Merge pull request #543 from jskeet/proto3-map

Proto3 map support for C#
10 years ago · 6b01539dfc
parent 68a4ee267f 286edc0fc2
commit 6b01539dfc
35 changed files with 8878 additions and 102 deletions
--- a/cmake/libprotoc.cmake
+++ b/cmake/libprotoc.cmake
@ -19,6 +19,7 @@ set(libprotoc_files
  ${protobuf_source_dir}/src/google/protobuf/compiler/csharp/csharp_field_base.cc
  ${protobuf_source_dir}/src/google/protobuf/compiler/csharp/csharp_generator.cc
  ${protobuf_source_dir}/src/google/protobuf/compiler/csharp/csharp_helpers.cc
+  ${protobuf_source_dir}/src/google/protobuf/compiler/csharp/csharp_map_field.cc
  ${protobuf_source_dir}/src/google/protobuf/compiler/csharp/csharp_message.cc
  ${protobuf_source_dir}/src/google/protobuf/compiler/csharp/csharp_message_field.cc
  ${protobuf_source_dir}/src/google/protobuf/compiler/csharp/csharp_primitive_field.cc
--- a/csharp/generate_protos.sh
+++ b/csharp/generate_protos.sh
@ -43,10 +43,12 @@ $PROTOC -Isrc --csharp_out=csharp/src/ProtocolBuffers/DescriptorProtos \
 rm src/google/protobuf/descriptor_proto_file.proto

 $PROTOC -Isrc --csharp_out=csharp/src/ProtocolBuffers.Test/TestProtos \
+    src/google/protobuf/map_unittest_proto3.proto \
    src/google/protobuf/unittest_proto3.proto \
    src/google/protobuf/unittest_import_proto3.proto \
    src/google/protobuf/unittest_import_public_proto3.proto

+
 $PROTOC -Icsharp/protos/extest --csharp_out=csharp/src/ProtocolBuffers.Test/TestProtos \
    csharp/protos/extest/unittest_issues.proto

--- a/csharp/src/AddressBook/Addressbook.cs
+++ b/csharp/src/AddressBook/Addressbook.cs
@ -155,7 +155,7 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (Name.Length != 0) hash ^= Name.GetHashCode();
      if (Id != 0) hash ^= Id.GetHashCode();
      if (Email.Length != 0) hash ^= Email.GetHashCode();
@ -200,6 +200,7 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
      }
      return size;
    }
+
    public void MergeFrom(Person other) {
      if (other == null) {
        return;
@ -329,7 +330,7 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
        }

        public override int GetHashCode() {
-          int hash = 0;
+          int hash = 1;
          if (Number.Length != 0) hash ^= Number.GetHashCode();
          if (Type != global::Google.ProtocolBuffers.Examples.AddressBook.Person.Types.PhoneType.HOME) hash ^= Type.GetHashCode();
          return hash;
@ -356,6 +357,7 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
          }
          return size;
        }
+
        public void MergeFrom(PhoneNumber other) {
          if (other == null) {
            return;
@ -456,7 +458,7 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      hash ^= person_.GetHashCode();
      return hash;
    }
@ -477,6 +479,7 @@ namespace Google.ProtocolBuffers.Examples.AddressBook {
      }
      return size;
    }
+
    public void MergeFrom(AddressBook other) {
      if (other == null) {
        return;
--- a/csharp/src/ProtocolBuffers.Test/Collections/MapFieldTest.cs
+++ b/csharp/src/ProtocolBuffers.Test/Collections/MapFieldTest.cs
@ -0,0 +1,354 @@
+#region Copyright notice and license
+// Protocol Buffers - Google's data interchange format
+// Copyright 2015 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#endregion
+
+using System;
+using System.Collections.Generic;
+using Google.Protobuf.TestProtos;
+using NUnit.Framework;
+
+namespace Google.Protobuf.Collections
+{
+    /// <summary>
+    /// Tests for MapField which aren't reliant on the encoded format -
+    /// tests for serialization/deserialization are part of GeneratedMessageTest.
+    /// </summary>
+    public class MapFieldTest
+    {
+        // Protobuf-specific tests
+        [Test]
+        public void Freeze_FreezesMessages()
+        {
+            var message = new ForeignMessage { C = 20 };
+            var map = new MapField<string, ForeignMessage> { { "x", message } };
+            map.Freeze();
+            Assert.IsTrue(message.IsFrozen);
+        }
+
+        [Test]
+        public void Freeze_PreventsMutation()
+        {
+            var map = new MapField<string, string>();
+            map.Freeze();
+            Assert.IsTrue(map.IsFrozen);
+            Assert.IsTrue(map.IsReadOnly);
+            ICollection<KeyValuePair<string, string>> collection = map;
+            Assert.Throws<InvalidOperationException>(() => map["x"] = "y");
+            Assert.Throws<InvalidOperationException>(() => map.Add("x", "y"));
+            Assert.Throws<InvalidOperationException>(() => map.Remove("x"));
+            Assert.Throws<InvalidOperationException>(() => map.Clear());
+            Assert.Throws<InvalidOperationException>(() => collection.Add(NewKeyValuePair("x", "y")));
+            Assert.Throws<InvalidOperationException>(() => collection.Remove(NewKeyValuePair("x", "y")));
+        }
+
+        [Test]
+        public void Clone_ReturnsNonFrozen()
+        {
+            var map = new MapField<string, string>();
+            map.Freeze();
+            var clone = map.Clone();
+            clone.Add("x", "y");
+        }
+
+        [Test]
+        public void Clone_ClonesMessages()
+        {
+            var message = new ForeignMessage { C = 20 };
+            var map = new MapField<string, ForeignMessage> { { "x", message } };
+            var clone = map.Clone();
+            map["x"].C = 30;
+            Assert.AreEqual(20, clone["x"].C);
+        }
+
+        [Test]
+        public void Add_ForbidsNullKeys()
+        {
+            var map = new MapField<string, ForeignMessage>();
+            Assert.Throws<ArgumentNullException>(() => map.Add(null, new ForeignMessage()));
+        }
+
+        [Test]
+        public void Add_AcceptsNullMessageValues()
+        {
+            var map = new MapField<string, ForeignMessage>();
+            map.Add("missing", null);
+            Assert.IsNull(map["missing"]);
+        }
+
+        [Test]
+        public void Add_ForbidsNullStringValues()
+        {
+            var map = new MapField<string, string>();
+            Assert.Throws<ArgumentNullException>(() => map.Add("missing", null));
+        }
+
+        [Test]
+        public void Add_ForbidsNullByteStringValues()
+        {
+            var map = new MapField<string, ByteString>();
+            Assert.Throws<ArgumentNullException>(() => map.Add("missing", null));
+        }
+
+        [Test]
+        public void Indexer_ForbidsNullKeys()
+        {
+            var map = new MapField<string, ForeignMessage>();
+            Assert.Throws<ArgumentNullException>(() => map[null] = new ForeignMessage());
+        }
+
+        [Test]
+        public void Indexer_AcceptsNullMessageValues()
+        {
+            var map = new MapField<string, ForeignMessage>();
+            map["missing"] = null;
+            Assert.IsNull(map["missing"]);
+        }
+
+        [Test]
+        public void Indexer_ForbidsNullStringValues()
+        {
+            var map = new MapField<string, string>();
+            Assert.Throws<ArgumentNullException>(() => map["missing"] = null);
+        }
+
+        [Test]
+        public void Indexer_ForbidsNullByteStringValues()
+        {
+            var map = new MapField<string, ByteString>();
+            Assert.Throws<ArgumentNullException>(() => map["missing"] = null);
+        }
+
+        [Test]
+        public void AddPreservesInsertionOrder()
+        {
+            var map = new MapField<string, string>();
+            map.Add("a", "v1");
+            map.Add("b", "v2");
+            map.Add("c", "v3");
+            map.Remove("b");
+            map.Add("d", "v4");
+            CollectionAssert.AreEqual(new[] { "a", "c", "d" }, map.Keys);
+            CollectionAssert.AreEqual(new[] { "v1", "v3", "v4" }, map.Values);
+        }
+
+        [Test]
+        public void EqualityIsOrderInsensitive()
+        {
+            var map1 = new MapField<string, string>();
+            map1.Add("a", "v1");
+            map1.Add("b", "v2");
+
+            var map2 = new MapField<string, string>();
+            map2.Add("b", "v2");
+            map2.Add("a", "v1");
+
+            EqualityTester.AssertEquality(map1, map2);
+        }
+
+        [Test]
+        public void EqualityIsKeySensitive()
+        {
+            var map1 = new MapField<string, string>();
+            map1.Add("first key", "v1");
+            map1.Add("second key", "v2");
+
+            var map2 = new MapField<string, string>();
+            map2.Add("third key", "v1");
+            map2.Add("fourth key", "v2");
+
+            EqualityTester.AssertInequality(map1, map2);
+        }
+
+        [Test]
+        public void EqualityIsValueSensitive()
+        {
+            // Note: Without some care, it's a little easier than one might
+            // hope to see hash collisions, but only in some environments...
+            var map1 = new MapField<string, string>();
+            map1.Add("a", "first value");
+            map1.Add("b", "second value");
+
+            var map2 = new MapField<string, string>();
+            map2.Add("a", "third value");
+            map2.Add("b", "fourth value");
+
+            EqualityTester.AssertInequality(map1, map2);
+        }
+
+        [Test]
+        public void EqualityHandlesNullValues()
+        {
+            var map1 = new MapField<string, ForeignMessage>();
+            map1.Add("a", new ForeignMessage { C = 10 });
+            map1.Add("b", null);
+
+            var map2 = new MapField<string, ForeignMessage>();
+            map2.Add("a", new ForeignMessage { C = 10 });
+            map2.Add("b", null);
+
+            EqualityTester.AssertEquality(map1, map2);
+            // Check the null value isn't ignored entirely...
+            Assert.IsTrue(map1.Remove("b"));
+            EqualityTester.AssertInequality(map1, map2);
+            map1.Add("b", new ForeignMessage());
+            EqualityTester.AssertInequality(map1, map2);
+            map1["b"] = null;
+            EqualityTester.AssertEquality(map1, map2);
+        }
+
+        [Test]
+        public void Add_Dictionary()
+        {
+            var map1 = new MapField<string, string>
+            {
+                { "x", "y" },
+                { "a", "b" }
+            };
+            var map2 = new MapField<string, string>
+            {
+                { "before", "" },
+                map1,
+                { "after", "" }
+            };
+            var expected = new MapField<string, string>
+            {
+                { "before", "" },
+                { "x", "y" },
+                { "a", "b" },
+                { "after", "" }
+            };
+            Assert.AreEqual(expected, map2);
+            CollectionAssert.AreEqual(new[] { "before", "x", "a", "after" }, map2.Keys);
+        }
+
+        // General IDictionary<TKey, TValue> behavior tests
+        [Test]
+        public void Add_KeyAlreadyExists()
+        {
+            var map = new MapField<string, string>();
+            map.Add("foo", "bar");
+            Assert.Throws<ArgumentException>(() => map.Add("foo", "baz"));
+        }
+
+        [Test]
+        public void Add_Pair()
+        {
+            var map = new MapField<string, string>();
+            ICollection<KeyValuePair<string, string>> collection = map;
+            collection.Add(NewKeyValuePair("x", "y"));
+            Assert.AreEqual("y", map["x"]);
+            Assert.Throws<ArgumentException>(() => collection.Add(NewKeyValuePair("x", "z")));
+        }
+
+        [Test]
+        public void Contains_Pair()
+        {
+            var map = new MapField<string, string> { { "x", "y" } };
+            ICollection<KeyValuePair<string, string>> collection = map;
+            Assert.IsTrue(collection.Contains(NewKeyValuePair("x", "y")));
+            Assert.IsFalse(collection.Contains(NewKeyValuePair("x", "z")));
+            Assert.IsFalse(collection.Contains(NewKeyValuePair("z", "y")));
+        }
+
+        [Test]
+        public void Remove_Key()
+        {
+            var map = new MapField<string, string>();
+            map.Add("foo", "bar");
+            Assert.AreEqual(1, map.Count);
+            Assert.IsFalse(map.Remove("missing"));
+            Assert.AreEqual(1, map.Count);
+            Assert.IsTrue(map.Remove("foo"));
+            Assert.AreEqual(0, map.Count);           
+        }
+
+        [Test]
+        public void Remove_Pair()
+        {
+            var map = new MapField<string, string>();
+            map.Add("foo", "bar");
+            ICollection<KeyValuePair<string, string>> collection = map;
+            Assert.AreEqual(1, map.Count);
+            Assert.IsFalse(collection.Remove(NewKeyValuePair("wrong key", "bar")));
+            Assert.AreEqual(1, map.Count);
+            Assert.IsFalse(collection.Remove(NewKeyValuePair("foo", "wrong value")));
+            Assert.AreEqual(1, map.Count);
+            Assert.IsTrue(collection.Remove(NewKeyValuePair("foo", "bar")));
+            Assert.AreEqual(0, map.Count);
+            Assert.Throws<ArgumentException>(() => collection.Remove(new KeyValuePair<string, string>(null, "")));
+        }
+
+        [Test]
+        public void CopyTo_Pair()
+        {
+            var map = new MapField<string, string>();
+            map.Add("foo", "bar");
+            ICollection<KeyValuePair<string, string>> collection = map;
+            KeyValuePair<string, string>[] array = new KeyValuePair<string, string>[3];
+            collection.CopyTo(array, 1);
+            Assert.AreEqual(NewKeyValuePair("foo", "bar"), array[1]);
+        }
+
+        [Test]
+        public void Clear()
+        {
+            var map = new MapField<string, string> { { "x", "y" } };
+            Assert.AreEqual(1, map.Count);
+            map.Clear();
+            Assert.AreEqual(0, map.Count);
+            map.Add("x", "y");
+            Assert.AreEqual(1, map.Count);
+        }
+
+        [Test]
+        public void Indexer_Get()
+        {
+            var map = new MapField<string, string> { { "x", "y" } };
+            Assert.AreEqual("y", map["x"]);
+            Assert.Throws<KeyNotFoundException>(() => { var ignored = map["z"]; });
+        }
+
+        [Test]
+        public void Indexer_Set()
+        {
+            var map = new MapField<string, string>();
+            map["x"] = "y";
+            Assert.AreEqual("y", map["x"]);
+            map["x"] = "z"; // This won't throw, unlike Add.
+            Assert.AreEqual("z", map["x"]);
+        }
+
+        private static KeyValuePair<TKey, TValue> NewKeyValuePair<TKey, TValue>(TKey key, TValue value)
+        {
+            return new KeyValuePair<TKey, TValue>(key, value);
+        }
+    }
+}
--- a/csharp/src/ProtocolBuffers.Test/Collections/RepeatedFieldTest.cs
+++ b/csharp/src/ProtocolBuffers.Test/Collections/RepeatedFieldTest.cs
@ -1,10 +1,9 @@
 using System;
 using System.Collections.Generic;
-using Google.Protobuf.Collections;
 using Google.Protobuf.TestProtos;
 using NUnit.Framework;

