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 > 17
27 
28 namespace ranges {
29 
30 struct view_base { };
31 
32 template<class _Derived>
33   requires is_class_v<_Derived> && same_as<_Derived, remove_cv_t<_Derived>>
34 class view_interface;
35 
36 template<class _Op, class _Yp>
37   requires is_convertible_v<_Op*, view_interface<_Yp>*>
38 void __is_derived_from_view_interface(const _Op*, const view_interface<_Yp>*);
39 
40 template <class _Tp>
41 inline constexpr bool enable_view = derived_from<_Tp, view_base> ||
42   requires { ranges::__is_derived_from_view_interface((_Tp*)nullptr, (_Tp*)nullptr); };
43 
44 } // namespace ranges
45 
46 #endif // _LIBCPP_STD_VER > 17
47 
48 _LIBCPP_END_NAMESPACE_STD
49 
50 #endif // _LIBCPP___RANGES_ENABLE_VIEW_H
51