c10/util/C++17.h

#pragma once
#ifndef C10_UTIL_CPP17_H_
#define C10_UTIL_CPP17_H_

#include <type_traits>
#include <utility>
#include <memory>
#include <sstream>
#include <string>
#include <cstdlib>
#include <functional>
#include <c10/macros/Macros.h>

/*
 * This header adds some polyfills with C++14 and C++17 functionality
 */

namespace c10 { namespace guts {



#ifdef __cpp_lib_transformation_trait_aliases
template<bool B, class T, class F> using conditional_t = std::conditional_t<B, T, F>;
template<bool B, class T = void> using enable_if_t = std::enable_if_t<B, T>;
template<class T> using add_lvalue_reference_t = std::add_lvalue_reference_t<T>;
template<class T> using remove_reference_t = std::remove_reference_t<T>;
template<class T> using remove_cv_t = std::remove_cv_t<T>;
template<class T> using result_of_t = std::result_of_t<T>;
template<class T> using decay_t = std::decay_t<T>;
template<class T> using remove_const_t = std::remove_const_t<T>;
template<class T> using remove_pointer_t = std::remove_pointer_t<T>;
template<class... T> using common_type_t = std::common_type_t<T...>;
#else
template<bool B, class T, class F> using conditional_t = typename std::conditional<B, T, F>::type;
template<bool B, class T = void> using enable_if_t = typename std::enable_if<B, T>::type;
template<class T> using add_lvalue_reference_t = typename std::add_lvalue_reference<T>::type;
template<class T> using remove_reference_t = typename std::remove_reference<T>::type;
template<class T> using remove_cv_t = typename std::remove_cv<T>::type;
template<class T> using result_of_t = typename std::result_of<T>::type;
template<class T> using decay_t = typename std::decay<T>::type;
template<class T> using remove_const_t = typename std::remove_const<T>::type;
template<class T> using remove_pointer_t = typename std::remove_pointer<T>::type;
template<class... T> using common_type_t = typename std::common_type<T...>::type;
#endif




// C++11 doesn't have constexpr std::move / std::forward.
// Implementation taken from libc++.
template<class T>
constexpr inline guts::remove_reference_t<T>&& move(T&& t) noexcept {
  return static_cast<guts::remove_reference_t<T>&&>(t);
}
template <class T>
constexpr inline T&& forward(guts::remove_reference_t<T>& t) noexcept {
    return static_cast<T&&>(t);
}
template <class T>
constexpr inline T&& forward(guts::remove_reference_t<T>&& t) noexcept {
    static_assert(!std::is_lvalue_reference<T>::value,
                  "can not forward an rvalue as an lvalue.");
    return static_cast<T&&>(t);
}




#if __cplusplus >= 201402L || defined(__cpp_lib_make_unique) && __cpp_lib_make_unique >= 201304L || \
  (defined(__ANDROID__) && __ANDROID__ && __cplusplus >= 201300L) || defined(_MSC_VER) && _MSC_VER >= 1900

/* using override */ using std::make_unique;

#else

// Implementation taken from folly
template <typename T, typename... Args>
typename std::enable_if<!std::is_array<T>::value, std::unique_ptr<T>>::type
make_unique(Args&&... args) {
  return std::unique_ptr<T>(new T(c10::guts::forward<Args>(args)...));
}
// Allows 'make_unique<T[]>(10)'. (N3690 s20.9.1.4 p3-4)
template <typename T>
typename std::enable_if<std::is_array<T>::value, std::unique_ptr<T>>::type
make_unique(const size_t n) {
  return std::unique_ptr<T>(new typename std::remove_extent<T>::type[n]());
}
// Disallows 'make_unique<T[10]>()'. (N3690 s20.9.1.4 p5)
template <typename T, typename... Args>
typename std::enable_if<std::extent<T>::value != 0, std::unique_ptr<T>>::type
make_unique(Args&&...) = delete;

#endif



#ifdef __cpp_lib_integer_sequence

template<class T, T... Ints> using integer_sequence = std::integer_sequence<T, Ints...>;
template<std::size_t... Ints> using index_sequence = std::index_sequence<Ints...>;
template<class T, T N> using make_integer_sequence = std::make_integer_sequence<T, N>;
template<std::size_t N> using make_index_sequence = std::make_index_sequence<N>;
template<class... T> using index_sequence_for = std::index_sequence_for<T...>;

#else

template<class T, T... Ints> struct integer_sequence {
  using value_type = T;
  static constexpr std::size_t size() noexcept {return sizeof...(Ints);}
};
template<std::size_t... Ints> using index_sequence = integer_sequence<std::size_t, Ints...>;
namespace detail {
  template<class T, std::size_t I, std::size_t N, T... Ints>
  struct make_integer_sequence_ {
    using type = typename make_integer_sequence_<T, I+1, N, Ints..., I>::type;
  };
  template<class T, std::size_t N, T... Ints>
  struct make_integer_sequence_<T, N, N, Ints...> {
    using type = integer_sequence<T, Ints...>;
  };
}
template<class T, T N> using make_integer_sequence = typename detail::make_integer_sequence_<T, 0, N>::type;
template<std::size_t N> using make_index_sequence = make_integer_sequence<std::size_t, N>;
static_assert(std::is_same<index_sequence<>, make_index_sequence<0>>::value, "");
static_assert(std::is_same<index_sequence<0, 1, 2>, make_index_sequence<3>>::value, "");
template<class... T> using index_sequence_for = make_index_sequence<sizeof...(T)>;

