+    }
+
+    protected override IBuilder CreateBuilderForTypeImpl() {
+      return new Builder(type);
+    }
+
+    /// <summary>
+    /// Verifies that the field is a field of this message.
+    /// </summary>
+    private void VerifyContainingType(FieldDescriptor field) {
+      if (field.ContainingType != type) {
+        throw new ArgumentException("FieldDescriptor does not match message type.");
+      }
+    }
+
+    public class Builder : AbstractBuilder {
+      private readonly MessageDescriptor type;
+      private FieldSet fields;
+      private UnknownFieldSet unknownFields;
+
+      internal Builder(MessageDescriptor type) {
+        this.type = type;
+        this.fields = FieldSet.CreateFieldSet();
+        this.unknownFields = UnknownFieldSet.DefaultInstance;
+      }
+
+      public override IBuilder Clear() {
+        fields.Clear();
+        return this;
+      }
+
+      public override IBuilder  MergeFrom(IMessage other) {
+        if (other.DescriptorForType != type) {
+          throw new ArgumentException("MergeFrom(IMessage) can only merge messages of the same type.");
+        }
+        fields.MergeFrom(other);
+        return this;
+      }
+
+      protected override IMessage BuildImpl() {
+   	    if (!Initialized) {
+          throw new UninitializedMessageException(new DynamicMessage(type, fields, unknownFields));
+        }
+        return BuildPartialImpl();
+      }
+
+      /// <summary>
+      /// Helper for DynamicMessage.ParseFrom() methods to call. Throws
+      /// InvalidProtocolBufferException 
+      /// </summary>
+      /// <returns></returns>
+      internal DynamicMessage BuildParsed() {
+        if (!Initialized) {
+          throw new UninitializedMessageException(new DynamicMessage(type, fields, unknownFields)).AsInvalidProtocolBufferException();
+        }
+        return (DynamicMessage) BuildPartialImpl();
+      }
+
+      protected override IMessage BuildPartialImpl() {
+        fields.MakeImmutable();
+        DynamicMessage result = new DynamicMessage(type, fields, unknownFields);
+        fields = null;
+        unknownFields = null;
+        return result;
+      }
+
+      protected override IBuilder CloneImpl() {
+        Builder result = new Builder(type);
+        result.fields.MergeFrom(fields);
+        return result;
+      }
+
+      public override bool Initialized {
+      	get { return fields.IsInitializedWithRespectTo(type); }
+      }
+
+      protected override IBuilder MergeFromImpl(CodedInputStream input, ExtensionRegistry extensionRegistry) {
+        UnknownFieldSet.Builder unknownFieldsBuilder = UnknownFieldSet.CreateBuilder(unknownFields);
+        FieldSet.MergeFrom(input, unknownFieldsBuilder, extensionRegistry, this);
+        unknownFields = unknownFieldsBuilder.Build();
+        return this;
+      }
+
+      public override MessageDescriptor DescriptorForType {
+        get { return type; }
+      }
+
+      protected override IMessage DefaultInstanceForTypeImpl {
+        get { return GetDefaultInstance(type); }
+      }
+
+      public override IDictionary<FieldDescriptor, object> AllFields {
+        get { return fields.AllFields; }
+      }
+
+      public override IBuilder CreateBuilderForField(FieldDescriptor field) {
+        VerifyContainingType(field);
+        if (field.MappedType != MappedType.Message) {
+          throw new ArgumentException("CreateBuilderForField is only valid for fields with message type.");
+        }
+        return new Builder(field.MessageType);        
+      }
+
+      public override bool HasField(FieldDescriptor field) {
+        VerifyContainingType(field);
+        return fields.HasField(field);
+      }
+
+      public override object this[FieldDescriptor field, int index] {
+        get {
+          VerifyContainingType(field);
+          return fields[field, index];
+        }
+        set {
+          VerifyContainingType(field);
+          fields[field, index] = value;
