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optional
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optional
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// <optional> -*- C++ -*-
// Copyright (C) 2013-2021 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/optional
* This is a Standard C++ Library header.
*/
#ifndef _GLIBCXX_OPTIONAL
#define _GLIBCXX_OPTIONAL 1
#pragma GCC system_header
#if __cplusplus >= 201703L
#include <utility>
#include <type_traits>
#include <exception>
#include <new>
#include <initializer_list>
#include <bits/exception_defines.h>
#include <bits/functional_hash.h>
#include <bits/enable_special_members.h>
#if __cplusplus > 201703L
# include <compare>
#endif
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
/**
* @addtogroup utilities
* @{
*/
#define __cpp_lib_optional 201606L
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) { }
};
/// Tag to disengage optional objects.
inline constexpr nullopt_t nullopt { nullopt_t::_Construct::_Token };
/**
* @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;
const char* what() const noexcept override
{ return "bad optional access"; }
};
void
__throw_bad_optional_access()
__attribute__((__noreturn__));
// XXX Does not belong here.
inline 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)...)
{ }
_Empty_byte _M_empty;
_Up _M_value;
};
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)...)
{ }
// User-provided destructor is needed when _Up has non-trivial dtor.
~_Storage() { }
_Empty_byte _M_empty;
_Up _M_value;
};
_Storage<_Stored_type> _M_payload;
bool _M_engaged = false;
template<typename... _Args>
void
_M_construct(_Args&&... __args)
noexcept(is_nothrow_constructible_v<_Stored_type, _Args...>)
{
::new ((void *) std::__addressof(this->_M_payload))
_Stored_type(std::forward<_Args>(__args)...);
this->_M_engaged = true;
}
constexpr void
_M_destroy() noexcept
{
_M_engaged = false;
_M_payload._M_value.~_Stored_type();
}
// 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();
}
};
// 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:
~_Optional_payload() { this->_M_reset(); }
};
// Common base class for _Optional_base<T> to avoid repeating these
// member functions in each specialization.
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>
void
_M_construct(_Args&&... __args)
noexcept(is_nothrow_constructible_v<_Stored_type, _Args...>)
{
::new
(std::__addressof(static_cast<_Dp*>(this)->_M_payload._M_payload))
_Stored_type(std::forward<_Args>(__args)...);
static_cast<_Dp*>(this)->_M_payload._M_engaged = true;
}
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
{
__glibcxx_assert(this->_M_is_engaged());
return static_cast<_Dp*>(this)->_M_payload._M_get();
}
constexpr const _Tp&
_M_get() const noexcept
{
__glibcxx_assert(this->_M_is_engaged());
return static_cast<const _Dp*>(this)->_M_payload._M_get();
}
};
/**
* @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
: _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)
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, false, true>
: _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>
: _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>
: _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;
};
template<typename _Tp>
class optional;
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>&&>>;
/**
* @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_same_v<remove_cv_t<_Tp>, nullopt_t>);
static_assert(!is_same_v<remove_cv_t<_Tp>, in_place_t>);
static_assert(!is_reference_v<_Tp>);
private:
using _Base = _Optional_base<_Tp>;
// SFINAE helpers
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>;
public:
using value_type = _Tp;
constexpr optional() noexcept { }
constexpr optional(nullopt_t) noexcept { }
// Converting constructors for engaged optionals.
