chromium/third_party/libc++/src/include/__ranges/non_propagating_cache.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_NON_PROPAGATING_CACHE_H
#define _LIBCPP___RANGES_NON_PROPAGATING_CACHE_H

#include <__config>
#include <__iterator/concepts.h>        // indirectly_readable
#include <__iterator/iterator_traits.h> // iter_reference_t
#include <__memory/addressof.h>
#include <__utility/forward.h>
#include <optional>

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

_LIBCPP_BEGIN_NAMESPACE_STD

#if _LIBCPP_STD_VER >= 20

namespace ranges {
// __non_propagating_cache is a helper type that allows storing an optional value in it,
// but which does not copy the source's value when it is copy constructed/assigned to,
// and which resets the source's value when it is moved-from.
//
// This type is used as an implementation detail of some views that need to cache the
// result of `begin()` in order to provide an amortized O(1) begin() method. Typically,
// we don't want to propagate the value of the cache upon copy because the cached iterator
// may refer to internal details of the source view.
template <class _Tp>
  requires is_object_v<_Tp>
class _LIBCPP_TEMPLATE_VIS __non_propagating_cache { … };

struct __empty_cache { … };
} // namespace ranges

#endif // _LIBCPP_STD_VER >= 20

_LIBCPP_END_NAMESPACE_STD

#endif // _LIBCPP___RANGES_NON_PROPAGATING_CACHE_H