concepts
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// <concepts> -*- C++ -*-
// Copyright (C) 2019-2025 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library. This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.
// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
// <http://www.gnu.org/licenses/>.
/** @file include/concepts
* This is a Standard C++ Library header.
* @ingroup concepts
*/
#ifndef _GLIBCXX_CONCEPTS
#define _GLIBCXX_CONCEPTS 1
#ifdef _GLIBCXX_SYSHDR
#pragma GCC system_header
#endif
#define __glibcxx_want_concepts
#include <bits/version.h>
#ifdef __cpp_lib_concepts // C++ >= 20 && concepts
/**
* @defgroup concepts Concepts
* @ingroup utilities
*
* Concepts for checking type requirements.
*/
#include <type_traits>
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
// [concepts.lang], language-related concepts
namespace __detail
{
template<typename _Tp, typename _Up>
concept __same_as = std::is_same_v<_Tp, _Up>;
} // namespace __detail
/// [concept.same], concept same_as
template<typename _Tp, typename _Up>
concept same_as
= __detail::__same_as<_Tp, _Up> && __detail::__same_as<_Up, _Tp>;
namespace __detail
{
template<typename _Tp, typename _Up>
concept __different_from
= !same_as<remove_cvref_t<_Tp>, remove_cvref_t<_Up>>;
} // namespace __detail
/// [concept.derived], concept derived_from
template<typename _Derived, typename _Base>
concept derived_from = __is_base_of(_Base, _Derived)
&& is_convertible_v<const volatile _Derived*, const volatile _Base*>;
/// [concept.convertible], concept convertible_to
template<typename _From, typename _To>
concept convertible_to = is_convertible_v<_From, _To>
&& requires { static_cast<_To>(std::declval<_From>()); };
/// [concept.commonref], concept common_reference_with
template<typename _Tp, typename _Up>
concept common_reference_with
= same_as<common_reference_t<_Tp, _Up>, common_reference_t<_Up, _Tp>>
&& convertible_to<_Tp, common_reference_t<_Tp, _Up>>
&& convertible_to<_Up, common_reference_t<_Tp, _Up>>;
/// [concept.common], concept common_with
template<typename _Tp, typename _Up>
concept common_with
= same_as<common_type_t<_Tp, _Up>, common_type_t<_Up, _Tp>>
&& requires {
static_cast<common_type_t<_Tp, _Up>>(std::declval<_Tp>());
static_cast<common_type_t<_Tp, _Up>>(std::declval<_Up>());
}
&& common_reference_with<add_lvalue_reference_t<const _Tp>,
add_lvalue_reference_t<const _Up>>
&& common_reference_with<add_lvalue_reference_t<common_type_t<_Tp, _Up>>,
common_reference_t<
add_lvalue_reference_t<const _Tp>,
add_lvalue_reference_t<const _Up>>>;
// [concepts.arithmetic], arithmetic concepts
template<typename _Tp>
concept integral = is_integral_v<_Tp>;
template<typename _Tp>
concept signed_integral = integral<_Tp> && is_signed_v<_Tp>;
template<typename _Tp>
concept unsigned_integral = integral<_Tp> && !signed_integral<_Tp>;
template<typename _Tp>
concept floating_point = is_floating_point_v<_Tp>;
namespace __detail
{
template<typename _Tp>
using __cref = const remove_reference_t<_Tp>&;
template<typename _Tp>
concept __class_or_enum
= is_class_v<_Tp> || is_union_v<_Tp> || is_enum_v<_Tp>;
template<typename _Tp>
constexpr bool __destructible_impl = false;
template<typename _Tp>
requires requires(_Tp& __t) { { __t.~_Tp() } noexcept; }
constexpr bool __destructible_impl<_Tp> = true;
template<typename _Tp>
constexpr bool __destructible = __destructible_impl<_Tp>;
template<typename _Tp>
constexpr bool __destructible<_Tp&> = true;
template<typename _Tp>
constexpr bool __destructible<_Tp&&> = true;
template<typename _Tp, size_t _Nm>
constexpr bool __destructible<_Tp[_Nm]> = __destructible<_Tp>;
} // namespace __detail
/// [concept.assignable], concept assignable_from
template<typename _Lhs, typename _Rhs>
concept assignable_from
= is_lvalue_reference_v<_Lhs>
&& common_reference_with<__detail::__cref<_Lhs>, __detail::__cref<_Rhs>>
&& requires(_Lhs __lhs, _Rhs&& __rhs) {
{ __lhs = static_cast<_Rhs&&>(__rhs) } -> same_as<_Lhs>;
};
/// [concept.destructible], concept destructible
template<typename _Tp>
concept destructible = __detail::__destructible<_Tp>;
/// [concept.constructible], concept constructible_from
template<typename _Tp, typename... _Args>
