optional
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// <optional> -*- C++ -*-
// Copyright (C) 2013-2026 Free Software Foundation, Inc.
// Copyright The GNU Toolchain Authors.
//
// 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/optional
* This is a Standard C++ Library header.
*/
#ifndef _GLIBCXX_OPTIONAL
#define _GLIBCXX_OPTIONAL 1
#ifdef _GLIBCXX_SYSHDR
#pragma GCC system_header
#endif
#define __glibcxx_want_freestanding_optional
#define __glibcxx_want_optional
#define __glibcxx_want_optional_range_support
#define __glibcxx_want_constrained_equality
#define __glibcxx_want_constexpr_exceptions
#include <bits/version.h>
#ifdef __cpp_lib_optional // C++ >= 17
#include <type_traits>
#include <exception>
#include <new>
#include <initializer_list>
#include <bits/enable_special_members.h>
#include <bits/exception_defines.h>
#include <bits/functional_hash.h>
#include <bits/stl_construct.h> // _Construct
#include <bits/utility.h> // in_place_t
#if __cplusplus > 201703L
# include <compare>
# include <bits/invoke.h> // std::__invoke
#endif
#if __cplusplus > 202002L
# include <concepts>
#endif
#ifdef __cpp_lib_optional_range_support // C++ >= 26
# include <bits/formatfwd.h>
# include <bits/ranges_base.h>
# include <bits/stl_iterator.h>
#endif
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
/**
* @addtogroup utilities
* @{
*/
template<typename _Tp>
class optional;
/// Tag type to disengage optional objects.
struct nullopt_t
{
// Do not user-declare default constructor at all for
// optional_value = {} syntax to work.
// nullopt_t() = delete;
// Used for constructing nullopt.
enum class _Construct { _Token };
// Must be constexpr for nullopt_t to be literal.
explicit constexpr nullopt_t(_Construct) noexcept { }
};
/// Tag to disengage optional objects.
inline constexpr nullopt_t nullopt { nullopt_t::_Construct::_Token };
template<typename _Fn> struct _Optional_func { _Fn& _M_f; };
/**
* @brief Exception class thrown when a disengaged optional object is
* dereferenced.
* @ingroup exceptions
*/
class bad_optional_access : public exception
{
public:
bad_optional_access() = default;
virtual ~bad_optional_access() = default;
#if __cpp_lib_constexpr_exceptions >= 202502L
constexpr
#endif
const char* what() const noexcept override
{ return "bad optional access"; }
};
// XXX Does not belong here.
[[__noreturn__]]
#if __cpp_lib_constexpr_exceptions >= 202502L
constexpr
#else
inline
#endif
void
__throw_bad_optional_access()
{ _GLIBCXX_THROW_OR_ABORT(bad_optional_access()); }
// This class template manages construction/destruction of
// the contained value for a std::optional.
template <typename _Tp>
struct _Optional_payload_base
{
using _Stored_type = remove_const_t<_Tp>;
_Optional_payload_base() = default;
~_Optional_payload_base() = default;
template<typename... _Args>
constexpr
_Optional_payload_base(in_place_t __tag, _Args&&... __args)
: _M_payload(__tag, std::forward<_Args>(__args)...),
_M_engaged(true)
{ }
template<typename _Up, typename... _Args>
constexpr
_Optional_payload_base(std::initializer_list<_Up> __il,
_Args&&... __args)
: _M_payload(__il, std::forward<_Args>(__args)...),
_M_engaged(true)
{ }
// Constructor used by _Optional_base copy constructor when the
// contained value is not trivially copy constructible.
constexpr
_Optional_payload_base(bool /* __engaged */,
const _Optional_payload_base& __other)
{
if (__other._M_engaged)
this->_M_construct(__other._M_get());
}
// Constructor used by _Optional_base move constructor when the
// contained value is not trivially move constructible.
constexpr
_Optional_payload_base(bool /* __engaged */,
_Optional_payload_base&& __other)
{
if (__other._M_engaged)
this->_M_construct(std::move(__other._M_get()));
}
// Copy constructor is only used to when the contained value is
// trivially copy constructible.
_Optional_payload_base(const _Optional_payload_base&) = default;
// Move constructor is only used to when the contained value is
// trivially copy constructible.
_Optional_payload_base(_Optional_payload_base&&) = default;
_Optional_payload_base&
operator=(const _Optional_payload_base&) = default;
_Optional_payload_base&
operator=(_Optional_payload_base&&) = default;
// used to perform non-trivial copy assignment.
constexpr void
_M_copy_assign(const _Optional_payload_base& __other)
{
if (this->_M_engaged && __other._M_engaged)
this->_M_get() = __other._M_get();
else
{
if (__other._M_engaged)
this->_M_construct(__other._M_get());
else
this->_M_reset();
}
}
// used to perform non-trivial move assignment.
constexpr void
_M_move_assign(_Optional_payload_base&& __other)
noexcept(__and_v<is_nothrow_move_constructible<_Tp>,
is_nothrow_move_assignable<_Tp>>)
{
if (this->_M_engaged && __other._M_engaged)
this->_M_get() = std::move(__other._M_get());
else
{
if (__other._M_engaged)
this->_M_construct(std::move(__other._M_get()));
else
this->_M_reset();
}
}
struct _Empty_byte { };
template<typename _Up, bool = is_trivially_destructible_v<_Up>>
union _Storage
{
constexpr _Storage() noexcept : _M_empty() { }
template<typename... _Args>
constexpr
_Storage(in_place_t, _Args&&... __args)
: _M_value(std::forward<_Args>(__args)...)
{ }
template<typename _Vp, typename... _Args>
constexpr
_Storage(std::initializer_list<_Vp> __il, _Args&&... __args)
: _M_value(__il, std::forward<_Args>(__args)...)
{ }
#if __cplusplus >= 202002L
template<typename _Fn, typename _Arg>
constexpr
_Storage(_Optional_func<_Fn> __f, _Arg&& __arg)
: _M_value(std::__invoke(std::forward<_Fn>(__f._M_f),
std::forward<_Arg>(__arg)))
{ }
#endif
#if __cpp_concepts >= 202002L // Conditionally trivial special member functions
~_Storage() = default;
// User-provided destructor is needed when _Up has non-trivial dtor.
_GLIBCXX20_CONSTEXPR
~_Storage() requires (!is_trivially_destructible_v<_Up>)
{ }
_Storage(const _Storage&) = default;
_Storage(_Storage&&) = default;
_Storage& operator=(const _Storage&) = default;
_Storage& operator=(_Storage&&) = default;
#endif
_Empty_byte _M_empty;
_Up _M_value;
};
#if __cpp_concepts < 202002L
template<typename _Up>
union _Storage<_Up, false>
{
constexpr _Storage() noexcept : _M_empty() { }
template<typename... _Args>
constexpr
_Storage(in_place_t, _Args&&... __args)
: _M_value(std::forward<_Args>(__args)...)
{ }
template<typename _Vp, typename... _Args>
constexpr
_Storage(std::initializer_list<_Vp> __il, _Args&&... __args)
: _M_value(__il, std::forward<_Args>(__args)...)
{ }
#if __cplusplus >= 202002L
template<typename _Fn, typename _Arg>
constexpr
_Storage(_Optional_func<_Fn> __f, _Arg&& __arg)
: _M_value(std::__invoke(std::forward<_Fn>(__f._M_f),
std::forward<_Arg>(__arg)))
{ }
#endif
// User-provided destructor is needed when _Up has non-trivial dtor.
_GLIBCXX20_CONSTEXPR ~_Storage() { }
_Storage(const _Storage&) = default;
_Storage(_Storage&&) = default;
_Storage& operator=(const _Storage&) = default;
_Storage& operator=(_Storage&&) = default;
_Empty_byte _M_empty;
_Up _M_value;
};
#endif
_Storage<_Stored_type> _M_payload;
bool _M_engaged = false;
template<typename... _Args>
constexpr void
_M_construct(_Args&&... __args)
noexcept(is_nothrow_constructible_v<_Stored_type, _Args...>)
{
std::_Construct(std::__addressof(this->_M_payload._M_value),
std::forward<_Args>(__args)...);
this->_M_engaged = true;
}
constexpr void
_M_destroy() noexcept
{
_M_engaged = false;
_M_payload._M_value.~_Stored_type();
}
#if __cplusplus >= 202002L
template<typename _Fn, typename _Up>
constexpr void
_M_apply(_Optional_func<_Fn> __f, _Up&& __x)
{
std::construct_at(std::__addressof(this->_M_payload),
__f, std::forward<_Up>(__x));
_M_engaged = true;
}
#endif
// The _M_get() operations have _M_engaged as a precondition.
