experimental/optional
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// <experimental/optional> -*- C++ -*-
// Copyright (C) 2013-2024 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 experimental/optional
* This is a TS C++ Library header.
* @ingroup libfund-ts
*/
#ifndef _GLIBCXX_EXPERIMENTAL_OPTIONAL
#define _GLIBCXX_EXPERIMENTAL_OPTIONAL 1
#include <bits/requires_hosted.h> // experimental is currently omitted
#if __cplusplus >= 201402L
#include <type_traits>
#include <stdexcept>
#include <new>
#include <initializer_list>
#include <bits/functexcept.h>
#include <bits/functional_hash.h>
#include <bits/enable_special_members.h>
#include <bits/move.h>
#include <experimental/bits/lfts_config.h>
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
namespace experimental
{
inline namespace fundamentals_v1
{
/**
* @defgroup optional Optional values
* @ingroup libfund-ts
*
* Class template for optional values and surrounding facilities, as
* described in n3793 "A proposal to add a utility class to represent
* optional objects (Revision 5)".
*
* @{
*/
#define __cpp_lib_experimental_optional 201411
// All subsequent [X.Y.n] references are against n3793.
// [X.Y.4]
template<typename _Tp>
class optional;
// [X.Y.5]
/// Tag type for in-place construction.
struct in_place_t { };
/// Tag for in-place construction.
constexpr in_place_t in_place { };
// [X.Y.6]
/// 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) { }
};
// [X.Y.6]
/// Tag to disengage optional objects.
constexpr nullopt_t nullopt { nullopt_t::_Construct::_Token };
// [X.Y.7]
/**
* @brief Exception class thrown when a disengaged optional object is
* dereferenced.
* @ingroup exceptions
*/
class bad_optional_access : public logic_error
{
public:
bad_optional_access() : logic_error("bad optional access") { }
// XXX This constructor is non-standard. Should not be inline
explicit bad_optional_access(const char* __arg) : logic_error(__arg) { }
virtual ~bad_optional_access() noexcept = default;
};
/// @cond undocumented
// XXX Does not belong here.
[[noreturn]] inline void
__throw_bad_optional_access(const char* __s)
{ _GLIBCXX_THROW_OR_ABORT(bad_optional_access(__s)); }
/**
* @brief Class template that holds the necessary state for @ref optional
* and that has the responsibility for construction and the special members.
*
* Such a separate base class template is necessary in order to
* conditionally enable the special members (e.g. copy/move constructors).
* Note that this means that @ref _Optional_base implements the
* functionality for copy and move assignment, but not for converting
* assignment.
*
* @see optional, _Enable_special_members
*/
template<typename _Tp, bool _ShouldProvideDestructor =
!is_trivially_destructible<_Tp>::value>
class _Optional_base
{
private:
// Remove const to avoid prohibition of reusing object storage for
// const-qualified types in [3.8/9]. This is strictly internal
// and even optional itself is oblivious to it.
using _Stored_type = remove_const_t<_Tp>;
public:
// [X.Y.4.1] Constructors.
// Constructors for disengaged optionals.
constexpr _Optional_base() noexcept
: _M_empty{} { }
constexpr _Optional_base(nullopt_t) noexcept
: _Optional_base{} { }
// Constructors for engaged optionals.
template<typename... _Args>
constexpr explicit _Optional_base(in_place_t, _Args&&... __args)
: _M_payload(std::forward<_Args>(__args)...), _M_engaged(true) { }
template<typename _Up, typename... _Args,
enable_if_t<is_constructible<_Tp,
initializer_list<_Up>&,
_Args&&...>::value,
int>...>
constexpr explicit _Optional_base(in_place_t,
initializer_list<_Up> __il,
_Args&&... __args)
: _M_payload(__il, std::forward<_Args>(__args)...),
_M_engaged(true) { }
// Copy and move constructors.
_Optional_base(const _Optional_base& __other)
{
if (__other._M_engaged)
this->_M_construct(__other._M_get());
}
_Optional_base(_Optional_base&& __other)
noexcept(is_nothrow_move_constructible<_Tp>())
{
if (__other._M_engaged)
this->_M_construct(std::move(__other._M_get()));
}
// [X.Y.4.3] (partly) Assignment.
