--- /dev/null
+
+#if !defined(INCLUDED_CALLBACKFWD_H)
+#define INCLUDED_CALLBACKFWD_H
+
+template<typename Return>
+class Callback0;
+typedef Callback0<void> Callback;
+
+template<typename FirstArgument, typename Result = void>
+class Callback1;
+
+template<typename FirstArgument, typename SecondArgument, typename Result = void>
+class Callback2;
+
+template<typename FirstArgument, typename SecondArgument, typename ThirdArgument, typename Result = void>
+class Callback3;
+
+#endif