Added enable_if for the EventHandler templates

SDL2pp/Private/EventHandler.hh

@@ -91,13 +91,15 @@ namespace Private {
 	struct IsEventHandler<
 		EventHandlerType,
 		EventType,
-		And<
+		typename std::enable_if<
-			Or<
+			And<
-				IsEventHandlerObject<EventHandlerType, EventType>,
+				Or<
-				IsEventHandlerFunctor<EventHandlerType, EventType>
+					IsEventHandlerObject<EventHandlerType, EventType>,
-			>,
+					IsEventHandlerFunctor<EventHandlerType, EventType>
-			TupleHasType<EventType, ValidEventTypes>
+				>,
-		>
+				TupleHasType<EventType, ValidEventTypes>
+			>::value
+		>::type
 	> : std::true_type { };
 }
 }

SDL2pp/Private/EventHandlerFunctor.hh

@@ -52,7 +52,9 @@ namespace Private {
 	struct IsEventHandlerFunctor<
 		EventHandlerType,
 		EventType,
-		std::is_convertible<EventHandlerType, EventHandlerFunctorSignature<EventType>>
+		typename std::enable_if<
+			std::is_convertible<EventHandlerType, EventHandlerFunctorSignature<EventType>>::value
+		>::type
 	> : std::true_type { };
 }
 }

SDL2pp/Private/EventHandlerObject.hh

@@ -29,6 +29,15 @@ namespace SDL2pp {
  * This is code not to be used directly by users of SDL2pp.
  */
 namespace Private {
+	/*
+	 * Templated class to detect if a given type can handle a given event.
+	 */
+	template <typename EventHandlerType, typename EventType>
+	struct HasEventHandlerMethod : std::is_same<
+		decltype(std::declval<EventHandlerType>().HandleEvent(std::declval<const EventType &>())),
+		void
+	> { };
+	
 	/*
 	 * Templated class to identify a class that is not an event handler object.
 	 */
@@ -45,10 +54,9 @@ namespace Private {
 	struct IsEventHandlerObject<
 		EventHandlerType,
 		EventType,
-		std::is_same<
+		typename std::enable_if<
-			decltype(std::declval<EventHandlerType>().HandleEvent(std::declval<const EventType &>())),
+			HasEventHandlerMethod<EventHandlerType, EventType>::value
-			void
+		>::type
-		>
 	> : std::true_type { };
 }
 }