+        }
+      }
+
+      public override object this[FieldDescriptor field] {
+        get {
+          VerifyContainingType(field);
+          object result = fields[field];
+          if (result == null) {
+            result = GetDefaultInstance(field.MessageType);
+          }
+          return result;
+        }
+        set {
+          VerifyContainingType(field);
+          fields[field] = value;
+        }
+      }
+
+      protected override IBuilder ClearFieldImpl(FieldDescriptor field) {
+        VerifyContainingType(field);
+        fields.ClearField(field);
+        return this;
+      }
+
+      public override int GetRepeatedFieldCount(FieldDescriptor field) {
+        VerifyContainingType(field);
+        return fields.GetRepeatedFieldCount(field);
+      }
+
+      protected override IBuilder AddRepeatedFieldImpl(FieldDescriptor field, object value) {
+        VerifyContainingType(field);
+        fields.AddRepeatedField(field, value);
+        return this;
+      }
+
+      public override UnknownFieldSet UnknownFields {
+        get {
+          return unknownFields;
+        }
+        set {
+          unknownFields = value;
+        }
+      }
+
+      /// <summary>
+      /// Verifies that the field is a field of this message.
+      /// </summary>
+      /// <param name="field"></param>
+      private void VerifyContainingType(FieldDescriptor field) {
+        if (field.ContainingType != type) {
+          throw new ArgumentException("FieldDescriptor does not match message type.");
+        }
+      }
     }
   }
 }
diff --git a/csharp/ProtocolBuffers/ExtendableBuilder.cs b/csharp/ProtocolBuffers/ExtendableBuilder.cs
new file mode 100644
index 00000000..3f5a8162
--- /dev/null
+++ b/csharp/ProtocolBuffers/ExtendableBuilder.cs
@@ -0,0 +1,147 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using Google.ProtocolBuffers.Descriptors;
+
+namespace Google.ProtocolBuffers {
+  public abstract class ExtendableBuilder<TMessage, TBuilder> : GeneratedBuilder<TMessage, TBuilder>
+    where TMessage : ExtendableMessage<TMessage, TBuilder>
+    where TBuilder : GeneratedBuilder<TMessage, TBuilder> {
+
+    protected ExtendableBuilder() {}
+
+    /// <summary>
+    /// Checks if a singular extension is present
+    /// </summary>
+    public bool HasExtension<TExtension>(GeneratedExtensionBase<TMessage, TExtension> extension) {
+      return MessageBeingBuilt.HasExtension(extension);
+    }
+
+    /// <summary>
+    /// Returns the number of elements in a repeated extension.
+    /// </summary>
+    public int GetExtensionCount<TExtension>(GeneratedExtensionBase<TMessage, IList<TExtension>> extension) {
+      return MessageBeingBuilt.GetExtensionCount(extension);
+    }
+
+    /// <summary>
+    /// Returns the value of an extension.
+    /// </summary>
+    public TExtension GetExtension<TExtension>(GeneratedExtensionBase<TMessage, TExtension> extension) {
+      return MessageBeingBuilt.GetExtension(extension);
+    }
+
+    /// <summary>
+    /// Returns one element of a repeated extension.
+    /// </summary>
+    public TExtension GetExtension<TExtension>(GeneratedExtensionBase<TMessage, IList<TExtension>> extension, int index) {
+      return MessageBeingBuilt.GetExtension(extension, index);
+    }
+
+    /// <summary>
+    /// Sets the value of an extension.
+    /// </summary>
+    public ExtendableBuilder<TMessage, TBuilder> SetExtension<TExtension>(GeneratedExtensionBase<TMessage, TExtension> extension, TExtension value) {
+      ExtendableMessage<TMessage, TBuilder> message = MessageBeingBuilt;
+      message.VerifyExtensionContainingType(extension);
+      message.Extensions[extension.Descriptor] = extension.ToReflectionType(value);
+      return this;
+    }
+
+    /// <summary>
+    /// Sets the value of one element of a repeated extension.
+    /// </summary>
+    public ExtendableBuilder<TMessage, TBuilder> SetExtension<TExtension>(