// They exist to access the contained value with the appropriate
// const-qualification, because _M_payload has had the const removed.
constexpr _Tp&
_M_get() noexcept
{ return this->_M_payload._M_value; }
constexpr const _Tp&
_M_get() const noexcept
{ return this->_M_payload._M_value; }
// _M_reset is a 'safe' operation with no precondition.
constexpr void
_M_reset() noexcept
{
if (this->_M_engaged)
_M_destroy();
else // This seems redundant but improves codegen, see PR 112480.
this->_M_engaged = false;
}
};
// Class template that manages the payload for optionals.
template <typename _Tp,
bool /*_HasTrivialDestructor*/ =
is_trivially_destructible_v<_Tp>,
bool /*_HasTrivialCopy */ =
is_trivially_copy_assignable_v<_Tp>
&& is_trivially_copy_constructible_v<_Tp>,
bool /*_HasTrivialMove */ =
is_trivially_move_assignable_v<_Tp>
&& is_trivially_move_constructible_v<_Tp>>
struct _Optional_payload;
// Payload for potentially-constexpr optionals (trivial copy/move/destroy).
template <typename _Tp>
struct _Optional_payload<_Tp, true, true, true>
: _Optional_payload_base<_Tp>
{
using _Optional_payload_base<_Tp>::_Optional_payload_base;
_Optional_payload() = default;
};
// Payload for optionals with non-trivial copy construction/assignment.
template <typename _Tp>
struct _Optional_payload<_Tp, true, false, true>
: _Optional_payload_base<_Tp>
{
using _Optional_payload_base<_Tp>::_Optional_payload_base;
_Optional_payload() = default;
~_Optional_payload() = default;
_Optional_payload(const _Optional_payload&) = default;
_Optional_payload(_Optional_payload&&) = default;
_Optional_payload& operator=(_Optional_payload&&) = default;
// Non-trivial copy assignment.
constexpr
_Optional_payload&
operator=(const _Optional_payload& __other)
{
this->_M_copy_assign(__other);
return *this;
}
};
// Payload for optionals with non-trivial move construction/assignment.
template <typename _Tp>
struct _Optional_payload<_Tp, true, true, false>
: _Optional_payload_base<_Tp>
{
using _Optional_payload_base<_Tp>::_Optional_payload_base;
_Optional_payload() = default;
~_Optional_payload() = default;
_Optional_payload(const _Optional_payload&) = default;
_Optional_payload(_Optional_payload&&) = default;
_Optional_payload& operator=(const _Optional_payload&) = default;
// Non-trivial move assignment.
constexpr
_Optional_payload&
operator=(_Optional_payload&& __other)
noexcept(__and_v<is_nothrow_move_constructible<_Tp>,
is_nothrow_move_assignable<_Tp>>)
{
this->_M_move_assign(std::move(__other));
return *this;
}
};
// Payload for optionals with non-trivial copy and move assignment.
template <typename _Tp>
struct _Optional_payload<_Tp, true, false, false>
: _Optional_payload_base<_Tp>
{
using _Optional_payload_base<_Tp>::_Optional_payload_base;
_Optional_payload() = default;
~_Optional_payload() = default;
_Optional_payload(const _Optional_payload&) = default;
_Optional_payload(_Optional_payload&&) = default;
// Non-trivial copy assignment.
constexpr
_Optional_payload&
operator=(const _Optional_payload& __other)
{
this->_M_copy_assign(__other);
return *this;
}
// Non-trivial move assignment.
constexpr
_Optional_payload&
operator=(_Optional_payload&& __other)
noexcept(__and_v<is_nothrow_move_constructible<_Tp>,
is_nothrow_move_assignable<_Tp>>)
{
this->_M_move_assign(std::move(__other));
return *this;
}
};
// Payload for optionals with non-trivial destructors.
template <typename _Tp, bool _Copy, bool _Move>
struct _Optional_payload<_Tp, false, _Copy, _Move>
: _Optional_payload<_Tp, true, false, false>
{
// Base class implements all the constructors and assignment operators:
using _Optional_payload<_Tp, true, false, false>::_Optional_payload;
_Optional_payload() = default;
_Optional_payload(const _Optional_payload&) = default;
_Optional_payload(_Optional_payload&&) = default;
_Optional_payload& operator=(const _Optional_payload&) = default;
_Optional_payload& operator=(_Optional_payload&&) = default;
// Destructor needs to destroy the contained value:
_GLIBCXX20_CONSTEXPR ~_Optional_payload() { this->_M_reset(); }
};
/**
* @brief Class template that provides copy/move constructors of optional.
*
* Such a separate base class template is necessary in order to
* conditionally make copy/move constructors trivial.
*
* When the contained value is trivially copy/move constructible,
* the copy/move constructors of _Optional_base will invoke the
* trivial copy/move constructor of _Optional_payload. Otherwise,
* they will invoke _Optional_payload(bool, const _Optional_payload&)
* or _Optional_payload(bool, _Optional_payload&&) to initialize
* the contained value, if copying/moving an engaged optional.
*
* Whether the other special members are trivial is determined by the
* _Optional_payload<_Tp> specialization used for the _M_payload member.
*
* @see optional, _Enable_special_members
*/
template<typename _Tp,
bool = is_trivially_copy_constructible_v<_Tp>,
bool = is_trivially_move_constructible_v<_Tp>>
struct _Optional_base
{
// Constructors for disengaged optionals.
constexpr _Optional_base() = default;
// Constructors for engaged optionals.
template<typename... _Args,
enable_if_t<is_constructible_v<_Tp, _Args...>, bool> = false>
constexpr explicit
_Optional_base(in_place_t, _Args&&... __args)
: _M_payload(in_place, std::forward<_Args>(__args)...)
{ }
template<typename _Up, typename... _Args,
enable_if_t<is_constructible_v<_Tp,
initializer_list<_Up>&,
_Args...>, bool> = false>
constexpr explicit
_Optional_base(in_place_t,
initializer_list<_Up> __il,
_Args&&... __args)
: _M_payload(in_place, __il, std::forward<_Args>(__args)...)
{ }
// Copy and move constructors.
constexpr
_Optional_base(const _Optional_base& __other)
noexcept(is_nothrow_copy_constructible_v<_Tp>)
: _M_payload(__other._M_payload._M_engaged, __other._M_payload)
{ }
constexpr
_Optional_base(_Optional_base&& __other)
noexcept(is_nothrow_move_constructible_v<_Tp>)
: _M_payload(__other._M_payload._M_engaged,
std::move(__other._M_payload))
{ }
#if __cpp_concepts >= 202002L // Conditionally trivial special member functions
// Define these in the primary template if possible, so that we don't
// need to use partial specializations of this class template.
constexpr _Optional_base(const _Optional_base&)
requires is_trivially_copy_constructible_v<_Tp> = default;
constexpr _Optional_base(_Optional_base&&)
requires is_trivially_move_constructible_v<_Tp> = default;
#endif
// Assignment operators.
_Optional_base& operator=(const _Optional_base&) = default;
_Optional_base& operator=(_Optional_base&&) = default;
_Optional_payload<_Tp> _M_payload;
protected:
// For the primary template, we define these functions here.
using _Stored_type = remove_const_t<_Tp>;
// The _M_construct operation has !_M_engaged as a precondition
// while _M_destruct has _M_engaged as a precondition.
template<typename... _Args>
constexpr void
_M_construct(_Args&&... __args)
noexcept(is_nothrow_constructible_v<_Stored_type, _Args...>)
{
_M_payload._M_construct(std::forward<_Args>(__args)...);
}
constexpr void
_M_destruct() noexcept
{ _M_payload._M_destroy(); }
// _M_reset is a 'safe' operation with no precondition.
constexpr void
_M_reset() noexcept
{ _M_payload._M_reset(); }
constexpr bool _M_is_engaged() const noexcept
{ return _M_payload._M_engaged; }
// The _M_get operations have _M_engaged as a precondition.
constexpr _Tp&
_M_get() noexcept
{ return _M_payload._M_get(); }
constexpr const _Tp&
_M_get() const noexcept
{ return _M_payload._M_get(); }
};
#if __cpp_concepts < 202002L
// If P0848R3 "Conditionally Trivial Special Member Functions" is not
// supported (as determined from the __cpp_concepts macro value), the
// _Optional_base primary template only has non-trivial copy and move
// constructors. Use partial specializations of _Optional_base<T, C, M>
// that have a trivial copy and/or move constructor.
// Common base class for _Optional_base<T> to avoid repeating these
// member functions in each partial specialization.
// Only used if P0848R3 "Conditionally Trivial Special Member Functions"
// is not supported, as indicated by the __cpp_concepts value.
template<typename _Tp, typename _Dp>
class _Optional_base_impl
{
protected:
using _Stored_type = remove_const_t<_Tp>;
// The _M_construct operation has !_M_engaged as a precondition
// while _M_destruct has _M_engaged as a precondition.
template<typename... _Args>
constexpr void
_M_construct(_Args&&... __args)
noexcept(is_nothrow_constructible_v<_Stored_type, _Args...>)
{
static_cast<_Dp*>(this)->_M_payload._M_construct(
std::forward<_Args>(__args)...);
}
constexpr void
_M_destruct() noexcept
{ static_cast<_Dp*>(this)->_M_payload._M_destroy(); }
// _M_reset is a 'safe' operation with no precondition.
constexpr void
_M_reset() noexcept
{ static_cast<_Dp*>(this)->_M_payload._M_reset(); }
constexpr bool _M_is_engaged() const noexcept
{ return static_cast<const _Dp*>(this)->_M_payload._M_engaged; }
// The _M_get operations have _M_engaged as a precondition.
constexpr _Tp&
_M_get() noexcept
{ return static_cast<_Dp*>(this)->_M_payload._M_get(); }
constexpr const _Tp&
_M_get() const noexcept
{ return static_cast<const _Dp*>(this)->_M_payload._M_get(); }
};
template<typename _Tp>
struct _Optional_base<_Tp, false, true> // trivial move ctor
: _Optional_base_impl<_Tp, _Optional_base<_Tp>>
{
// Constructors for disengaged optionals.
constexpr _Optional_base() = default;
// Constructors for engaged optionals.
template<typename... _Args,
enable_if_t<is_constructible_v<_Tp, _Args...>, bool> = false>
constexpr explicit
_Optional_base(in_place_t, _Args&&... __args)
: _M_payload(in_place, std::forward<_Args>(__args)...)
