method_choice.cpp

#include <utility>

template<typename T, T... PMFs>
struct method_choice;

template<typename C, typename R, R C::* PMF, R C::*... PMFs>
struct method_choice<R C::*, PMF, PMFs...> {
  template<typename... A>
  method_choice(int choice, C &subject, A... args) {
    if (choice == 0) {
      (subject.*PMF)(std::forward<A>(args)...);
    } else {
      method_choice<R C::*, PMFs...>(choice - 1, subject, std::forward<A>(args)...);
    }
  }
};

template<typename C, typename R>
struct method_choice<R C::*> {
  template<typename... A>
  method_choice(int, C &, A...) {
    // die?
  }
};

extern volatile int poop;

struct what {
  void f(int x) { poop += x; }
  void g(int x) { poop *= x; }
  void h(int x) { poop -= x; }
};

void hello(int k) {
  what w;
  method_choice<void (what::*)(int), &what::f, &what::g, &what::h>(k, w, 42);
}