Fixes from PR review.

2 files changed, 21 insertions, 11 deletions

diff --git a/csharp/src/ProtocolBuffers/Collections/MapField.cs b/csharp/src/ProtocolBuffers/Collections/MapField.cs
index ead45737..f5e4fd3a 100644
--- a/csharp/src/ProtocolBuffers/Collections/MapField.cs
+++ b/csharp/src/ProtocolBuffers/Collections/MapField.cs
@@ -51,7 +51,7 @@ namespace Google.Protobuf.Collections
     public sealed class MapField<TKey, TValue> : IDeepCloneable<MapField<TKey, TValue>>, IFreezable, IDictionary<TKey, TValue>, IEquatable<MapField<TKey, TValue>>, IDictionary
     {
         // TODO: Don't create the map/list until we have an entry. (Assume many maps will be empty.)
-        private bool allowNullValues;
+        private readonly bool allowNullValues;
         private bool frozen;
         private readonly Dictionary<TKey, LinkedListNode<KeyValuePair<TKey, TValue>>> map =
             new Dictionary<TKey, LinkedListNode<KeyValuePair<TKey, TValue>>>();
diff --git a/csharp/src/ProtocolBuffers/FieldCodec.cs b/csharp/src/ProtocolBuffers/FieldCodec.cs
index caf03286..85462787 100644
--- a/csharp/src/ProtocolBuffers/FieldCodec.cs
+++ b/csharp/src/ProtocolBuffers/FieldCodec.cs
@@ -161,20 +161,30 @@ namespace Google.Protobuf
                 null); // Default value for the wrapper
         }
 
-        // Helper code to create codecs for wrapper types. Somewhat ugly with all the 
+        /// <summary>
+        /// Helper code to create codecs for wrapper types.
+        /// </summary>
+        /// <remarks>
+        /// Somewhat ugly with all the static methods, but the conversions involved to/from nullable types make it
+        /// slightly tricky to improve. So long as we keep the public API (ForClassWrapper, ForStructWrapper) in place,
+        /// we can refactor later if we come up with something cleaner.
+        /// </remarks>
         private static class WrapperCodecs
         {
+            // All the field numbers are the same (1).
+            private const int WrapperValueFieldNumber = Google.Protobuf.WellKnownTypes.Int32Value.ValueFieldNumber;
+
             private static readonly Dictionary<Type, object> Codecs = new Dictionary<Type, object>
             {
-                { typeof(bool), ForBool(WireFormat.MakeTag(1, WireFormat.WireType.Varint)) },
-                { typeof(int), ForInt32(WireFormat.MakeTag(1, WireFormat.WireType.Varint)) },
-                { typeof(long), ForInt64(WireFormat.MakeTag(1, WireFormat.WireType.Varint)) },
-                { typeof(uint), ForUInt32(WireFormat.MakeTag(1, WireFormat.WireType.Varint)) },
-                { typeof(ulong), ForUInt64(WireFormat.MakeTag(1, WireFormat.WireType.Varint)) },
-                { typeof(float), ForFloat(WireFormat.MakeTag(1, WireFormat.WireType.Fixed32)) },
-                { typeof(double), ForDouble(WireFormat.MakeTag(1, WireFormat.WireType.Fixed64)) },
-                { typeof(string), ForString(WireFormat.MakeTag(1, WireFormat.WireType.LengthDelimited)) },
-                { typeof(ByteString), ForBytes(WireFormat.MakeTag(1, WireFormat.WireType.LengthDelimited)) }
+                { typeof(bool), ForBool(WireFormat.MakeTag(WrapperValueFieldNumber, WireFormat.WireType.Varint)) },
+                { typeof(int), ForInt32(WireFormat.MakeTag(WrapperValueFieldNumber, WireFormat.WireType.Varint)) },
+                { typeof(long), ForInt64(WireFormat.MakeTag(WrapperValueFieldNumber, WireFormat.WireType.Varint)) },
+                { typeof(uint), ForUInt32(WireFormat.MakeTag(WrapperValueFieldNumber, WireFormat.WireType.Varint)) },
+                { typeof(ulong), ForUInt64(WireFormat.MakeTag(WrapperValueFieldNumber, WireFormat.WireType.Varint)) },
+                { typeof(float), ForFloat(WireFormat.MakeTag(WrapperValueFieldNumber, WireFormat.WireType.Fixed32)) },
+                { typeof(double), ForDouble(WireFormat.MakeTag(WrapperValueFieldNumber, WireFormat.WireType.Fixed64)) },
+                { typeof(string), ForString(WireFormat.MakeTag(WrapperValueFieldNumber, WireFormat.WireType.LengthDelimited)) },
+                { typeof(ByteString), ForBytes(WireFormat.MakeTag(WrapperValueFieldNumber, WireFormat.WireType.LengthDelimited)) }
             };
 
             /// <summary>