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 _LIBCPP_NODEBUG = 51 _If<_UseCache, __non_propagating_cache<reverse_iterator<iterator_t<_View>>>, __empty_cache>; 52 _LIBCPP_NO_UNIQUE_ADDRESS _Cache __cached_begin_ = _Cache(); 53 _LIBCPP_NO_UNIQUE_ADDRESS _View __base_ = _View(); 54 55 public: 56 _LIBCPP_HIDE_FROM_ABI reverse_view() 57 requires default_initializable<_View> 58 = default; 59 60 _LIBCPP_HIDE_FROM_ABI constexpr explicit reverse_view(_View __view) : __base_(std::move(__view)) {} 61 62 _LIBCPP_HIDE_FROM_ABI constexpr _View base() const& 63 requires copy_constructible<_View> 64 { 65 return __base_; 66 } 67 68 _LIBCPP_HIDE_FROM_ABI constexpr _View base() && { return std::move(__base_); } 69 70 _LIBCPP_HIDE_FROM_ABI constexpr reverse_iterator<iterator_t<_View>> begin() { 71 if constexpr (_UseCache) 72 if (__cached_begin_.__has_value()) 73 return *__cached_begin_; 74 75 auto __tmp = std::make_reverse_iterator(ranges::next(ranges::begin(__base_), ranges::end(__base_))); 76 if constexpr (_UseCache) 77 __cached_begin_.__emplace(__tmp); 78 return __tmp; 79 } 80 81 _LIBCPP_HIDE_FROM_ABI constexpr reverse_iterator<iterator_t<_View>> begin() 82 requires common_range<_View> 83 { 84 return std::make_reverse_iterator(ranges::end(__base_)); 85 } 86 87 _LIBCPP_HIDE_FROM_ABI constexpr auto begin() const 88 requires common_range<const _View> 89 { 90 return std::make_reverse_iterator(ranges::end(__base_)); 91 } 92 93 _LIBCPP_HIDE_FROM_ABI constexpr reverse_iterator<iterator_t<_View>> end() { 94 return std::make_reverse_iterator(ranges::begin(__base_)); 95 } 96 97 _LIBCPP_HIDE_FROM_ABI constexpr auto end() const 98 requires common_range<const _View> 99 { 100 return std::make_reverse_iterator(ranges::begin(__base_)); 101 } 102 103 _LIBCPP_HIDE_FROM_ABI constexpr auto size() 104 requires sized_range<_View> 105 { 106 return ranges::size(__base_); 107 } 108 109 _LIBCPP_HIDE_FROM_ABI constexpr auto size() const 110 requires sized_range<const _View> 111 { 112 return ranges::size(__base_); 113 } 114 }; 115 116 template <class _Range> 117 reverse_view(_Range&&) -> reverse_view<views::all_t<_Range>>; 118 119 template <class _Tp> 120 inline constexpr bool enable_borrowed_range<reverse_view<_Tp>> = enable_borrowed_range<_Tp>; 121 122 namespace views { 123 namespace __reverse { 124 template <class _Tp> 125 inline constexpr bool __is_reverse_view = false; 126 127 template <class _Tp> 128 inline constexpr bool __is_reverse_view<reverse_view<_Tp>> = true; 129 130 template <class _Tp> 131 inline constexpr bool __is_sized_reverse_subrange = false; 132 133 template <class _Iter> 134 inline constexpr bool 135 __is_sized_reverse_subrange<subrange<reverse_iterator<_Iter>, reverse_iterator<_Iter>, subrange_kind::sized>> = 136 true; 137 138 template <class _Tp> 139 inline constexpr bool __is_unsized_reverse_subrange = false; 140 141 template <class _Iter, subrange_kind _Kind> 142 inline constexpr bool __is_unsized_reverse_subrange<subrange<reverse_iterator<_Iter>, reverse_iterator<_Iter>, _Kind>> = 143 _Kind == subrange_kind::unsized; 144 145 template <class _Tp> 146 struct __unwrapped_reverse_subrange { 147 using type = 148 void; // avoid SFINAE-ing out the overload below -- let the concept requirements do it for better diagnostics 149 }; 150 151 template <class _Iter, subrange_kind _Kind> 152 struct __unwrapped_reverse_subrange<subrange<reverse_iterator<_Iter>, reverse_iterator<_Iter>, _Kind>> { 153 using type = subrange<_Iter, _Iter, _Kind>; 154 }; 155 156 struct __fn : __range_adaptor_closure<__fn> { 157 template <class _Range> 158 requires __is_reverse_view<remove_cvref_t<_Range>> 159 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __range) const 160 noexcept(noexcept(std::forward<_Range>(__range).base())) -> decltype(std::forward<_Range>(__range).base()) { 161 return std::forward<_Range>(__range).base(); 162 } 163 164 template <class _Range, 165 class _UnwrappedSubrange = typename __unwrapped_reverse_subrange<remove_cvref_t<_Range>>::type> 166 requires __is_sized_reverse_subrange<remove_cvref_t<_Range>> 167 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __range) const 168 noexcept(noexcept(_UnwrappedSubrange(__range.end().base(), __range.begin().base(), __range.size()))) 169 -> decltype(_UnwrappedSubrange(__range.end().base(), __range.begin().base(), __range.size())) { 170 return _UnwrappedSubrange(__range.end().base(), __range.begin().base(), __range.size()); 171 } 172 173 template <class _Range, 174 class _UnwrappedSubrange = typename __unwrapped_reverse_subrange<remove_cvref_t<_Range>>::type> 175 requires __is_unsized_reverse_subrange<remove_cvref_t<_Range>> 176 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __range) const 177 noexcept(noexcept(_UnwrappedSubrange(__range.end().base(), __range.begin().base()))) 178 -> decltype(_UnwrappedSubrange(__range.end().base(), __range.begin().base())) { 179 return _UnwrappedSubrange(__range.end().base(), __range.begin().base()); 180 } 181 182 template <class _Range> 183 requires(!__is_reverse_view<remove_cvref_t<_Range>> && !__is_sized_reverse_subrange<remove_cvref_t<_Range>> && 184 !__is_unsized_reverse_subrange<remove_cvref_t<_Range>>) 185 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __range) const noexcept(noexcept(reverse_view{ 186 std::forward<_Range>(__range)})) -> decltype(reverse_view{std::forward<_Range>(__range)}) { 187 return reverse_view{std::forward<_Range>(__range)}; 188 } 189 }; 190 } // namespace __reverse 191 192 inline namespace __cpo { 193 inline constexpr auto reverse = __reverse::__fn{}; 194 } // namespace __cpo 195 } // namespace views 196 } // namespace ranges 197 198 #endif // _LIBCPP_STD_VER >= 20 199 200 _LIBCPP_END_NAMESPACE_STD 201 202 _LIBCPP_POP_MACROS 203 204 #endif // _LIBCPP___RANGES_REVERSE_VIEW_H 205