ivalue.cpp

template<bool...> struct bool_pack;
template<bool... bs> 
using all_true = std::is_same<bool_pack<bs..., true>, bool_pack<true, bs...>>;

template<class R, class... Ts>
using are_all_constructible = all_true<std::is_constructible<R, Ts>::value...>;

template<typename... Ts>
struct ivalue_constructible_tuple {
  constexpr static bool value = are_all_constructible<c10::IValue, Ts...>::value;
};

template<typename... Ts>
struct ivalue_constructible_tuple<std::tuple<Ts...>> {
  constexpr static bool value = are_all_constructible<c10::IValue, Ts...>::value;
};

template <typename R, typename...Args>
struct lazy_wrap {
  lazy_wrap(std::function<R(Args...)> f, const char* s) : f_(f), s_(s) {
    std::cerr << "Return type is not Tensor: " << typeid(R).name() << "\n";
  }
  std::function<R(Args...)> f_;
  const char* s_;
  R operator()(Args... a) {
    return f_(a...);
  }
};

template <typename T>
void debugIValue(std::ostream& out, T t) {
  out << std::is_constructible<c10::IValue, T>::value << " " << typeid(t).name();
}

template <typename T, typename U, typename... Args>
void debugIValue(std::ostream& out, T t, U u, Args... args) {
  out << std::is_constructible<c10::IValue, T>::value << " " << typeid(t).name() << ',';
  debugIValue(out, u, args...);
}

template<typename... Args>
struct lazy_wrap<Tensor, Args...> {
  lazy_wrap(std::function<Tensor(Args...)> f, const char* s) : f_(f), s_(s) {
    std::cerr << "Return type is Tensor\n";
  }
  std::function<Tensor(Args...)> f_;
  const char* s_;

  template <typename T = std::tuple<Args...>,
    typename std::enable_if<!ivalue_constructible_tuple<T>::value>::type* = nullptr>
  Tensor operator()(Args... as) {
    std::cerr << "Args are NOT IValue-able " <<
      ivalue_constructible_tuple<T>::value << "\n";
    debugIValue(std::cerr, as...);
    return f_(as...);
  }

  template <typename T = std::tuple<Args...>,
    typename std::enable_if<ivalue_constructible_tuple<T>::value>::type* = nullptr>
  Tensor operator()(Args... as) {
    std::cerr << "Args ARE IValue-able\n";
    std::vector<c10::IValue> inps = {{ c10::IValue(as)... }};
    return at::single_output(s_, inps);
  }

};