+        GeneratedExtensionBase<TMessage, IList<TExtension>> extension, int index, Type value) {
+      ExtendableMessage<TMessage, TBuilder> message = MessageBeingBuilt;
+      message.VerifyExtensionContainingType(extension);
+      message.Extensions[extension.Descriptor, index] = extension.SingularToReflectionType(value);
+      return this;
+    }
+
+    /// <summary>
+    /// Appends a value to a repeated extension.
+    /// </summary>
+    public ExtendableBuilder<TMessage, TBuilder> AddExtension<TExtension>(
+        GeneratedExtensionBase<TMessage, IList<TExtension>> extension, TExtension value) {
+      ExtendableMessage<TMessage, TBuilder> message = MessageBeingBuilt;
+      message.VerifyExtensionContainingType(extension);
+      message.Extensions.AddRepeatedField(extension.Descriptor, extension.SingularToReflectionType(value));
+      return this;
+    }
+
+    /// <summary>
+    /// Clears an extension.
+    /// </summary>
+    public ExtendableBuilder<TMessage, TBuilder> ClearExtension<TExtension>(
+        GeneratedExtensionBase<TMessage, TExtension> extension) {
+      ExtendableMessage<TMessage, TBuilder> message = MessageBeingBuilt;
+      message.VerifyExtensionContainingType(extension);
+      message.Extensions.ClearField(extension.Descriptor);
+      return this;
+    }
+
+    /// <summary>
+    /// Called by subclasses to parse an unknown field or an extension.
+    /// </summary>
+    /// <returns>true unless the tag is an end-group tag</returns>
+    protected override bool ParseUnknownField(CodedInputStream input, UnknownFieldSet.Builder unknownFields,
+        ExtensionRegistry extensionRegistry, uint tag) {
+      return FieldSet.MergeFieldFrom(input, unknownFields, extensionRegistry, this, tag);
+    }
+
+    // ---------------------------------------------------------------
+    // Reflection
+
+
+    public override object this[FieldDescriptor field, int index] {
+      set {
+        if (field.IsExtension) {
+          ExtendableMessage<TMessage, TBuilder> message = MessageBeingBuilt;
+          // TODO(jonskeet): Figure out how to call this!
+          // message.VerifyExtensionContainingType(field);
+          message.Extensions[field, index] = value;
+        } else {
+          base[field, index] = value;
+        }
+      }
+    }
+
+    
+    public override object this[FieldDescriptor field] {
+      set {
+        if (field.IsExtension) {
+          ExtendableMessage<TMessage, TBuilder> message = MessageBeingBuilt;
+          // TODO(jonskeet): Figure out how to call this!
+          // message.VerifyExtensionContainingType(field);
+          message.Extensions[field] = value;
+        } else {
+          base[field] = value;
+        }
+        InternalFieldAccessors[field].SetValue(this, value);
+      }
+    }
+
+    public override IBuilder<TMessage> ClearField(FieldDescriptor field) {
+      if (field.IsExtension) {
+        ExtendableMessage<TMessage, TBuilder> message = MessageBeingBuilt;
+        message.VerifyContainingType(field);
+        message.Extensions.ClearField(field);
+        return this;
+      } else {
+        return base.ClearField(field);
+      }
+    }
+
+    public override IBuilder<TMessage> AddRepeatedField(FieldDescriptor field, object value) {
+      if (field.IsExtension) {
+        ExtendableMessage<TMessage, TBuilder> message = MessageBeingBuilt;
+        message.VerifyContainingType(field); 
+        message.Extensions.AddRepeatedField(field, value);
+        return this;
+      } else {
+        return base.AddRepeatedField(field, value);
+      }
+    }
+  }
+}
diff --git a/csharp/ProtocolBuffers/ExtendableMessage.cs b/csharp/ProtocolBuffers/ExtendableMessage.cs
index 872b15b6..0a2d0317 100644
--- a/csharp/ProtocolBuffers/ExtendableMessage.cs
+++ b/csharp/ProtocolBuffers/ExtendableMessage.cs
@@ -13,9 +13,16 @@ namespace Google.ProtocolBuffers {
     private readonly FieldSet extensions = FieldSet.CreateFieldSet();
 
