| // Copyright 2020 The Chromium Authors |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #ifndef BASE_RANGES_RANGES_H_ |
| #define BASE_RANGES_RANGES_H_ |
| |
| #include <array> |
| #include <iterator> |
| #include <type_traits> |
| #include <utility> |
| |
| #include "base/template_util.h" |
| |
| namespace gurl_base { |
| |
| namespace internal { |
| |
| // Overload for C array. |
| template <typename T, size_t N> |
| constexpr T* begin(T (&array)[N], priority_tag<2>) { |
| return array; |
| } |
| |
| // Overload for mutable std::array. Required since std::array::begin is not |
| // constexpr prior to C++17. Needs to dispatch to the const overload since only |
| // const operator[] is constexpr in C++14. |
| template <typename T, size_t N> |
| constexpr T* begin(std::array<T, N>& array, priority_tag<2> tag) { |
| return const_cast<T*>(begin(const_cast<const std::array<T, N>&>(array), tag)); |
| } |
| |
| // Overload for const std::array. Required since std::array::begin is not |
| // constexpr prior to C++17. |
| template <typename T, size_t N> |
| constexpr const T* begin(const std::array<T, N>& array, priority_tag<2>) { |
| return N != 0 ? &array[0] : nullptr; |
| } |
| |
| // Generic container overload. |
| template <typename Range> |
| constexpr auto begin(Range&& range, priority_tag<1>) |
| -> decltype(std::forward<Range>(range).begin()) { |
| return std::forward<Range>(range).begin(); |
| } |
| |
| // Overload for free begin() function. |
| template <typename Range> |
| constexpr auto begin(Range&& range, priority_tag<0>) |
| -> decltype(begin(std::forward<Range>(range))) { |
| return begin(std::forward<Range>(range)); |
| } |
| |
| // Overload for C array. |
| template <typename T, size_t N> |
| constexpr T* end(T (&array)[N], priority_tag<2>) { |
| return array + N; |
| } |
| |
| // Overload for mutable std::array. Required since std::array::end is not |
| // constexpr prior to C++17. Needs to dispatch to the const overload since only |
| // const operator[] is constexpr in C++14. |
| template <typename T, size_t N> |
| constexpr T* end(std::array<T, N>& array, priority_tag<2> tag) { |
| return const_cast<T*>(end(const_cast<const std::array<T, N>&>(array), tag)); |
| } |
| |
| // Overload for const std::array. Required since std::array::end is not |
| // constexpr prior to C++17. |
| template <typename T, size_t N> |
| constexpr const T* end(const std::array<T, N>& array, priority_tag<2>) { |
| return N != 0 ? (&array[0]) + N : nullptr; |
| } |
| |
| // Generic container overload. |
| template <typename Range> |
| constexpr auto end(Range&& range, priority_tag<1>) |
| -> decltype(std::forward<Range>(range).end()) { |
| return std::forward<Range>(range).end(); |
| } |
| |
| // Overload for free end() function. |
| template <typename Range> |
| constexpr auto end(Range&& range, priority_tag<0>) |
| -> decltype(end(std::forward<Range>(range))) { |
| return end(std::forward<Range>(range)); |
| } |
| |
| } // namespace internal |
| |
| namespace ranges { |
| |
| // Simplified implementation of C++20's std::ranges::begin. |
| // As opposed to std::ranges::begin, this implementation does does not check |
| // whether begin() returns an iterator and does not inhibit ADL. |
| // |
| // The trailing return type and dispatch to the internal implementation is |
| // necessary to be SFINAE friendly. |
| // |
| // Reference: https://wg21.link/range.access.begin |
| template <typename Range> |
| constexpr auto begin(Range&& range) noexcept |
| -> decltype(internal::begin(std::forward<Range>(range), |
| internal::priority_tag<2>())) { |
| return internal::begin(std::forward<Range>(range), |
| internal::priority_tag<2>()); |
| } |
| |
| // Simplified implementation of C++20's std::ranges::end. |
| // As opposed to std::ranges::end, this implementation does does not check |
| // whether end() returns an iterator and does not inhibit ADL. |
| // |
| // The trailing return type and dispatch to the internal implementation is |
| // necessary to be SFINAE friendly. |
| // |
| // Reference: - https://wg21.link/range.access.end |
| template <typename Range> |
| constexpr auto end(Range&& range) noexcept |
| -> decltype(internal::end(std::forward<Range>(range), |
| internal::priority_tag<2>())) { |
| return internal::end(std::forward<Range>(range), internal::priority_tag<2>()); |
| } |
| |
| // Implementation of C++20's std::ranges::iterator_t. |
| // |
| // Reference: https://wg21.link/ranges.syn#:~:text=iterator_t |
| template <typename Range> |
| using iterator_t = decltype(ranges::begin(std::declval<Range&>())); |
| |
| // Implementation of C++20's std::ranges::range_value_t. |
| // |
| // Reference: https://wg21.link/ranges.syn#:~:text=range_value_t |
| template <typename Range> |
| using range_value_t = iter_value_t<iterator_t<Range>>; |
| |
| } // namespace ranges |
| |
| } // namespace base |
| |
| #endif // BASE_RANGES_RANGES_H_ |