concept constructible_from
= destructible<_Tp> && is_constructible_v<_Tp, _Args...>;
/// [concept.defaultinitializable], concept default_initializable
template<typename _Tp>
concept default_initializable = constructible_from<_Tp>
&& requires
{
_Tp{};
(void) ::new _Tp;
};
/// [concept.moveconstructible], concept move_constructible
template<typename _Tp>
concept move_constructible
= constructible_from<_Tp, _Tp> && convertible_to<_Tp, _Tp>;
/// [concept.copyconstructible], concept copy_constructible
template<typename _Tp>
concept copy_constructible
= move_constructible<_Tp>
&& constructible_from<_Tp, _Tp&> && convertible_to<_Tp&, _Tp>
&& constructible_from<_Tp, const _Tp&> && convertible_to<const _Tp&, _Tp>
&& constructible_from<_Tp, const _Tp> && convertible_to<const _Tp, _Tp>;
// [concept.swappable], concept swappable
namespace ranges
{
/// @cond undocumented
namespace __swap
{
template<typename _Tp> void swap(_Tp&, _Tp&) = delete;
template<typename _Tp, typename _Up>
concept __adl_swap
= (std::__detail::__class_or_enum<remove_reference_t<_Tp>>
|| std::__detail::__class_or_enum<remove_reference_t<_Up>>)
&& requires(_Tp&& __t, _Up&& __u) {
swap(static_cast<_Tp&&>(__t), static_cast<_Up&&>(__u));
};
struct _Swap
{
private:
template<typename _Tp, typename _Up>
static constexpr bool
_S_noexcept()
{
if constexpr (__adl_swap<_Tp, _Up>)
return noexcept(swap(std::declval<_Tp>(), std::declval<_Up>()));
else
return is_nothrow_move_constructible_v<remove_reference_t<_Tp>>
&& is_nothrow_move_assignable_v<remove_reference_t<_Tp>>;
}
public:
template<typename _Tp, typename _Up>
requires __adl_swap<_Tp, _Up>
|| (same_as<_Tp, _Up> && is_lvalue_reference_v<_Tp>
&& move_constructible<remove_reference_t<_Tp>>
&& assignable_from<_Tp, remove_reference_t<_Tp>>)
constexpr void
operator()(_Tp&& __t, _Up&& __u) const
noexcept(_S_noexcept<_Tp, _Up>())
{
if constexpr (__adl_swap<_Tp, _Up>)
swap(static_cast<_Tp&&>(__t), static_cast<_Up&&>(__u));
else
{
auto __tmp = static_cast<remove_reference_t<_Tp>&&>(__t);
__t = static_cast<remove_reference_t<_Tp>&&>(__u);
__u = static_cast<remove_reference_t<_Tp>&&>(__tmp);
}
}
template<typename _Tp, typename _Up, size_t _Num>
requires requires(const _Swap& __swap, _Tp& __e1, _Up& __e2) {
__swap(__e1, __e2);
}
constexpr void
operator()(_Tp (&__e1)[_Num], _Up (&__e2)[_Num]) const
noexcept(noexcept(std::declval<const _Swap&>()(*__e1, *__e2)))
{
for (size_t __n = 0; __n < _Num; ++__n)
(*this)(__e1[__n], __e2[__n]);
}
};
} // namespace __swap
/// @endcond
inline namespace _Cpo {
inline constexpr __swap::_Swap swap{};
}
} // namespace ranges
template<typename _Tp>
concept swappable
= requires(_Tp& __a, _Tp& __b) { ranges::swap(__a, __b); };
template<typename _Tp, typename _Up>
concept swappable_with = common_reference_with<_Tp, _Up>
&& requires(_Tp&& __t, _Up&& __u) {
ranges::swap(static_cast<_Tp&&>(__t), static_cast<_Tp&&>(__t));
ranges::swap(static_cast<_Up&&>(__u), static_cast<_Up&&>(__u));
ranges::swap(static_cast<_Tp&&>(__t), static_cast<_Up&&>(__u));
ranges::swap(static_cast<_Up&&>(__u), static_cast<_Tp&&>(__t));
};
// [concepts.object], Object concepts
template<typename _Tp>
concept movable = is_object_v<_Tp> && move_constructible<_Tp>
&& assignable_from<_Tp&, _Tp> && swappable<_Tp>;
template<typename _Tp>
concept copyable = copy_constructible<_Tp> && movable<_Tp>
&& assignable_from<_Tp&, _Tp&> && assignable_from<_Tp&, const _Tp&>
&& assignable_from<_Tp&, const _Tp>;
template<typename _Tp>
concept semiregular = copyable<_Tp> && default_initializable<_Tp>;
// [concepts.compare], comparison concepts
// [concept.booleantestable], Boolean testability
namespace __detail
{
template<typename _Tp>
concept __boolean_testable_impl = convertible_to<_Tp, bool>;
template<typename _Tp>
concept __boolean_testable
= __boolean_testable_impl<_Tp>
&& requires(_Tp&& __t)
{ { !static_cast<_Tp&&>(__t) } -> __boolean_testable_impl; };
} // namespace __detail
// [concept.equalitycomparable], concept equality_comparable
namespace __detail
{
template<typename _Tp, typename _Up>
concept __weakly_eq_cmp_with
= requires(__detail::__cref<_Tp> __t, __detail::__cref<_Up> __u) {
{ __t == __u } -> __boolean_testable;
{ __t != __u } -> __boolean_testable;