_Optional_base&
operator=(const _Optional_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();
}
return *this;
}
_Optional_base&
operator=(_Optional_base&& __other)
noexcept(__and_<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();
}
return *this;
}
// [X.Y.4.2] Destructor.
~_Optional_base()
{
if (this->_M_engaged)
this->_M_payload.~_Stored_type();
}
// The following functionality is also needed by optional, hence the
// protected accessibility.
protected:
constexpr bool _M_is_engaged() const noexcept
{ return this->_M_engaged; }
// The _M_get operations have _M_engaged as a precondition.
constexpr _Tp&
_M_get() noexcept
{ return _M_payload; }
constexpr const _Tp&
_M_get() const noexcept
{ return _M_payload; }
// The _M_construct operation has !_M_engaged as a precondition
// while _M_destruct has _M_engaged as a precondition.
template<typename... _Args>
void
_M_construct(_Args&&... __args)
noexcept(is_nothrow_constructible<_Stored_type, _Args...>())
{
::new (std::__addressof(this->_M_payload))
_Stored_type(std::forward<_Args>(__args)...);
this->_M_engaged = true;
}
void
_M_destruct()
{
this->_M_engaged = false;
this->_M_payload.~_Stored_type();
}
// _M_reset is a 'safe' operation with no precondition.
void
_M_reset()
{
if (this->_M_engaged)
this->_M_destruct();
}
private:
struct _Empty_byte { };
union {
_Empty_byte _M_empty;
_Stored_type _M_payload;
};
bool _M_engaged = false;
};
/// Partial specialization that is exactly identical to the primary template
/// save for not providing a destructor, to fulfill triviality requirements.
template<typename _Tp>
class _Optional_base<_Tp, false>
{
private:
using _Stored_type = remove_const_t<_Tp>;
public:
constexpr _Optional_base() noexcept
: _M_empty{} { }
constexpr _Optional_base(nullopt_t) noexcept
: _Optional_base{} { }
template<typename... _Args>
constexpr explicit _Optional_base(in_place_t, _Args&&... __args)
: _M_payload(std::forward<_Args>(__args)...), _M_engaged(true) { }
template<typename _Up, typename... _Args,
enable_if_t<is_constructible<_Tp,
initializer_list<_Up>&,
_Args&&...>::value,
int>...>
constexpr explicit _Optional_base(in_place_t,
initializer_list<_Up> __il,
_Args&&... __args)
: _M_payload(__il, std::forward<_Args>(__args)...),
_M_engaged(true) { }
_Optional_base(const _Optional_base& __other)
{
if (__other._M_engaged)
this->_M_construct(__other._M_get());
}
_Optional_base(_Optional_base&& __other)
noexcept(is_nothrow_move_constructible<_Tp>())
{
if (__other._M_engaged)
this->_M_construct(std::move(__other._M_get()));
}
_Optional_base&
operator=(const _Optional_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();
}
return *this;
}
_Optional_base&
operator=(_Optional_base&& __other)
noexcept(__and_<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();
}
return *this;
}
// Sole difference
// ~_Optional_base() noexcept = default;
protected:
constexpr bool _M_is_engaged() const noexcept
{ return this->_M_engaged; }
_Tp&
_M_get() noexcept
{ return _M_payload; }
constexpr const _Tp&
_M_get() const noexcept
{ return _M_payload; }
template<typename... _Args>
void
_M_construct(_Args&&... __args)
noexcept(is_nothrow_constructible<_Stored_type, _Args...>())
{
::new (std::__addressof(this->_M_payload))
_Stored_type(std::forward<_Args>(__args)...);
this->_M_engaged = true;
}
void
_M_destruct()
{
this->_M_engaged = false;
this->_M_payload.~_Stored_type();
}
void
_M_reset()
{
if (this->_M_engaged)
this->_M_destruct();
}
private:
struct _Empty_byte { };
union
{
_Empty_byte _M_empty;
_Stored_type _M_payload;
};
bool _M_engaged = false;
};
template<typename _Tp, typename _Up>
using __converts_from_optional =
__or_<is_constructible<_Tp, const optional<_Up>&>,
is_constructible<_Tp, optional<_Up>&>,
is_constructible<_Tp, const optional<_Up>&&>,
is_constructible<_Tp, optional<_Up>&&>,
is_convertible<const optional<_Up>&, _Tp>,
is_convertible<optional<_Up>&, _Tp>,
is_convertible<const optional<_Up>&&, _Tp>,
is_convertible<optional<_Up>&&, _Tp>>;
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>&&>>;
/// @endcond
/**
* @brief Class template for optional values.