{ }
template<typename _Up, typename... _Args,
enable_if_t<is_constructible_v<_Tp,
initializer_list<_Up>&,
_Args...>, bool> = false>
constexpr explicit
_Optional_base(in_place_t,
initializer_list<_Up> __il,
_Args... __args)
: _M_payload(in_place, __il, std::forward<_Args>(__args)...)
{ }
// Copy and move constructors.
constexpr _Optional_base(const _Optional_base& __other)
: _M_payload(__other._M_payload._M_engaged, __other._M_payload)
{ }
constexpr _Optional_base(_Optional_base&& __other) = default;
// Assignment operators.
_Optional_base& operator=(const _Optional_base&) = default;
_Optional_base& operator=(_Optional_base&&) = default;
_Optional_payload<_Tp> _M_payload;
};
template<typename _Tp>
struct _Optional_base<_Tp, true, false> // trivial copy ctor
: _Optional_base_impl<_Tp, _Optional_base<_Tp>>
{
// Constructors for disengaged optionals.
constexpr _Optional_base() = default;
// Constructors for engaged optionals.
template<typename... _Args,
enable_if_t<is_constructible_v<_Tp, _Args...>, bool> = false>
constexpr explicit
_Optional_base(in_place_t, _Args&&... __args)
: _M_payload(in_place, std::forward<_Args>(__args)...)
{ }
template<typename _Up, typename... _Args,
enable_if_t<is_constructible_v<_Tp,
initializer_list<_Up>&,
_Args...>, bool> = false>
constexpr explicit
_Optional_base(in_place_t,
initializer_list<_Up> __il,
_Args&&... __args)
: _M_payload(in_place, __il, std::forward<_Args>(__args)...)
{ }
// Copy and move constructors.
constexpr _Optional_base(const _Optional_base& __other) = default;
constexpr
_Optional_base(_Optional_base&& __other)
noexcept(is_nothrow_move_constructible_v<_Tp>)
: _M_payload(__other._M_payload._M_engaged,
std::move(__other._M_payload))
{ }
// Assignment operators.
_Optional_base& operator=(const _Optional_base&) = default;
_Optional_base& operator=(_Optional_base&&) = default;
_Optional_payload<_Tp> _M_payload;
};
template<typename _Tp>
struct _Optional_base<_Tp, true, true> // trivial copy and move ctors
: _Optional_base_impl<_Tp, _Optional_base<_Tp>>
{
// Constructors for disengaged optionals.
constexpr _Optional_base() = default;
// Constructors for engaged optionals.
template<typename... _Args,
enable_if_t<is_constructible_v<_Tp, _Args...>, bool> = false>
constexpr explicit
_Optional_base(in_place_t, _Args&&... __args)
: _M_payload(in_place, std::forward<_Args>(__args)...)
{ }
template<typename _Up, typename... _Args,
enable_if_t<is_constructible_v<_Tp,
initializer_list<_Up>&,
_Args...>, bool> = false>
constexpr explicit
_Optional_base(in_place_t,
initializer_list<_Up> __il,
_Args&&... __args)
: _M_payload(in_place, __il, std::forward<_Args>(__args)...)
{ }
// Copy and move constructors.
constexpr _Optional_base(const _Optional_base& __other) = default;
constexpr _Optional_base(_Optional_base&& __other) = default;
// Assignment operators.
_Optional_base& operator=(const _Optional_base&) = default;
_Optional_base& operator=(_Optional_base&&) = default;
_Optional_payload<_Tp> _M_payload;
};
#endif // __cpp_concepts
template<typename _Tp>
inline constexpr bool __is_optional_v = false;
template<typename _Tp>
inline constexpr bool __is_optional_v<optional<_Tp>> = true;
template<typename _Tp, typename _Wp>
using __converts_from_any_cvref = __or_<
is_constructible<_Tp, _Wp&>, is_convertible<_Wp&, _Tp>,
is_constructible<_Tp, _Wp>, is_convertible<_Wp, _Tp>,
is_constructible<_Tp, const _Wp&>, is_convertible<const _Wp&, _Tp>,
is_constructible<_Tp, const _Wp>, is_convertible<const _Wp, _Tp>
>;
template<typename _Tp, typename _Up>
using __converts_from_optional
= __converts_from_any_cvref<_Tp, optional<_Up>>;
template<typename _Tp, typename _Up>
using __assigns_from_optional =
__or_<is_assignable<_Tp&, const optional<_Up>&>,
is_assignable<_Tp&, optional<_Up>&>,
is_assignable<_Tp&, const optional<_Up>&&>,
is_assignable<_Tp&, optional<_Up>&&>>;
#if __cpp_concepts && __cpp_conditional_explicit && __glibcxx_remove_cvref
# define _GLIBCXX_USE_CONSTRAINTS_FOR_OPTIONAL 1
#endif
template<typename _Tp>
inline constexpr bool __is_valid_contained_type_for_optional =
(
#if __cpp_lib_optional >= 202506L
is_lvalue_reference_v<_Tp> ||
#endif
(is_object_v<_Tp> && is_destructible_v<_Tp> && !is_array_v<_Tp>)
)
&& !is_same_v<remove_cv_t<remove_reference_t<_Tp>>, nullopt_t>
&& !is_same_v<remove_cv_t<remove_reference_t<_Tp>>, in_place_t>;
/**
* @brief Class template for optional values.
*/
template<typename _Tp>
class optional
: private _Optional_base<_Tp>,
private _Enable_copy_move<
// Copy constructor.
is_copy_constructible_v<_Tp>,
// Copy assignment.
__and_v<is_copy_constructible<_Tp>, is_copy_assignable<_Tp>>,
// Move constructor.
is_move_constructible_v<_Tp>,
// Move assignment.
__and_v<is_move_constructible<_Tp>, is_move_assignable<_Tp>>,
// Unique tag type.
optional<_Tp>>
{
static_assert(__is_valid_contained_type_for_optional<_Tp>);
private:
using _Base = _Optional_base<_Tp>;
// SFINAE helpers
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 3836. std::expected<bool, E1> conversion constructor
// expected(const expected<U, G>&) should take precedence over
// expected(U&&) with operator bool
#ifdef _GLIBCXX_USE_CONSTRAINTS_FOR_OPTIONAL
template<typename _From, typename = remove_cv_t<_Tp>>
static constexpr bool __not_constructing_bool_from_optional
= true;
// If T is cv bool, remove_cvref_t<U> is not a specialization of optional
// i.e. do not initialize a bool from optional<U>::operator bool().
template<typename _From>
static constexpr bool
__not_constructing_bool_from_optional<_From, bool>
= !__is_optional_v<remove_cvref_t<_From>>;
// If T is not cv bool, converts-from-any-cvref<T, optional<U>> is false.
// The constructor that converts from optional<U> is disabled if the
// contained value can be initialized from optional<U>, so that the
// optional(U&&) constructor can be used instead.
template<typename _From, typename = remove_cv_t<_Tp>>
static constexpr bool __construct_from_contained_value
= !__converts_from_optional<_Tp, _From>::value;
// However, optional<U> can always be converted to bool, so don't apply
// this constraint when T is cv bool.
template<typename _From>
static constexpr bool __construct_from_contained_value<_From, bool>
= true;
#else
template<typename _From, typename = remove_cv_t<_Tp>>
struct __not_constructing_bool_from_optional
: true_type
{ };
template<typename _From>
struct __not_constructing_bool_from_optional<_From, bool>
: bool_constant<!__is_optional_v<__remove_cvref_t<_From>>>
{ };
template<typename _From, typename = remove_cv_t<_Tp>>
struct __construct_from_contained_value
: __not_<__converts_from_optional<_Tp, _From>>
{ };
template<typename _From>
struct __construct_from_contained_value<_From, bool>
: true_type
{ };
template<typename _Up>
using __not_self = __not_<is_same<optional, __remove_cvref_t<_Up>>>;
template<typename _Up>
using __not_tag = __not_<is_same<in_place_t, __remove_cvref_t<_Up>>>;
template<typename... _Cond>
using _Requires = enable_if_t<__and_v<_Cond...>, bool>;
#endif
public:
using value_type = _Tp;
#ifdef __cpp_lib_optional_range_support // >= C++26
using iterator = __gnu_cxx::__normal_iterator<_Tp*, optional>;
using const_iterator = __gnu_cxx::__normal_iterator<const _Tp*, optional>;
#endif
constexpr optional() noexcept { }
constexpr optional(nullopt_t) noexcept { }
// Converting constructors for engaged optionals.