{ __u == __t } -> __boolean_testable;
{ __u != __t } -> __boolean_testable;
};
} // namespace __detail
template<typename _Tp>
concept equality_comparable = __detail::__weakly_eq_cmp_with<_Tp, _Tp>;
template<typename _Tp, typename _Up>
concept equality_comparable_with
= equality_comparable<_Tp> && equality_comparable<_Up>
&& common_reference_with<__detail::__cref<_Tp>, __detail::__cref<_Up>>
&& equality_comparable<common_reference_t<__detail::__cref<_Tp>,
__detail::__cref<_Up>>>
&& __detail::__weakly_eq_cmp_with<_Tp, _Up>;
namespace __detail
{
template<typename _Tp, typename _Up>
concept __partially_ordered_with
= requires(const remove_reference_t<_Tp>& __t,
const remove_reference_t<_Up>& __u) {
{ __t < __u } -> __boolean_testable;
{ __t > __u } -> __boolean_testable;
{ __t <= __u } -> __boolean_testable;
{ __t >= __u } -> __boolean_testable;
{ __u < __t } -> __boolean_testable;
{ __u > __t } -> __boolean_testable;
{ __u <= __t } -> __boolean_testable;
{ __u >= __t } -> __boolean_testable;
};
} // namespace __detail
// [concept.totallyordered], concept totally_ordered
template<typename _Tp>
concept totally_ordered
= equality_comparable<_Tp>
&& __detail::__partially_ordered_with<_Tp, _Tp>;
template<typename _Tp, typename _Up>
concept totally_ordered_with
= totally_ordered<_Tp> && totally_ordered<_Up>
&& equality_comparable_with<_Tp, _Up>
&& totally_ordered<common_reference_t<__detail::__cref<_Tp>,
__detail::__cref<_Up>>>
&& __detail::__partially_ordered_with<_Tp, _Up>;
template<typename _Tp>
concept regular = semiregular<_Tp> && equality_comparable<_Tp>;
// [concepts.callable], callable concepts
/// [concept.invocable], concept invocable
template<typename _Fn, typename... _Args>
concept invocable = is_invocable_v<_Fn, _Args...>;
/// [concept.regularinvocable], concept regular_invocable
template<typename _Fn, typename... _Args>
concept regular_invocable = invocable<_Fn, _Args...>;
/// [concept.predicate], concept predicate
template<typename _Fn, typename... _Args>
concept predicate = regular_invocable<_Fn, _Args...>
&& __detail::__boolean_testable<invoke_result_t<_Fn, _Args...>>;
/// [concept.relation], concept relation
template<typename _Rel, typename _Tp, typename _Up>
concept relation
= predicate<_Rel, _Tp, _Tp> && predicate<_Rel, _Up, _Up>
&& predicate<_Rel, _Tp, _Up> && predicate<_Rel, _Up, _Tp>;
/// [concept.equiv], concept equivalence_relation
template<typename _Rel, typename _Tp, typename _Up>
concept equivalence_relation = relation<_Rel, _Tp, _Up>;
/// [concept.strictweakorder], concept strict_weak_order
template<typename _Rel, typename _Tp, typename _Up>
concept strict_weak_order = relation<_Rel, _Tp, _Up>;
namespace __detail
{
// operator<=> are automatically reversed, so we need to consider
// both directions if types are different.
template<typename _Tp, typename _Up>
concept __not_overloaded_spaceship
= ! requires(_Tp&& __t, _Up&& __u)
{ operator<=>(static_cast<_Tp&&>(__t), static_cast<_Up&&>(__u)); }
&& ! requires(_Tp&& __t, _Up&& __u)
{ static_cast<_Tp&&>(__t).operator<=>(static_cast<_Up&&>(__u)); }
&& (is_same_v<_Tp, _Up>
|| (! requires(_Tp&& __t, _Up&& __u)
{ operator<=>(static_cast<_Up&&>(__u), static_cast<_Tp&&>(__t)); }
&& ! requires(_Tp&& __t, _Up&& __u)
{ static_cast<_Up&&>(__u).operator<=>(static_cast<_Tp&&>(__t)); }));
}
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
#endif // __cpp_lib_concepts
#endif /* _GLIBCXX_CONCEPTS */
type_traits
version.h
std::common_reference_t
typename common_reference< _Tp... >::type common_reference_t
Definition type_traits:4102
std::add_lvalue_reference_t
typename add_lvalue_reference< _Tp >::type add_lvalue_reference_t
Alias template for add_lvalue_reference.
Definition type_traits:1803
std::remove_reference_t
typename remove_reference< _Tp >::type remove_reference_t
Alias template for remove_reference.
Definition type_traits:1799
std::common_type_t
typename common_type< _Tp... >::type common_type_t
Alias template for common_type.
Definition type_traits:2844
std::declval
auto declval() noexcept -> decltype(__declval< _Tp >(0))
Definition type_traits:2610
std
ISO C++ entities toplevel namespace is std.
std::__detail
Implementation details not part of the namespace std interface.