*/
template<typename _Tp>
class optional
: private _Optional_base<_Tp>,
private _Enable_copy_move<
// Copy constructor.
is_copy_constructible<_Tp>::value,
// Copy assignment.
__and_<is_copy_constructible<_Tp>, is_copy_assignable<_Tp>>::value,
// Move constructor.
is_move_constructible<_Tp>::value,
// Move assignment.
__and_<is_move_constructible<_Tp>, is_move_assignable<_Tp>>::value,
// Unique tag type.
optional<_Tp>>
{
static_assert(__and_<__not_<is_same<remove_cv_t<_Tp>, nullopt_t>>,
__not_<is_same<remove_cv_t<_Tp>, in_place_t>>,
__not_<is_reference<_Tp>>>(),
"Invalid instantiation of optional<T>");
private:
using _Base = _Optional_base<_Tp>;
public:
using value_type = _Tp;
// _Optional_base has the responsibility for construction.
using _Base::_Base;
constexpr optional() = default;
// Converting constructors for engaged optionals.
template <typename _Up = _Tp,
enable_if_t<__and_<
__not_<is_same<optional<_Tp>, decay_t<_Up>>>,
is_constructible<_Tp, _Up&&>,
is_convertible<_Up&&, _Tp>
>::value, bool> = true>
constexpr optional(_Up&& __t)
: _Base(in_place, std::forward<_Up>(__t)) { }
template <typename _Up = _Tp,
enable_if_t<__and_<
__not_<is_same<optional<_Tp>, decay_t<_Up>>>,
is_constructible<_Tp, _Up&&>,
__not_<is_convertible<_Up&&, _Tp>>
>::value, bool> = false>
explicit constexpr optional(_Up&& __t)
: _Base(in_place, std::forward<_Up>(__t)) { }
template <typename _Up,
enable_if_t<__and_<
__not_<is_same<_Tp, _Up>>,
is_constructible<_Tp, const _Up&>,
is_convertible<const _Up&, _Tp>,
__not_<__converts_from_optional<_Tp, _Up>>
>::value, bool> = true>
constexpr optional(const optional<_Up>& __t)
{
if (__t)
emplace(*__t);
}
template <typename _Up,
enable_if_t<__and_<
__not_<is_same<_Tp, _Up>>,
is_constructible<_Tp, const _Up&>,
__not_<is_convertible<const _Up&, _Tp>>,
__not_<__converts_from_optional<_Tp, _Up>>
>::value, bool> = false>
explicit constexpr optional(const optional<_Up>& __t)
{
if (__t)
emplace(*__t);
}
template <typename _Up,
enable_if_t<__and_<
__not_<is_same<_Tp, _Up>>,
is_constructible<_Tp, _Up&&>,
is_convertible<_Up&&, _Tp>,
__not_<__converts_from_optional<_Tp, _Up>>
>::value, bool> = true>
constexpr optional(optional<_Up>&& __t)
{
if (__t)
emplace(std::move(*__t));
}
template <typename _Up,
enable_if_t<__and_<
__not_<is_same<_Tp, _Up>>,
is_constructible<_Tp, _Up&&>,
__not_<is_convertible<_Up&&, _Tp>>,
__not_<__converts_from_optional<_Tp, _Up>>
>::value, bool> = false>
explicit constexpr optional(optional<_Up>&& __t)
{
if (__t)
emplace(std::move(*__t));
}
// [X.Y.4.3] (partly) Assignment.