#ifdef _GLIBCXX_USE_CONSTRAINTS_FOR_OPTIONAL
template<typename _Up = remove_cv_t<_Tp>>
requires (!is_same_v<optional, remove_cvref_t<_Up>>)
&& (!is_same_v<in_place_t, remove_cvref_t<_Up>>)
&& is_constructible_v<_Tp, _Up>
&& __not_constructing_bool_from_optional<_Up>
constexpr explicit(!is_convertible_v<_Up, _Tp>)
optional(_Up&& __t)
noexcept(is_nothrow_constructible_v<_Tp, _Up>)
: _Base(std::in_place, std::forward<_Up>(__t)) { }
template<typename _Up>
requires (!is_same_v<_Tp, _Up>)
&& is_constructible_v<_Tp, const _Up&>
&& __construct_from_contained_value<_Up>
constexpr explicit(!is_convertible_v<const _Up&, _Tp>)
optional(const optional<_Up>& __t)
noexcept(is_nothrow_constructible_v<_Tp, const _Up&>)
{
if (__t)
emplace(__t._M_fwd());
}
template<typename _Up>
requires (!is_same_v<_Tp, _Up>)
&& is_constructible_v<_Tp, _Up>
&& __construct_from_contained_value<_Up>
constexpr explicit(!is_convertible_v<_Up, _Tp>)
optional(optional<_Up>&& __t)
noexcept(is_nothrow_constructible_v<_Tp, _Up>)
{
if (__t)
emplace(std::move(__t)._M_fwd());
}
template<typename... _Args>
requires is_constructible_v<_Tp, _Args...>
explicit constexpr
optional(in_place_t, _Args&&... __args)
noexcept(is_nothrow_constructible_v<_Tp, _Args...>)
: _Base(std::in_place, std::forward<_Args>(__args)...)
{ }
template<typename _Up, typename... _Args>
requires is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>
explicit constexpr
optional(in_place_t, initializer_list<_Up> __il, _Args&&... __args)
noexcept(is_nothrow_constructible_v<_Tp, initializer_list<_Up>&,
_Args...>)
: _Base(std::in_place, __il, std::forward<_Args>(__args)...)
{ }
#else
template<typename _Up = remove_cv_t<_Tp>,
_Requires<__not_self<_Up>, __not_tag<_Up>,
is_constructible<_Tp, _Up>,
is_convertible<_Up, _Tp>,
__not_constructing_bool_from_optional<_Up>> = true>
constexpr
optional(_Up&& __t)
noexcept(is_nothrow_constructible_v<_Tp, _Up>)
: _Base(std::in_place, std::forward<_Up>(__t)) { }
template<typename _Up = remove_cv_t<_Tp>,
_Requires<__not_self<_Up>, __not_tag<_Up>,
is_constructible<_Tp, _Up>,
__not_<is_convertible<_Up, _Tp>>,
__not_constructing_bool_from_optional<_Up>> = false>
explicit constexpr
optional(_Up&& __t)
noexcept(is_nothrow_constructible_v<_Tp, _Up>)
: _Base(std::in_place, std::forward<_Up>(__t)) { }
template<typename _Up,
_Requires<__not_<is_same<_Tp, _Up>>,
is_constructible<_Tp, const _Up&>,
is_convertible<const _Up&, _Tp>,
__construct_from_contained_value<_Up>> = true>
constexpr
optional(const optional<_Up>& __t)
noexcept(is_nothrow_constructible_v<_Tp, const _Up&>)
{
if (__t)
emplace(__t._M_fwd());
}
template<typename _Up,
_Requires<__not_<is_same<_Tp, _Up>>,
is_constructible<_Tp, const _Up&>,
__not_<is_convertible<const _Up&, _Tp>>,
__construct_from_contained_value<_Up>> = false>
explicit constexpr
optional(const optional<_Up>& __t)
noexcept(is_nothrow_constructible_v<_Tp, const _Up&>)
{
if (__t)
emplace(__t._M_fwd());
}
template<typename _Up,
_Requires<__not_<is_same<_Tp, _Up>>,
is_constructible<_Tp, _Up>,
is_convertible<_Up, _Tp>,
__construct_from_contained_value<_Up>> = true>
constexpr
optional(optional<_Up>&& __t)
noexcept(is_nothrow_constructible_v<_Tp, _Up>)
{
if (__t)
emplace(std::move(__t)._M_fwd());
}
template<typename _Up,
_Requires<__not_<is_same<_Tp, _Up>>,
is_constructible<_Tp, _Up>,
__not_<is_convertible<_Up, _Tp>>,
__construct_from_contained_value<_Up>> = false>
explicit constexpr
optional(optional<_Up>&& __t)
noexcept(is_nothrow_constructible_v<_Tp, _Up>)
{
if (__t)
emplace(std::move(__t)._M_fwd());
}
template<typename... _Args,
_Requires<is_constructible<_Tp, _Args...>> = false>
explicit constexpr
optional(in_place_t, _Args&&... __args)
noexcept(is_nothrow_constructible_v<_Tp, _Args...>)
: _Base(std::in_place, std::forward<_Args>(__args)...) { }
template<typename _Up, typename... _Args,
_Requires<is_constructible<_Tp,
initializer_list<_Up>&,
_Args...>> = false>
explicit constexpr
optional(in_place_t, initializer_list<_Up> __il, _Args&&... __args)
noexcept(is_nothrow_constructible_v<_Tp, initializer_list<_Up>&,
_Args...>)
: _Base(std::in_place, __il, std::forward<_Args>(__args)...) { }
#endif
// Assignment operators.
_GLIBCXX20_CONSTEXPR optional&
operator=(nullopt_t) noexcept
{
this->_M_reset();
return *this;
}
template<typename _Up = remove_cv_t<_Tp>>
#ifdef _GLIBCXX_USE_CONSTRAINTS_FOR_OPTIONAL
requires (!is_same_v<optional, remove_cvref_t<_Up>>)
&& (!(is_scalar_v<_Tp> && is_same_v<_Tp, decay_t<_Up>>))
&& is_constructible_v<_Tp, _Up>
&& is_assignable_v<_Tp&, _Up>
constexpr optional&
#else
enable_if_t<__and_v<__not_self<_Up>,
__not_<__and_<is_scalar<_Tp>,
is_same<_Tp, decay_t<_Up>>>>,
is_constructible<_Tp, _Up>,
is_assignable<_Tp&, _Up>>,
optional&>
#endif
operator=(_Up&& __u)
noexcept(__and_v<is_nothrow_constructible<_Tp, _Up>,
is_nothrow_assignable<_Tp&, _Up>>)
{
if (this->_M_is_engaged())
this->_M_get() = std::forward<_Up>(__u);
else
this->_M_construct(std::forward<_Up>(__u));
return *this;
}
template<typename _Up>
#ifdef _GLIBCXX_USE_CONSTRAINTS_FOR_OPTIONAL
requires (!is_same_v<_Tp, _Up>)
&& is_constructible_v<_Tp, const _Up&>
&& is_assignable_v<_Tp&, const _Up&>
&& (!__converts_from_optional<_Tp, _Up>::value)
&& (!__assigns_from_optional<_Tp, _Up>::value)
constexpr optional&
#else
enable_if_t<__and_v<__not_<is_same<_Tp, _Up>>,
is_constructible<_Tp, const _Up&>,
is_assignable<_Tp&, const _Up&>,
__not_<__converts_from_optional<_Tp, _Up>>,
__not_<__assigns_from_optional<_Tp, _Up>>>,
optional&>
#endif
operator=(const optional<_Up>& __u)
noexcept(__and_v<is_nothrow_constructible<_Tp, const _Up&>,
is_nothrow_assignable<_Tp&, const _Up&>>)
{
if (__u)
{
if (this->_M_is_engaged())
this->_M_get() = __u._M_fwd();
else
this->_M_construct(__u._M_fwd());
}
else
{
this->_M_reset();
}
return *this;
}
template<typename _Up>
#ifdef _GLIBCXX_USE_CONSTRAINTS_FOR_OPTIONAL
requires (!is_same_v<_Tp, _Up>)
&& is_constructible_v<_Tp, _Up>
&& is_assignable_v<_Tp&, _Up>
&& (!__converts_from_optional<_Tp, _Up>::value)
&& (!__assigns_from_optional<_Tp, _Up>::value)
constexpr optional&
#else
enable_if_t<__and_v<__not_<is_same<_Tp, _Up>>,
is_constructible<_Tp, _Up>,
is_assignable<_Tp&, _Up>,
__not_<__converts_from_optional<_Tp, _Up>>,
__not_<__assigns_from_optional<_Tp, _Up>>>,
optional&>
#endif
operator=(optional<_Up>&& __u)
noexcept(__and_v<is_nothrow_constructible<_Tp, _Up>,
is_nothrow_assignable<_Tp&, _Up>>)
{
if (__u)
{
if (this->_M_is_engaged())
this->_M_get() = std::move(__u)._M_fwd();
else
this->_M_construct(std::move(__u)._M_fwd());
}
else
{
this->_M_reset();
}
return *this;
}
template<typename... _Args>
_GLIBCXX20_CONSTEXPR
enable_if_t<is_constructible_v<_Tp, _Args...>, _Tp&>
emplace(_Args&&... __args)
noexcept(is_nothrow_constructible_v<_Tp, _Args...>)
{
this->_M_reset();
this->_M_construct(std::forward<_Args>(__args)...);
return this->_M_get();
}
template<typename _Up, typename... _Args>
_GLIBCXX20_CONSTEXPR
enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>,
_Tp&>
emplace(initializer_list<_Up> __il, _Args&&... __args)
noexcept(is_nothrow_constructible_v<_Tp, initializer_list<_Up>&,
_Args...>)
{
this->_M_reset();
this->_M_construct(__il, std::forward<_Args>(__args)...);
return this->_M_get();
}
// Destructor is implicit, implemented in _Optional_base.
// Swap.