     /// <summary>
+    /// Access for the builder.
+    /// </summary>
+    internal FieldSet Extensions {
+      get { return extensions; }
+    }
+
+    /// <summary>
     /// Checks if a singular extension is present.
     /// </summary>
-    public bool HasExtension(GeneratedExtensionBase<TMessage, TBuilder> extension) {
+    public bool HasExtension<TExtension>(GeneratedExtensionBase<TMessage, TExtension> extension) {
       return extensions.HasField(extension.Descriptor);
     }
 
@@ -111,7 +118,7 @@ namespace Google.ProtocolBuffers {
       }
     }
   
-    private void VerifyContainingType(FieldDescriptor field) {
+    internal void VerifyContainingType(FieldDescriptor field) {
       if (field.ContainingType != DescriptorForType) {
         throw new ArgumentException("FieldDescriptor does not match message type.");
       }
@@ -161,5 +168,13 @@ namespace Google.ProtocolBuffers {
     protected int ExtensionsSerializedSize {
       get { return extensions.SerializedSize; }
     }
+
+    internal void VerifyExtensionContainingType<TExtension>(GeneratedExtensionBase<TMessage, TExtension> extension) {
+      if (extension.Descriptor.ContainingType != DescriptorForType) {
+        // This can only happen if someone uses unchecked operations.
+        throw new ArgumentException("Extension is for type \"" + extension.Descriptor.ContainingType.FullName
+          + "\" which does not match message type \"" + DescriptorForType.FullName + "\".");
+      }
+    }
   }
 }
diff --git a/csharp/ProtocolBuffers/FieldAccess/RepeatedPrimitiveAccessor.cs b/csharp/ProtocolBuffers/FieldAccess/RepeatedPrimitiveAccessor.cs
index 11611b64..15ea6253 100644
--- a/csharp/ProtocolBuffers/FieldAccess/RepeatedPrimitiveAccessor.cs
+++ b/csharp/ProtocolBuffers/FieldAccess/RepeatedPrimitiveAccessor.cs
@@ -73,7 +73,7 @@ namespace Google.ProtocolBuffers.FieldAccess {
     }
 
     public int GetRepeatedCount(IMessage message) {
-      return (int) countProperty.GetValue(null, null);
+      return (int) countProperty.GetValue(message, null);
     }
 
     public virtual object GetRepeatedValue(IMessage message, int index) {
diff --git a/csharp/ProtocolBuffers/GeneratedBuilder.cs b/csharp/ProtocolBuffers/GeneratedBuilder.cs
index 4b3567d0..154aa05f 100644
--- a/csharp/ProtocolBuffers/GeneratedBuilder.cs
+++ b/csharp/ProtocolBuffers/GeneratedBuilder.cs
@@ -65,7 +65,7 @@ namespace Google.ProtocolBuffers {
     /// Called by derived classes to parse an unknown field.
     /// </summary>
     /// <returns>true unless the tag is an end-group tag</returns>
-    protected bool ParseUnknownField(CodedInputStream input, UnknownFieldSet.Builder unknownFields,
+    protected virtual bool ParseUnknownField(CodedInputStream input, UnknownFieldSet.Builder unknownFields,
                                      ExtensionRegistry extensionRegistry, uint tag) {
       return unknownFields.MergeFieldFrom(tag, input);
     }
@@ -115,7 +115,7 @@ namespace Google.ProtocolBuffers {
       return AddRepeatedField(field, value);
     }
 
-    public IBuilder<TMessage> ClearField(FieldDescriptor field) {
+    public virtual IBuilder<TMessage> ClearField(FieldDescriptor field) {
       InternalFieldAccessors[field].Clear(this);
       return this;
     }
@@ -155,7 +155,7 @@ namespace Google.ProtocolBuffers {
       return this;
     }
 
-    public IBuilder<TMessage> AddRepeatedField(FieldDescriptor field, object value) {
+    public virtual IBuilder<TMessage> AddRepeatedField(FieldDescriptor field, object value) {
       InternalFieldAccessors[field].AddRepeated(this, value);
       return this;
     }
@@ -190,19 +190,21 @@ namespace Google.ProtocolBuffers {
       return this;
     }
 
+    /// <summary>
+    /// Overridden when optimized for speed.
+    /// </summary>
     public virtual IBuilder<TMessage> MergeFrom(CodedInputStream input) {
       ((IBuilder)this).MergeFrom(input);
       return this;
     }
 
+    /// <summary>
+    /// Overridden when optimized for speed.
+    /// </summary>
     public virtual IBuilder<TMessage> MergeFrom(CodedInputStream input, ExtensionRegistry extensionRegistry) {
       ((IBuilder)this).MergeFrom(input, extensionRegistry);
       return this;
     }
-
-    protected override IBuilder MergeFromImpl(CodedInputStream data, ExtensionRegistry extensionRegistry) {
-      return MergeFrom(data, extensionRegistry);
-    }
     
