libcxx/include/__ranges/single_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_SINGLE_VIEW_H
  11 #define _LIBCPP___RANGES_SINGLE_VIEW_H
  12
  13 #include <__concepts/constructible.h>
  14 #include <__config>
  15 #include <__ranges/movable_box.h>
  16 #include <__ranges/range_adaptor.h>
  17 #include <__ranges/view_interface.h>
  18 #include <__type_traits/decay.h>
  19 #include <__type_traits/is_object.h>
  20 #include <__utility/forward.h>
  21 #include <__utility/in_place.h>
  22 #include <__utility/move.h>
  23 #include <cstddef>
  24
  25 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  26 #  pragma GCC system_header
  27 #endif
  28
  29 _LIBCPP_BEGIN_NAMESPACE_STD
  30
  31 #if _LIBCPP_STD_VER >= 20
  32
  33 namespace ranges {
  34 #  if _LIBCPP_STD_VER >= 23
  35 template <move_constructible _Tp>
  36 #  else
  37 template <copy_constructible _Tp>
  38 #  endif
  39   requires is_object_v<_Tp>
  40 class single_view : public view_interface<single_view<_Tp>> {
  41   __movable_box<_Tp> __value_;
  42
  43 public:
  44   _LIBCPP_HIDE_FROM_ABI single_view()
  45     requires default_initializable<_Tp>
  46   = default;
  47
  48   _LIBCPP_HIDE_FROM_ABI constexpr explicit single_view(const _Tp& __t)
  49 #  if _LIBCPP_STD_VER >= 23
  50     requires copy_constructible<_Tp>
  51 #  endif
  52       : __value_(in_place, __t) {
  53   }
  54
  55   _LIBCPP_HIDE_FROM_ABI constexpr explicit single_view(_Tp&& __t) : __value_(in_place, std::move(__t)) {}
  56
  57   template <class... _Args>
  58     requires constructible_from<_Tp, _Args...>
  59   _LIBCPP_HIDE_FROM_ABI constexpr explicit single_view(in_place_t, _Args&&... __args)
  60       : __value_{in_place, std::forward<_Args>(__args)...} {}
  61
  62   _LIBCPP_HIDE_FROM_ABI constexpr _Tp* begin() noexcept { return data(); }
  63
  64   _LIBCPP_HIDE_FROM_ABI constexpr const _Tp* begin() const noexcept { return data(); }
  65
  66   _LIBCPP_HIDE_FROM_ABI constexpr _Tp* end() noexcept { return data() + 1; }
  67
  68   _LIBCPP_HIDE_FROM_ABI constexpr const _Tp* end() const noexcept { return data() + 1; }
  69
  70   _LIBCPP_HIDE_FROM_ABI static constexpr size_t size() noexcept { return 1; }
  71
  72   _LIBCPP_HIDE_FROM_ABI constexpr _Tp* data() noexcept { return __value_.operator->(); }
  73
  74   _LIBCPP_HIDE_FROM_ABI constexpr const _Tp* data() const noexcept { return __value_.operator->(); }
  75 };
  76
  77 template<class _Tp>
  78 single_view(_Tp) -> single_view<_Tp>;
  79
  80 namespace views {
  81 namespace __single_view {
  82
  83 struct __fn : __range_adaptor_closure<__fn> {
  84   template<class _Range>
  85   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI
  86   constexpr auto operator()(_Range&& __range) const
  87     noexcept(noexcept(single_view<decay_t<_Range&&>>(std::forward<_Range>(__range))))
  88     -> decltype(      single_view<decay_t<_Range&&>>(std::forward<_Range>(__range)))
  89     { return          single_view<decay_t<_Range&&>>(std::forward<_Range>(__range)); }
  90 };
  91 } // namespace __single_view
  92
  93 inline namespace __cpo {
  94   inline constexpr auto single = __single_view::__fn{};
  95 } // namespace __cpo
  96
  97 } // namespace views
  98 } // namespace ranges
  99
 100 #endif // _LIBCPP_STD_VER >= 20
 101
 102 _LIBCPP_END_NAMESPACE_STD
 103
 104 #endif // _LIBCPP___RANGES_SINGLE_VIEW_H