-namespace Google.Protobuf
+namespace Google.Protobuf.Collections
 {
    public class RepeatedFieldTest
    {
--- a/csharp/src/ProtocolBuffers.Test/EqualityTester.cs
+++ b/csharp/src/ProtocolBuffers.Test/EqualityTester.cs
@ -0,0 +1,63 @@
+#region Copyright notice and license
+// Protocol Buffers - Google's data interchange format
+// Copyright 2015 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using NUnit.Framework;
+
+namespace Google.Protobuf
+{
+    /// <summary>
+    /// Helper methods when testing equality. NUnit's Assert.AreEqual and
+    /// Assert.AreNotEqual methods try to be clever with collections, which can
+    /// be annoying...
+    /// </summary>
+    internal static class EqualityTester
+    {
+        public static void AssertEquality<T>(T first, T second) where T : IEquatable<T>
+        {
+            Assert.IsTrue(first.Equals(second));
+            Assert.AreEqual(first.GetHashCode(), second.GetHashCode());
+        }
+
+        public static void AssertInequality<T>(T first, T second) where T : IEquatable<T>
+        {
+            Assert.IsFalse(first.Equals(second));
+            // While this isn't a requirement, the chances of this test failing due to
+            // coincidence rather than a bug are very small.
+            Assert.AreNotEqual(first.GetHashCode(), second.GetHashCode());
+        }
+    }
+}
--- a/csharp/src/ProtocolBuffers.Test/FieldCodecTest.cs
+++ b/csharp/src/ProtocolBuffers.Test/FieldCodecTest.cs
@ -0,0 +1,149 @@
+#region Copyright notice and license
+// Protocol Buffers - Google's data interchange format
+// Copyright 2015 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#endregion
+
+using System.Collections.Generic;
+using System.IO;
+using Google.Protobuf.TestProtos;
+using NUnit.Framework;
+
+namespace Google.Protobuf
+{
+    public class FieldCodecTest
+    {
+        private static readonly List<ICodecTestData> Codecs = new List<ICodecTestData>
+        {
+            new FieldCodecTestData<bool>(FieldCodec.ForBool(100), true, "Bool"),
+            new FieldCodecTestData<string>(FieldCodec.ForString(100), "sample", "String"),
+            new FieldCodecTestData<ByteString>(FieldCodec.ForBytes(100), ByteString.CopyFrom(1, 2, 3), "Bytes"),
+            new FieldCodecTestData<int>(FieldCodec.ForInt32(100), -1000, "Int32"),
+            new FieldCodecTestData<int>(FieldCodec.ForSInt32(100), -1000, "SInt32"),
+            new FieldCodecTestData<int>(FieldCodec.ForSFixed32(100), -1000, "SFixed32"),
+            new FieldCodecTestData<uint>(FieldCodec.ForUInt32(100), 1234, "UInt32"),
+            new FieldCodecTestData<uint>(FieldCodec.ForFixed32(100), 1234, "Fixed32"),
+            new FieldCodecTestData<long>(FieldCodec.ForInt64(100), -1000, "Int64"),
+            new FieldCodecTestData<long>(FieldCodec.ForSInt64(100), -1000, "SInt64"),
+            new FieldCodecTestData<long>(FieldCodec.ForSFixed64(100), -1000, "SFixed64"),
+            new FieldCodecTestData<ulong>(FieldCodec.ForUInt64(100), 1234, "UInt64"),
+            new FieldCodecTestData<ulong>(FieldCodec.ForFixed64(100), 1234, "Fixed64"),
+            new FieldCodecTestData<float>(FieldCodec.ForFloat(100), 1234.5f, "Float"),
+            new FieldCodecTestData<double>(FieldCodec.ForDouble(100), 1234567890.5d, "Double"),
+            new FieldCodecTestData<ForeignEnum>(
+                FieldCodec.ForEnum(100, t => (int) t, t => (ForeignEnum) t), ForeignEnum.FOREIGN_BAZ, "Enum"),
+            new FieldCodecTestData<ForeignMessage>(
+                FieldCodec.ForMessage(100, ForeignMessage.Parser), new ForeignMessage { C = 10 }, "Message"),
+        };
+
+        [Test, TestCaseSource("Codecs")]
+        public void RoundTrip(ICodecTestData codec)
+        {
+            codec.TestRoundTrip();
+        }
+
+        [Test, TestCaseSource("Codecs")]
+        public void CalculateSize(ICodecTestData codec)
+        {
+            codec.TestCalculateSize();
+        }
+
+        [Test, TestCaseSource("Codecs")]
+        public void DefaultValue(ICodecTestData codec)
+        {
+            codec.TestDefaultValue();
+        }
+
+        public interface ICodecTestData
+        {
+            void TestRoundTrip();
+            void TestCalculateSize();
+            void TestDefaultValue();
+        }
+
+        public class FieldCodecTestData<T> : ICodecTestData
+        {
+            private readonly FieldCodec<T> codec;
+            private readonly T sampleValue;
+            private readonly string name;
+
+            public FieldCodecTestData(FieldCodec<T> codec, T sampleValue, string name)
+            {
+                this.codec = codec;
+                this.sampleValue = sampleValue;
+                this.name = name;
+            }
+
+            public void TestRoundTrip()
+            {
+                var stream = new MemoryStream();
+                var codedOutput = CodedOutputStream.CreateInstance(stream);
+                codec.Write(codedOutput, sampleValue);
+                codedOutput.Flush();
+                stream.Position = 0;
+                var codedInput = CodedInputStream.CreateInstance(stream);
+                uint tag;
+                Assert.IsTrue(codedInput.ReadTag(out tag));
+                Assert.AreEqual(codec.Tag, tag);
+                Assert.AreEqual(sampleValue, codec.Read(codedInput));
+                Assert.IsTrue(codedInput.IsAtEnd);
+            }
+
+            public void TestCalculateSize()
+            {
+                var stream = new MemoryStream();
+                var codedOutput = CodedOutputStream.CreateInstance(stream);
+                codec.Write(codedOutput, sampleValue);
+                codedOutput.Flush();
+                Assert.AreEqual(stream.Position, codec.CalculateSize(sampleValue));
+            }
+
+            public void TestDefaultValue()
+            {
+                var stream = new MemoryStream();
+                var codedOutput = CodedOutputStream.CreateInstance(stream);
+                codec.Write(codedOutput, codec.DefaultValue);
+                codedOutput.Flush();
+                Assert.AreEqual(0, stream.Position);
+                Assert.AreEqual(0, codec.CalculateSize(codec.DefaultValue));
+                if (typeof(T).IsValueType)
+                {
+                    Assert.AreEqual(default(T), codec.DefaultValue);
+                }
+            }
+
+            public string Description { get { return name; } }
+
+            public override string ToString()
+            {
+                return name;
+            }
+        }
+    }
+}
--- a/csharp/src/ProtocolBuffers.Test/GeneratedMessageTest.cs
+++ b/csharp/src/ProtocolBuffers.Test/GeneratedMessageTest.cs
@ -1,4 +1,5 @@
 using System;
+using System.IO;
 using Google.Protobuf.TestProtos;
 using NUnit.Framework;

@ -9,6 +10,15 @@ namespace Google.Protobuf
    /// </summary>
    public class GeneratedMessageTest
    {
+        [Test]
+        public void EmptyMessageFieldDistinctFromMissingMessageField()
+        {
+            // This demonstrates what we're really interested in...
+            var message1 = new TestAllTypes { SingleForeignMessage = new ForeignMessage() };
+            var message2 = new TestAllTypes(); // SingleForeignMessage is null
+            EqualityTester.AssertInequality(message1, message2);
+        }
+
        [Test]
        public void DefaultValues()
        {
@ -146,6 +156,206 @@ namespace Google.Protobuf
            Assert.AreEqual(message, parsed);
        }

