unpack tuple and apply them to a function

apply.hpp

#include <tuple>
#include <type_traits>
#include "integer_sequence.hpp"

template <typename T>
using resultof = typename std::result_of<T>::type;

template <typename F, typename... Args, size_t... I>
auto apply_(F&& f, std::tuple<Args...>&& args, IntegerSeq<I...>)
    -> resultof<F(Args...)> {
  using T = std::tuple<Args...>;
  return f(std::get<I>(std::forward<T>(args))...);
}

template <typename F, typename... Args>
auto apply(F&& f, std::tuple<Args...>&& args) -> resultof<F(Args...)> {
  using T = std::tuple<Args...>;
  using S = MakeSeq<sizeof...(Args)>;
  return apply_(std::forward<F>(f), std::forward<T>(args), S());
}