     /// <summary>
     /// Like Build(), but will wrap UninitializedMessageException in
diff --git a/csharp/ProtocolBuffers/GeneratedExtensionBase.cs b/csharp/ProtocolBuffers/GeneratedExtensionBase.cs
index 40118388..2ab6d7a6 100644
--- a/csharp/ProtocolBuffers/GeneratedExtensionBase.cs
+++ b/csharp/ProtocolBuffers/GeneratedExtensionBase.cs
@@ -1,4 +1,5 @@
 using System;
+using System.Collections;
 using System.Collections.Generic;
 using System.Reflection;
 using System.Text;
@@ -33,14 +34,14 @@ namespace Google.ProtocolBuffers {
     private readonly FieldDescriptor descriptor;
     private readonly IMessage messageDefaultInstance;
 
-    protected GeneratedExtensionBase(FieldDescriptor descriptor) {
+    protected GeneratedExtensionBase(FieldDescriptor descriptor, Type singularExtensionType) {
       if (!descriptor.IsExtension) {
         throw new ArgumentException("GeneratedExtension given a regular (non-extension) field.");
       }
 
       this.descriptor = descriptor;
       if (descriptor.MappedType == MappedType.Message) {
-        PropertyInfo defaultInstanceProperty = typeof(TExtension)
+        PropertyInfo defaultInstanceProperty = singularExtensionType
             .GetProperty("DefaultInstance", BindingFlags.Static | BindingFlags.Public);
         if (defaultInstanceProperty == null) {
           throw new ArgumentException("No public static DefaultInstance property for type " + typeof(TExtension).Name);
@@ -83,6 +84,38 @@ namespace Google.ProtocolBuffers {
       }
     }
 
+    /// <summary>
+    /// Converts from the type used by the native accessors to the type
+    /// used by reflection accessors. For example, the reflection accessors
+    /// for enums use EnumValueDescriptors but the native accessors use
+    /// the generated enum type.
+    /// </summary>
+    public object ToReflectionType(object value) {
+      if (descriptor.IsRepeated) {
+        if (descriptor.MappedType == MappedType.Enum) {
+          // Must convert the whole list.
+          IList<object> result = new List<object>();
+          foreach (object element in (IEnumerable) value) {
+            result.Add(SingularToReflectionType(element));
+          }
+          return result;
+        } else {
+          return value;
+        }
+      } else {
+        return SingularToReflectionType(value);
+      }
+    }
+
+    /// <summary>
+    /// Like ToReflectionType(object) but for a single element.
+    /// </summary>
+    internal Object SingularToReflectionType(object value) {
+      return descriptor.MappedType == MappedType.Enum
+          ? descriptor.EnumType.FindValueByNumber((int) value)
+          : value;
+    }
+
     public abstract object FromReflectionType(object value);
   }
 }
\ No newline at end of file
diff --git a/csharp/ProtocolBuffers/GeneratedMessage.cs b/csharp/ProtocolBuffers/GeneratedMessage.cs
index 2aa8e842..37fd2e6b 100644
--- a/csharp/ProtocolBuffers/GeneratedMessage.cs
+++ b/csharp/ProtocolBuffers/GeneratedMessage.cs
@@ -48,8 +48,11 @@ namespace Google.ProtocolBuffers {
       MessageDescriptor descriptor = DescriptorForType;
       foreach (FieldDescriptor field in descriptor.Fields) {
         IFieldAccessor accessor = InternalFieldAccessors[field];
-        if ((field.IsRepeated && accessor.GetRepeatedCount(this) != 0)
-            || accessor.Has(this)) {
+        if (field.IsRepeated) {
+          if (accessor.GetRepeatedCount(this) != 0) {
+            ret[field] = accessor.GetValue(this);
+          }
+        } else if (HasField(field)) {
           ret[field] = accessor.GetValue(this);
         }
       }
diff --git a/csharp/ProtocolBuffers/GeneratedRepeatException.cs b/csharp/ProtocolBuffers/GeneratedRepeatException.cs
index d766d7f6..a38f5c1b 100644
--- a/csharp/ProtocolBuffers/GeneratedRepeatException.cs
+++ b/csharp/ProtocolBuffers/GeneratedRepeatException.cs
@@ -8,11 +8,11 @@ namespace Google.ProtocolBuffers {
   /// Class used to represent repeat extensions in generated classes.
   /// </summary>
   public class GeneratedRepeatExtension<TContainer, TExtensionElement> : GeneratedExtensionBase<TContainer, IList<TExtensionElement>> {
-    private GeneratedRepeatExtension(FieldDescriptor field) : base(field) {
+    private GeneratedRepeatExtension(FieldDescriptor field) : base(field, typeof(TExtensionElement)) {
     }
 