+        // Note that not every map within map_unittest_proto3 is used. They all go through very
+        // similar code paths. The fact that all maps are present is validation that we have codecs
+        // for every type.
+        [Test]
+        public void RoundTrip_Maps()
+        {
+            var message = new TestMap
+            {
+                MapBoolBool = {
+                    { false, true },
+                    { true, false }
+                },
+                MapInt32Bytes = {
+                    { 5, ByteString.CopyFrom(6, 7, 8) },
+                    { 25, ByteString.CopyFrom(1, 2, 3, 4, 5) },
+                    { 10, ByteString.Empty }
+                },
+                MapInt32ForeignMessage = {
+                    { 0, new ForeignMessage { C = 10 } },
+                    { 5, null },
+                },
+                MapInt32Enum = {
+                    { 1, MapEnum.MAP_ENUM_BAR },
+                    { 2000, MapEnum.MAP_ENUM_FOO }
+                }
+            };
+
+            byte[] bytes = message.ToByteArray();
+            TestMap parsed = TestMap.Parser.ParseFrom(bytes);
+            Assert.AreEqual(message, parsed);
+        }
+
+        [Test]
+        public void MapWithEmptyEntry()
+        {
+            var message = new TestMap
+            {
+                MapInt32Bytes = { { 0, ByteString.Empty } }
+            };
+
+            byte[] bytes = message.ToByteArray();
+            Assert.AreEqual(2, bytes.Length); // Tag for field entry (1 byte), length of entry (0; 1 byte)
+
+            var parsed = TestMap.Parser.ParseFrom(bytes);
+            Assert.AreEqual(1, parsed.MapInt32Bytes.Count);
+            Assert.AreEqual(ByteString.Empty, parsed.MapInt32Bytes[0]);
+        }
+        
+        [Test]
+        public void MapWithOnlyValue()
+        {
+            // Hand-craft the stream to contain a single entry with just a value.
+            var memoryStream = new MemoryStream();
+            var output = CodedOutputStream.CreateInstance(memoryStream);
+            output.WriteTag(TestMap.MapInt32ForeignMessageFieldNumber, WireFormat.WireType.LengthDelimited);
+            var nestedMessage = new ForeignMessage { C = 20 };
+            // Size of the entry (tag, size written by WriteMessage, data written by WriteMessage)
+            output.WriteRawVarint32((uint)(nestedMessage.CalculateSize() + 3));
+            output.WriteTag(2, WireFormat.WireType.LengthDelimited);
+            output.WriteMessage(nestedMessage);
+            output.Flush();
+
+            var parsed = TestMap.Parser.ParseFrom(memoryStream.ToArray());
+            Assert.AreEqual(nestedMessage, parsed.MapInt32ForeignMessage[0]);
+        }
+
+        [Test]
+        public void MapIgnoresExtraFieldsWithinEntryMessages()
+        {
+            // Hand-craft the stream to contain a single entry with three fields
+            var memoryStream = new MemoryStream();
+            var output = CodedOutputStream.CreateInstance(memoryStream);
+
+            output.WriteTag(TestMap.MapInt32Int32FieldNumber, WireFormat.WireType.LengthDelimited);
+
+            var key = 10; // Field 1 
+            var value = 20; // Field 2
+            var extra = 30; // Field 3
+
+            // Each field can be represented in a single byte, with a single byte tag.
+            // Total message size: 6 bytes.
+            output.WriteRawVarint32(6);
+            output.WriteTag(1, WireFormat.WireType.Varint);
+            output.WriteInt32(key);
+            output.WriteTag(2, WireFormat.WireType.Varint);
+            output.WriteInt32(value);
+            output.WriteTag(3, WireFormat.WireType.Varint);
+            output.WriteInt32(extra);
+            output.Flush();
+
+            var parsed = TestMap.Parser.ParseFrom(memoryStream.ToArray());
+            Assert.AreEqual(value, parsed.MapInt32Int32[key]);
+        }
+
+        [Test]
+        public void MapFieldOrderIsIrrelevant()
+        {
+            var memoryStream = new MemoryStream();
+            var output = CodedOutputStream.CreateInstance(memoryStream);
+
+            output.WriteTag(TestMap.MapInt32Int32FieldNumber, WireFormat.WireType.LengthDelimited);
+
+            var key = 10;
+            var value = 20;
+
+            // Each field can be represented in a single byte, with a single byte tag.
+            // Total message size: 4 bytes.
+            output.WriteRawVarint32(4);
+            output.WriteTag(2, WireFormat.WireType.Varint);
+            output.WriteInt32(value);
+            output.WriteTag(1, WireFormat.WireType.Varint);
+            output.WriteInt32(key);
+            output.Flush();
+
+            var parsed = TestMap.Parser.ParseFrom(memoryStream.ToArray());
+            Assert.AreEqual(value, parsed.MapInt32Int32[key]);
+        }
+
+        [Test]
+        public void MapNonContiguousEntries()
+        {
+            var memoryStream = new MemoryStream();
+            var output = CodedOutputStream.CreateInstance(memoryStream);
+
+            // Message structure:
+            // Entry for MapInt32Int32
+            // Entry for MapStringString
+            // Entry for MapInt32Int32
+
+            // First entry
+            var key1 = 10;
+            var value1 = 20;
+            output.WriteTag(TestMap.MapInt32Int32FieldNumber, WireFormat.WireType.LengthDelimited);
+            output.WriteRawVarint32(4);
+            output.WriteTag(1, WireFormat.WireType.Varint);
+            output.WriteInt32(key1);
+            output.WriteTag(2, WireFormat.WireType.Varint);
+            output.WriteInt32(value1);
+
+            // Second entry
+            var key2 = "a";
+            var value2 = "b";
+            output.WriteTag(TestMap.MapStringStringFieldNumber, WireFormat.WireType.LengthDelimited);
+            output.WriteRawVarint32(6); // 3 bytes per entry: tag, size, character
+            output.WriteTag(1, WireFormat.WireType.LengthDelimited);
+            output.WriteString(key2);
+            output.WriteTag(2, WireFormat.WireType.LengthDelimited);
+            output.WriteString(value2);
+
+            // Third entry
+            var key3 = 15;
+            var value3 = 25;
+            output.WriteTag(TestMap.MapInt32Int32FieldNumber, WireFormat.WireType.LengthDelimited);
+            output.WriteRawVarint32(4);
+            output.WriteTag(1, WireFormat.WireType.Varint);
+            output.WriteInt32(key3);
+            output.WriteTag(2, WireFormat.WireType.Varint);
+            output.WriteInt32(value3);
+
+            output.Flush();
+            var parsed = TestMap.Parser.ParseFrom(memoryStream.ToArray());
+            var expected = new TestMap
+            {
+                MapInt32Int32 = { { key1, value1 }, { key3, value3 } },
+                MapStringString = { { key2, value2 } }
+            };
+            Assert.AreEqual(expected, parsed);
+        }
+
+        [Test]
+        public void DuplicateKeys_LastEntryWins()
+        {
+            var memoryStream = new MemoryStream();
+            var output = CodedOutputStream.CreateInstance(memoryStream);
+
+            var key = 10;
+            var value1 = 20;
+            var value2 = 30;
+
+            // First entry
+            output.WriteTag(TestMap.MapInt32Int32FieldNumber, WireFormat.WireType.LengthDelimited);
+            output.WriteRawVarint32(4);
+            output.WriteTag(1, WireFormat.WireType.Varint);
+            output.WriteInt32(key);
+            output.WriteTag(2, WireFormat.WireType.Varint);
+            output.WriteInt32(value1);
+
+            // Second entry - same key, different value
+            output.WriteTag(TestMap.MapInt32Int32FieldNumber, WireFormat.WireType.LengthDelimited);
+            output.WriteRawVarint32(4);
+            output.WriteTag(1, WireFormat.WireType.Varint);
+            output.WriteInt32(key);
+            output.WriteTag(2, WireFormat.WireType.Varint);
+            output.WriteInt32(value2);
+            output.Flush();
+
+            var parsed = TestMap.Parser.ParseFrom(memoryStream.ToArray());
+            Assert.AreEqual(value2, parsed.MapInt32Int32[key]);
+        }
+
        [Test]
        public void CloneSingleNonMessageValues()
        {
--- a/csharp/src/ProtocolBuffers.Test/ProtocolBuffers.Test.csproj
+++ b/csharp/src/ProtocolBuffers.Test/ProtocolBuffers.Test.csproj
@ -74,8 +74,12 @@
    <Compile Include="ByteStringTest.cs" />
    <Compile Include="CodedInputStreamTest.cs" />
    <Compile Include="CodedOutputStreamTest.cs" />
+    <Compile Include="EqualityTester.cs" />
+    <Compile Include="FieldCodecTest.cs" />
    <Compile Include="GeneratedMessageTest.cs" />
-    <Compile Include="RepeatedFieldTest.cs" />
+    <Compile Include="Collections\MapFieldTest.cs" />
+    <Compile Include="Collections\RepeatedFieldTest.cs" />
+    <Compile Include="TestProtos\MapUnittestProto3.cs" />
    <Compile Include="TestProtos\UnittestImportProto3.cs" />
    <Compile Include="TestProtos\UnittestImportPublicProto3.cs" />
    <Compile Include="TestProtos\UnittestIssues.cs" />
@ -99,9 +103,7 @@
  <ItemGroup>
    <Service Include="{82A7F48D-3B50-4B1E-B82E-3ADA8210C358}" />
  </ItemGroup>
-  <ItemGroup>
-    <Folder Include="Collections\" />
-  </ItemGroup>
+  <ItemGroup />
  <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
  <!-- To modify your build process, add your task inside one of the targets below and uncomment it. 
       Other similar extension points exist, see Microsoft.Common.targets.
--- a/csharp/src/ProtocolBuffers.Test/TestProtos/MapUnittestProto3.cs
+++ b/csharp/src/ProtocolBuffers.Test/TestProtos/MapUnittestProto3.cs
--- a/csharp/src/ProtocolBuffers.Test/TestProtos/UnittestImportProto3.cs
+++ b/csharp/src/ProtocolBuffers.Test/TestProtos/UnittestImportProto3.cs
@ -120,7 +120,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (D != 0) hash ^= D.GetHashCode();
      return hash;
    }
@ -139,6 +139,7 @@ namespace Google.Protobuf.TestProtos {
      }
      return size;
    }
+
    public void MergeFrom(ImportMessage other) {
      if (other == null) {
        return;
--- a/csharp/src/ProtocolBuffers.Test/TestProtos/UnittestImportPublicProto3.cs
+++ b/csharp/src/ProtocolBuffers.Test/TestProtos/UnittestImportPublicProto3.cs
@ -105,7 +105,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (E != 0) hash ^= E.GetHashCode();
      return hash;
    }
@ -124,6 +124,7 @@ namespace Google.Protobuf.TestProtos {
      }
      return size;
    }
+
    public void MergeFrom(PublicImportMessage other) {
      if (other == null) {
        return;
--- a/csharp/src/ProtocolBuffers.Test/TestProtos/UnittestIssues.cs
+++ b/csharp/src/ProtocolBuffers.Test/TestProtos/UnittestIssues.cs
@ -168,7 +168,7 @@ namespace UnitTest.Issues.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (Value != global::UnitTest.Issues.TestProtos.NegativeEnum.NEGATIVE_ENUM_ZERO) hash ^= Value.GetHashCode();
      hash ^= values_.GetHashCode();
      hash ^= packedValues_.GetHashCode();
@ -212,6 +212,7 @@ namespace UnitTest.Issues.TestProtos {
      }
      return size;
    }
+
    public void MergeFrom(NegativeEnumMessage other) {
      if (other == null) {
        return;
@ -303,7 +304,7 @@ namespace UnitTest.Issues.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      return hash;
    }

@ -314,6 +315,7 @@ namespace UnitTest.Issues.TestProtos {
      int size = 0;
      return size;
    }
+
    public void MergeFrom(DeprecatedChild other) {
      if (other == null) {
        return;
@ -456,7 +458,7 @@ namespace UnitTest.Issues.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (PrimitiveValue != 0) hash ^= PrimitiveValue.GetHashCode();
      hash ^= primitiveArray_.GetHashCode();
      if (messageValue_ != null) hash ^= MessageValue.GetHashCode();
@ -527,6 +529,7 @@ namespace UnitTest.Issues.TestProtos {
      }
      return size;
    }
+
    public void MergeFrom(DeprecatedFieldsMessage other) {
      if (other == null) {
        return;
@ -655,7 +658,7 @@ namespace UnitTest.Issues.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (Item != 0) hash ^= Item.GetHashCode();
      return hash;
    }
@ -674,6 +677,7 @@ namespace UnitTest.Issues.TestProtos {
      }
      return size;
    }
+
    public void MergeFrom(ItemField other) {
      if (other == null) {
        return;
--- a/csharp/src/ProtocolBuffers.Test/TestProtos/UnittestProto3.cs
+++ b/csharp/src/ProtocolBuffers.Test/TestProtos/UnittestProto3.cs
@ -995,7 +995,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (SingleInt32 != 0) hash ^= SingleInt32.GetHashCode();
      if (SingleInt64 != 0L) hash ^= SingleInt64.GetHashCode();
      if (SingleUint32 != 0) hash ^= SingleUint32.GetHashCode();
@ -1472,6 +1472,7 @@ namespace Google.Protobuf.TestProtos {
      }
      return size;
    }
+
    public void MergeFrom(TestAllTypes other) {
      if (other == null) {
        return;
@ -1905,7 +1906,7 @@ namespace Google.Protobuf.TestProtos {
        }

        public override int GetHashCode() {
-          int hash = 0;
+          int hash = 1;
          if (Bb != 0) hash ^= Bb.GetHashCode();
          return hash;
        }
@ -1924,6 +1925,7 @@ namespace Google.Protobuf.TestProtos {
          }
          return size;
        }
+
        public void MergeFrom(NestedMessage other) {
          if (other == null) {
            return;
@ -2043,7 +2045,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (child_ != null) hash ^= Child.GetHashCode();
      if (payload_ != null) hash ^= Payload.GetHashCode();
      hash ^= repeatedChild_.GetHashCode();
@ -2080,6 +2082,7 @@ namespace Google.Protobuf.TestProtos {
      }
      return size;
    }
+
    public void MergeFrom(NestedTestAllTypes other) {
      if (other == null) {
        return;
@ -2196,7 +2199,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (DeprecatedInt32 != 0) hash ^= DeprecatedInt32.GetHashCode();
      return hash;
    }
@ -2215,6 +2218,7 @@ namespace Google.Protobuf.TestProtos {
      }
      return size;
    }
+
    public void MergeFrom(TestDeprecatedFields other) {
      if (other == null) {
        return;
@ -2306,7 +2310,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (C != 0) hash ^= C.GetHashCode();
      return hash;
    }
@ -2325,6 +2329,7 @@ namespace Google.Protobuf.TestProtos {
      }
      return size;
    }
+
    public void MergeFrom(ForeignMessage other) {
      if (other == null) {
        return;
@ -2404,7 +2409,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      return hash;
    }

@ -2415,6 +2420,7 @@ namespace Google.Protobuf.TestProtos {
      int size = 0;
      return size;
    }
+
    public void MergeFrom(TestReservedFields other) {
      if (other == null) {
        return;
@ -2500,7 +2506,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (foreignNested_ != null) hash ^= ForeignNested.GetHashCode();
      return hash;
    }
@ -2519,6 +2525,7 @@ namespace Google.Protobuf.TestProtos {
      }
      return size;
    }
+
    public void MergeFrom(TestForeignNested other) {
      if (other == null) {
        return;
@ -2628,7 +2635,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (A != 0) hash ^= A.GetHashCode();
      if (Bb != 0) hash ^= Bb.GetHashCode();
      return hash;
@ -2655,6 +2662,7 @@ namespace Google.Protobuf.TestProtos {
      }
      return size;
    }
+
    public void MergeFrom(TestReallyLargeTagNumber other) {
      if (other == null) {
        return;
@ -2766,7 +2774,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (a_ != null) hash ^= A.GetHashCode();
      if (I != 0) hash ^= I.GetHashCode();
      return hash;
@ -2793,6 +2801,7 @@ namespace Google.Protobuf.TestProtos {
      }
      return size;
    }
+
    public void MergeFrom(TestRecursiveMessage other) {
      if (other == null) {
        return;
@ -2898,7 +2907,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (bb_ != null) hash ^= Bb.GetHashCode();
      return hash;
    }
@ -2917,6 +2926,7 @@ namespace Google.Protobuf.TestProtos {
      }
      return size;
    }
+
    public void MergeFrom(TestMutualRecursionA other) {
      if (other == null) {
        return;
@ -3027,7 +3037,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (a_ != null) hash ^= A.GetHashCode();
      if (OptionalInt32 != 0) hash ^= OptionalInt32.GetHashCode();
      return hash;
@ -3054,6 +3064,7 @@ namespace Google.Protobuf.TestProtos {
      }
      return size;
    }
+
    public void MergeFrom(TestMutualRecursionB other) {
      if (other == null) {
        return;
@ -3231,7 +3242,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (PrimitiveField != 0) hash ^= PrimitiveField.GetHashCode();
      if (StringField.Length != 0) hash ^= StringField.GetHashCode();
      if (EnumField != global::Google.Protobuf.TestProtos.ForeignEnum.FOREIGN_UNSPECIFIED) hash ^= EnumField.GetHashCode();
@ -3322,6 +3333,7 @@ namespace Google.Protobuf.TestProtos {
      }
      return size;
    }
+
    public void MergeFrom(TestCamelCaseFieldNames other) {
      if (other == null) {
        return;
@ -3499,7 +3511,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (MyString.Length != 0) hash ^= MyString.GetHashCode();
      if (MyInt != 0L) hash ^= MyInt.GetHashCode();
      if (MyFloat != 0F) hash ^= MyFloat.GetHashCode();
@ -3542,6 +3554,7 @@ namespace Google.Protobuf.TestProtos {
      }
      return size;
    }
+
    public void MergeFrom(TestFieldOrderings other) {
      if (other == null) {
        return;
@ -3673,7 +3686,7 @@ namespace Google.Protobuf.TestProtos {
        }