optional&
operator=(nullopt_t) noexcept
{
this->_M_reset();
return *this;
}
template<typename _Up = _Tp>
enable_if_t<__and_<
__not_<is_same<optional<_Tp>, decay_t<_Up>>>,
is_constructible<_Tp, _Up>,
__not_<__and_<is_scalar<_Tp>,
is_same<_Tp, decay_t<_Up>>>>,
is_assignable<_Tp&, _Up>>::value,
optional&>
operator=(_Up&& __u)
{
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>
enable_if_t<__and_<
__not_<is_same<_Tp, _Up>>,
is_constructible<_Tp, const _Up&>,
is_assignable<_Tp&, _Up>,
__not_<__converts_from_optional<_Tp, _Up>>,
__not_<__assigns_from_optional<_Tp, _Up>>
>::value,
optional&>
operator=(const optional<_Up>& __u)
{
if (__u)
{
if (this->_M_is_engaged())
this->_M_get() = *__u;
else
this->_M_construct(*__u);
}
else
{
this->_M_reset();
}
return *this;
}
template<typename _Up>
enable_if_t<__and_<
__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>>
>::value,
optional&>
operator=(optional<_Up>&& __u)
{
if (__u)
{
if (this->_M_is_engaged())
this->_M_get() = std::move(*__u);
else
this->_M_construct(std::move(*__u));
}
else
{
this->_M_reset();
}
return *this;
}
template<typename... _Args>
enable_if_t<is_constructible<_Tp, _Args&&...>::value>
emplace(_Args&&... __args)
{
this->_M_reset();
this->_M_construct(std::forward<_Args>(__args)...);
}
template<typename _Up, typename... _Args>
enable_if_t<is_constructible<_Tp, initializer_list<_Up>&,
_Args&&...>::value>
emplace(initializer_list<_Up> __il, _Args&&... __args)
{
this->_M_reset();
this->_M_construct(__il, std::forward<_Args>(__args)...);
}
// [X.Y.4.2] Destructor is implicit, implemented in _Optional_base.
// [X.Y.4.4] Swap.
void
swap(optional& __other)
noexcept(is_nothrow_move_constructible<_Tp>()
&& __is_nothrow_swappable<_Tp>::value)
{
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();
}
}
// [X.Y.4.5] Observers.
constexpr const _Tp*
operator->() const
{ return std::__addressof(this->_M_get()); }
_Tp*
operator->()
{ return std::__addressof(this->_M_get()); }
constexpr const _Tp&
operator*() const&
{ return this->_M_get(); }
constexpr _Tp&
operator*()&
{ return this->_M_get(); }
constexpr _Tp&&
operator*()&&
{ return std::move(this->_M_get()); }
constexpr const _Tp&&
operator*() const&&
{ return std::move(this->_M_get()); }
constexpr explicit operator bool() 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("Attempt to access value of a "
"disengaged optional object");
}
constexpr _Tp&
value()&
{
if (this->_M_is_engaged())
return this->_M_get();
__throw_bad_optional_access("Attempt to access value of a "
"disengaged optional object");
}
constexpr _Tp&&
value()&&
{
if (this->_M_is_engaged())
return std::move(this->_M_get());
__throw_bad_optional_access("Attempt to access value of a "
"disengaged optional object");
}
constexpr const _Tp&&
value() const&&
{
if (this->_M_is_engaged())
return std::move(this->_M_get());
__throw_bad_optional_access("Attempt to access value of a "
"disengaged optional object");
}
template<typename _Up>
constexpr _Tp
value_or(_Up&& __u) const&
{
static_assert(__and_<is_copy_constructible<_Tp>,
is_convertible<_Up&&, _Tp>>(),
"Cannot return value");
if (this->_M_is_engaged())
return this->_M_get();
else
return static_cast<_Tp>(std::forward<_Up>(__u));
}
template<typename _Up>
_Tp
value_or(_Up&& __u) &&
{
static_assert(__and_<is_move_constructible<_Tp>,
is_convertible<_Up&&, _Tp>>(),
"Cannot return value" );
if (this->_M_is_engaged())
return std::move(this->_M_get());
else
return static_cast<_Tp>(std::forward<_Up>(__u));
}
};
/// @relates experimental::optional @{
// [X.Y.8] Comparisons between optional values.
