f2ptr

f2ptr.cpp

#include <cassert>
#include <cstdio>
#include <string>

using namespace std;

namespace f2ptr {

namespace details {
template <class...> struct type_list {};

// Helper meta-function needed to derive correct signature of our C-style
// function.
template <class F>
struct func_traits : public func_traits<decltype(&F::operator())> {};
template <class ClassType, class R, class... Args>
struct func_traits<R (ClassType::*)(Args...) const> {
  using return_type = R;
  using args_type = type_list<Args...>;
};


class f2ptr_impl {
public:
  template <class F> static auto get(F f) {
    return get_impl(typename func_traits<F>::args_type{}, std::move(f));
  }

private:
  template <class F, class... Args>
  static auto get_impl(type_list<Args...>, F f) {
    static F std_func = std::move(f);
    return +[](Args... args) ->
           typename func_traits<F>::return_type { return std_func(args...); };
  }
};
} // namespace details

template <class F> auto f2ptr(F f) {
  return details::f2ptr_impl::get(std::move(f));
}

} // namespace f2ptr

void take_callbacks(void (*cb1)(int, char), void (*cb2)(int));

int main() {
    int local_i = 0;
  take_callbacks(f2ptr::f2ptr([&](int i, char) { puts("f1"); }),
                 f2ptr::f2ptr([&](int i) { puts("f2"); }));
}