libcxx/include/__concepts/swappable.h

//===----------------------------------------------------------------------===//
//
// 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___CONCEPTS_SWAPPABLE_H
#define _LIBCPP___CONCEPTS_SWAPPABLE_H

#include <__concepts/assignable.h>
#include <__concepts/class_or_enum.h>
#include <__concepts/common_reference_with.h>
#include <__concepts/constructible.h>
#include <__config>
#include <__cstddef/size_t.h>
#include <__type_traits/extent.h>
#include <__type_traits/is_nothrow_assignable.h>
#include <__type_traits/is_nothrow_constructible.h>
#include <__type_traits/remove_cvref.h>
#include <__utility/exchange.h>
#include <__utility/forward.h>
#include <__utility/move.h>

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

_LIBCPP_PUSH_MACROS
#include <__undef_macros>

_LIBCPP_BEGIN_NAMESPACE_STD

#if _LIBCPP_STD_VER >= 20

// [concept.swappable]

namespace ranges {
namespace __swap {

template <class _Tp>
void swap(_Tp&, _Tp&) = delete;

// clang-format off
template <class _Tp, class _Up>
concept __unqualified_swappable_with =
    (__class_or_enum<remove_cvref_t<_Tp>> || __class_or_enum<remove_cvref_t<_Up>>) &&
    requires(_Tp&& __t, _Up&& __u) {
        swap(std::forward<_Tp>(__t), std::forward<_Up>(__u));
    };
// clang-format on

struct __fn;

// clang-format off
template <class _Tp, class _Up, size_t _Size>
concept __swappable_arrays =
    !__unqualified_swappable_with<_Tp (&)[_Size], _Up (&)[_Size]> &&
    extent_v<_Tp> == extent_v<_Up> &&
    requires(_Tp (&__t)[_Size], _Up (&__u)[_Size], const __fn& __swap) {
        __swap(__t[0], __u[0]);
    };
// clang-format on

template <class _Tp>
concept __exchangeable =
    !__unqualified_swappable_with<_Tp&, _Tp&> && move_constructible<_Tp> && assignable_from<_Tp&, _Tp>;

struct __fn {
  // 2.1   `S` is `(void)swap(E1, E2)`* if `E1` or `E2` has class or enumeration type and...
  // *The name `swap` is used here unqualified.
  template <class _Tp, class _Up>
    requires __unqualified_swappable_with<_Tp, _Up>
  _LIBCPP_HIDE_FROM_ABI constexpr void operator()(_Tp&& __t, _Up&& __u) const
      noexcept(noexcept(swap(std::forward<_Tp>(__t), std::forward<_Up>(__u)))) {
    swap(std::forward<_Tp>(__t), std::forward<_Up>(__u));
  }

  // 2.2   Otherwise, if `E1` and `E2` are lvalues of array types with equal extent and...
  template <class _Tp, class _Up, size_t _Size>
    requires __swappable_arrays<_Tp, _Up, _Size>
  _LIBCPP_HIDE_FROM_ABI constexpr void operator()(_Tp (&__t)[_Size], _Up (&__u)[_Size]) const
      noexcept(noexcept((*this)(*__t, *__u))) {
    // TODO(cjdb): replace with `ranges::swap_ranges`.
    for (size_t __i = 0; __i < _Size; ++__i) {
      (*this)(__t[__i], __u[__i]);
    }
  }

  // 2.3   Otherwise, if `E1` and `E2` are lvalues of the same type `T` that models...
  template <__exchangeable _Tp>
  _LIBCPP_HIDE_FROM_ABI constexpr void operator()(_Tp& __x, _Tp& __y) const
      noexcept(is_nothrow_move_constructible_v<_Tp> && is_nothrow_move_assignable_v<_Tp>) {
    __y = std::exchange(__x, std::move(__y));
  }
};
} // namespace __swap

inline namespace __cpo {
inline constexpr auto swap = __swap::__fn{};
} // namespace __cpo
} // namespace ranges

template <class _Tp>
concept swappable = requires(_Tp& __a, _Tp& __b) { ranges::swap(__a, __b); };

template <class _Tp, class _Up>
concept swappable_with = common_reference_with<_Tp, _Up> && requires(_Tp&& __t, _Up&& __u) {
  ranges::swap(std::forward<_Tp>(__t), std::forward<_Tp>(__t));
  ranges::swap(std::forward<_Up>(__u), std::forward<_Up>(__u));
  ranges::swap(std::forward<_Tp>(__t), std::forward<_Up>(__u));
  ranges::swap(std::forward<_Up>(__u), std::forward<_Tp>(__t));
};

#endif // _LIBCPP_STD_VER >= 20

_LIBCPP_END_NAMESPACE_STD

_LIBCPP_POP_MACROS

#endif // _LIBCPP___CONCEPTS_SWAPPABLE_H