        public override int GetHashCode() {
-          int hash = 0;
+          int hash = 1;
          if (Oo != 0L) hash ^= Oo.GetHashCode();
          if (Bb != 0) hash ^= Bb.GetHashCode();
          return hash;
@ -3700,6 +3713,7 @@ namespace Google.Protobuf.TestProtos {
          }
          return size;
        }
+
        public void MergeFrom(NestedMessage other) {
          if (other == null) {
            return;
@ -3803,7 +3817,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (SparseEnum != global::Google.Protobuf.TestProtos.TestSparseEnum.TEST_SPARSE_ENUM_UNSPECIFIED) hash ^= SparseEnum.GetHashCode();
      return hash;
    }
@ -3822,6 +3836,7 @@ namespace Google.Protobuf.TestProtos {
      }
      return size;
    }
+
    public void MergeFrom(SparseEnumMessage other) {
      if (other == null) {
        return;
@ -3913,7 +3928,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (Data.Length != 0) hash ^= Data.GetHashCode();
      return hash;
    }
@ -3932,6 +3947,7 @@ namespace Google.Protobuf.TestProtos {
      }
      return size;
    }
+
    public void MergeFrom(OneString other) {
      if (other == null) {
        return;
@ -4020,7 +4036,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      hash ^= data_.GetHashCode();
      return hash;
    }
@ -4043,6 +4059,7 @@ namespace Google.Protobuf.TestProtos {
      }
      return size;
    }
+
    public void MergeFrom(MoreString other) {
      if (other == null) {
        return;
@ -4132,7 +4149,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (Data.Length != 0) hash ^= Data.GetHashCode();
      return hash;
    }
@ -4151,6 +4168,7 @@ namespace Google.Protobuf.TestProtos {
      }
      return size;
    }
+
    public void MergeFrom(OneBytes other) {
      if (other == null) {
        return;
@ -4242,7 +4260,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (Data.Length != 0) hash ^= Data.GetHashCode();
      return hash;
    }
@ -4261,6 +4279,7 @@ namespace Google.Protobuf.TestProtos {
      }
      return size;
    }
+
    public void MergeFrom(MoreBytes other) {
      if (other == null) {
        return;
@ -4352,7 +4371,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (Data != 0) hash ^= Data.GetHashCode();
      return hash;
    }
@ -4371,6 +4390,7 @@ namespace Google.Protobuf.TestProtos {
      }
      return size;
    }
+
    public void MergeFrom(Int32Message other) {
      if (other == null) {
        return;
@ -4462,7 +4482,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (Data != 0) hash ^= Data.GetHashCode();
      return hash;
    }
@ -4481,6 +4501,7 @@ namespace Google.Protobuf.TestProtos {
      }
      return size;
    }
+
    public void MergeFrom(Uint32Message other) {
      if (other == null) {
        return;
@ -4572,7 +4593,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (Data != 0L) hash ^= Data.GetHashCode();
      return hash;
    }
@ -4591,6 +4612,7 @@ namespace Google.Protobuf.TestProtos {
      }
      return size;
    }
+
    public void MergeFrom(Int64Message other) {
      if (other == null) {
        return;
@ -4682,7 +4704,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (Data != 0UL) hash ^= Data.GetHashCode();
      return hash;
    }
@ -4701,6 +4723,7 @@ namespace Google.Protobuf.TestProtos {
      }
      return size;
    }
+
    public void MergeFrom(Uint64Message other) {
      if (other == null) {
        return;
@ -4792,7 +4815,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (Data != false) hash ^= Data.GetHashCode();
      return hash;
    }
@ -4811,6 +4834,7 @@ namespace Google.Protobuf.TestProtos {
      }
      return size;
    }
+
    public void MergeFrom(BoolMessage other) {
      if (other == null) {
        return;
@ -4954,7 +4978,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (fooCase_ == FooOneofCase.FooInt) hash ^= FooInt.GetHashCode();
      if (fooCase_ == FooOneofCase.FooString) hash ^= FooString.GetHashCode();
      if (fooCase_ == FooOneofCase.FooMessage) hash ^= FooMessage.GetHashCode();
@ -4989,6 +5013,7 @@ namespace Google.Protobuf.TestProtos {
      }
      return size;
    }
+
    public void MergeFrom(TestOneof other) {
      if (other == null) {
        return;
@ -5216,7 +5241,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      hash ^= packedInt32_.GetHashCode();
      hash ^= packedInt64_.GetHashCode();
      hash ^= packedUint32_.GetHashCode();
@ -5395,6 +5420,7 @@ namespace Google.Protobuf.TestProtos {
      }
      return size;
    }
+
    public void MergeFrom(TestPackedTypes other) {
      if (other == null) {
        return;
@ -5677,7 +5703,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      hash ^= unpackedInt32_.GetHashCode();
      hash ^= unpackedInt64_.GetHashCode();
      hash ^= unpackedUint32_.GetHashCode();
@ -5842,6 +5868,7 @@ namespace Google.Protobuf.TestProtos {
      }
      return size;
    }
+
    public void MergeFrom(TestUnpackedTypes other) {
      if (other == null) {
        return;
@ -6052,7 +6079,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      hash ^= repeatedFixed32_.GetHashCode();
      hash ^= repeatedInt32_.GetHashCode();
      hash ^= repeatedFixed64_.GetHashCode();
@ -6135,6 +6162,7 @@ namespace Google.Protobuf.TestProtos {
      }
      return size;
    }
+
    public void MergeFrom(TestRepeatedScalarDifferentTagSizes other) {
      if (other == null) {
        return;
@ -6255,7 +6283,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (A.Length != 0) hash ^= A.GetHashCode();
      return hash;
    }
@ -6274,6 +6302,7 @@ namespace Google.Protobuf.TestProtos {
      }
      return size;
    }
+
    public void MergeFrom(TestCommentInjectionMessage other) {
      if (other == null) {
        return;
@ -6353,7 +6382,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      return hash;
    }

@ -6364,6 +6393,7 @@ namespace Google.Protobuf.TestProtos {
      int size = 0;
      return size;
    }
+
    public void MergeFrom(FooRequest other) {
      if (other == null) {
        return;
@ -6436,7 +6466,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      return hash;
    }

@ -6447,6 +6477,7 @@ namespace Google.Protobuf.TestProtos {
      int size = 0;
      return size;
    }
+
    public void MergeFrom(FooResponse other) {
      if (other == null) {
        return;
@ -6519,7 +6550,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      return hash;
    }

@ -6530,6 +6561,7 @@ namespace Google.Protobuf.TestProtos {
      int size = 0;
      return size;
    }
+
    public void MergeFrom(FooClientMessage other) {
      if (other == null) {
        return;
@ -6602,7 +6634,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      return hash;
    }

@ -6613,6 +6645,7 @@ namespace Google.Protobuf.TestProtos {
      int size = 0;
      return size;
    }
+
    public void MergeFrom(FooServerMessage other) {
      if (other == null) {
        return;
@ -6685,7 +6718,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      return hash;
    }

@ -6696,6 +6729,7 @@ namespace Google.Protobuf.TestProtos {
      int size = 0;
      return size;
    }
+
    public void MergeFrom(BarRequest other) {
      if (other == null) {
        return;
@ -6768,7 +6802,7 @@ namespace Google.Protobuf.TestProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      return hash;
    }

@ -6779,6 +6813,7 @@ namespace Google.Protobuf.TestProtos {
      int size = 0;
      return size;
    }
+
    public void MergeFrom(BarResponse other) {
      if (other == null) {
        return;
--- a/csharp/src/ProtocolBuffers/CodedInputStream.cs
+++ b/csharp/src/ProtocolBuffers/CodedInputStream.cs
@ -456,14 +456,16 @@ namespace Google.Protobuf
        }

        /// <summary>
-        /// Returns true if the next tag is also part of the same unpacked array.
+        /// Peeks at the next tag in the stream. If it matches <paramref name="tag"/>,
+        /// the tag is consumed and the method returns <c>true</c>; otherwise, the
+        /// stream is left in the original position and the method returns <c>false</c>.
        /// </summary>
-        private bool ContinueArray(uint currentTag)
+        public bool MaybeConsumeTag(uint tag)
        {
            uint next;
            if (PeekNextTag(out next))
            {
-                if (next == currentTag)
+                if (next == tag)
                {
                    hasNextTag = false;
                    return true;
@ -486,17 +488,7 @@ namespace Google.Protobuf
                }
                return true;
            }
-
-            uint next;
-            if (PeekNextTag(out next))
-            {
-                if (next == currentTag)
-                {
-                    hasNextTag = false;
-                    return true;
-                }
-            }
-            return false;
+            return MaybeConsumeTag(currentTag);
        }

        /// <summary>
@ -512,7 +504,7 @@ namespace Google.Protobuf
            do
            {
                list.Add(ReadString());
-            } while (ContinueArray(fieldTag));
+            } while (MaybeConsumeTag(fieldTag));
        }

        public void ReadBytesArray(ICollection<ByteString> list)
@ -521,7 +513,7 @@ namespace Google.Protobuf
            do
            {
                list.Add(ReadBytes());
-            } while (ContinueArray(fieldTag));
+            } while (MaybeConsumeTag(fieldTag));
        }

        public void ReadBoolArray(ICollection<bool> list)
@ -729,7 +721,7 @@ namespace Google.Protobuf
                do
                {
                    list.Add((T)(object) ReadEnum());
-                } while (ContinueArray(fieldTag));
+                } while (MaybeConsumeTag(fieldTag));
            }
        }

@ -742,7 +734,7 @@ namespace Google.Protobuf
                T message = messageParser.CreateTemplate();
                ReadMessage(message);
                list.Add(message);
-            } while (ContinueArray(fieldTag));
+            } while (MaybeConsumeTag(fieldTag));
        }
        #endregion

--- a/csharp/src/ProtocolBuffers/CodedOutputStream.cs
+++ b/csharp/src/ProtocolBuffers/CodedOutputStream.cs
@ -475,6 +475,14 @@ namespace Google.Protobuf
            WriteRawVarint32(WireFormat.MakeTag(fieldNumber, type));
        }

