1. namespace mystd {
    3. template <typename T>
    4. struct decay {
    5.  private:
    6.   typedef typename std::remove_reference<T>::type U;
    8.  public:
    9.   typedef typename std::conditional<
    10.       std::is_array<U>::value, typename std::remove_extent<U>::type *,
    11.       typename std::conditional<
    12.           std::is_function<U>::value, typename std::add_pointer<U>::type,
    13.           typename std::remove_cv<U>::type>::type>::type type;
    14. };
    16. template <typename T>
    17. using decay_t = typename decay<T>::type;
    19. }  // namespace mystd
    22. // test 
    23. int main(int argc, char **argv) {
    24.   mystd::decay_t<int> a = 1000;
    25.   std::cout << std::is_same<int, mystd::decay_t<int>>::value << std::endl;
    26.   return 0;
    27. }