xref: /freebsd/contrib/llvm-project/libcxx/include/__ranges/single_view.h (revision 22d7dd834bc5cd189810e414701e3ad1e98102e4)
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/copyable_box.h>
16 #include <__ranges/range_adaptor.h>
17 #include <__ranges/view_interface.h>
18 #include <__utility/forward.h>
19 #include <__utility/in_place.h>
20 #include <__utility/move.h>
21 #include <type_traits>
22 
23 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
24 #  pragma GCC system_header
25 #endif
26 
27 _LIBCPP_BEGIN_NAMESPACE_STD
28 
29 #if _LIBCPP_STD_VER > 17
30 
31 namespace ranges {
32   template<copy_constructible _Tp>
33     requires is_object_v<_Tp>
34   class single_view : public view_interface<single_view<_Tp>> {
35     __copyable_box<_Tp> __value_;
36 
37   public:
38     _LIBCPP_HIDE_FROM_ABI
39     single_view() requires default_initializable<_Tp> = default;
40 
41     _LIBCPP_HIDE_FROM_ABI
42     constexpr explicit single_view(const _Tp& __t) : __value_(in_place, __t) {}
43 
44     _LIBCPP_HIDE_FROM_ABI
45     constexpr explicit single_view(_Tp&& __t) : __value_(in_place, std::move(__t)) {}
46 
47     template<class... _Args>
48       requires constructible_from<_Tp, _Args...>
49     _LIBCPP_HIDE_FROM_ABI
50     constexpr explicit single_view(in_place_t, _Args&&... __args)
51       : __value_{in_place, std::forward<_Args>(__args)...} {}
52 
53     _LIBCPP_HIDE_FROM_ABI
54     constexpr _Tp* begin() noexcept { return data(); }
55 
56     _LIBCPP_HIDE_FROM_ABI
57     constexpr const _Tp* begin() const noexcept { return data(); }
58 
59     _LIBCPP_HIDE_FROM_ABI
60     constexpr _Tp* end() noexcept { return data() + 1; }
61 
62     _LIBCPP_HIDE_FROM_ABI
63     constexpr const _Tp* end() const noexcept { return data() + 1; }
64 
65     _LIBCPP_HIDE_FROM_ABI
66     static constexpr size_t size() noexcept { return 1; }
67 
68     _LIBCPP_HIDE_FROM_ABI
69     constexpr _Tp* data() noexcept { return __value_.operator->(); }
70 
71     _LIBCPP_HIDE_FROM_ABI
72     constexpr const _Tp* data() const noexcept { return __value_.operator->(); }
73   };
74 
75 template<class _Tp>
76 single_view(_Tp) -> single_view<_Tp>;
77 
78 namespace views {
79 namespace __single_view {
80 
81 struct __fn : __range_adaptor_closure<__fn> {
82   template<class _Range>
83   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI
84   constexpr auto operator()(_Range&& __range) const
85     noexcept(noexcept(single_view<decay_t<_Range&&>>(std::forward<_Range>(__range))))
86     -> decltype(      single_view<decay_t<_Range&&>>(std::forward<_Range>(__range)))
87     { return          single_view<decay_t<_Range&&>>(std::forward<_Range>(__range)); }
88 };
89 } // namespace __single_view
90 
91 inline namespace __cpo {
92   inline constexpr auto single = __single_view::__fn{};
93 } // namespace __cpo
94 
95 } // namespace views
96 } // namespace ranges
97 
98 #endif // _LIBCPP_STD_VER > 17
99 
100 _LIBCPP_END_NAMESPACE_STD
101 
102 #endif // _LIBCPP___RANGES_SINGLE_VIEW_H
103