+        /// <summary>
+        /// Writes an already-encoded tag.
+        /// </summary>
+        public void WriteTag(uint tag)
+        {
+            WriteRawVarint32(tag);
+        }
+
        /// <summary>
        /// Writes the given single-byte tag directly to the stream.
        /// </summary>
--- a/csharp/src/ProtocolBuffers/Collections/MapField.cs
+++ b/csharp/src/ProtocolBuffers/Collections/MapField.cs
@ -0,0 +1,433 @@
+#region Copyright notice and license
+// Protocol Buffers - Google's data interchange format
+// Copyright 2015 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#endregion
+
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace Google.Protobuf.Collections
+{
+    /// <summary>
+    /// Representation of a map field in a Protocol Buffer message.
+    /// </summary>
+    /// <remarks>
+    /// This implementation preserves insertion order for simplicity of testing
+    /// code using maps fields. Overwriting an existing entry does not change the
+    /// position of that entry within the map. Equality is not order-sensitive.
+    /// For string keys, the equality comparison is provided by <see cref="StringComparer.Ordinal"/>.
+    /// </remarks>
+    /// <typeparam name="TKey">Key type in the map. Must be a type supported by Protocol Buffer map keys.</typeparam>
+    /// <typeparam name="TValue">Value type in the map. Must be a type supported by Protocol Buffers.</typeparam>
+    public sealed class MapField<TKey, TValue> : IDeepCloneable<MapField<TKey, TValue>>, IFreezable, IDictionary<TKey, TValue>, IEquatable<MapField<TKey, TValue>>
+    {
+        // TODO: Don't create the map/list until we have an entry. (Assume many maps will be empty.)
+        private bool frozen;
+        private readonly Dictionary<TKey, LinkedListNode<KeyValuePair<TKey, TValue>>> map =
+            new Dictionary<TKey, LinkedListNode<KeyValuePair<TKey, TValue>>>();
+        private readonly LinkedList<KeyValuePair<TKey, TValue>> list = new LinkedList<KeyValuePair<TKey, TValue>>();
+
+        public MapField<TKey, TValue> Clone()
+        {
+            var clone = new MapField<TKey, TValue>();
+            // Keys are never cloneable. Values might be.
+            if (typeof(IDeepCloneable<TValue>).IsAssignableFrom(typeof(TValue)))
+            {
+                foreach (var pair in list)
+                {
+                    clone.Add(pair.Key, pair.Value == null ? pair.Value : ((IDeepCloneable<TValue>) pair.Value).Clone());
+                }
+            }
+            else
+            {
+                // Nothing is cloneable, so we don't need to worry.
+                clone.Add(this);
+            }
+            return clone;
+        }
+
+        public void Add(TKey key, TValue value)
+        {
+            // Validation of arguments happens in ContainsKey and the indexer
+            if (ContainsKey(key))
+            {
+                throw new ArgumentException("Key already exists in map", "key");
+            }
+            this[key] = value;
+        }
+
+        public bool ContainsKey(TKey key)
+        {
+            ThrowHelper.ThrowIfNull(key, "key");
+            return map.ContainsKey(key);
+        }
+
+        public bool Remove(TKey key)
+        {
+            this.CheckMutable();
+            ThrowHelper.ThrowIfNull(key, "key");
+            LinkedListNode<KeyValuePair<TKey, TValue>> node;
+            if (map.TryGetValue(key, out node))
+            {
+                map.Remove(key);
+                node.List.Remove(node);
+                return true;
+            }
+            else
+            {
+                return false;
+            }
+        }
+
+        public bool TryGetValue(TKey key, out TValue value)
+        {
+            LinkedListNode<KeyValuePair<TKey, TValue>> node;
+            if (map.TryGetValue(key, out node))
+            {
+                value = node.Value.Value;
+                return true;
+            }
+            else
+            {
+                value = default(TValue);
+                return false;
+            }
+        }
+
+        public TValue this[TKey key]
+        {
+            get
+            {
+                ThrowHelper.ThrowIfNull(key, "key");
+                TValue value;
+                if (TryGetValue(key, out value))
+                {
+                    return value;
+                }
+                throw new KeyNotFoundException();
+            }
+            set
+            {
+                ThrowHelper.ThrowIfNull(key, "key");
+                if (value == null && (typeof(TValue) == typeof(ByteString) || typeof(TValue) == typeof(string)))
+                {
+                    ThrowHelper.ThrowIfNull(value, "value");
+                }
+                this.CheckMutable();
+                LinkedListNode<KeyValuePair<TKey, TValue>> node;
+                var pair = new KeyValuePair<TKey, TValue>(key, value);
+                if (map.TryGetValue(key, out node))
+                {
+                    node.Value = pair;
+                }
+                else
+                {
+                    node = list.AddLast(pair);
+                    map[key] = node;
+                }
+            }
+        }
+
+        // TODO: Make these views?
+        public ICollection<TKey> Keys { get { return list.Select(t => t.Key).ToList(); } }
+        public ICollection<TValue> Values { get { return list.Select(t => t.Value).ToList(); } }
+
+        public void Add(IDictionary<TKey, TValue> entries)
+        {
+            ThrowHelper.ThrowIfNull(entries, "entries");
+            foreach (var pair in entries)
+            {
+                Add(pair.Key, pair.Value);
+            }
+        }
+
+        public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator()
+        {
+            return list.GetEnumerator();
+        }
+
+        IEnumerator IEnumerable.GetEnumerator()
+        {
+            return GetEnumerator();
+        }
+
+        void ICollection<KeyValuePair<TKey, TValue>>.Add(KeyValuePair<TKey, TValue> item)
+        {
+            Add(item.Key, item.Value);
+        }
+
+        public void Clear()
+        {
+            this.CheckMutable();
+            list.Clear();
+            map.Clear();
+        }
+
+        bool ICollection<KeyValuePair<TKey, TValue>>.Contains(KeyValuePair<TKey, TValue> item)
+        {
+            TValue value;
+            return TryGetValue(item.Key, out value)
+                && EqualityComparer<TValue>.Default.Equals(item.Value, value);
+        }
+
+        void ICollection<KeyValuePair<TKey, TValue>>.CopyTo(KeyValuePair<TKey, TValue>[] array, int arrayIndex)
+        {
+            list.CopyTo(array, arrayIndex);
+        }
+
+        bool ICollection<KeyValuePair<TKey, TValue>>.Remove(KeyValuePair<TKey, TValue> item)
+        {
+            this.CheckMutable();
+            if (item.Key == null)
+            {
+                throw new ArgumentException("Key is null", "item");
+            }
+            LinkedListNode<KeyValuePair<TKey, TValue>> node;
+            if (map.TryGetValue(item.Key, out node) &&
+                EqualityComparer<TValue>.Default.Equals(item.Value, node.Value.Value))
+            {
+                map.Remove(item.Key);
+                node.List.Remove(node);
+                return true;
+            }
+            else
+            {
+                return false;
+            }
+        }
+
+        public int Count { get { return list.Count; } }
+        public bool IsReadOnly { get { return frozen; } }
+
+        public void Freeze()
+        {
+            if (IsFrozen)
+            {
+                return;
+            }
+            frozen = true;
+            // Only values can be frozen, as all the key types are simple.
+            // Everything can be done in-place, as we're just freezing objects.
+            if (typeof(IFreezable).IsAssignableFrom(typeof(TValue)))
+            {
+                for (var node = list.First; node != null; node = node.Next)
+                {
+                    var pair = node.Value;
+                    IFreezable freezableValue = pair.Value as IFreezable;
+                    if (freezableValue != null)
+                    {
+                        freezableValue.Freeze();
+                    }
+                }
+            }
+        }
+
+        public bool IsFrozen { get { return frozen; } }
+
+        public override bool Equals(object other)
+        {
+            return Equals(other as MapField<TKey, TValue>);
+        }
+
+        public override int GetHashCode()
+        {
+            var valueComparer = EqualityComparer<TValue>.Default;
+            int hash = 0;
+            foreach (var pair in list)
+            {
+                hash ^= pair.Key.GetHashCode() * 31 + valueComparer.GetHashCode(pair.Value);
+            }
+            return hash;
+        }
+
+        public bool Equals(MapField<TKey, TValue> other)
+        {
+            if (other == null)
+            {
+                return false;
+            }
+            if (other == this)
+            {
+                return true;
+            }
+            if (other.Count != this.Count)
+            {
+                return false;
+            }
+            var valueComparer = EqualityComparer<TValue>.Default;
+            foreach (var pair in this)
+            {
+                TValue value;
+                if (!other.TryGetValue(pair.Key, out value))
+                {
+                    return false;
+                }
+                if (!valueComparer.Equals(value, pair.Value))
+                {
+                    return false;
+                }
+            }
+            return true;
+        }
+
+        /// <summary>
+        /// Adds entries to the map from the given stream.
+        /// </summary>
+        /// <remarks>
+        /// It is assumed that the stream is initially positioned after the tag specified by the codec.
+        /// This method will continue reading entries from the stream until the end is reached, or
+        /// a different tag is encountered.
+        /// </remarks>
+        /// <param name="input">Stream to read from</param>
+        /// <param name="codec">Codec describing how the key/value pairs are encoded</param>
+        public void AddEntriesFrom(CodedInputStream input, Codec codec)            
+        {
+            var adapter = new Codec.MessageAdapter(codec);
+            do
+            {
+                adapter.Reset();
+                input.ReadMessage(adapter);
+                this[adapter.Key] = adapter.Value;
+            } while (input.MaybeConsumeTag(codec.MapTag));
+        }        
+
+        public void WriteTo(CodedOutputStream output, Codec codec)
+        {
+            var message = new Codec.MessageAdapter(codec);
+            foreach (var entry in list)
+            {
+                message.Key = entry.Key;
+                message.Value = entry.Value;
+                output.WriteTag(codec.MapTag);
+                output.WriteMessage(message);
+            }
+        }
+
+        public int CalculateSize(Codec codec)
+        {
+            var message = new Codec.MessageAdapter(codec);
+            int size = 0;
+            foreach (var entry in list)
+            {
+                message.Key = entry.Key;
+                message.Value = entry.Value;
+                size += CodedOutputStream.ComputeRawVarint32Size(codec.MapTag);
+                size += CodedOutputStream.ComputeMessageSize(message);
+            }
+            return size;
+        }
+
+        /// <summary>
+        /// A codec for a specific map field. This contains all the information required to encoded and
+        /// decode the nested messages.
+        /// </summary>
+        public sealed class Codec
+        {
+            private readonly FieldCodec<TKey> keyCodec;
+            private readonly FieldCodec<TValue> valueCodec;
+            private readonly uint mapTag;
+
+            public Codec(FieldCodec<TKey> keyCodec, FieldCodec<TValue> valueCodec, uint mapTag)
+            {
+                this.keyCodec = keyCodec;
+                this.valueCodec = valueCodec;
+                this.mapTag = mapTag;
+            }
+
+            /// <summary>
+            /// The tag used in the enclosing message to indicate map entries.
+            /// </summary>
+            internal uint MapTag { get { return mapTag; } }
+
+            /// <summary>
+            /// A mutable message class, used for parsing and serializing. This
+            /// delegates the work to a codec, but implements the <see cref="IMessage"/> interface
+            /// for interop with <see cref="CodedInputStream"/> and <see cref="CodedOutputStream"/>.
+            /// This is nested inside Codec as it's tightly coupled to the associated codec,
+            /// and it's simpler if it has direct access to all its fields.
+            /// </summary>
+            internal class MessageAdapter : IMessage
+            {
+                private readonly Codec codec;
+                internal TKey Key { get; set; }
+                internal TValue Value { get; set; }
+
+                internal MessageAdapter(Codec codec)
+                {
+                    this.codec = codec;
+                }
+
+                internal void Reset()
+                {
+                    Key = codec.keyCodec.DefaultValue;
+                    Value = codec.valueCodec.DefaultValue;
+                }
+
+                public void MergeFrom(CodedInputStream input)
+                {
+                    uint tag;
+                    while (input.ReadTag(out tag))
+                    {
+                        if (tag == 0)
+                        {
+                            throw InvalidProtocolBufferException.InvalidTag();
+                        }
+                        if (tag == codec.keyCodec.Tag)
+                        {
+                            Key = codec.keyCodec.Read(input);
+                        }
+                        else if (tag == codec.valueCodec.Tag)
+                        {
+                            Value = codec.valueCodec.Read(input);
+                        }
+                        else if (WireFormat.IsEndGroupTag(tag))
+                        {
+                            // TODO(jonskeet): Do we need this? (Given that we don't support groups...)
+                            return;
+                        }
+                    }
+                }
+
+                public void WriteTo(CodedOutputStream output)
+                {
+                    codec.keyCodec.Write(output, Key);
+                    codec.valueCodec.Write(output, Value);
+                }
+
+                public int CalculateSize()
+                {
+                    return codec.keyCodec.CalculateSize(Key) + codec.valueCodec.CalculateSize(Value);
+                }
+            }
+        }
+    }
+}
--- a/csharp/src/ProtocolBuffers/Collections/RepeatedField.cs
+++ b/csharp/src/ProtocolBuffers/Collections/RepeatedField.cs
@ -193,7 +193,7 @@ namespace Google.Protobuf.Collections

        public override int GetHashCode()
        {
-            int hash = 23;
+            int hash = 0;
            for (int i = 0; i < count; i++)
            {
                hash = hash * 31 + array[i].GetHashCode();
--- a/csharp/src/ProtocolBuffers/DescriptorProtos/DescriptorProtoFile.cs
+++ b/csharp/src/ProtocolBuffers/DescriptorProtos/DescriptorProtoFile.cs
@ -335,7 +335,7 @@ namespace Google.Protobuf.DescriptorProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      hash ^= file_.GetHashCode();
      return hash;
    }
@ -356,6 +356,7 @@ namespace Google.Protobuf.DescriptorProtos {
      }
      return size;
    }
+
    public void MergeFrom(FileDescriptorSet other) {
      if (other == null) {
        return;
@ -558,7 +559,7 @@ namespace Google.Protobuf.DescriptorProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (Name.Length != 0) hash ^= Name.GetHashCode();
      if (Package.Length != 0) hash ^= Package.GetHashCode();
      hash ^= dependency_.GetHashCode();
@ -685,6 +686,7 @@ namespace Google.Protobuf.DescriptorProtos {
      }
      return size;
    }
+
    public void MergeFrom(FileDescriptorProto other) {
      if (other == null) {
        return;
@ -938,7 +940,7 @@ namespace Google.Protobuf.DescriptorProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (Name.Length != 0) hash ^= Name.GetHashCode();
      hash ^= field_.GetHashCode();
      hash ^= extension_.GetHashCode();
@ -1047,6 +1049,7 @@ namespace Google.Protobuf.DescriptorProtos {
      }
      return size;
    }
+
    public void MergeFrom(DescriptorProto other) {
      if (other == null) {
        return;
@ -1204,7 +1207,7 @@ namespace Google.Protobuf.DescriptorProtos {
        }

        public override int GetHashCode() {
-          int hash = 0;
+          int hash = 1;
          if (Start != 0) hash ^= Start.GetHashCode();
          if (End != 0) hash ^= End.GetHashCode();
          return hash;
@ -1231,6 +1234,7 @@ namespace Google.Protobuf.DescriptorProtos {
          }
          return size;
        }
+
        public void MergeFrom(ExtensionRange other) {
          if (other == null) {
            return;
@ -1341,7 +1345,7 @@ namespace Google.Protobuf.DescriptorProtos {
        }