     public static GeneratedExtensionBase<TContainer, IList<TExtensionElement>> CreateInstance(FieldDescriptor descriptor) {
-      if (descriptor.IsRepeated) {
+      if (!descriptor.IsRepeated) {
         throw new ArgumentException("Must call GeneratedRepeatExtension.CreateInstance() for repeated types.");
       }
       return new GeneratedRepeatExtension<TContainer, TExtensionElement>(descriptor);
diff --git a/csharp/ProtocolBuffers/GeneratedSingleExtension.cs b/csharp/ProtocolBuffers/GeneratedSingleExtension.cs
index 11805293..0adcd7ef 100644
--- a/csharp/ProtocolBuffers/GeneratedSingleExtension.cs
+++ b/csharp/ProtocolBuffers/GeneratedSingleExtension.cs
@@ -9,7 +9,7 @@ namespace Google.ProtocolBuffers {
   public class GeneratedSingleExtension<TContainer, TExtension> : GeneratedExtensionBase<TContainer, TExtension>    
       where TContainer : IMessage<TContainer> {
 
-    internal GeneratedSingleExtension(FieldDescriptor descriptor) : base(descriptor) {
+    internal GeneratedSingleExtension(FieldDescriptor descriptor) : base(descriptor, typeof(TExtension)) {
     }
 
     public static GeneratedSingleExtension<TContainer, TExtension> CreateInstance(FieldDescriptor descriptor) {
diff --git a/csharp/ProtocolBuffers/IBuilder.cs b/csharp/ProtocolBuffers/IBuilder.cs
index f847f217..b46842cd 100644
--- a/csharp/ProtocolBuffers/IBuilder.cs
+++ b/csharp/ProtocolBuffers/IBuilder.cs
@@ -51,6 +51,18 @@ namespace Google.ProtocolBuffers {
     object this[FieldDescriptor field] { get; set; }
 
     /// <summary>
+    /// Only present in the nongeneric interface - useful for tests, but
+    /// not as much in real life.
+    /// </summary>
+    IBuilder SetField(FieldDescriptor field, object value);
+
+    /// <summary>
+    /// Only present in the nongeneric interface - useful for tests, but
+    /// not as much in real life.
+    /// </summary>
+    IBuilder SetRepeatedField(FieldDescriptor field, int index, object value);
+
+    /// <summary>
     /// Get the message's type's descriptor.
     /// <see cref="IMessage{T}.DescriptorForType"/>
     /// </summary>
diff --git a/csharp/ProtocolBuffers/ProtocolBuffers.csproj b/csharp/ProtocolBuffers/ProtocolBuffers.csproj
index 3735adb7..6c97e8d1 100644
--- a/csharp/ProtocolBuffers/ProtocolBuffers.csproj
+++ b/csharp/ProtocolBuffers/ProtocolBuffers.csproj
@@ -68,6 +68,7 @@
     <Compile Include="Descriptors\PackageDescriptor.cs" />
     <Compile Include="Descriptors\ServiceDescriptor.cs" />
     <Compile Include="DynamicMessage.cs" />
+    <Compile Include="ExtendableBuilder.cs" />
     <Compile Include="ExtendableMessage.cs" />
     <Compile Include="ExtensionInfo.cs" />
     <Compile Include="ExtensionRegistry.cs" />
diff --git a/csharp/ProtocolBuffers/TextGenerator.cs b/csharp/ProtocolBuffers/TextGenerator.cs
index 724c1a8f..b5837504 100644
--- a/csharp/ProtocolBuffers/TextGenerator.cs
+++ b/csharp/ProtocolBuffers/TextGenerator.cs
@@ -70,6 +70,9 @@ namespace Google.ProtocolBuffers {
     }
 
     private void Write(string data) {
+      if (data.Length == 0) {
+        return;
+      }
       if (atStartOfLine) {
         atStartOfLine = false;
         writer.Write(indent);