template<typename _Up = _Tp,
_Requires<__not_self<_Up>, __not_tag<_Up>,
is_constructible<_Tp, _Up>,
is_convertible<_Up, _Tp>> = true>
constexpr
optional(_Up&& __t)
noexcept(is_nothrow_constructible_v<_Tp, _Up>)
: _Base(std::in_place, std::forward<_Up>(__t)) { }
template<typename _Up = _Tp,
_Requires<__not_self<_Up>, __not_tag<_Up>,
is_constructible<_Tp, _Up>,
__not_<is_convertible<_Up, _Tp>>> = 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>,
__not_<__converts_from_optional<_Tp, _Up>>> = true>
constexpr
optional(const optional<_Up>& __t)
noexcept(is_nothrow_constructible_v<_Tp, const _Up&>)
{
if (__t)
emplace(*__t);
}
template<typename _Up,
_Requires<__not_<is_same<_Tp, _Up>>,
is_constructible<_Tp, const _Up&>,
__not_<is_convertible<const _Up&, _Tp>>,
__not_<__converts_from_optional<_Tp, _Up>>> = false>
explicit constexpr
optional(const optional<_Up>& __t)
noexcept(is_nothrow_constructible_v<_Tp, const _Up&>)
{
if (__t)
emplace(*__t);
}
template<typename _Up,
_Requires<__not_<is_same<_Tp, _Up>>,
is_constructible<_Tp, _Up>,
is_convertible<_Up, _Tp>,
__not_<__converts_from_optional<_Tp, _Up>>> = true>
constexpr
optional(optional<_Up>&& __t)
noexcept(is_nothrow_constructible_v<_Tp, _Up>)
{
if (__t)
emplace(std::move(*__t));
}
template<typename _Up,
_Requires<__not_<is_same<_Tp, _Up>>,
is_constructible<_Tp, _Up>,
__not_<is_convertible<_Up, _Tp>>,
__not_<__converts_from_optional<_Tp, _Up>>> = false>
explicit constexpr
optional(optional<_Up>&& __t)
noexcept(is_nothrow_constructible_v<_Tp, _Up>)
{
if (__t)
emplace(std::move(*__t));
}
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)...) { }
// Assignment operators.
optional&
operator=(nullopt_t) noexcept
{
this->_M_reset();
return *this;
}
template<typename _Up = _Tp>
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&>
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>
enable_if_t<__and_v<__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>>>,
optional&>
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;
else
this->_M_construct(*__u);
}
else
{
this->_M_reset();
}
return *this;
}
template<typename _Up>
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&>
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);
else
this->_M_construct(std::move(*__u));
}
else
{
this->_M_reset();
}
return *this;
}
template<typename... _Args>
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>
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.
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();
}
}
// Observers.
constexpr const _Tp*
operator->() const noexcept
{ return std::__addressof(this->_M_get()); }
constexpr _Tp*
operator->() noexcept
{ return std::__addressof(this->_M_get()); }
constexpr const _Tp&
operator*() const& noexcept
{ return this->_M_get(); }
constexpr _Tp&
operator*()& noexcept
{ return this->_M_get(); }
constexpr _Tp&&
operator*()&& noexcept
{ return std::move(this->_M_get()); }
constexpr const _Tp&&
operator*() const&& noexcept
{ 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&
{
return this->_M_is_engaged()
? this->_M_get()
: (__throw_bad_optional_access(), this->_M_get());
}
constexpr _Tp&
value()&
{
return this->_M_is_engaged()
? this->_M_get()
: (__throw_bad_optional_access(), this->_M_get());
}
constexpr _Tp&&
value()&&
{
return this->_M_is_engaged()
? std::move(this->_M_get())
: (__throw_bad_optional_access(), std::move(this->_M_get()));
}
constexpr const _Tp&&
value() const&&
{
return this->_M_is_engaged()
? std::move(this->_M_get())
: (__throw_bad_optional_access(), std::move(this->_M_get()));
}
template<typename _Up>
constexpr _Tp
value_or(_Up&& __u) const&
{
static_assert(is_copy_constructible_v<_Tp>);
static_assert(is_convertible_v<_Up&&, _Tp>);
return this->_M_is_engaged()
? this->_M_get() : static_cast<_Tp>(std::forward<_Up>(__u));
}
template<typename _Up>
constexpr _Tp
value_or(_Up&& __u) &&
{
static_assert(is_move_constructible_v<_Tp>);
static_assert(is_convertible_v<_Up&&, _Tp>);
return this->_M_is_engaged()
? std::move(this->_M_get())
: static_cast<_Tp>(std::forward<_Up>(__u));
}
void reset() noexcept { this->_M_reset(); }
};