libcxx/include/__ranges/reverse_view.h

   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