_GLIBCXX20_CONSTEXPR void
swap(optional& __other)
noexcept(is_nothrow_move_constructible_v<_Tp>
&& is_nothrow_swappable_v<_Tp>)
{
using std::swap;
if (this->_M_is_engaged() && __other._M_is_engaged())
swap(this->_M_get(), __other._M_get());
else if (this->_M_is_engaged())
{
__other._M_construct(std::move(this->_M_get()));
this->_M_destruct();
}
else if (__other._M_is_engaged())
{
this->_M_construct(std::move(__other._M_get()));
__other._M_destruct();
}
}
#ifdef __cpp_lib_optional_range_support // >= C++26
// Iterator support.
constexpr iterator begin() noexcept
{
return iterator(
this->_M_is_engaged() ? std::addressof(this->_M_get()) : nullptr
);
}
constexpr const_iterator begin() const noexcept
{
return const_iterator(
this->_M_is_engaged() ? std::addressof(this->_M_get()) : nullptr
);
}
constexpr iterator end() noexcept
{
return begin() + has_value();
}
constexpr const_iterator end() const noexcept
{
return begin() + has_value();
}
#endif // __cpp_lib_optional_range_support
// Observers.
constexpr const _Tp*
operator->() const noexcept
{
__glibcxx_assert(this->_M_is_engaged());
return std::__addressof(this->_M_get());
}
constexpr _Tp*
operator->() noexcept
{
__glibcxx_assert(this->_M_is_engaged());
return std::__addressof(this->_M_get());
}
constexpr const _Tp&
operator*() const& noexcept
{
__glibcxx_assert(this->_M_is_engaged());
return this->_M_get();
}
constexpr _Tp&
operator*()& noexcept
{
__glibcxx_assert(this->_M_is_engaged());
return this->_M_get();
}
constexpr _Tp&&
operator*()&& noexcept
{
__glibcxx_assert(this->_M_is_engaged());
return std::move(this->_M_get());
}
constexpr const _Tp&&
operator*() const&& noexcept
{
__glibcxx_assert(this->_M_is_engaged());
return std::move(this->_M_get());
}
constexpr explicit operator bool() const noexcept
{ return this->_M_is_engaged(); }
constexpr bool has_value() const noexcept
{ return this->_M_is_engaged(); }
constexpr const _Tp&
value() const&
{
if (this->_M_is_engaged())
return this->_M_get();
__throw_bad_optional_access();
}
constexpr _Tp&
value()&
{
if (this->_M_is_engaged())
return this->_M_get();
__throw_bad_optional_access();
}
constexpr _Tp&&
value()&&
{
if (this->_M_is_engaged())
return std::move(this->_M_get());
__throw_bad_optional_access();
}
constexpr const _Tp&&
value() const&&
{
if (this->_M_is_engaged())
return std::move(this->_M_get());
__throw_bad_optional_access();
}
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 4406. value_or return statement is inconsistent with Mandates
template<typename _Up = remove_cv_t<_Tp>>
constexpr remove_cv_t<_Tp>
value_or(_Up&& __u) const&
{
using _Xp = remove_cv_t<_Tp>;
static_assert(is_convertible_v<const _Tp&, _Xp>);
static_assert(is_convertible_v<_Up, _Xp>);
if (this->_M_is_engaged())
return this->_M_get();
return std::forward<_Up>(__u);
}
template<typename _Up = remove_cv_t<_Tp>>
constexpr remove_cv_t<_Tp>
value_or(_Up&& __u) &&
{
using _Xp = remove_cv_t<_Tp>;
static_assert(is_convertible_v<_Tp, _Xp>);
static_assert(is_convertible_v<_Up, _Xp>);
if (this->_M_is_engaged())
return std::move(this->_M_get());
return std::forward<_Up>(__u);
}
#if __cpp_lib_optional >= 202110L // C++23
// [optional.monadic]
template<typename _Fn>
constexpr auto
and_then(_Fn&& __f) &
{
using _Up = remove_cvref_t<invoke_result_t<_Fn, _Tp&>>;
static_assert(__is_optional_v<_Up>,
"the function passed to std::optional<T>::and_then "
"must return a std::optional");
if (has_value())
return std::__invoke(std::forward<_Fn>(__f), _M_get());
else
return _Up();
}
template<typename _Fn>
constexpr auto
and_then(_Fn&& __f) const &
{
using _Up = remove_cvref_t<invoke_result_t<_Fn, const _Tp&>>;
static_assert(__is_optional_v<_Up>,
"the function passed to std::optional<T>::and_then "
"must return a std::optional");
if (has_value())
return std::__invoke(std::forward<_Fn>(__f), _M_get());
else
return _Up();
}
template<typename _Fn>
constexpr auto
and_then(_Fn&& __f) &&
{
using _Up = remove_cvref_t<invoke_result_t<_Fn, _Tp>>;
static_assert(__is_optional_v<_Up>,
"the function passed to std::optional<T>::and_then "
"must return a std::optional");
if (has_value())
return std::__invoke(std::forward<_Fn>(__f), std::move(_M_get()));
else
return _Up();
}
template<typename _Fn>
constexpr auto
and_then(_Fn&& __f) const &&
{
using _Up = remove_cvref_t<invoke_result_t<_Fn, const _Tp>>;
static_assert(__is_optional_v<_Up>,
"the function passed to std::optional<T>::and_then "
"must return a std::optional");
if (has_value())
return std::__invoke(std::forward<_Fn>(__f), std::move(_M_get()));
else
return _Up();
}
template<typename _Fn>
constexpr auto
transform(_Fn&& __f) &
{
using _Up = remove_cv_t<invoke_result_t<_Fn, _Tp&>>;
if (has_value())
return optional<_Up>(_Optional_func<_Fn>{__f}, _M_get());
else
return optional<_Up>();
}
template<typename _Fn>
constexpr auto
transform(_Fn&& __f) const &
{
using _Up = remove_cv_t<invoke_result_t<_Fn, const _Tp&>>;
if (has_value())
return optional<_Up>(_Optional_func<_Fn>{__f}, _M_get());
else
return optional<_Up>();
}
template<typename _Fn>
constexpr auto
transform(_Fn&& __f) &&
{
using _Up = remove_cv_t<invoke_result_t<_Fn, _Tp>>;
if (has_value())
return optional<_Up>(_Optional_func<_Fn>{__f}, std::move(_M_get()));
else
return optional<_Up>();
}
template<typename _Fn>
constexpr auto
transform(_Fn&& __f) const &&
{
using _Up = remove_cv_t<invoke_result_t<_Fn, const _Tp>>;
if (has_value())
return optional<_Up>(_Optional_func<_Fn>{__f}, std::move(_M_get()));
else
return optional<_Up>();
}
template<typename _Fn> requires invocable<_Fn> && copy_constructible<_Tp>
constexpr optional
or_else(_Fn&& __f) const&
{
using _Up = invoke_result_t<_Fn>;
static_assert(is_same_v<remove_cvref_t<_Up>, optional>,
"the function passed to std::optional<T>::or_else "
"must return a std::optional<T>");
if (has_value())
return *this;
else
return std::forward<_Fn>(__f)();
}
template<typename _Fn> requires invocable<_Fn> && move_constructible<_Tp>
constexpr optional
or_else(_Fn&& __f) &&
{
using _Up = invoke_result_t<_Fn>;
static_assert(is_same_v<remove_cvref_t<_Up>, optional>,
"the function passed to std::optional<T>::or_else "
"must return a std::optional<T>");
if (has_value())
return std::move(*this);
else
return std::forward<_Fn>(__f)();
}
#endif
_GLIBCXX20_CONSTEXPR void reset() noexcept { this->_M_reset(); }
private:
using _Base::_M_get;
[[__gnu__::__always_inline__]]
constexpr _Tp&
_M_fwd() & noexcept
{ return _M_get(); }
[[__gnu__::__always_inline__]]
constexpr _Tp&&
_M_fwd() && noexcept
{ return std::move(_M_get()); }
[[__gnu__::__always_inline__]]
constexpr const _Tp&
_M_fwd() const& noexcept
{ return _M_get(); }
[[__gnu__::__always_inline__]]
constexpr const _Tp&&
_M_fwd() const&& noexcept
{ return std::move(_M_get()); }
template<typename _Up> friend class optional;
#if __cpp_lib_optional >= 202110L // C++23
template<typename _Fn, typename _Value>
explicit constexpr
optional(_Optional_func<_Fn> __f, _Value&& __v)
{
this->_M_payload._M_apply(__f, std::forward<_Value>(__v));
}
#endif
};
#if __cpp_lib_optional >= 202506L // C++26
template<typename _Tp>
class optional<_Tp&>;
template<typename _Tp>
constexpr bool __is_optional_ref_v = false;
template<typename _Tp>
constexpr bool __is_optional_ref_v<optional<_Tp&>> = true;
template<typename _Tp>
struct __optional_ref_base
{};
#ifdef __cpp_lib_optional_range_support // >= C++26
template<typename _Tp>
struct __optional_ref_base<_Tp[]>
{};
template<typename _Tp>
requires is_object_v<_Tp>
struct __optional_ref_base<_Tp>
{
using iterator = __gnu_cxx::__normal_iterator<_Tp*, optional<_Tp&>>;
};
#endif // __cpp_lib_optional_range_support
template<typename _Tp>
class optional<_Tp&> : public __optional_ref_base<_Tp>
{
static_assert(__is_valid_contained_type_for_optional<_Tp&>);
public:
using value_type = _Tp;
// Constructors.
