| // Copyright 2021 The Chromium 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 BASE_CXX17_BACKPORTS_H_ |
| #define BASE_CXX17_BACKPORTS_H_ |
| |
| #include <array> |
| #include <initializer_list> |
| #include <memory> |
| #include <string> |
| |
| namespace gurl_base { |
| |
| // C++14 implementation of C++17's std::size(): |
| // http://en.cppreference.com/w/cpp/iterator/size |
| template <typename Container> |
| constexpr auto size(const Container& c) -> decltype(c.size()) { |
| return c.size(); |
| } |
| |
| template <typename T, size_t N> |
| constexpr size_t size(const T (&array)[N]) noexcept { |
| return N; |
| } |
| |
| // C++14 implementation of C++17's std::empty(): |
| // http://en.cppreference.com/w/cpp/iterator/empty |
| template <typename Container> |
| constexpr auto empty(const Container& c) -> decltype(c.empty()) { |
| return c.empty(); |
| } |
| |
| template <typename T, size_t N> |
| constexpr bool empty(const T (&array)[N]) noexcept { |
| return false; |
| } |
| |
| template <typename T> |
| constexpr bool empty(std::initializer_list<T> il) noexcept { |
| return il.size() == 0; |
| } |
| |
| // C++14 implementation of C++17's std::data(): |
| // http://en.cppreference.com/w/cpp/iterator/data |
| template <typename Container> |
| constexpr auto data(Container& c) -> decltype(c.data()) { |
| return c.data(); |
| } |
| |
| // std::basic_string::data() had no mutable overload prior to C++17 [1]. |
| // Hence this overload is provided. |
| // Note: str[0] is safe even for empty strings, as they are guaranteed to be |
| // null-terminated [2]. |
| // |
| // [1] http://en.cppreference.com/w/cpp/string/basic_string/data |
| // [2] http://en.cppreference.com/w/cpp/string/basic_string/operator_at |
| template <typename CharT, typename Traits, typename Allocator> |
| CharT* data(std::basic_string<CharT, Traits, Allocator>& str) { |
| return std::addressof(str[0]); |
| } |
| |
| template <typename Container> |
| constexpr auto data(const Container& c) -> decltype(c.data()) { |
| return c.data(); |
| } |
| |
| template <typename T, size_t N> |
| constexpr T* data(T (&array)[N]) noexcept { |
| return array; |
| } |
| |
| template <typename T> |
| constexpr const T* data(std::initializer_list<T> il) noexcept { |
| return il.begin(); |
| } |
| |
| // std::array::data() was not constexpr prior to C++17 [1]. |
| // Hence these overloads are provided. |
| // |
| // [1] https://en.cppreference.com/w/cpp/container/array/data |
| template <typename T, size_t N> |
| constexpr T* data(std::array<T, N>& array) noexcept { |
| return !array.empty() ? &array[0] : nullptr; |
| } |
| |
| template <typename T, size_t N> |
| constexpr const T* data(const std::array<T, N>& array) noexcept { |
| return !array.empty() ? &array[0] : nullptr; |
| } |
| |
| } // namespace base |
| |
| #endif // BASE_CXX17_BACKPORTS_H_ |