#include <iostream>
#include <tuple>
#include <typeinfo>

template <typename T>
struct function_traits;

struct void_type { using type = void; };

template <typename T_Ret, typename ...T_Args>
struct function_traits<T_Ret(T_Args...)> {
    // Number of arguments.
    enum { arity = sizeof...(T_Args) };

    // Argument types.
    template <size_t i>
    struct args {
        using type
            = typename std::conditional<(i < sizeof...(T_Args)),
                                        std::tuple_element<i, std::tuple<T_Args...>>,
                                        void_type>::type::type;
    };
};

int main() {
	using Arg0 = function_traits<int(float)>::args<0>::type;
	using Arg1 = function_traits<int(float)>::args<1>::type;
	
	std::cout << typeid(Arg0).name() << std::endl;
	std::cout << typeid(Arg1).name() << std::endl;
}