constexpr optional() noexcept = default;
constexpr optional(nullopt_t) noexcept : optional() {}
constexpr optional(const optional&) noexcept = default;
template<typename _Arg>
requires is_constructible_v<_Tp&, _Arg>
&& (!reference_constructs_from_temporary_v<_Tp&, _Arg>)
explicit constexpr
optional(in_place_t, _Arg&& __arg)
{
__convert_ref_init_val(std::forward<_Arg>(__arg));
}
template<typename _Up>
requires (!is_same_v<remove_cvref_t<_Up>, optional>)
&& (!is_same_v<remove_cvref_t<_Up>, in_place_t>)
&& is_constructible_v<_Tp&, _Up>
&& (!reference_constructs_from_temporary_v<_Tp&, _Up>)
explicit(!is_convertible_v<_Up, _Tp&>)
constexpr
optional(_Up&& __u)
noexcept(is_nothrow_constructible_v<_Tp&, _Up>)
{
__convert_ref_init_val(std::forward<_Up>(__u));
}
template<typename _Up>
requires (!is_same_v<remove_cvref_t<_Up>, optional>)
&& (!is_same_v<remove_cvref_t<_Up>, in_place_t>)
&& is_constructible_v<_Tp&, _Up>
&& reference_constructs_from_temporary_v<_Tp&, _Up>
explicit(!is_convertible_v<_Up, _Tp&>)
constexpr
optional(_Up&& __u) = delete;
// optional<U> &
template<typename _Up>
requires (!is_same_v<remove_cv_t<_Tp>, optional<_Up>>)
&& (!is_same_v<_Tp&, _Up>)
&& is_constructible_v<_Tp&, _Up&>
&& (!reference_constructs_from_temporary_v<_Tp&, _Up&>)
explicit(!is_convertible_v<_Up&, _Tp&>)
constexpr
optional(optional<_Up>& __rhs)
noexcept(is_nothrow_constructible_v<_Tp&, _Up&>)
{
if (__rhs)
__convert_ref_init_val(__rhs._M_fwd());
}
template<typename _Up>
requires (!is_same_v<remove_cv_t<_Tp>, optional<_Up>>)
&& (!is_same_v<_Tp&, _Up>)
&& is_constructible_v<_Tp&, _Up&>
&& reference_constructs_from_temporary_v<_Tp&, _Up&>
explicit(!is_convertible_v<_Up&, _Tp&>)
constexpr
optional(optional<_Up>& __rhs) = delete;
// const optional<U>&
template<typename _Up>
requires (!is_same_v<remove_cv_t<_Tp>, optional<_Up>>)
&& (!is_same_v<_Tp&, _Up>)
&& is_constructible_v<_Tp&, const _Up&>
&& (!reference_constructs_from_temporary_v<_Tp&, const _Up&>)
explicit(!is_convertible_v<const _Up&, _Tp&>)
constexpr
optional(const optional<_Up>& __rhs)
noexcept(is_nothrow_constructible_v<_Tp&, _Up&>)
{
if (__rhs)
__convert_ref_init_val(__rhs._M_fwd());
}
template<typename _Up>
requires (!is_same_v<remove_cv_t<_Tp>, optional<_Up>>)
&& (!is_same_v<_Tp&, _Up>)
&& is_constructible_v<_Tp&, const _Up&>
&& reference_constructs_from_temporary_v<_Tp&, const _Up&>
explicit(!is_convertible_v<const _Up&, _Tp&>)
constexpr
optional(const optional<_Up>& __rhs) = delete;
// optional<U>&&
template<typename _Up>
requires (!is_same_v<remove_cv_t<_Tp>, optional<_Up>>)
&& (!is_same_v<_Tp&, _Up>)
&& is_constructible_v<_Tp&, _Up>
&& (!reference_constructs_from_temporary_v<_Tp&, _Up>)
explicit(!is_convertible_v<_Up, _Tp&>)
constexpr
optional(optional<_Up>&& __rhs)
noexcept(is_nothrow_constructible_v<_Tp&, _Up>)
{
if (__rhs)
__convert_ref_init_val(std::move(__rhs)._M_fwd());
}
template<typename _Up>
requires (!is_same_v<remove_cv_t<_Tp>, optional<_Up>>)
&& (!is_same_v<_Tp&, _Up>)
&& is_constructible_v<_Tp&, _Up>
&& reference_constructs_from_temporary_v<_Tp&, _Up>
explicit(!is_convertible_v<_Up, _Tp&>)
constexpr
optional(optional<_Up>&& __rhs) = delete;
// const optional<U>&&
template<typename _Up>
requires (!is_same_v<remove_cv_t<_Tp>, optional<_Up>>)
&& (!is_same_v<_Tp&, _Up>)
&& is_constructible_v<_Tp&, const _Up>
&& (!reference_constructs_from_temporary_v<_Tp&, _Up>)
explicit(!is_convertible_v<const _Up, _Tp&>)
constexpr
optional(const optional<_Up>&& __rhs)
noexcept(is_nothrow_constructible_v<_Tp&, const _Up>)
{
if (__rhs)
__convert_ref_init_val(std::move(__rhs)._M_fwd());
}
template<typename _Up>
requires (!is_same_v<remove_cv_t<_Tp>, optional<_Up>>)
&& (!is_same_v<_Tp&, _Up>)
&& is_constructible_v<_Tp&, const _Up>
&& reference_constructs_from_temporary_v<_Tp&, const _Up>
explicit(!is_convertible_v<const _Up, _Tp&>)
constexpr
optional(const optional<_Up>&& __rhs) = delete;
constexpr ~optional() = default;
// Assignment.
constexpr optional& operator=(nullopt_t) noexcept
{
_M_val = nullptr;
return *this;
}
constexpr optional& operator=(const optional&) noexcept = default;
template<typename _Up>
requires is_constructible_v<_Tp&, _Up>
&& (!reference_constructs_from_temporary_v<_Tp&, _Up>)
constexpr _Tp&
emplace(_Up&& __u)
noexcept(is_nothrow_constructible_v<_Tp&, _Up>)
{
__convert_ref_init_val(std::forward<_Up>(__u));
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 4300. Missing Returns: element in optional<T&>::emplace
return *_M_val;
}
// Swap.
constexpr void swap(optional& __rhs) noexcept
{ std::swap(_M_val, __rhs._M_val); }
#ifdef __cpp_lib_optional_range_support // >= C++26
// Iterator support.
constexpr auto begin() const noexcept
requires is_object_v<_Tp> && (!is_unbounded_array_v<_Tp>)
{ return __gnu_cxx::__normal_iterator<_Tp*, optional>(_M_val); }
constexpr auto end() const noexcept
requires is_object_v<_Tp> && (!is_unbounded_array_v<_Tp>)
{ return begin() + has_value(); }
#endif // __cpp_lib_optional_range_support
// Observers.
constexpr _Tp* operator->() const noexcept
{
__glibcxx_assert(_M_val); // hardened precondition
return _M_val;
}
constexpr _Tp& operator*() const noexcept
{
__glibcxx_assert(_M_val); // hardened precondition
return *_M_val;
}
constexpr explicit operator bool() const noexcept
{
return _M_val;
}
constexpr bool has_value() const noexcept
{
return _M_val;
}
constexpr _Tp& value() const
{
if (_M_val)
return *_M_val;
__throw_bad_optional_access();
}
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 4304. std::optional<NonReturnable&> is ill-formed due to value_or
template<typename _Up = remove_cv_t<_Tp>>
requires is_object_v<_Tp> && (!is_array_v<_Tp>)
constexpr decay_t<_Tp>
value_or(_Up&& __u) const
{
using _Xp = remove_cv_t<_Tp>;
static_assert(is_convertible_v<_Tp&, _Xp>);
static_assert(is_convertible_v<_Up, _Xp>);
if (_M_val)
return *_M_val;
return std::forward<_Up>(__u);
}
// Monadic operations.
template<typename _Fn>
constexpr auto
and_then(_Fn&& __f) const
{
using _Up = remove_cvref_t<invoke_result_t<_Fn, _Tp&>>;
static_assert(__is_optional_v<_Up>,
"the function passed to std::optional<T&>::and_then "
"must return a std::optional");
if (has_value())
return std::__invoke(std::forward<_Fn>(__f), *_M_val);
else
return _Up();
}
template<typename _Fn>
constexpr
optional<remove_cv_t<invoke_result_t<_Fn, _Tp&>>>
transform(_Fn&& __f) const
{
using _Up = remove_cv_t<invoke_result_t<_Fn, _Tp&>>;
if (has_value())
return optional<_Up>(_Optional_func<_Fn>{__f}, *_M_val);
else
return optional<_Up>();
}
template<typename _Fn>
requires invocable<_Fn>
constexpr
optional
or_else(_Fn&& __f) const
{
static_assert(is_same_v<remove_cvref_t<invoke_result_t<_Fn>>, optional>,
"the function passed to std::optional<T&>::or_else "
"must return a std::optional<T&>");
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 4367. Improve optional<T&>::or_else
if (has_value())
return *this;
else
return std::forward<_Fn>(__f)();
}
// Modifiers.
