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