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
105