constexpr void reset() noexcept
{
_M_val = nullptr;
}
private:
_Tp *_M_val = nullptr;
[[__gnu__::__always_inline__]]
constexpr _Tp&
_M_fwd() const noexcept
{ return *_M_val; }
template<typename _Up> friend class optional;
template<typename _Up>
constexpr
void
__convert_ref_init_val(_Up&& __u)
noexcept
{
_Tp& __r(std::forward<_Up>(__u));
_M_val = std::addressof(__r);
}
template<typename _Fn, typename _Value>
explicit constexpr
optional(_Optional_func<_Fn> __f, _Value&& __v)
{
_Tp& __r = std::__invoke(std::forward<_Fn>(__f._M_f), std::forward<_Value>(__v));
_M_val = std::addressof(__r);
}
};
#endif // __cpp_lib_optional >= 202506L
template<typename _Tp>
using __optional_relop_t =
enable_if_t<is_convertible_v<_Tp, bool>, bool>;
template<typename _Tp, typename _Up>
using __optional_eq_t = __optional_relop_t<
decltype(std::declval<const _Tp&>() == std::declval<const _Up&>())
>;
template<typename _Tp, typename _Up>
using __optional_ne_t = __optional_relop_t<
decltype(std::declval<const _Tp&>() != std::declval<const _Up&>())
>;
template<typename _Tp, typename _Up>
using __optional_lt_t = __optional_relop_t<
decltype(std::declval<const _Tp&>() < std::declval<const _Up&>())
>;
template<typename _Tp, typename _Up>
using __optional_gt_t = __optional_relop_t<
decltype(std::declval<const _Tp&>() > std::declval<const _Up&>())
>;
template<typename _Tp, typename _Up>
using __optional_le_t = __optional_relop_t<
decltype(std::declval<const _Tp&>() <= std::declval<const _Up&>())
>;
template<typename _Tp, typename _Up>
using __optional_ge_t = __optional_relop_t<
decltype(std::declval<const _Tp&>() >= std::declval<const _Up&>())
>;
// Comparisons between optional values.
template<typename _Tp, typename _Up>
constexpr auto
operator==(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
-> __optional_eq_t<_Tp, _Up>
{
if (__lhs.has_value() != __rhs.has_value())
return false;
if (!__lhs.has_value())
return true;
return *__lhs == *__rhs;
}
template<typename _Tp, typename _Up>
constexpr auto
operator!=(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
-> __optional_ne_t<_Tp, _Up>
{
if (__lhs.has_value() != __rhs.has_value())
return true;
if (!__lhs.has_value())
return false;
return *__lhs != *__rhs;
}
template<typename _Tp, typename _Up>
constexpr auto
operator<(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
-> __optional_lt_t<_Tp, _Up>
{
if (!__rhs.has_value())
return false;
if (!__lhs.has_value())
return true;
return *__lhs < *__rhs;
}
template<typename _Tp, typename _Up>
constexpr auto
operator>(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
-> __optional_gt_t<_Tp, _Up>
{
if (!__lhs.has_value())
return false;
if (!__rhs.has_value())
return true;
return *__lhs > *__rhs;
}
template<typename _Tp, typename _Up>
constexpr auto
operator<=(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
-> __optional_le_t<_Tp, _Up>
{
if (!__lhs.has_value())
return true;
if (!__rhs.has_value())
return false;
return *__lhs <= *__rhs;
}
template<typename _Tp, typename _Up>
constexpr auto
operator>=(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
-> __optional_ge_t<_Tp, _Up>
{
if (!__rhs.has_value())
return true;
if (!__lhs.has_value())
return false;
return *__lhs >= *__rhs;
}
#ifdef __cpp_lib_three_way_comparison
template<typename _Tp, three_way_comparable_with<_Tp> _Up>
[[nodiscard]]
constexpr compare_three_way_result_t<_Tp, _Up>
operator<=>(const optional<_Tp>& __x, const optional<_Up>& __y)
{
return __x && __y ? *__x <=> *__y : bool(__x) <=> bool(__y);
}
#endif
// Comparisons with nullopt.
template<typename _Tp>
[[nodiscard]]
constexpr bool
operator==(const optional<_Tp>& __lhs, nullopt_t) noexcept
{ return !__lhs; }
#ifdef __cpp_lib_three_way_comparison
template<typename _Tp>
[[nodiscard]]
constexpr strong_ordering
operator<=>(const optional<_Tp>& __x, nullopt_t) noexcept
{ return bool(__x) <=> false; }
#else
template<typename _Tp>
constexpr bool
operator==(nullopt_t, const optional<_Tp>& __rhs) noexcept
{ return !__rhs; }
template<typename _Tp>
constexpr bool
operator!=(const optional<_Tp>& __lhs, nullopt_t) noexcept
{ return static_cast<bool>(__lhs); }
template<typename _Tp>
constexpr bool
operator!=(nullopt_t, const optional<_Tp>& __rhs) noexcept
{ return static_cast<bool>(__rhs); }
template<typename _Tp>
constexpr bool
operator<(const optional<_Tp>& /* __lhs */, nullopt_t) noexcept
{ return false; }
template<typename _Tp>
constexpr bool
operator<(nullopt_t, const optional<_Tp>& __rhs) noexcept
{ return static_cast<bool>(__rhs); }
template<typename _Tp>
constexpr bool
operator>(const optional<_Tp>& __lhs, nullopt_t) noexcept
{ return static_cast<bool>(__lhs); }
template<typename _Tp>
constexpr bool
operator>(nullopt_t, const optional<_Tp>& /* __rhs */) noexcept
{ return false; }
template<typename _Tp>
constexpr bool
operator<=(const optional<_Tp>& __lhs, nullopt_t) noexcept
{ return !__lhs; }
template<typename _Tp>
constexpr bool
operator<=(nullopt_t, const optional<_Tp>& /* __rhs */) noexcept
{ return true; }
template<typename _Tp>
constexpr bool
operator>=(const optional<_Tp>& /* __lhs */, nullopt_t) noexcept
{ return true; }
template<typename _Tp>
constexpr bool
operator>=(nullopt_t, const optional<_Tp>& __rhs) noexcept
{ return !__rhs; }
#endif // three-way-comparison
#if __cpp_lib_concepts
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 4072. std::optional comparisons: constrain harder
# define _REQUIRES_NOT_OPTIONAL(T) requires (!__is_optional_v<T>)
#else
# define _REQUIRES_NOT_OPTIONAL(T)
#endif
// Comparisons with value type.
template<typename _Tp, typename _Up>
_REQUIRES_NOT_OPTIONAL(_Up)
constexpr auto
operator== [[nodiscard]] (const optional<_Tp>& __lhs, const _Up& __rhs)
-> __optional_eq_t<_Tp, _Up>
{
if (__lhs.has_value())
return *__lhs == __rhs;
return false;
}
template<typename _Tp, typename _Up>
_REQUIRES_NOT_OPTIONAL(_Tp)
constexpr auto
operator== [[nodiscard]] (const _Tp& __lhs, const optional<_Up>& __rhs)
-> __optional_eq_t<_Tp, _Up>
{
if (__rhs.has_value())
return __lhs == *__rhs;
return false;
}
template<typename _Tp, typename _Up>
_REQUIRES_NOT_OPTIONAL(_Up)
constexpr auto
operator!= [[nodiscard]] (const optional<_Tp>& __lhs, const _Up& __rhs)
-> __optional_ne_t<_Tp, _Up>
{
if (__lhs.has_value())
return *__lhs != __rhs;
return true;
}
template<typename _Tp, typename _Up>
_REQUIRES_NOT_OPTIONAL(_Tp)
constexpr auto
operator!= [[nodiscard]] (const _Tp& __lhs, const optional<_Up>& __rhs)
-> __optional_ne_t<_Tp, _Up>
{
if (__rhs.has_value())
return __lhs != *__rhs;
return true;
}
template<typename _Tp, typename _Up>
_REQUIRES_NOT_OPTIONAL(_Up)
constexpr auto
operator< [[nodiscard]] (const optional<_Tp>& __lhs, const _Up& __rhs)
-> __optional_lt_t<_Tp, _Up>
{
if (__lhs.has_value())
return *__lhs < __rhs;
return true;
}
template<typename _Tp, typename _Up>
_REQUIRES_NOT_OPTIONAL(_Tp)
constexpr auto
operator< [[nodiscard]] (const _Tp& __lhs, const optional<_Up>& __rhs)
-> __optional_lt_t<_Tp, _Up>
{
if (__rhs.has_value())
return __lhs < *__rhs;
return false;
}
template<typename _Tp, typename _Up>
_REQUIRES_NOT_OPTIONAL(_Up)
constexpr auto
operator> [[nodiscard]] (const optional<_Tp>& __lhs, const _Up& __rhs)
-> __optional_gt_t<_Tp, _Up>
{
if (__lhs.has_value())
return *__lhs > __rhs;
return false;
}
template<typename _Tp, typename _Up>
_REQUIRES_NOT_OPTIONAL(_Tp)
constexpr auto
operator> [[nodiscard]] (const _Tp& __lhs, const optional<_Up>& __rhs)
-> __optional_gt_t<_Tp, _Up>
{
if (__rhs.has_value())
return __lhs > *__rhs;
return true;
}
template<typename _Tp, typename _Up>
_REQUIRES_NOT_OPTIONAL(_Up)
constexpr auto
operator<= [[nodiscard]] (const optional<_Tp>& __lhs, const _Up& __rhs)
-> __optional_le_t<_Tp, _Up>
{
if (__lhs.has_value())
return *__lhs <= __rhs;
return true;
}
template<typename _Tp, typename _Up>
_REQUIRES_NOT_OPTIONAL(_Tp)
constexpr auto
operator<= [[nodiscard]] (const _Tp& __lhs, const optional<_Up>& __rhs)
-> __optional_le_t<_Tp, _Up>
{
if (__rhs.has_value())
return __lhs <= *__rhs;
return false;
}
template<typename _Tp, typename _Up>
_REQUIRES_NOT_OPTIONAL(_Up)
constexpr auto
operator>= [[nodiscard]] (const optional<_Tp>& __lhs, const _Up& __rhs)
-> __optional_ge_t<_Tp, _Up>
{
if (__lhs.has_value())
return *__lhs >= __rhs;
return false;
}
template<typename _Tp, typename _Up>
_REQUIRES_NOT_OPTIONAL(_Tp)
constexpr auto
operator>= [[nodiscard]] (const _Tp& __lhs, const optional<_Up>& __rhs)
-> __optional_ge_t<_Tp, _Up>
{
if (__rhs.has_value())
return __lhs >= *__rhs;
return true;
}
#ifdef __cpp_lib_three_way_comparison
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 3746. optional's spaceship with U with a type derived from optional
// causes infinite constraint meta-recursion
template<typename _Tp>
concept __is_derived_from_optional = requires (const _Tp& __t) {
[]<typename _Up>(const optional<_Up>&){ }(__t);
};
template<typename _Tp, typename _Up>
requires (!__is_derived_from_optional<_Up>)
&& requires { typename compare_three_way_result_t<_Tp, _Up>; }
&& three_way_comparable_with<_Tp, _Up>
constexpr compare_three_way_result_t<_Tp, _Up>
operator<=> [[nodiscard]] (const optional<_Tp>& __x, const _Up& __v)
{ return bool(__x) ? *__x <=> __v : strong_ordering::less; }
#endif
// Swap and creation functions.
