Revert changes for FieldPresenceAccessor

csharp/src/Google.Protobuf.Test/Reflection/FieldAccessTest.cs

@@ -101,7 +101,7 @@ namespace Google.Protobuf.Reflection
         {
             IMessage message = SampleMessages.CreateFullTestAllTypes();
             var fields = message.Descriptor.Fields;
-            Assert.Throws<InvalidOperationException>(() => (fields[TestProtos.TestAllTypes.SingleBoolFieldNumber].Accessor as IFieldPresenceAccessor).HasValue(message));
+            Assert.Throws<InvalidOperationException>(() => fields[TestProtos.TestAllTypes.SingleBoolFieldNumber].Accessor.HasValue(message));
         }
 
         [Test]
@@ -109,7 +109,7 @@ namespace Google.Protobuf.Reflection
         {
             IMessage message = new Proto2.TestAllTypes();
             var fields = message.Descriptor.Fields;
-            var accessor = fields[Proto2.TestAllTypes.OptionalBoolFieldNumber].Accessor as IFieldPresenceAccessor;
+            var accessor = fields[Proto2.TestAllTypes.OptionalBoolFieldNumber].Accessor;
 
             Assert.False(accessor.HasValue(message));
 

csharp/src/Google.Protobuf/MessageExtensions.cs

@@ -183,7 +183,7 @@ namespace Google.Protobuf
                     }
                     else if (f.FieldType == FieldType.Message || f.FieldType == FieldType.Group)
                     {
-                        if ((f.Accessor as IFieldPresenceAccessor).HasValue(message))
+                        if (f.Accessor.HasValue(message))
                         {
                             return ((IMessage)f.Accessor.GetValue(message)).IsInitialized();
                         }
@@ -194,7 +194,7 @@ namespace Google.Protobuf
                     }
                     else if (f.IsRequired)
                     {
-                        return (f.Accessor as IFieldPresenceAccessor).HasValue(message);
+                        return f.Accessor.HasValue(message);
                     }
                     else
                     {

csharp/src/Google.Protobuf/Reflection/IFieldAccessor.cs

@@ -58,6 +58,11 @@ namespace Google.Protobuf.Reflection
         /// </summary>
         object GetValue(IMessage message);
 
+        /// <summary>
+        /// Indicates whether the field in the specified message is set. For proto3 fields, this throws an <see cref="InvalidOperationException"/>
+        /// </summary>
+        bool HasValue(IMessage message);
+
         /// <summary>
         /// Mutator for single "simple" fields only.
         /// </summary>
@@ -68,15 +73,4 @@ namespace Google.Protobuf.Reflection
         /// <exception cref="InvalidOperationException">The field is not a "simple" field.</exception>
         void SetValue(IMessage message, object value);
     }
-
-    /// <summary>
-    /// Allows field presence to be checked reflectively. This is implemented for all single field accessors
-    /// </summary>
-    public interface IFieldPresenceAccessor : IFieldAccessor
-    {
-        /// <summary>
-        /// Indicates whether the field in the specified message is set. For proto3 fields, this throws an <see cref="InvalidOperationException"/>
-        /// </summary>
-        bool HasValue(IMessage message);
-    }
 }

csharp/src/Google.Protobuf/Reflection/SingleFieldAccessor.cs

@@ -39,7 +39,7 @@ namespace Google.Protobuf.Reflection
     /// <summary>
     /// Accessor for single fields.
     /// </summary>
-    internal sealed class SingleFieldAccessor : FieldAccessorBase, IFieldPresenceAccessor
+    internal sealed class SingleFieldAccessor : FieldAccessorBase
     {
         // All the work here is actually done in the constructor - it creates the appropriate delegates.
         // There are various cases to consider, based on the property type (message, string/bytes, or "genuine" primitive)