関数オブジェクトのシグニチャーでオーバーロード

overload_by_functor.cpp

#include <type_traits>
#include <functional>
#include <utility>
#include <iostream>

namespace
{
struct wildcard { wildcard(...); };

template<typename ...Args> inline auto invoke(wildcard, Args &&...args) -> wildcard;
template<typename ...Args, typename Func>
inline auto invoke(Func &&func, Args &&...args) -> decltype
(std::forward<Func>(func)(std::forward<Args>(args)...));

}

template<typename X, typename Y>
struct is_callable {};

template<typename Func, typename Ret, typename ...Args>
struct is_callable<Func,Ret(Args...)>
{
  static constexpr bool value = std::is_same<Ret, decltype(invoke
			( std::declval<Func>()
			, std::declval<Args>()...))>::value;
};

extern void *enabler;

struct ser_tag {};
struct par_tag {};
struct Task
{
	template<typename Func, typename std::enable_if<
			is_callable<Func,void(int,par_tag)>::value>::type *& = enabler>
	Task(Func &&func)
	{
		std::cerr << "Task: par" << std::endl;
		func(3, par_tag());
	}

	template<typename Func, typename std::enable_if<
			is_callable<Func,void(int,ser_tag)>::value>::type *& = enabler>
	Task(Func &&func)
	{
		std::cerr << "Task: ser" << std::endl;
		func(5, ser_tag());
	}
};

int main()
{
	Task task1([] (int n, ser_tag) { std::cerr << "ser func:" << n << std::endl; });
	Task task2([] (int n, par_tag) { std::cerr << "par func:" << n << std::endl; });
	return 0;
}