libcxx/include/__cxx03/__ranges/enable_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___CXX03___RANGES_ENABLE_VIEW_H
  11 #define _LIBCPP___CXX03___RANGES_ENABLE_VIEW_H
  12
  13 #include <__cxx03/__concepts/derived_from.h>
  14 #include <__cxx03/__concepts/same_as.h>
  15 #include <__cxx03/__config>
  16 #include <__cxx03/__type_traits/is_class.h>
  17 #include <__cxx03/__type_traits/is_convertible.h>
  18 #include <__cxx03/__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
  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> || 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___CXX03___RANGES_ENABLE_VIEW_H