        public override int GetHashCode() {
-          int hash = 0;
+          int hash = 1;
          if (Start != 0) hash ^= Start.GetHashCode();
          if (End != 0) hash ^= End.GetHashCode();
          return hash;
@ -1368,6 +1372,7 @@ namespace Google.Protobuf.DescriptorProtos {
          }
          return size;
        }
+
        public void MergeFrom(ReservedRange other) {
          if (other == null) {
            return;
@ -1568,7 +1573,7 @@ namespace Google.Protobuf.DescriptorProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (Name.Length != 0) hash ^= Name.GetHashCode();
      if (Number != 0) hash ^= Number.GetHashCode();
      if (Label != global::Google.Protobuf.DescriptorProtos.FieldDescriptorProto.Types.Label.LABEL_OPTIONAL) hash ^= Label.GetHashCode();
@ -1651,6 +1656,7 @@ namespace Google.Protobuf.DescriptorProtos {
      }
      return size;
    }
+
    public void MergeFrom(FieldDescriptorProto other) {
      if (other == null) {
        return;
@ -1837,7 +1843,7 @@ namespace Google.Protobuf.DescriptorProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (Name.Length != 0) hash ^= Name.GetHashCode();
      return hash;
    }
@ -1856,6 +1862,7 @@ namespace Google.Protobuf.DescriptorProtos {
      }
      return size;
    }
+
    public void MergeFrom(OneofDescriptorProto other) {
      if (other == null) {
        return;
@ -1969,7 +1976,7 @@ namespace Google.Protobuf.DescriptorProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (Name.Length != 0) hash ^= Name.GetHashCode();
      hash ^= value_.GetHashCode();
      if (options_ != null) hash ^= Options.GetHashCode();
@ -2006,6 +2013,7 @@ namespace Google.Protobuf.DescriptorProtos {
      }
      return size;
    }
+
    public void MergeFrom(EnumDescriptorProto other) {
      if (other == null) {
        return;
@ -2140,7 +2148,7 @@ namespace Google.Protobuf.DescriptorProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (Name.Length != 0) hash ^= Name.GetHashCode();
      if (Number != 0) hash ^= Number.GetHashCode();
      if (options_ != null) hash ^= Options.GetHashCode();
@ -2175,6 +2183,7 @@ namespace Google.Protobuf.DescriptorProtos {
      }
      return size;
    }
+
    public void MergeFrom(EnumValueDescriptorProto other) {
      if (other == null) {
        return;
@ -2308,7 +2317,7 @@ namespace Google.Protobuf.DescriptorProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (Name.Length != 0) hash ^= Name.GetHashCode();
      hash ^= method_.GetHashCode();
      if (options_ != null) hash ^= Options.GetHashCode();
@ -2345,6 +2354,7 @@ namespace Google.Protobuf.DescriptorProtos {
      }
      return size;
    }
+
    public void MergeFrom(ServiceDescriptorProto other) {
      if (other == null) {
        return;
@ -2515,7 +2525,7 @@ namespace Google.Protobuf.DescriptorProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (Name.Length != 0) hash ^= Name.GetHashCode();
      if (InputType.Length != 0) hash ^= InputType.GetHashCode();
      if (OutputType.Length != 0) hash ^= OutputType.GetHashCode();
@ -2574,6 +2584,7 @@ namespace Google.Protobuf.DescriptorProtos {
      }
      return size;
    }
+
    public void MergeFrom(MethodDescriptorProto other) {
      if (other == null) {
        return;
@ -2871,7 +2882,7 @@ namespace Google.Protobuf.DescriptorProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (JavaPackage.Length != 0) hash ^= JavaPackage.GetHashCode();
      if (JavaOuterClassname.Length != 0) hash ^= JavaOuterClassname.GetHashCode();
      if (JavaMultipleFiles != false) hash ^= JavaMultipleFiles.GetHashCode();
@ -3004,6 +3015,7 @@ namespace Google.Protobuf.DescriptorProtos {
      }
      return size;
    }
+
    public void MergeFrom(FileOptions other) {
      if (other == null) {
        return;
@ -3248,7 +3260,7 @@ namespace Google.Protobuf.DescriptorProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (MessageSetWireFormat != false) hash ^= MessageSetWireFormat.GetHashCode();
      if (NoStandardDescriptorAccessor != false) hash ^= NoStandardDescriptorAccessor.GetHashCode();
      if (Deprecated != false) hash ^= Deprecated.GetHashCode();
@ -3301,6 +3313,7 @@ namespace Google.Protobuf.DescriptorProtos {
      }
      return size;
    }
+
    public void MergeFrom(MessageOptions other) {
      if (other == null) {
        return;
@ -3487,7 +3500,7 @@ namespace Google.Protobuf.DescriptorProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (Ctype != global::Google.Protobuf.DescriptorProtos.FieldOptions.Types.CType.STRING) hash ^= Ctype.GetHashCode();
      if (Packed != false) hash ^= Packed.GetHashCode();
      if (Jstype != global::Google.Protobuf.DescriptorProtos.FieldOptions.Types.JSType.JS_NORMAL) hash ^= Jstype.GetHashCode();
@ -3556,6 +3569,7 @@ namespace Google.Protobuf.DescriptorProtos {
      }
      return size;
    }
+
    public void MergeFrom(FieldOptions other) {
      if (other == null) {
        return;
@ -3726,7 +3740,7 @@ namespace Google.Protobuf.DescriptorProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (AllowAlias != false) hash ^= AllowAlias.GetHashCode();
      if (Deprecated != false) hash ^= Deprecated.GetHashCode();
      hash ^= uninterpretedOption_.GetHashCode();
@ -3763,6 +3777,7 @@ namespace Google.Protobuf.DescriptorProtos {
      }
      return size;
    }
+
    public void MergeFrom(EnumOptions other) {
      if (other == null) {
        return;
@ -3875,7 +3890,7 @@ namespace Google.Protobuf.DescriptorProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (Deprecated != false) hash ^= Deprecated.GetHashCode();
      hash ^= uninterpretedOption_.GetHashCode();
      return hash;
@ -3904,6 +3919,7 @@ namespace Google.Protobuf.DescriptorProtos {
      }
      return size;
    }
+
    public void MergeFrom(EnumValueOptions other) {
      if (other == null) {
        return;
@ -4009,7 +4025,7 @@ namespace Google.Protobuf.DescriptorProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (Deprecated != false) hash ^= Deprecated.GetHashCode();
      hash ^= uninterpretedOption_.GetHashCode();
      return hash;
@ -4038,6 +4054,7 @@ namespace Google.Protobuf.DescriptorProtos {
      }
      return size;
    }
+
    public void MergeFrom(ServiceOptions other) {
      if (other == null) {
        return;
@ -4143,7 +4160,7 @@ namespace Google.Protobuf.DescriptorProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      if (Deprecated != false) hash ^= Deprecated.GetHashCode();
      hash ^= uninterpretedOption_.GetHashCode();
      return hash;
@ -4172,6 +4189,7 @@ namespace Google.Protobuf.DescriptorProtos {
      }
      return size;
    }
+
    public void MergeFrom(MethodOptions other) {
      if (other == null) {
        return;
@ -4337,7 +4355,7 @@ namespace Google.Protobuf.DescriptorProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      hash ^= name_.GetHashCode();
      if (IdentifierValue.Length != 0) hash ^= IdentifierValue.GetHashCode();
      if (PositiveIntValue != 0UL) hash ^= PositiveIntValue.GetHashCode();
@ -4406,6 +4424,7 @@ namespace Google.Protobuf.DescriptorProtos {
      }
      return size;
    }
+
    public void MergeFrom(UninterpretedOption other) {
      if (other == null) {
        return;
@ -4550,7 +4569,7 @@ namespace Google.Protobuf.DescriptorProtos {
        }

        public override int GetHashCode() {
-          int hash = 0;
+          int hash = 1;
          if (NamePart_.Length != 0) hash ^= NamePart_.GetHashCode();
          if (IsExtension != false) hash ^= IsExtension.GetHashCode();
          return hash;
@ -4577,6 +4596,7 @@ namespace Google.Protobuf.DescriptorProtos {
          }
          return size;
        }
+
        public void MergeFrom(NamePart other) {
          if (other == null) {
            return;
@ -4677,7 +4697,7 @@ namespace Google.Protobuf.DescriptorProtos {
    }

    public override int GetHashCode() {
-      int hash = 0;
+      int hash = 1;
      hash ^= location_.GetHashCode();
      return hash;
    }
@ -4698,6 +4718,7 @@ namespace Google.Protobuf.DescriptorProtos {
      }
      return size;
    }
+
    public void MergeFrom(SourceCodeInfo other) {
      if (other == null) {
        return;
@ -4827,7 +4848,7 @@ namespace Google.Protobuf.DescriptorProtos {
        }

