So you think you know C++ #1

gistfile1.cpp

// Today we learn about the insane things that can be done with variadic templates.

template <int N> struct A {
  template <typename O, typename R, typename... FArgs, typename... TArgs, typename... Args>
  R operator()(O* o, R (O::*f)(FArgs...), const std::tuple<TArgs...>& t, Args... args) {
    return A<N-1>()(o, f, t, std::get<N>(t), args...);
  }
};

template <> struct A<-1> {
  template <typename O, typename R, typename... FArgs, typename... TArgs, typename... Args>
  R operator()(O* o, R (O::*f)(FArgs...), const std::tuple<TArgs...>& t, Args... args) {
    return (o->*f)(args...);
  }
};

// What is the effect of function |b|?
template <typename O, typename R, typename... FArgs, typename... TArgs, typename... Args>
R b(O* o, R (O::*f)(FArgs...), const std::tuple<TArgs...>& t) {
  return A<sizeof...(TArgs)-1>()(o, f, t);
}

Function b() calls the member function pointed to by f on the instance of type O pointed to by o with arguments consisting of elements of the tuple t. The relative order of the arguments passed into the member function is the same is their original order in the tuple.

Edit: Although in reality the effect is probably a compile error when you try to write code that uses b(), then a segfault when you finally run the code.