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 2748. swappable traits for optionals
template<typename _Tp>
_GLIBCXX20_CONSTEXPR
inline enable_if_t<is_move_constructible_v<_Tp> && is_swappable_v<_Tp>>
swap(optional<_Tp>& __lhs, optional<_Tp>& __rhs)
noexcept(noexcept(__lhs.swap(__rhs)))
{ __lhs.swap(__rhs); }
#if __cpp_lib_optional >= 202506L
// We deviate from standard, that do not declared separate swap overload
// from optional<T&>.
template<typename _Tp>
constexpr void
swap(optional<_Tp&>& __lhs, optional<_Tp&>& __rhs) noexcept
{ __lhs.swap(__rhs); }
#endif
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 2766. Swapping non-swappable types
template<typename _Tp>
enable_if_t<!(is_move_constructible_v<_Tp> && is_swappable_v<_Tp>)>
swap(optional<_Tp>&, optional<_Tp>&) = delete;
#if __cpp_lib_optional >= 202506L
template<int = 0, typename _Tp>
#else
template<typename _Tp>
#endif
constexpr
enable_if_t<is_constructible_v<decay_t<_Tp>, _Tp>,
optional<decay_t<_Tp>>>
make_optional(_Tp&& __t)
noexcept(is_nothrow_constructible_v<optional<decay_t<_Tp>>, _Tp>)
{ return optional<decay_t<_Tp>>( std::forward<_Tp>(__t) ); }
template<typename _Tp, typename... _Args>
constexpr
enable_if_t<is_constructible_v<_Tp, _Args...>,
optional<_Tp>>
make_optional(_Args&&... __args)
noexcept(is_nothrow_constructible_v<_Tp, _Args...>)
{ return optional<_Tp>( in_place, std::forward<_Args>(__args)... ); }
template<typename _Tp, typename _Up, typename... _Args>
constexpr
enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>,
optional<_Tp>>
make_optional(initializer_list<_Up> __il, _Args&&... __args)
noexcept(is_nothrow_constructible_v<_Tp, initializer_list<_Up>&, _Args...>)
{ return optional<_Tp>( in_place, __il, std::forward<_Args>(__args)... ); }
// Hash.
template<typename _Tp, typename _Up = remove_const_t<_Tp>>
struct __optional_hash
#if ! _GLIBCXX_INLINE_VERSION
: public __hash_empty_base<_Up>
#endif
{
#if __cplusplus < 202002L
using result_type [[__deprecated__]] = size_t;
using argument_type [[__deprecated__]] = optional<_Tp>;
#endif
size_t
operator()(const optional<_Tp>& __t) const
noexcept(noexcept(hash<_Up>{}(*__t)))
{
// We pick an arbitrary hash for disengaged optionals which hopefully
// usual values of _Tp won't typically hash to.
constexpr size_t __magic_disengaged_hash = static_cast<size_t>(-3333);
return __t ? hash<_Up>{}(*__t) : __magic_disengaged_hash;
}
};
template<typename _Tp>
struct hash<optional<_Tp>>
// hash for optional<T&> is disabled because is_hash_enabled_for<T&> is false
: public __conditional_t<__is_hash_enabled_for<remove_const_t<_Tp>>,
__optional_hash<_Tp>,
__hash_not_enabled<_Tp>>
{ };
template<typename _Tp>
struct __is_fast_hash<hash<optional<_Tp>>> : __is_fast_hash<hash<_Tp>>
{ };
/// @}
#if __cpp_deduction_guides >= 201606
template <typename _Tp> optional(_Tp) -> optional<_Tp>;
#endif
#ifdef __cpp_lib_optional_range_support // >= C++26
template<typename _Tp>
inline constexpr bool
ranges::enable_view<optional<_Tp>> = true;
#if __cpp_lib_optional >= 202506L // C++26
template<typename _Tp>
constexpr bool
ranges::enable_borrowed_range<optional<_Tp&>> = true;
#endif
template<typename _Tp>
inline constexpr range_format
format_kind<optional<_Tp>> = range_format::disabled;
#endif // __cpp_lib_optional_range_support
#undef _GLIBCXX_USE_CONSTRAINTS_FOR_OPTIONAL
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std
#endif // __cpp_lib_optional
#endif // _GLIBCXX_OPTIONAL
compare
exception
initializer_list
new
concepts
type_traits
stl_construct.h
functional_hash.h
invoke.h
exception_defines.h
formatfwd.h
ranges_base.h
std::ranges::enable_view
constexpr bool enable_view
[range.view] The ranges::enable_view boolean.
Definition ranges_base.h:582
utility.h
version.h
enable_special_members.h
std::operator*
constexpr complex< _Tp > operator*(const complex< _Tp > &__x, const complex< _Tp > &__y)
Return new complex value x times y.
Definition complex:434
std::true_type
__bool_constant< true > true_type
The type used as a compile-time boolean with true value.
Definition type_traits:119
std::remove_reference_t
typename remove_reference< _Tp >::type remove_reference_t
Alias template for remove_reference.
Definition type_traits:1886
std::enable_if_t
typename enable_if< _Cond, _Tp >::type enable_if_t
Alias template for enable_if.
Definition type_traits:2940
std::decay_t
typename decay< _Tp >::type decay_t
Alias template for decay.
Definition type_traits:2936
std::declval
auto declval() noexcept -> decltype(__declval< _Tp >(0))
Definition type_traits:2714
std::addressof
constexpr _Tp * addressof(_Tp &__r) noexcept
Returns the actual address of the object or function referenced by r, even in the presence of an over...
Definition move.h:176
std::move
constexpr std::remove_reference< _Tp >::type && move(_Tp &&__t) noexcept
Convert a value to an rvalue.
Definition move.h:138
std::__invoke
constexpr __invoke_result< _Callable, _Args... >::type __invoke(_Callable &&__fn, _Args &&... __args) noexcept(__is_nothrow_invocable< _Callable, _Args... >::value)
Invoke a callable object.
Definition invoke.h:92
std::__addressof
constexpr _Tp * __addressof(_Tp &__r) noexcept
Same as C++11 std::addressof.
Definition move.h:52
std::forward
constexpr _Tp && forward(typename std::remove_reference< _Tp >::type &__t) noexcept
Forward an lvalue.
Definition move.h:72
std::end
_Tp * end(valarray< _Tp > &__va) noexcept
Return an iterator pointing to one past the last element of the valarray.
Definition valarray:1251
std::begin
_Tp * begin(valarray< _Tp > &__va) noexcept
Return an iterator pointing to the first element of the valarray.
Definition valarray:1229
std::experimental::fundamentals_v1::nullopt
constexpr nullopt_t nullopt
Tag to disengage optional objects.
Definition experimental/optional:98
std
ISO C++ entities toplevel namespace is std.
std::compare_three_way_result_t
typename __detail::__cmp3way_res_impl< _Tp, _Up >::type compare_three_way_result_t
[cmp.result], result of three-way comparison
Definition compare:547
std::_Construct
constexpr void _Construct(_Tp *__p, _Args &&... __args)
Definition stl_construct.h:123
std::initializer_list
initializer_list
Definition initializer_list:48
std::hash
Primary class template hash.
Definition functional_hash.h:106
std::is_constructible
is_constructible
Definition type_traits:1238
std::is_assignable
is_assignable
Definition type_traits:1357
std::exception
Base class for all library exceptions.
Definition exception.h:62
std::__is_fast_hash
Definition functional_hash.h:308
std::value_type
std::invocable
[concept.invocable], concept invocable
Definition concepts:383
stl_iterator.h