libcxx/include/__iterator/iter_move.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___ITERATOR_ITER_MOVE_H
#define _LIBCPP___ITERATOR_ITER_MOVE_H

#include <__config>
#include <__iterator/iterator_traits.h>
#include <__utility/forward.h>
#include <__utility/move.h>
#include <concepts> // __class_or_enum
#include <type_traits>

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

_LIBCPP_BEGIN_NAMESPACE_STD

#if !defined(_LIBCPP_HAS_NO_CONCEPTS)

// [iterator.cust.move]

namespace ranges {
namespace __iter_move {

void iter_move();

template <class _Tp>
concept __unqualified_iter_move =
  __class_or_enum<remove_cvref_t<_Tp>> &&
  requires (_Tp&& __t) {
    iter_move(_VSTD::forward<_Tp>(__t));
  };

// [iterator.cust.move]/1
// The name ranges::iter_move denotes a customization point object.
// The expression ranges::iter_move(E) for a subexpression E is
// expression-equivalent to:
struct __fn {
  // [iterator.cust.move]/1.1
  // iter_move(E), if E has class or enumeration type and iter_move(E) is a
  // well-formed expression when treated as an unevaluated operand, [...]
  template<class _Ip>
    requires __class_or_enum<remove_cvref_t<_Ip>> && __unqualified_iter_move<_Ip>
  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr decltype(auto) operator()(_Ip&& __i) const
    noexcept(noexcept(iter_move(_VSTD::forward<_Ip>(__i))))
  {
    return iter_move(_VSTD::forward<_Ip>(__i));
  }

  // [iterator.cust.move]/1.2
  // Otherwise, if the expression *E is well-formed:
  //  1.2.1 if *E is an lvalue, std::move(*E);
  //  1.2.2 otherwise, *E.
  template<class _Ip>
    requires (!(__class_or_enum<remove_cvref_t<_Ip>> && __unqualified_iter_move<_Ip>)) &&
    requires(_Ip&& __i) { *_VSTD::forward<_Ip>(__i); }
  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr decltype(auto) operator()(_Ip&& __i) const
    noexcept(noexcept(*_VSTD::forward<_Ip>(__i)))
  {
    if constexpr (is_lvalue_reference_v<decltype(*_VSTD::forward<_Ip>(__i))>) {
      return _VSTD::move(*_VSTD::forward<_Ip>(__i));
    } else {
      return *_VSTD::forward<_Ip>(__i);
    }
  }

  // [iterator.cust.move]/1.3
  // Otherwise, ranges::iter_move(E) is ill-formed.
};
} // namespace __iter_move

inline namespace __cpo {
  inline constexpr auto iter_move = __iter_move::__fn{};
} // namespace __cpo
} // namespace ranges

template<__dereferenceable _Tp>
  requires requires(_Tp& __t) { { ranges::iter_move(__t) } -> __can_reference; }
using iter_rvalue_reference_t = decltype(ranges::iter_move(declval<_Tp&>()));

#endif // !defined(_LIBCPP_HAS_NO_CONCEPTS)

_LIBCPP_END_NAMESPACE_STD

#endif // _LIBCPP___ITERATOR_ITER_MOVE_H