        public override int GetHashCode() {
-          int hash = 0;
+          int hash = 1;
          hash ^= path_.GetHashCode();
          hash ^= span_.GetHashCode();
          if (LeadingComments.Length != 0) hash ^= LeadingComments.GetHashCode();
@ -4892,6 +4913,7 @@ namespace Google.Protobuf.DescriptorProtos {
          }
          return size;
        }
+
        public void MergeFrom(Location other) {
          if (other == null) {
            return;
--- a/csharp/src/ProtocolBuffers/FieldCodec.cs
+++ b/csharp/src/ProtocolBuffers/FieldCodec.cs
@ -0,0 +1,188 @@
+using System;
+using System.Collections.Generic;
+
+namespace Google.Protobuf
+{
+    /// <summary>
+    /// Factory methods for <see cref="FieldCodec{T}"/>.
+    /// </summary>
+    public static class FieldCodec
+    {
+        public static FieldCodec<string> ForString(uint tag)
+        {
+            return new FieldCodec<string>(input => input.ReadString(), (output, value) => output.WriteString(value), CodedOutputStream.ComputeStringSize, tag); 
+        }
+
+        public static FieldCodec<ByteString> ForBytes(uint tag)
+        {
+            return new FieldCodec<ByteString>(input => input.ReadBytes(), (output, value) => output.WriteBytes(value), CodedOutputStream.ComputeBytesSize, tag);
+        }
+
+        public static FieldCodec<bool> ForBool(uint tag)
+        {
+            return new FieldCodec<bool>(input => input.ReadBool(), (output, value) => output.WriteBool(value), CodedOutputStream.ComputeBoolSize, tag);
+        }
+
+        public static FieldCodec<int> ForInt32(uint tag)
+        {
+            return new FieldCodec<int>(input => input.ReadInt32(), (output, value) => output.WriteInt32(value), CodedOutputStream.ComputeInt32Size, tag);
+        }
+
+        public static FieldCodec<int> ForSInt32(uint tag)
+        {
+            return new FieldCodec<int>(input => input.ReadSInt32(), (output, value) => output.WriteSInt32(value), CodedOutputStream.ComputeSInt32Size, tag);
+        }
+
+        public static FieldCodec<uint> ForFixed32(uint tag)
+        {
+            return new FieldCodec<uint>(input => input.ReadFixed32(), (output, value) => output.WriteFixed32(value), CodedOutputStream.ComputeFixed32Size, tag);
+        }
+
+        public static FieldCodec<int> ForSFixed32(uint tag)
+        {
+            return new FieldCodec<int>(input => input.ReadSFixed32(), (output, value) => output.WriteSFixed32(value), CodedOutputStream.ComputeSFixed32Size, tag);
+        }
+
+        public static FieldCodec<uint> ForUInt32(uint tag)
+        {
+            return new FieldCodec<uint>(input => input.ReadUInt32(), (output, value) => output.WriteUInt32(value), CodedOutputStream.ComputeUInt32Size, tag);
+        }
+
+        public static FieldCodec<long> ForInt64(uint tag)
+        {
+            return new FieldCodec<long>(input => input.ReadInt64(), (output, value) => output.WriteInt64(value), CodedOutputStream.ComputeInt64Size, tag);
+        }
+
+        public static FieldCodec<long> ForSInt64(uint tag)
+        {
+            return new FieldCodec<long>(input => input.ReadSInt64(), (output, value) => output.WriteSInt64(value), CodedOutputStream.ComputeSInt64Size, tag);
+        }
+
+        public static FieldCodec<ulong> ForFixed64(uint tag)
+        {
+            return new FieldCodec<ulong>(input => input.ReadFixed64(), (output, value) => output.WriteFixed64(value), CodedOutputStream.ComputeFixed64Size, tag);
+        }
+
+        public static FieldCodec<long> ForSFixed64(uint tag)
+        {
+            return new FieldCodec<long>(input => input.ReadSFixed64(), (output, value) => output.WriteSFixed64(value), CodedOutputStream.ComputeSFixed64Size, tag);
+        }
+
+        public static FieldCodec<ulong> ForUInt64(uint tag)
+        {
+            return new FieldCodec<ulong>(input => input.ReadUInt64(), (output, value) => output.WriteUInt64(value), CodedOutputStream.ComputeUInt64Size, tag);
+        }
+
+        public static FieldCodec<float> ForFloat(uint tag)
+        {
+            return new FieldCodec<float>(input => input.ReadFloat(), (output, value) => output.WriteFloat(value), CodedOutputStream.ComputeFloatSize, tag);
+        }
+
+        public static FieldCodec<double> ForDouble(uint tag)
+        {
+            return new FieldCodec<double>(input => input.ReadDouble(), (output, value) => output.WriteDouble(value), CodedOutputStream.ComputeDoubleSize, tag);
+        }
+
+        // Enums are tricky. We can probably use expression trees to build these delegates automatically,
+        // but it's easy to generate the code fdor it.
+        public static FieldCodec<T> ForEnum<T>(uint tag, Func<T, int> toInt32, Func<int, T> fromInt32)
+        {
+            return new FieldCodec<T>(input => fromInt32(
+                input.ReadEnum()),
+                (output, value) => output.WriteEnum(toInt32(value)),
+                value => CodedOutputStream.ComputeEnumSize(toInt32(value)), tag);
+        }
+
+        public static FieldCodec<T> ForMessage<T>(uint tag, MessageParser<T> parser) where T : IMessage<T>
+        {
+            return new FieldCodec<T>(input => { T message = parser.CreateTemplate(); input.ReadMessage(message); return message; },
+                (output, value) => output.WriteMessage(value), message => CodedOutputStream.ComputeMessageSize(message), tag);
+        }
+    }
+
+    /// <summary>
+    /// An encode/decode pair for a single field. This effectively encapsulates
+    /// all the information needed to read or write the field value from/to a coded
+    /// stream.
+    /// </summary>
+    /// <remarks>
+    /// This never writes default values to the stream, and is not currently designed
+    /// to play well with packed arrays.
+    /// </remarks>
+    public sealed class FieldCodec<T>
+    {
+        private static readonly Func<T, bool> IsDefault;
+        private static readonly T Default;
+
+        static FieldCodec()
+        {
+            if (typeof(T) == typeof(string))
+            {
+                Default = (T)(object)"";
+                IsDefault = CreateDefaultValueCheck<string>(x => x.Length == 0);
+            }
+            else if (typeof(T) == typeof(ByteString))
+            {
+                Default = (T)(object)ByteString.Empty;
+                IsDefault = CreateDefaultValueCheck<ByteString>(x => x.Length == 0);
+            }
+            else if (!typeof(T).IsValueType)
+            {
+                // Default default
+                IsDefault = CreateDefaultValueCheck<T>(x => x == null);
+            }
+            else
+            {
+                // Default default
+                IsDefault = CreateDefaultValueCheck<T>(x => EqualityComparer<T>.Default.Equals(x, default(T)));
+            }
+        }
+
+        private static Func<T, bool> CreateDefaultValueCheck<TTmp>(Func<TTmp, bool> check)
+        {
+            return (Func<T, bool>)(object)check;
+        }
+
+        private readonly Func<CodedInputStream, T> reader;
+        private readonly Action<CodedOutputStream, T> writer;
+        private readonly Func<T, int> sizeComputer;
+        private readonly uint tag;
+        private readonly int tagSize;
+
+        internal FieldCodec(
+            Func<CodedInputStream, T> reader,
+            Action<CodedOutputStream, T> writer,
+            Func<T, int> sizeComputer,
+            uint tag)
+        {
+            this.reader = reader;
+            this.writer = writer;
+            this.sizeComputer = sizeComputer;
+            this.tag = tag;
+            tagSize = CodedOutputStream.ComputeRawVarint32Size(tag);
+        }
+
+        public uint Tag { get { return tag; } }
+
+        public T DefaultValue { get { return Default; } }
+
+        public void Write(CodedOutputStream output, T value)
+        {
+            if (!IsDefault(value))
+            {
+                output.WriteTag(tag);
+                writer(output, value);
+            }
+        }
+
+        public T Read(CodedInputStream input)
+        {
+            return reader(input);
+        }
+
+        public int CalculateSize(T value)
+        {
+            return IsDefault(value) ? 0 : sizeComputer(value) + CodedOutputStream.ComputeRawVarint32Size(tag);
+        }        
+    }
+}
--- a/csharp/src/ProtocolBuffers/ProtocolBuffers.csproj
+++ b/csharp/src/ProtocolBuffers/ProtocolBuffers.csproj
@ -60,6 +60,7 @@
    <Compile Include="CodedOutputStream.cs" />
    <Compile Include="Collections\Dictionaries.cs" />
    <Compile Include="Collections\Lists.cs" />
+    <Compile Include="Collections\MapField.cs" />
    <Compile Include="Collections\ReadOnlyDictionary.cs" />
    <Compile Include="Collections\RepeatedField.cs" />
    <Compile Include="Collections\RepeatedFieldExtensions.cs" />
@ -84,6 +85,7 @@
    <Compile Include="Descriptors\MethodDescriptor.cs" />
    <Compile Include="Descriptors\PackageDescriptor.cs" />
    <Compile Include="Descriptors\ServiceDescriptor.cs" />
+    <Compile Include="FieldCodec.cs" />
    <Compile Include="FrameworkPortability.cs" />
    <Compile Include="Freezable.cs" />
    <Compile Include="MessageExtensions.cs" />
--- a/src/Makefile.am
+++ b/src/Makefile.am
@ -425,6 +425,8 @@ libprotoc_la_SOURCES =                                         \
  google/protobuf/compiler/csharp/csharp_generator.cc          \
  google/protobuf/compiler/csharp/csharp_helpers.cc            \
  google/protobuf/compiler/csharp/csharp_helpers.h             \
+  google/protobuf/compiler/csharp/csharp_map_field.cc          \
+  google/protobuf/compiler/csharp/csharp_map_field.h           \
  google/protobuf/compiler/csharp/csharp_message.cc            \
  google/protobuf/compiler/csharp/csharp_message.h             \
  google/protobuf/compiler/csharp/csharp_message_field.cc      \
--- a/src/google/protobuf/compiler/csharp/csharp_enum_field.cc
+++ b/src/google/protobuf/compiler/csharp/csharp_enum_field.cc
@ -74,6 +74,12 @@ void EnumFieldGenerator::GenerateSerializedSizeCode(io::Printer* printer) {
    "}\n");
 }

+void EnumFieldGenerator::GenerateCodecCode(io::Printer* printer) {
+    printer->Print(
+        variables_,
+        "pb::FieldCodec.ForEnum($tag$, x => (int) x, x => ($type_name$) x)");
+}
+
 EnumOneofFieldGenerator::EnumOneofFieldGenerator(const FieldDescriptor* descriptor,
 						 int fieldOrdinal)
  : PrimitiveOneofFieldGenerator(descriptor, fieldOrdinal) {
--- a/src/google/protobuf/compiler/csharp/csharp_enum_field.h
+++ b/src/google/protobuf/compiler/csharp/csharp_enum_field.h
@ -46,6 +46,7 @@ class EnumFieldGenerator : public PrimitiveFieldGenerator {
  EnumFieldGenerator(const FieldDescriptor* descriptor, int fieldOrdinal);
  ~EnumFieldGenerator();

+  virtual void GenerateCodecCode(io::Printer* printer);
  virtual void GenerateParsingCode(io::Printer* printer);
  virtual void GenerateSerializationCode(io::Printer* printer);
  virtual void GenerateSerializedSizeCode(io::Printer* printer);
--- a/src/google/protobuf/compiler/csharp/csharp_field_base.cc
+++ b/src/google/protobuf/compiler/csharp/csharp_field_base.cc
@ -65,6 +65,7 @@ void FieldGeneratorBase::SetCommonFieldVariables(
    tag_bytes += ", " + SimpleItoa(tag_array[i]);
  }

+  (*variables)["tag"] = SimpleItoa(tag);
  (*variables)["tag_size"] = SimpleItoa(tag_size);
  (*variables)["tag_bytes"] = tag_bytes;

@ -112,6 +113,11 @@ void FieldGeneratorBase::GenerateFreezingCode(io::Printer* printer) {
  // special handling for freezing, so default to not generating any code.
 }

+void FieldGeneratorBase::GenerateCodecCode(io::Printer* printer) {
+    // No-op: expect this to be overridden by appropriate types.
+    // Could fail if we get called here though...
+}
+
 void FieldGeneratorBase::AddDeprecatedFlag(io::Printer* printer) {
  if (descriptor_->options().deprecated())
  {
@ -151,12 +157,16 @@ std::string FieldGeneratorBase::name() {
 }

 std::string FieldGeneratorBase::type_name() {
-  switch (descriptor_->type()) {
+  return type_name(descriptor_);
+}
+
+std::string FieldGeneratorBase::type_name(const FieldDescriptor* descriptor) {
+  switch (descriptor->type()) {
    case FieldDescriptor::TYPE_ENUM:
-      return GetClassName(descriptor_->enum_type());
+      return GetClassName(descriptor->enum_type());
    case FieldDescriptor::TYPE_MESSAGE:
    case FieldDescriptor::TYPE_GROUP:
-      return GetClassName(descriptor_->message_type());
+      return GetClassName(descriptor->message_type());
    case FieldDescriptor::TYPE_DOUBLE:
      return "double";
    case FieldDescriptor::TYPE_FLOAT:
--- a/src/google/protobuf/compiler/csharp/csharp_field_base.h
+++ b/src/google/protobuf/compiler/csharp/csharp_field_base.h
@ -49,6 +49,7 @@ class FieldGeneratorBase : public SourceGeneratorBase {

  virtual void GenerateCloningCode(io::Printer* printer) = 0;
  virtual void GenerateFreezingCode(io::Printer* printer);
+  virtual void GenerateCodecCode(io::Printer* printer);
  virtual void GenerateMembers(io::Printer* printer) = 0;
  virtual void GenerateMergingCode(io::Printer* printer) = 0;
  virtual void GenerateParsingCode(io::Printer* printer) = 0;
@ -76,6 +77,7 @@ class FieldGeneratorBase : public SourceGeneratorBase {
  std::string property_name();
  std::string name();
  std::string type_name();
+  std::string type_name(const FieldDescriptor* descriptor);
  bool has_default_value();
  bool is_nullable_type();
  std::string default_value();
--- a/src/google/protobuf/compiler/csharp/csharp_helpers.cc
+++ b/src/google/protobuf/compiler/csharp/csharp_helpers.cc
@ -46,6 +46,7 @@

