1 // -*- C++ -*- 2 //===----------------------------------------------------------------------===// 3 // 4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 5 // See https://llvm.org/LICENSE.txt for license information. 6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 7 // 8 //===----------------------------------------------------------------------===// 9 10 #ifndef _LIBCPP___RANGES_REVERSE_VIEW_H 11 #define _LIBCPP___RANGES_REVERSE_VIEW_H 12 13 #include <__concepts/constructible.h> 14 #include <__config> 15 #include <__iterator/concepts.h> 16 #include <__iterator/next.h> 17 #include <__iterator/reverse_iterator.h> 18 #include <__ranges/access.h> 19 #include <__ranges/all.h> 20 #include <__ranges/concepts.h> 21 #include <__ranges/enable_borrowed_range.h> 22 #include <__ranges/non_propagating_cache.h> 23 #include <__ranges/range_adaptor.h> 24 #include <__ranges/size.h> 25 #include <__ranges/subrange.h> 26 #include <__ranges/view_interface.h> 27 #include <__type_traits/conditional.h> 28 #include <__type_traits/remove_cvref.h> 29 #include <__utility/forward.h> 30 #include <__utility/move.h> 31 32 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 33 # pragma GCC system_header 34 #endif 35 36 _LIBCPP_BEGIN_NAMESPACE_STD 37 38 #if _LIBCPP_STD_VER >= 20 39 40 namespace ranges { 41 template <view _View> 42 requires bidirectional_range<_View> 43 class reverse_view : public view_interface<reverse_view<_View>> { 44 // We cache begin() whenever ranges::next is not guaranteed O(1) to provide an 45 // amortized O(1) begin() method. 46 static constexpr bool _UseCache = !random_access_range<_View> && !common_range<_View>; 47 using _Cache = _If<_UseCache, __non_propagating_cache<reverse_iterator<iterator_t<_View>>>, __empty_cache>; 48 _LIBCPP_NO_UNIQUE_ADDRESS _Cache __cached_begin_ = _Cache(); 49 _LIBCPP_NO_UNIQUE_ADDRESS _View __base_ = _View(); 50 51 public: 52 _LIBCPP_HIDE_FROM_ABI reverse_view() 53 requires default_initializable<_View> 54 = default; 55 56 _LIBCPP_HIDE_FROM_ABI constexpr explicit reverse_view(_View __view) : __base_(std::move(__view)) {} 57 58 _LIBCPP_HIDE_FROM_ABI constexpr _View base() const& 59 requires copy_constructible<_View> 60 { 61 return __base_; 62 } 63 64 _LIBCPP_HIDE_FROM_ABI constexpr _View base() && { return std::move(__base_); } 65 66 _LIBCPP_HIDE_FROM_ABI constexpr reverse_iterator<iterator_t<_View>> begin() { 67 if constexpr (_UseCache) 68 if (__cached_begin_.__has_value()) 69 return *__cached_begin_; 70 71 auto __tmp = std::make_reverse_iterator(ranges::next(ranges::begin(__base_), ranges::end(__base_))); 72 if constexpr (_UseCache) 73 __cached_begin_.__emplace(__tmp); 74 return __tmp; 75 } 76 77 _LIBCPP_HIDE_FROM_ABI constexpr reverse_iterator<iterator_t<_View>> begin() 78 requires common_range<_View> 79 { 80 return std::make_reverse_iterator(ranges::end(__base_)); 81 } 82 83 _LIBCPP_HIDE_FROM_ABI constexpr auto begin() const 84 requires common_range<const _View> 85 { 86 return std::make_reverse_iterator(ranges::end(__base_)); 87 } 88 89 _LIBCPP_HIDE_FROM_ABI constexpr reverse_iterator<iterator_t<_View>> end() { 90 return std::make_reverse_iterator(ranges::begin(__base_)); 91 } 92 93 _LIBCPP_HIDE_FROM_ABI constexpr auto end() const 94 requires common_range<const _View> 95 { 96 return std::make_reverse_iterator(ranges::begin(__base_)); 97 } 98 99 _LIBCPP_HIDE_FROM_ABI constexpr auto size() 100 requires sized_range<_View> 101 { 102 return ranges::size(__base_); 103 } 104 105 _LIBCPP_HIDE_FROM_ABI constexpr auto size() const 106 requires sized_range<const _View> 107 { 108 return ranges::size(__base_); 109 } 110 }; 111 112 template <class _Range> 113 