#endif




#ifdef __cpp_lib_logical_traits

template <class... B>
using conjunction = std::conjunction<B...>;
template <class... B>
using disjunction = std::disjunction<B...>;
template <bool B>
using bool_constant = std::bool_constant<B>;
template <class B>
using negation = std::negation<B>;

#else

// Implementation taken from http://en.cppreference.com/w/cpp/types/conjunction
template<class...> struct conjunction : std::true_type { };
template<class B1> struct conjunction<B1> : B1 { };
template<class B1, class... Bn>
struct conjunction<B1, Bn...>
    : conditional_t<bool(B1::value), conjunction<Bn...>, B1> {};

// Implementation taken from http://en.cppreference.com/w/cpp/types/disjunction
template<class...> struct disjunction : std::false_type { };
template<class B1> struct disjunction<B1> : B1 { };
template<class B1, class... Bn>
struct disjunction<B1, Bn...>
    : conditional_t<bool(B1::value), B1, disjunction<Bn...>>  { };

// Implementation taken from http://en.cppreference.com/w/cpp/types/integral_constant
template <bool B>
using bool_constant = std::integral_constant<bool, B>;

// Implementation taken from http://en.cppreference.com/w/cpp/types/negation
template<class B>
struct negation : bool_constant<!bool(B::value)> { };

#endif



#ifdef __cpp_lib_void_t

template<class T> using void_t = std::void_t<T>;

#else

// Implementation taken from http://en.cppreference.com/w/cpp/types/void_t
// (it takes CWG1558 into account and also works for older compilers)
template<typename... Ts> struct make_void { typedef void type;};
template<typename... Ts> using void_t = typename make_void<Ts...>::type;

#endif



#ifdef __cpp_lib_apply

template <class F, class Tuple>
inline constexpr decltype(auto) apply(F&& f, Tuple&& t) {
  return std::apply(std::forward<F>(f), std::forward<Tuple>(t));
}

#else

// Implementation from http://en.cppreference.com/w/cpp/utility/apply (but modified)
// TODO This is an incomplete implementation of std::apply, not working for member functions.
namespace detail {
template <class F, class Tuple, std::size_t... I>
constexpr auto apply_impl(F&& f, Tuple&& t, guts::index_sequence<I...>) -> decltype(c10::guts::forward<F>(f)(std::get<I>(c10::guts::forward<Tuple>(t))...))
{
    return c10::guts::forward<F>(f)(std::get<I>(c10::guts::forward<Tuple>(t))...);
}
}  // namespace detail

template <class F, class Tuple>
constexpr auto apply(F&& f, Tuple&& t) -> decltype(detail::apply_impl(
    c10::guts::forward<F>(f), c10::guts::forward<Tuple>(t),
    guts::make_index_sequence<std::tuple_size<guts::remove_reference_t<Tuple>>::value>{}))
{
    return detail::apply_impl(
        c10::guts::forward<F>(f), c10::guts::forward<Tuple>(t),
        guts::make_index_sequence<std::tuple_size<guts::remove_reference_t<Tuple>>::value>{});
}

#endif




#if defined(_MSC_VER) && defined(__CUDACC__) && \
    (__CUDACC_VER_MAJOR__ >= 10 || (__CUDACC_VER_MAJOR__ == 9 && __CUDACC_VER_MINOR__ >= 2))
// workaround: CUDA >= v9.2 compiler cannot compile correctly on Windows.
#  define AT_CPP14_CONSTEXPR
#else
#if defined(__cpp_constexpr) && __cpp_constexpr >= 201304
#  define AT_CPP14_CONSTEXPR constexpr
#else
#  define AT_CPP14_CONSTEXPR
#endif
#endif

template <typename Functor, typename... Args>
typename std::enable_if<
    std::is_member_pointer<typename std::decay<Functor>::type>::value,
    typename std::result_of<Functor && (Args && ...)>::type>::type
invoke(Functor&& f, Args&&... args) {
  return std::mem_fn(f)(std::forward<Args>(args)...);
}

template <typename Functor, typename... Args>
typename std::enable_if<
    !std::is_member_pointer<typename std::decay<Functor>::type>::value,
    typename std::result_of<Functor && (Args && ...)>::type>::type
invoke(Functor&& f, Args&&... args) {
  return std::forward<Functor>(f)(std::forward<Args>(args)...);
}



// GCC 4.8 doesn't define std::to_string, even though that's in C++11. Let's define it.
namespace detail {
class DummyClassForToString final {};
}}}
namespace std {
// We use SFINAE to detect if std::to_string exists for a type, but that only works
// if the function name is defined. So let's define a std::to_string for a dummy type.
// If you're getting an error here saying that this overload doesn't match your
// std::to_string() call, then you're calling std::to_string() but should be calling
// c10::guts::to_string().
inline std::string to_string(c10::guts::detail::DummyClassForToString) { return ""; }

}
namespace c10 { namespace guts { namespace detail {

template<class T, class Enable = void>
struct to_string_ final {
    static std::string call(T value) {
        std::ostringstream str;
        str << value;
        return str.str();
    }
};
// If a std::to_string exists, use that instead
template<class T>
struct to_string_<T, void_t<decltype(std::to_string(std::declval<T>()))>> final {
    static std::string call(T value) {
        return std::to_string(value);
    }
};
}
template<class T> inline std::string to_string(T value) {
    return detail::to_string_<T>::call(value);
}

}}

#endif // C10_UTIL_CPP17_H_