libcxx/include/__ranges/enable_view.h

// -*- C++ -*-
//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef _LIBCPP___RANGES_ENABLE_VIEW_H
#define _LIBCPP___RANGES_ENABLE_VIEW_H

#include <__concepts/derived_from.h>
#include <__concepts/same_as.h>
#include <__config>
#include <__type_traits/is_class.h>
#include <__type_traits/remove_cv.h>

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#  pragma GCC system_header
#endif

_LIBCPP_BEGIN_NAMESPACE_STD

#if _LIBCPP_STD_VER >= 20

namespace ranges {

struct view_base {};

template <class _Derived>
  requires is_class_v<_Derived> && same_as<_Derived, remove_cv_t<_Derived>>
class view_interface;

template <class _Op, class _Yp>
  requires(!same_as<_Op, view_interface<_Yp>>)
void __is_derived_from_view_interface(view_interface<_Yp>*);

template <class _Tp>
inline constexpr bool enable_view = derived_from<_Tp, view_base> || requires {
  ranges::__is_derived_from_view_interface<remove_cv_t<_Tp>>((remove_cv_t<_Tp>*)nullptr);
};

} // namespace ranges

#endif // _LIBCPP_STD_VER >= 20

_LIBCPP_END_NAMESPACE_STD

#endif // _LIBCPP___RANGES_ENABLE_VIEW_H