template<typename _Tp>
constexpr bool
operator==(const optional<_Tp>& __lhs, const optional<_Tp>& __rhs)
{
return static_cast<bool>(__lhs) == static_cast<bool>(__rhs)
&& (!__lhs || *__lhs == *__rhs);
}
template<typename _Tp>
constexpr bool
operator!=(const optional<_Tp>& __lhs, const optional<_Tp>& __rhs)
{ return !(__lhs == __rhs); }
template<typename _Tp>
constexpr bool
operator<(const optional<_Tp>& __lhs, const optional<_Tp>& __rhs)
{
return static_cast<bool>(__rhs) && (!__lhs || *__lhs < *__rhs);
}
template<typename _Tp>
constexpr bool
operator>(const optional<_Tp>& __lhs, const optional<_Tp>& __rhs)
{ return __rhs < __lhs; }
template<typename _Tp>
constexpr bool
operator<=(const optional<_Tp>& __lhs, const optional<_Tp>& __rhs)
{ return !(__rhs < __lhs); }
template<typename _Tp>
constexpr bool
operator>=(const optional<_Tp>& __lhs, const optional<_Tp>& __rhs)
{ return !(__lhs < __rhs); }
// [X.Y.9] Comparisons with nullopt.
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 !__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; }
// [X.Y.10] Comparisons with value type.
template<typename _Tp>
constexpr bool
operator==(const optional<_Tp>& __lhs, const _Tp& __rhs)
{ return __lhs && *__lhs == __rhs; }
template<typename _Tp>
constexpr bool
operator==(const _Tp& __lhs, const optional<_Tp>& __rhs)
{ return __rhs && __lhs == *__rhs; }
template<typename _Tp>
constexpr bool
operator!=(const optional<_Tp>& __lhs, _Tp const& __rhs)
{ return !__lhs || !(*__lhs == __rhs); }
template<typename _Tp>
constexpr bool
operator!=(const _Tp& __lhs, const optional<_Tp>& __rhs)
{ return !__rhs || !(__lhs == *__rhs); }
template<typename _Tp>
constexpr bool
operator<(const optional<_Tp>& __lhs, const _Tp& __rhs)
{ return !__lhs || *__lhs < __rhs; }
template<typename _Tp>
constexpr bool
operator<(const _Tp& __lhs, const optional<_Tp>& __rhs)
{ return __rhs && __lhs < *__rhs; }
template<typename _Tp>
constexpr bool
operator>(const optional<_Tp>& __lhs, const _Tp& __rhs)
{ return __lhs && __rhs < *__lhs; }
template<typename _Tp>
constexpr bool
operator>(const _Tp& __lhs, const optional<_Tp>& __rhs)
{ return !__rhs || *__rhs < __lhs; }
template<typename _Tp>
constexpr bool
operator<=(const optional<_Tp>& __lhs, const _Tp& __rhs)
{ return !__lhs || !(__rhs < *__lhs); }
template<typename _Tp>
constexpr bool
operator<=(const _Tp& __lhs, const optional<_Tp>& __rhs)
{ return __rhs && !(*__rhs < __lhs); }
template<typename _Tp>
constexpr bool
operator>=(const optional<_Tp>& __lhs, const _Tp& __rhs)
{ return __lhs && !(*__lhs < __rhs); }
template<typename _Tp>
constexpr bool
operator>=(const _Tp& __lhs, const optional<_Tp>& __rhs)
{ return !__rhs || !(__lhs < *__rhs); }
// [X.Y.11]
template<typename _Tp>
inline void
swap(optional<_Tp>& __lhs, optional<_Tp>& __rhs)
noexcept(noexcept(__lhs.swap(__rhs)))
{ __lhs.swap(__rhs); }
template<typename _Tp>
constexpr optional<decay_t<_Tp>>
make_optional(_Tp&& __t)
{ return optional<decay_t<_Tp>> { std::forward<_Tp>(__t) }; }
/// @} relates experimental::optional
/// @} group optional
} // namespace fundamentals_v1
} // namespace experimental
// [X.Y.12]
/// std::hash partial specialization for experimental::optional
/// @relates experimental::optional
template<typename _Tp>
struct hash<experimental::optional<_Tp>>
{
using result_type = size_t;
using argument_type = experimental::optional<_Tp>;
size_t
operator()(const experimental::optional<_Tp>& __t) const
noexcept(noexcept(hash<_Tp> {}(*__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<_Tp> {}(*__t) : __magic_disengaged_hash;
}
};
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std
#endif // C++14
#endif // _GLIBCXX_EXPERIMENTAL_OPTIONAL