C++模板 index_sequence使用示例详解

template<typename _Tp, _Tp... _Idx>
  struct integer_sequence
  {
    typedef _Tp value_type;
    static constexpr size_t size() noexcept { return sizeof...(_Idx); }
  };

template <size_t... N> void print(std::index_sequence<N...>) {
  std::vector<int> res;
  (void)std::initializer_list<int>{
      ((res.push_back(N), std::cout << N << " "), 0)...};
  std::for_each(res.begin(), res.end(), [](int x) {std::cout << x << " ";});
}
int main() {
  auto t = std::make_index_sequence<10>();
  print(t);
  return 0;
}

template <int... N> struct index_seq {};
template <int N, int... M>
struct make_index_seq : public make_index_seq<N - 1, N - 1, M...> {};
template <int... M> struct make_index_seq<0, M...> : public index_seq<M...> {};

template <int... N> void print(index_seq<N...>) {
  (void)std::initializer_list<int>{((std::cout << N << " "), 0)...};
}
int main() {
  auto r = make_index_seq<100>();
  print(r);
  return 0;
}

template <typename T, typename F, int...N>
void exec_for_tuple(const T& tup, F&& func, index_seq<N...>) {
  (void)std::initializer_list<int> {
      (func(std::get<N>(tup)), 0)...
  };
}
template <typename Func, typename ...Arg>
void for_tuple(Func&& func, std::tuple<Arg...> tuple) {
  exec_for_tuple(tuple, std::forward<Func>(func), make_index_seq<sizeof...(Arg)>());
}

std::tuple<int, int, double> tuple{1, 2, 3.0};
for_tuple([](auto t) {
  std::cout << t << " ";
}, tuple);

template<typename... _Types>
using index_sequence_for = make_index_seq<sizeof...(_Types)>;