add MethodResultCallback_0_0

src/google/protobuf/stubs/callback.h

@@ -346,6 +346,29 @@ struct InternalConstRef {
   typedef const base_type& type;
 };
 
+template<typename R, typename T>
+class MethodResultCallback_0_0 : public ResultCallback<R> {
+ public:
+  typedef R (T::*MethodType)();
+  MethodResultCallback_0_0(T* object, MethodType method, bool self_deleting)
+      : object_(object),
+        method_(method),
+        self_deleting_(self_deleting) {}
+  ~MethodResultCallback_0_0() {}
+
+  R Run() {
+    bool needs_delete = self_deleting_;
+    R result = (object_->*method_)();
+    if (needs_delete) delete this;
+    return result;
+  }
+
+ private:
+  T* object_;
+  MethodType method_;
+  bool self_deleting_;
+};
+
 template <typename R, typename T, typename P1, typename P2, typename P3,
           typename P4, typename P5, typename A1, typename A2>
 class MethodResultCallback_5_2 : public ResultCallback2<R, A1, A2> {
@@ -520,6 +543,13 @@ inline ResultCallback1<R, A1>* NewPermanentCallback(
       function, false, p1);
 }
 
+// See MethodResultCallback_0_0
+template <typename R, typename T1, typename T2>
+inline ResultCallback<R>* NewPermanentCallback(
+    T1* object, R (T2::*function)()) {
+  return new internal::MethodResultCallback_0_0<R, T1>(object, function, false);
+}
+
 // See MethodResultCallback_5_2
 template <typename R, typename T, typename P1, typename P2, typename P3,
           typename P4, typename P5, typename A1, typename A2>