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_PUSH_MACROS 37 #include <__undef_macros> 38 39 _LIBCPP_BEGIN_NAMESPACE_STD 40 41 #if _LIBCPP_STD_VER >= 20 42 43 namespace ranges { 44 template <view _View> 45 requires bidirectional_range<_View> 46 class reverse_view : public view_interface<reverse_view<_View>> { 47 // We cache begin() whenever ranges::next is not guaranteed O(1) to provide an 48 // amortized O(1) begin() method. 49 static constexpr bool _UseCache = !random_access_range<_View> && !common_range<_View>; 50 using _Cache = _If<_UseCache, __non_propagating_cache<reverse_iterator<iterator_t<_View>>>, __empty_cache>; 51 _LIBCPP_NO_UNIQUE_ADDRESS _Cache __cached_begin_ = _Cache(); 52 _LIBCPP_NO_UNIQUE_ADDRESS _View __base_ = _View(); 53 54 public: 55 _LIBCPP_HIDE_FROM_ABI reverse_view() 56 requires default_initializable<_View> 57 = default; 58 59 _LIBCPP_HIDE_FROM_ABI constexpr explicit reverse_view(_View __view) : __base_(std::move(__view)) {} 60 61 _LIBCPP_HIDE_FROM_ABI constexpr _View base() const& 62 requires copy_constructible<_View> 63 { 64 return __base_; 65 } 66 67 _LIBCPP_HIDE_FROM_ABI constexpr _View base() && { return std::move(__base_); } 68 69 _LIBCPP_HIDE_FROM_ABI constexpr reverse_iterator<iterator_t<_View>> begin() { 70 if constexpr (_UseCache) 71 if (__cached_begin_.__has_value()) 72 return *__cached_begin_; 73 74 auto __tmp = std::make_reverse_iterator(ranges::next(ranges::begin(__base_), ranges::end(__base_))); 75 if constexpr (_UseCache) 76 __cached_begin_.__emplace(__tmp); 77 return __tmp; 78 } 79 80 _LIBCPP_HIDE_FROM_ABI constexpr reverse_iterator<iterator_t<_View>> begin() 81 requires common_range<_View> 82 { 83 return std::make_reverse_iterator(ranges::end(__base_)); 84 } 85 86 _LIBCPP_HIDE_FROM_ABI constexpr auto begin() const 87 requires common_range<const _View> 88 { 89 return std::make_reverse_iterator(ranges::end(__base_)); 90 } 91 92 _LIBCPP_HIDE_FROM_ABI constexpr reverse_iterator<iterator_t<_View>> end() { 93 return std::make_reverse_iterator(ranges::begin(__base_)); 94 } 95 96 _LIBCPP_HIDE_FROM_ABI constexpr auto end() const 97 requires common_range<const _View> 98 { 99 return std::make_reverse_iterator(ranges::begin(__base_)); 100 } 101 102 _LIBCPP_HIDE_FROM_ABI constexpr auto size() 103 requires sized_range<_View> 104 { 105 return ranges::size(__base_); 106 } 107 108 _LIBCPP_HIDE_FROM_ABI constexpr auto size() const 109 requires sized_range<const _View> 110 { 111 return ranges::size(__base_); 112 } 113 }; 114 115 template <class _Range> 116 reverse_view(_Range&&) -> reverse_view<views::all_t<_Range>>; 117 118 template <class _Tp> 119 inline constexpr bool enable_borrowed_range<reverse_view<_Tp>> = enable_borrowed_range<_Tp>; 120 121 namespace views { 122 namespace __reverse { 123 template <class _Tp> 124 inline constexpr bool __is_reverse_view = false; 125 126 template <class _Tp> 127 inline constexpr bool __is_reverse_view<reverse_view<_Tp>> = true; 128 129 template <class _Tp> 130 inline constexpr bool __is_sized_reverse_subrange = false; 131 132 template <class _Iter> 133 inline constexpr bool 134 __is_sized_reverse_subrange<subrange<reverse_iterator<_Iter>, reverse_iterator<_Iter>, subrange_kind::sized>> = 135 true; 136 137 template <class _Tp> 138 inline constexpr bool __is_unsized_reverse_subrange = false; 139 140 template <class _Iter, subrange_kind _Kind> 141 inline constexpr bool __is_unsized_reverse_subrange<subrange<reverse_iterator<_Iter>, reverse_iterator<_Iter>, _Kind>> = 142 _Kind == subrange_kind::unsized; 143 144 template <class _Tp> 145 struct __unwrapped_reverse_subrange { 146 using type = 147 void; // avoid SFINAE-ing out the overload below -- let the concept requirements do it for better diagnostics 148 }; 149 150 template <class _Iter, subrange_kind _Kind> 151 struct __unwrapped_reverse_subrange<subrange<reverse_iterator<_Iter>, reverse_iterator<_Iter>, _Kind>> { 152 using type = subrange<_Iter, _Iter, _Kind>; 153 }; 154 155 struct __fn : __range_adaptor_closure<__fn> { 156 template <class _Range> 157 requires __is_reverse_view<remove_cvref_t<_Range>> 158 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __range) const 159 noexcept(noexcept(std::forward<_Range>(__range).base())) -> decltype(std::forward<_Range>(__range).base()) { 160 return std::forward<_Range>(__range).base(); 161 } 162 163 template <class _Range, 164 class _UnwrappedSubrange = typename __unwrapped_reverse_subrange<remove_cvref_t<_Range>>::type> 165 requires __is_sized_reverse_subrange<remove_cvref_t<_Range>> 166 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __range) const 167 noexcept(noexcept(_UnwrappedSubrange(__range.end().base(), __range.begin().base(), __range.size()))) 168 -> decltype(_UnwrappedSubrange(__range.end().base(), __range.begin().base(), __range.size())) { 169 return _UnwrappedSubrange(__range.end().base(), __range.begin().base(), __range.size()); 170 } 171 172 template <class _Range, 173 class _UnwrappedSubrange = typename __unwrapped_reverse_subrange<remove_cvref_t<_Range>>::type> 174 requires __is_unsized_reverse_subrange<remove_cvref_t<_Range>> 175 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __range) const 176 noexcept(noexcept(_UnwrappedSubrange(__range.end().base(), __range.begin().base()))) 177 -> decltype(_UnwrappedSubrange(__range.end().base(), __range.begin().base())) { 178 return _UnwrappedSubrange(__range.end().base(), __range.begin().base()); 179 } 180 181 template <class _Range> 182 requires(!__is_reverse_view<remove_cvref_t<_Range>> && !__is_sized_reverse_subrange<remove_cvref_t<_Range>> && 183 !__is_unsized_reverse_subrange<remove_cvref_t<_Range>>) 184 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __range) const noexcept(noexcept(reverse_view{ 185 std::forward<_Range>(__range)})) -> decltype(reverse_view{std::forward<_Range>(__range)}) { 186 return reverse_view{std::forward<_Range>(__range)}; 187 } 188 }; 189 } // namespace __reverse 190 191 inline namespace __cpo { 192 inline constexpr auto reverse = __reverse::__fn{}; 193 } // namespace __cpo 194 } // namespace views 195 } // namespace ranges 196 197 #endif // _LIBCPP_STD_VER >= 20 198 199 _LIBCPP_END_NAMESPACE_STD 200 201 _LIBCPP_POP_MACROS 202 203 #endif // _LIBCPP___RANGES_REVERSE_VIEW_H 204