reverse_view(_Range&&) -> reverse_view<views::all_t<_Range>>; 114 115 template <class _Tp> 116 inline constexpr bool enable_borrowed_range<reverse_view<_Tp>> = enable_borrowed_range<_Tp>; 117 118 namespace views { 119 namespace __reverse { 120 template <class _Tp> 121 inline constexpr bool __is_reverse_view = false; 122 123 template <class _Tp> 124 inline constexpr bool __is_reverse_view<reverse_view<_Tp>> = true; 125 126 template <class _Tp> 127 inline constexpr bool __is_sized_reverse_subrange = false; 128 129 template <class _Iter> 130 inline constexpr bool 131 __is_sized_reverse_subrange<subrange<reverse_iterator<_Iter>, reverse_iterator<_Iter>, subrange_kind::sized>> = 132 true; 133 134 template <class _Tp> 135 inline constexpr bool __is_unsized_reverse_subrange = false; 136 137 template <class _Iter, subrange_kind _Kind> 138 inline constexpr bool __is_unsized_reverse_subrange<subrange<reverse_iterator<_Iter>, reverse_iterator<_Iter>, _Kind>> = 139 _Kind == subrange_kind::unsized; 140 141 template <class _Tp> 142 struct __unwrapped_reverse_subrange { 143 using type = 144 void; // avoid SFINAE-ing out the overload below -- let the concept requirements do it for better diagnostics 145 }; 146 147 template <class _Iter, subrange_kind _Kind> 148 struct __unwrapped_reverse_subrange<subrange<reverse_iterator<_Iter>, reverse_iterator<_Iter>, _Kind>> { 149 using type = subrange<_Iter, _Iter, _Kind>; 150 }; 151 152 struct __fn : __range_adaptor_closure<__fn> { 153 template <class _Range> 154 requires __is_reverse_view<remove_cvref_t<_Range>> 155 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __range) const 156 noexcept(noexcept(std::forward<_Range>(__range).base())) -> decltype(std::forward<_Range>(__range).base()) { 157 return std::forward<_Range>(__range).base(); 158 } 159 160 template <class _Range, 161 class _UnwrappedSubrange = typename __unwrapped_reverse_subrange<remove_cvref_t<_Range>>::type> 162 requires __is_sized_reverse_subrange<remove_cvref_t<_Range>> 163 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __range) const 164 noexcept(noexcept(_UnwrappedSubrange(__range.end().base(), __range.begin().base(), __range.size()))) 165 -> decltype(_UnwrappedSubrange(__range.end().base(), __range.begin().base(), __range.size())) { 166 return _UnwrappedSubrange(__range.end().base(), __range.begin().base(), __range.size()); 167 } 168 169 template <class _Range, 170 class _UnwrappedSubrange = typename __unwrapped_reverse_subrange<remove_cvref_t<_Range>>::type> 171 requires __is_unsized_reverse_subrange<remove_cvref_t<_Range>> 172 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __range) const 173 noexcept(noexcept(_UnwrappedSubrange(__range.end().base(), __range.begin().base()))) 174 -> decltype(_UnwrappedSubrange(__range.end().base(), __range.begin().base())) { 175 return _UnwrappedSubrange(__range.end().base(), __range.begin().base()); 176 } 177 178 template <class _Range> 179 requires(!__is_reverse_view<remove_cvref_t<_Range>> && !__is_sized_reverse_subrange<remove_cvref_t<_Range>> && 180 !__is_unsized_reverse_subrange<remove_cvref_t<_Range>>) 181 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __range) const 182 noexcept(noexcept(reverse_view{std::forward<_Range>(__range)})) 183 -> decltype(reverse_view{std::forward<_Range>(__range)}) { 184 return reverse_view{std::forward<_Range>(__range)}; 185 } 186 }; 187 } // namespace __reverse 188 189 inline namespace __cpo { 190 inline constexpr auto reverse = __reverse::__fn{}; 191 } // namespace __cpo 192 } // namespace views 193 } // namespace ranges 194 195 #endif // _LIBCPP_STD_VER >= 20 196 197 _LIBCPP_END_NAMESPACE_STD 198 199 #endif // _LIBCPP___RANGES_REVERSE_VIEW_H 200