Revamp to reflection.

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

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

Generated code changes coming in the next commit.

1 files changed, 28 insertions, 0 deletions

diff --git a/csharp/src/Google.Protobuf/Reflection/FieldDescriptor.cs b/csharp/src/Google.Protobuf/Reflection/FieldDescriptor.cs
index 3d9d0d75..57378e4c 100644
--- a/csharp/src/Google.Protobuf/Reflection/FieldDescriptor.cs
+++ b/csharp/src/Google.Protobuf/Reflection/FieldDescriptor.cs
@@ -31,6 +31,7 @@
 #endregion
 
 using System;
+using System.Linq;
 
 namespace Google.Protobuf.Reflection
 {
@@ -45,6 +46,7 @@ namespace Google.Protobuf.Reflection
         private readonly MessageDescriptor containingType;
         private readonly OneofDescriptor containingOneof;
         private FieldType fieldType;
+        private IFieldAccessor accessor;
 
         internal FieldDescriptor(FieldDescriptorProto proto, FileDescriptor file,
                                  MessageDescriptor parent, int index)
@@ -82,6 +84,8 @@ namespace Google.Protobuf.Reflection
         public override string Name { get { return proto.Name; } }
 
         internal FieldDescriptorProto Proto { get { return proto; } }
+
+        public IFieldAccessor Accessor { get { return accessor; } }
         
         /// <summary>
         /// Maps a field type as included in the .proto file to a FieldType.
@@ -287,6 +291,30 @@ namespace Google.Protobuf.Reflection
             {
                 throw new DescriptorValidationException(this, "MessageSet format is not supported.");
             }
+
+            accessor = CreateAccessor();
+        }
+
+        private IFieldAccessor CreateAccessor()
+        {
+            // TODO: Check the performance of this with some large protos. Each message is O(N^2) in the number of fields,
+            // which isn't great...
+            if (containingType.GeneratedType == null)
+            {
+                return null;
+            }
+            var property = containingType
+                .GeneratedType
+                .GetProperties()
+                .FirstOrDefault(p => p.IsDefined(typeof(ProtobufFieldAttribute), false) &&
+                                     p.GetCustomAttributes(typeof(ProtobufFieldAttribute), false).Cast<ProtobufFieldAttribute>().Single().Number == FieldNumber);
+            if (property == null)
+            {
+                return null;
+            }
+            return IsMap ? new MapFieldAccessor(property, this)
+                : IsRepeated ? new RepeatedFieldAccessor(property, this)
+                : (IFieldAccessor) new SingleFieldAccessor(property, this);
         }
     }
 }
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