| // Copyright 2019 The Fuchsia Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #ifndef LIB_STDCOMPAT_UTILITY_H_ |
| #define LIB_STDCOMPAT_UTILITY_H_ |
| |
| #include <cstddef> |
| #include <type_traits> |
| #include <utility> |
| |
| #include "internal/utility.h" |
| #include "version.h" |
| |
| namespace cpp17 { |
| // Use alias for cpp17 and above. |
| #if __cplusplus >= 201411L && !defined(LIB_STDCOMPAT_USE_POLYFILLS) |
| |
| using std::in_place; |
| using std::in_place_t; |
| |
| using std::in_place_index; |
| using std::in_place_index_t; |
| |
| using std::in_place_type; |
| using std::in_place_type_t; |
| |
| #else // Provide provide polyfills for |in_place*| types and variables. |
| |
| // Tag for requesting in-place initialization. |
| struct in_place_t { |
| explicit constexpr in_place_t() = default; |
| }; |
| |
| // Tag for requesting in-place initialization by type. |
| template <typename T> |
| struct in_place_type_t { |
| explicit constexpr in_place_type_t() = default; |
| }; |
| |
| // Tag for requesting in-place initialization by index. |
| template <std::size_t Index> |
| struct in_place_index_t final { |
| explicit constexpr in_place_index_t() = default; |
| }; |
| |
| // Use inline variables if available. |
| #if defined(__cpp_inline_variables) && __cpp_inline_variables >= 201606L && \ |
| !defined(LIB_STDCOMPAT_USE_POLYFILLS) |
| |
| constexpr in_place_t in_place{}; |
| |
| template <typename T> |
| constexpr in_place_type_t<T> in_place_type{}; |
| |
| template <std::size_t Index> |
| constexpr in_place_index_t<Index> in_place_index{}; |
| |
| #else // Provide polyfill reference to provided variable storage. |
| |
| static constexpr const in_place_t& in_place = |
| internal::instantiate_templated_tag<in_place_t>::storage; |
| |
| template <typename T> |
| static constexpr const in_place_type_t<T>& in_place_type = |
| internal::instantiate_templated_tag<in_place_type_t<T>>::storage; |
| |
| template <std::size_t Index> |
| static constexpr const in_place_index_t<Index>& in_place_index = |
| internal::instantiate_templated_tag<in_place_index_t<Index>>::storage; |
| |
| #endif // __cpp_inline_variables >= 201606L && !defined(LIB_STDCOMPAT_USE_POLYFILLS) |
| |
| #endif // __cplusplus >= 201411L && !defined(LIB_STDCOMPAT_USE_POLYFILLS) |
| |
| #if defined(__cpp_lib_as_const) && __cpp_lib_as_const >= 201510L && \ |
| !defined(LIB_STDCOMPAT_USE_POLYFILLS) |
| |
| using std::as_const; |
| |
| #else // Provide as_const polyfill. |
| |
| template <typename T> |
| constexpr std::add_const_t<T>& as_const(T& t) noexcept { |
| return t; |
| } |
| |
| template <typename T> |
| void as_const(T&&) = delete; |
| |
| #endif // __cpp_lib_as_const >= 201510L && !defined(LIB_STDCOMPAT_USE_POLYFILLS) |
| |
| } // namespace cpp17 |
| |
| namespace cpp20 { |
| |
| #if defined(__cpp_lib_constexpr_algorithms) && __cpp_lib_constexpr_algorithms >= 201806L && \ |
| !defined(LIB_STDCOMPAT_USE_POLYFILLS) |
| |
| using std::exchange; |
| |
| #else // Add swap constexpr polyfill. |
| |
| template < |
| typename T, typename U = T, |
| typename std::enable_if<std::is_move_assignable<T>::value && cpp17::is_assignable_v<T&, U>, |
| bool>::type = true> |
| constexpr T exchange(T& obj, U&& new_value) { |
| T old = std::move(obj); |
| obj = std::forward<U>(new_value); |
| return old; |
| } |
| |
| #endif // __cpp_lib_constexpr_algorithms >= 201806L && !defined(LIB_STDCOMPAT_USE_POLYFILLS) |
| |
| } // namespace cpp20 |
| |
| #endif // LIB_STDCOMPAT_UTILITY_H_ |