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// 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_