1 files changed, 24 insertions, 9 deletions
diff --git a/csharp/src/Google.Protobuf/Reflection/SingleFieldAccessor.cs b/csharp/src/Google.Protobuf/Reflection/SingleFieldAccessor.cs
index bbac2173..d541570f 100644
--- a/csharp/src/Google.Protobuf/Reflection/SingleFieldAccessor.cs
+++ b/csharp/src/Google.Protobuf/Reflection/SingleFieldAccessor.cs
@@ -48,6 +48,7 @@ namespace Google.Protobuf.Reflection
 
         private readonly Action<IMessage, object> setValueDelegate;
         private readonly Action<IMessage> clearDelegate;
+        private readonly Func<IMessage, bool> hasDelegate;
 
         internal SingleFieldAccessor(PropertyInfo property, FieldDescriptor descriptor) : base(property, descriptor)
         {
@@ -56,16 +57,25 @@ namespace Google.Protobuf.Reflection
                 throw new ArgumentException("Not all required properties/methods available");
             }
             setValueDelegate = ReflectionUtil.CreateActionIMessageObject(property.GetSetMethod());
+            if (descriptor.File.Proto.Syntax == "proto2")
+            {
+                MethodInfo hasMethod = property.DeclaringType.GetRuntimeProperty("Has" + property.Name).GetMethod;
+                hasDelegate = ReflectionUtil.CreateFuncIMessageBool(hasMethod ?? throw new ArgumentException("Not all required properties/methods are available"));
+                MethodInfo clearMethod = property.DeclaringType.GetRuntimeMethod("Clear" + property.Name, ReflectionUtil.EmptyTypes);
+                clearDelegate = ReflectionUtil.CreateActionIMessage(clearMethod ?? throw new ArgumentException("Not all required properties/methods are available"));
+            }
+            else
+            {
+                hasDelegate = (_) => throw new InvalidOperationException("HasValue is not implemented for proto3 fields"); var clrType = property.PropertyType;
 
-            var clrType = property.PropertyType;
-            
-            // TODO: Validate that this is a reasonable single field? (Should be a value type, a message type, or string/ByteString.)
-            object defaultValue =
-                descriptor.FieldType == FieldType.Message ? null
-                : clrType == typeof(string) ? ""
-                : clrType == typeof(ByteString) ? ByteString.Empty
-                : Activator.CreateInstance(clrType);
-            clearDelegate = message => SetValue(message, defaultValue);
+                // TODO: Validate that this is a reasonable single field? (Should be a value type, a message type, or string/ByteString.) 
+                object defaultValue =
+                    descriptor.FieldType == FieldType.Message ? null
+                    : clrType == typeof(string) ? ""
+                    : clrType == typeof(ByteString) ? ByteString.Empty
+                    : Activator.CreateInstance(clrType);
+                clearDelegate = message => SetValue(message, defaultValue);
+            }
         }
 
         public override void Clear(IMessage message)
@@ -73,6 +83,11 @@ namespace Google.Protobuf.Reflection
             clearDelegate(message);
         }
 
+        public override bool HasValue(IMessage message)
+        {
+            return hasDelegate(message);
+        }
+
         public override void SetValue(IMessage message, object value)
         {
             setValueDelegate(message, value);