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_ENABLE_VIEW_H
11#define _LIBCPP___RANGES_ENABLE_VIEW_H
12
13#include <__concepts/derived_from.h>
14#include <__concepts/same_as.h>
15#include <__config>
16#include <__type_traits/is_class.h>
17#include <__type_traits/is_convertible.h>
18#include <__type_traits/remove_cv.h>
19
20#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
21# pragma GCC system_header
22#endif
23
24_LIBCPP_BEGIN_NAMESPACE_STD
25
26#if _LIBCPP_STD_VER >= 20
27
28namespace ranges {
29
30struct view_base {};
31
32template <class _Derived>
33 requires is_class_v<_Derived> && same_as<_Derived, remove_cv_t<_Derived>>
34class view_interface;
35
36template <class _Op, class _Yp>
37 requires is_convertible_v<_Op*, view_interface<_Yp>*>
38void __is_derived_from_view_interface(const _Op*, const view_interface<_Yp>*);
39
40template <class _Tp>
41inline constexpr bool enable_view = derived_from<_Tp, view_base> || requires {
42 ranges::__is_derived_from_view_interface((_Tp*)nullptr, (_Tp*)nullptr);
43};
44
45} // namespace ranges
46
47#endif // _LIBCPP_STD_VER >= 20
48
49_LIBCPP_END_NAMESPACE_STD
50
51#endif // _LIBCPP___RANGES_ENABLE_VIEW_H
52