 #include <google/protobuf/compiler/csharp/csharp_field_base.h>
 #include <google/protobuf/compiler/csharp/csharp_enum_field.h>
+#include <google/protobuf/compiler/csharp/csharp_map_field.h>
 #include <google/protobuf/compiler/csharp/csharp_message_field.h>
 #include <google/protobuf/compiler/csharp/csharp_primitive_field.h>
 #include <google/protobuf/compiler/csharp/csharp_repeated_enum_field.h>
@ -355,7 +356,11 @@ FieldGeneratorBase* CreateFieldGenerator(const FieldDescriptor* descriptor,
    case FieldDescriptor::TYPE_GROUP:
    case FieldDescriptor::TYPE_MESSAGE:
      if (descriptor->is_repeated()) {
-        return new RepeatedMessageFieldGenerator(descriptor, fieldOrdinal);
+        if (descriptor->is_map()) {
+          return new MapFieldGenerator(descriptor, fieldOrdinal);
+        } else {
+          return new RepeatedMessageFieldGenerator(descriptor, fieldOrdinal);
+        }
      } else {
 	if (descriptor->containing_oneof()) {
 	  return new MessageOneofFieldGenerator(descriptor, fieldOrdinal);
--- a/src/google/protobuf/compiler/csharp/csharp_map_field.cc
+++ b/src/google/protobuf/compiler/csharp/csharp_map_field.cc
@ -0,0 +1,141 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2015 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include <sstream>
+
+#include <google/protobuf/compiler/code_generator.h>
+#include <google/protobuf/compiler/plugin.h>
+#include <google/protobuf/descriptor.h>
+#include <google/protobuf/descriptor.pb.h>
+#include <google/protobuf/io/printer.h>
+#include <google/protobuf/io/zero_copy_stream.h>
+#include <google/protobuf/stubs/strutil.h>
+
+#include <google/protobuf/compiler/csharp/csharp_helpers.h>
+#include <google/protobuf/compiler/csharp/csharp_map_field.h>
+
+namespace google {
+namespace protobuf {
+namespace compiler {
+namespace csharp {
+
+MapFieldGenerator::MapFieldGenerator(const FieldDescriptor* descriptor,
+                                             int fieldOrdinal)
+    : FieldGeneratorBase(descriptor, fieldOrdinal) {
+}
+
+MapFieldGenerator::~MapFieldGenerator() {
+}
+
+void MapFieldGenerator::GenerateMembers(io::Printer* printer) {   
+  const FieldDescriptor* key_descriptor =
+      descriptor_->message_type()->FindFieldByName("key");
+  const FieldDescriptor* value_descriptor =
+      descriptor_->message_type()->FindFieldByName("value");
+  variables_["key_type_name"] = type_name(key_descriptor);
+  variables_["value_type_name"] = type_name(value_descriptor);
+  scoped_ptr<FieldGeneratorBase> key_generator(CreateFieldGenerator(key_descriptor, 1));  
+  scoped_ptr<FieldGeneratorBase> value_generator(CreateFieldGenerator(value_descriptor, 2));
+
+  printer->Print(
+    variables_,
+    "private static readonly pbc::MapField<$key_type_name$, $value_type_name$>.Codec _map_$name$_codec\n"
+    "    = new pbc::MapField<$key_type_name$, $value_type_name$>.Codec(");
+  key_generator->GenerateCodecCode(printer);
+  printer->Print(", ");
+  value_generator->GenerateCodecCode(printer);
+  printer->Print(
+    variables_,
+    ", $tag$);\n"
+    "private readonly pbc::MapField<$key_type_name$, $value_type_name$> $name$_ = new pbc::MapField<$key_type_name$, $value_type_name$>();\n");
+  AddDeprecatedFlag(printer);
+  printer->Print(
+    variables_,
+    "public pbc::MapField<$key_type_name$, $value_type_name$> $property_name$ {\n"
+    "  get { return $name$_; }\n"
+    "}\n");
+}
+
+void MapFieldGenerator::GenerateMergingCode(io::Printer* printer) {
+  printer->Print(
+      variables_,
+      "$name$_.Add(other.$name$_);\n");
+}
+
+void MapFieldGenerator::GenerateParsingCode(io::Printer* printer) {
+  printer->Print(
+    variables_,
+    "$name$_.AddEntriesFrom(input, _map_$name$_codec);\n");
+}
+
+void MapFieldGenerator::GenerateSerializationCode(io::Printer* printer) {
+  printer->Print(
+    variables_,
+    "$name$_.WriteTo(output, _map_$name$_codec);\n");
+}
+
+void MapFieldGenerator::GenerateSerializedSizeCode(io::Printer* printer) {
+  printer->Print(
+    variables_,
+    "size += $name$_.CalculateSize(_map_$name$_codec);\n");
+}
+
+void MapFieldGenerator::WriteHash(io::Printer* printer) {
+  printer->Print(
+    variables_,
+    "hash ^= $property_name$.GetHashCode();\n");
+}
+void MapFieldGenerator::WriteEquals(io::Printer* printer) {
+  printer->Print(
+    variables_,
+    "if (!$property_name$.Equals(other.$property_name$)) return false;\n");
+}
+void MapFieldGenerator::WriteToString(io::Printer* printer) {
+    /*
+  variables_["field_name"] = GetFieldName(descriptor_);
+  printer->Print(
+    variables_,
+    "PrintField(\"$field_name$\", has$property_name$, $name$_, writer);\n");*/
+}
+
+void MapFieldGenerator::GenerateCloningCode(io::Printer* printer) {
+  printer->Print(variables_,
+    "$name$_ = other.$name$_.Clone();\n");
+}
+
+void MapFieldGenerator::GenerateFreezingCode(io::Printer* printer) {
+  printer->Print(variables_,
+    "$name$_.Freeze();\n");
+}
+
+}  // namespace csharp
+}  // namespace compiler
+}  // namespace protobuf
+}  // namespace google
--- a/src/google/protobuf/compiler/csharp/csharp_map_field.h
+++ b/src/google/protobuf/compiler/csharp/csharp_map_field.h
@ -0,0 +1,71 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef GOOGLE_PROTOBUF_COMPILER_CSHARP_MAP_FIELD_H__
+#define GOOGLE_PROTOBUF_COMPILER_CSHARP_MAP_FIELD_H__
+
+#include <string>
+
+#include <google/protobuf/compiler/code_generator.h>
+#include <google/protobuf/compiler/csharp/csharp_field_base.h>
+
+namespace google {
+namespace protobuf {
+namespace compiler {
+namespace csharp {
+
+class MapFieldGenerator : public FieldGeneratorBase {
+ public:
+  MapFieldGenerator(const FieldDescriptor* descriptor, int fieldOrdinal);
+  ~MapFieldGenerator();
+
+  virtual void GenerateCloningCode(io::Printer* printer);
+  virtual void GenerateFreezingCode(io::Printer* printer);
+  virtual void GenerateMembers(io::Printer* printer);
+  virtual void GenerateMergingCode(io::Printer* printer);
+  virtual void GenerateParsingCode(io::Printer* printer);
+  virtual void GenerateSerializationCode(io::Printer* printer);
+  virtual void GenerateSerializedSizeCode(io::Printer* printer);
+
+  virtual void WriteHash(io::Printer* printer);
+  virtual void WriteEquals(io::Printer* printer);
+  virtual void WriteToString(io::Printer* printer);
+
+ private:
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(MapFieldGenerator);
+};
+
+}  // namespace csharp
+}  // namespace compiler
+}  // namespace protobuf
+}  // namespace google
+
+#endif  // GOOGLE_PROTOBUF_COMPILER_CSHARP_MAP_FIELD_H__
+
--- a/src/google/protobuf/compiler/csharp/csharp_message.cc
+++ b/src/google/protobuf/compiler/csharp/csharp_message.cc
@ -268,8 +268,6 @@ void MessageGenerator::Generate(io::Printer* printer) {
      "}\n\n");
  }

-  // TODO(jonskeet): Map properties
-
  // Standard methods
  GenerateFrameworkMethods(printer);
  GenerateMessageSerializationMethods(printer);
@ -299,7 +297,6 @@ void MessageGenerator::Generate(io::Printer* printer) {
  printer->Outdent();
  printer->Print("}\n");
  printer->Print("\n");
-
 }

 void MessageGenerator::GenerateCloningCode(io::Printer* printer) {
@ -408,9 +405,10 @@ void MessageGenerator::GenerateFrameworkMethods(io::Printer* printer) {
        "}\n\n");

    // GetHashCode
+    // Start with a non-zero value to easily distinguish between null and "empty" messages.
    printer->Print(
        "public override int GetHashCode() {\n"
-        "  int hash = 0;\n");
+        "  int hash = 1;\n");
    printer->Indent();
    for (int i = 0; i < descriptor_->field_count(); i++) {
        scoped_ptr<FieldGeneratorBase> generator(
@ -451,7 +449,7 @@ void MessageGenerator::GenerateMessageSerializationMethods(io::Printer* printer)
  }
  printer->Print("return size;\n");
  printer->Outdent();
-  printer->Print("}\n");
+  printer->Print("}\n\n");
 }

 void MessageGenerator::GenerateMergingMethods(io::Printer* printer) {
@ -469,7 +467,6 @@ void MessageGenerator::GenerateMergingMethods(io::Printer* printer) {
    "if (other == null) {\n"
    "  return;\n"
    "}\n");
-  // TODO(jonskeet): Maps?
  // Merge non-oneof fields
  for (int i = 0; i < descriptor_->field_count(); i++) {
    if (!descriptor_->field(i)->containing_oneof()) {      
--- a/src/google/protobuf/compiler/csharp/csharp_message_field.cc
+++ b/src/google/protobuf/compiler/csharp/csharp_message_field.cc
@ -138,6 +138,12 @@ void MessageFieldGenerator::GenerateFreezingCode(io::Printer* printer) {
    "if ($has_property_check$) $property_name$.Freeze();\n");
 }

+void MessageFieldGenerator::GenerateCodecCode(io::Printer* printer) {
+  printer->Print(
+    variables_,
+    "pb::FieldCodec.ForMessage($tag$, $type_name$.Parser)");
+}
+
 MessageOneofFieldGenerator::MessageOneofFieldGenerator(const FieldDescriptor* descriptor,
 						       int fieldOrdinal)
    : MessageFieldGenerator(descriptor, fieldOrdinal) {
--- a/src/google/protobuf/compiler/csharp/csharp_message_field.h
+++ b/src/google/protobuf/compiler/csharp/csharp_message_field.h
@ -46,6 +46,7 @@ class MessageFieldGenerator : public FieldGeneratorBase {
  MessageFieldGenerator(const FieldDescriptor* descriptor, int fieldOrdinal);
  ~MessageFieldGenerator();

+  virtual void GenerateCodecCode(io::Printer* printer);
  virtual void GenerateCloningCode(io::Printer* printer);
  virtual void GenerateFreezingCode(io::Printer* printer);
  virtual void GenerateMembers(io::Printer* printer);
--- a/src/google/protobuf/compiler/csharp/csharp_primitive_field.cc
+++ b/src/google/protobuf/compiler/csharp/csharp_primitive_field.cc
@ -129,7 +129,7 @@ void PrimitiveFieldGenerator::GenerateSerializedSizeCode(io::Printer* printer) {
      "size += $tag_size$ + $fixed_size$;\n",
      "fixed_size", SimpleItoa(fixedSize),
      "tag_size", variables_["tag_size"]);
-  }    
+  }
  printer->Outdent();
  printer->Print("}\n");
 }
@ -155,6 +155,12 @@ void PrimitiveFieldGenerator::GenerateCloningCode(io::Printer* printer) {
    "$name$_ = other.$name$_;\n");
 }

+void PrimitiveFieldGenerator::GenerateCodecCode(io::Printer* printer) {
+  printer->Print(
+    variables_,
+    "pb::FieldCodec.For$capitalized_type_name$($tag$)");
+}
+
 PrimitiveOneofFieldGenerator::PrimitiveOneofFieldGenerator(
    const FieldDescriptor* descriptor, int fieldOrdinal)
    : PrimitiveFieldGenerator(descriptor, fieldOrdinal) {
--- a/src/google/protobuf/compiler/csharp/csharp_primitive_field.h
+++ b/src/google/protobuf/compiler/csharp/csharp_primitive_field.h
@ -46,6 +46,7 @@ class PrimitiveFieldGenerator : public FieldGeneratorBase {
  PrimitiveFieldGenerator(const FieldDescriptor* descriptor, int fieldOrdinal);
  ~PrimitiveFieldGenerator();

+  virtual void GenerateCodecCode(io::Printer* printer);
  virtual void GenerateCloningCode(io::Printer* printer);
  virtual void GenerateMembers(io::Printer* printer);
  virtual void GenerateMergingCode(io::Printer* printer);
--- a/src/google/protobuf/map_unittest_proto3.proto
+++ b/src/google/protobuf/map_unittest_proto3.proto
@ -0,0 +1,120 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// This file is mostly equivalent to map_unittest.proto, but imports
+// unittest_proto3.proto instead of unittest.proto, so that it only
+// uses proto3 messages. This makes it suitable for testing
+// implementations which only support proto3.
+// The TestRequiredMessageMap message has been removed as there are no
+// required fields in proto3.
+syntax = "proto3";
+
+option cc_enable_arenas = true;
+option csharp_namespace = "Google.Protobuf.TestProtos";
+
+import "google/protobuf/unittest_proto3.proto";
+
+// We don't put this in a package within proto2 because we need to make sure
+// that the generated code doesn't depend on being in the proto2 namespace.
+// In map_test_util.h we do "using namespace unittest = protobuf_unittest".
+package protobuf_unittest;
+
+// Tests maps.
+message TestMap {
+  map<int32   , int32   > map_int32_int32       = 1;
+  map<int64   , int64   > map_int64_int64       = 2;
+  map<uint32  , uint32  > map_uint32_uint32     = 3;
+  map<uint64  , uint64  > map_uint64_uint64     = 4;
+  map<sint32  , sint32  > map_sint32_sint32     = 5;
+  map<sint64  , sint64  > map_sint64_sint64     = 6;
+  map<fixed32 , fixed32 > map_fixed32_fixed32   = 7;
+  map<fixed64 , fixed64 > map_fixed64_fixed64   = 8;
+  map<sfixed32, sfixed32> map_sfixed32_sfixed32 = 9;
+  map<sfixed64, sfixed64> map_sfixed64_sfixed64 = 10;
+  map<int32   , float   > map_int32_float       = 11;
+  map<int32   , double  > map_int32_double      = 12;
+  map<bool    , bool    > map_bool_bool         = 13;
+  map<string  , string  > map_string_string     = 14;
+  map<int32   , bytes   > map_int32_bytes       = 15;
+  map<int32   , MapEnum > map_int32_enum        = 16;
+  map<int32   , ForeignMessage> map_int32_foreign_message = 17;
+}
+
+message TestMapSubmessage {
+  TestMap test_map = 1;
+}
+
+message TestMessageMap {
+  map<int32, TestAllTypes> map_int32_message = 1;
+}
+
+// Two map fields share the same entry default instance.
+message TestSameTypeMap {
+  map<int32, int32> map1 = 1;
+  map<int32, int32> map2 = 2;
+}
+
+enum MapEnum {
+  MAP_ENUM_FOO = 0;
+  MAP_ENUM_BAR = 1;
+  MAP_ENUM_BAZ = 2;
+}
+
+message TestArenaMap {
+  map<int32   , int32   > map_int32_int32       = 1;
+  map<int64   , int64   > map_int64_int64       = 2;
+  map<uint32  , uint32  > map_uint32_uint32     = 3;
+  map<uint64  , uint64  > map_uint64_uint64     = 4;
+  map<sint32  , sint32  > map_sint32_sint32     = 5;
+  map<sint64  , sint64  > map_sint64_sint64     = 6;
+  map<fixed32 , fixed32 > map_fixed32_fixed32   = 7;
+  map<fixed64 , fixed64 > map_fixed64_fixed64   = 8;
+  map<sfixed32, sfixed32> map_sfixed32_sfixed32 = 9;
+  map<sfixed64, sfixed64> map_sfixed64_sfixed64 = 10;
+  map<int32   , float   > map_int32_float       = 11;
+  map<int32   , double  > map_int32_double      = 12;
+  map<bool    , bool    > map_bool_bool         = 13;
+  map<int32   , MapEnum > map_int32_enum        = 14;
+  map<int32   , ForeignMessage> map_int32_foreign_message = 15;
+}
+
+// Previously, message containing enum called Type cannot be used as value of
+// map field.
+message MessageContainingEnumCalledType {
+  enum Type {
+    TYPE_FOO = 0;
+  }
+  map<int32, MessageContainingEnumCalledType> type = 1;
+}
+
+// Previously, message cannot contain map field called "entry".
+message MessageContainingMapCalledEntry {
+  map<int32, int32> entry = 1;
+}