1 // <optional> -*- C++ -*-
3 // Copyright (C) 2013-2025 Free Software Foundation, Inc.
4 // Copyright The GNU Toolchain Authors.
6 // This file is part of the GNU ISO C++ Library. This library is free
7 // software; you can redistribute it and/or modify it under the
8 // terms of the GNU General Public License as published by the
9 // Free Software Foundation; either version 3, or (at your option)
12 // This library is distributed in the hope that it will be useful,
13 // but WITHOUT ANY WARRANTY; without even the implied warranty of
14 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 // GNU General Public License for more details.
17 // Under Section 7 of GPL version 3, you are granted additional
18 // permissions described in the GCC Runtime Library Exception, version
19 // 3.1, as published by the Free Software Foundation.
21 // You should have received a copy of the GNU General Public License and
22 // a copy of the GCC Runtime Library Exception along with this program;
23 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
24 // <http://www.gnu.org/licenses/>.
26 /** @file include/optional
27 * This is a Standard C++ Library header.
30 #ifndef _GLIBCXX_OPTIONAL
31 #define _GLIBCXX_OPTIONAL 1
33 #ifdef _GLIBCXX_SYSHDR
34 #pragma GCC system_header
37 #define __glibcxx_want_freestanding_optional
38 #define __glibcxx_want_optional
39 #define __glibcxx_want_constrained_equality
40 #include <bits/version.h>
42 #ifdef __cpp_lib_optional // C++ >= 17
44 #include <type_traits>
47 #include <initializer_list>
48 #include <bits/enable_special_members.h>
49 #include <bits/exception_defines.h>
50 #include <bits/functional_hash.h>
51 #include <bits/stl_construct.h> // _Construct
52 #include <bits/utility.h> // in_place_t
53 #if __cplusplus > 201703L
55 # include <bits/invoke.h> // std::__invoke
57 #if __cplusplus > 202002L
61 namespace std _GLIBCXX_VISIBILITY(default)
63 _GLIBCXX_BEGIN_NAMESPACE_VERSION
66 * @addtogroup utilities
70 template<typename _Tp>
73 /// Tag type to disengage optional objects.
76 // Do not user-declare default constructor at all for
77 // optional_value = {} syntax to work.
78 // nullopt_t() = delete;
80 // Used for constructing nullopt.
81 enum class _Construct { _Token };
83 // Must be constexpr for nullopt_t to be literal.
84 explicit constexpr nullopt_t(_Construct) noexcept { }
87 /// Tag to disengage optional objects.
88 inline constexpr nullopt_t nullopt { nullopt_t::_Construct::_Token };
90 template<typename _Fn> struct _Optional_func { _Fn& _M_f; };
93 * @brief Exception class thrown when a disengaged optional object is
97 class bad_optional_access : public exception
100 bad_optional_access() = default;
101 virtual ~bad_optional_access() = default;
103 const char* what() const noexcept override
104 { return "bad optional access"; }
107 // XXX Does not belong here.
108 [[__noreturn__]] inline void
109 __throw_bad_optional_access()
110 { _GLIBCXX_THROW_OR_ABORT(bad_optional_access()); }
112 // This class template manages construction/destruction of
113 // the contained value for a std::optional.
114 template <typename _Tp>
115 struct _Optional_payload_base
117 using _Stored_type = remove_const_t<_Tp>;
119 _Optional_payload_base() = default;
120 ~_Optional_payload_base() = default;
122 template<typename... _Args>
124 _Optional_payload_base(in_place_t __tag, _Args&&... __args)
125 : _M_payload(__tag, std::forward<_Args>(__args)...),
129 template<typename _Up, typename... _Args>
131 _Optional_payload_base(std::initializer_list<_Up> __il,
133 : _M_payload(__il, std::forward<_Args>(__args)...),
137 // Constructor used by _Optional_base copy constructor when the
138 // contained value is not trivially copy constructible.
140 _Optional_payload_base(bool /* __engaged */,
141 const _Optional_payload_base& __other)
143 if (__other._M_engaged)
144 this->_M_construct(__other._M_get());
147 // Constructor used by _Optional_base move constructor when the
148 // contained value is not trivially move constructible.
150 _Optional_payload_base(bool /* __engaged */,
151 _Optional_payload_base&& __other)
153 if (__other._M_engaged)
154 this->_M_construct(std::move(__other._M_get()));
157 // Copy constructor is only used to when the contained value is
158 // trivially copy constructible.
159 _Optional_payload_base(const _Optional_payload_base&) = default;
161 // Move constructor is only used to when the contained value is
162 // trivially copy constructible.
163 _Optional_payload_base(_Optional_payload_base&&) = default;
165 _Optional_payload_base&
166 operator=(const _Optional_payload_base&) = default;
168 _Optional_payload_base&
169 operator=(_Optional_payload_base&&) = default;
171 // used to perform non-trivial copy assignment.
173 _M_copy_assign(const _Optional_payload_base& __other)
175 if (this->_M_engaged && __other._M_engaged)
176 this->_M_get() = __other._M_get();
179 if (__other._M_engaged)
180 this->_M_construct(__other._M_get());
186 // used to perform non-trivial move assignment.
188 _M_move_assign(_Optional_payload_base&& __other)
189 noexcept(__and_v<is_nothrow_move_constructible<_Tp>,
190 is_nothrow_move_assignable<_Tp>>)
192 if (this->_M_engaged && __other._M_engaged)
193 this->_M_get() = std::move(__other._M_get());
196 if (__other._M_engaged)
197 this->_M_construct(std::move(__other._M_get()));
203 struct _Empty_byte { };
205 template<typename _Up, bool = is_trivially_destructible_v<_Up>>
208 constexpr _Storage() noexcept : _M_empty() { }
210 template<typename... _Args>
212 _Storage(in_place_t, _Args&&... __args)
213 : _M_value(std::forward<_Args>(__args)...)
216 template<typename _Vp, typename... _Args>
218 _Storage(std::initializer_list<_Vp> __il, _Args&&... __args)
219 : _M_value(__il, std::forward<_Args>(__args)...)
222 #if __cplusplus >= 202002L
223 template<typename _Fn, typename _Arg>
225 _Storage(_Optional_func<_Fn> __f, _Arg&& __arg)
226 : _M_value(std::__invoke(std::forward<_Fn>(__f._M_f),
227 std::forward<_Arg>(__arg)))
231 #if __cpp_concepts >= 202002L // Conditionally trivial special member functions
232 ~_Storage() = default;
234 // User-provided destructor is needed when _Up has non-trivial dtor.
236 ~_Storage() requires (!is_trivially_destructible_v<_Up>)
239 _Storage(const _Storage&) = default;
240 _Storage(_Storage&&) = default;
241 _Storage& operator=(const _Storage&) = default;
242 _Storage& operator=(_Storage&&) = default;
245 _Empty_byte _M_empty;
249 #if __cpp_concepts < 202002L
250 template<typename _Up>
251 union _Storage<_Up, false>
253 constexpr _Storage() noexcept : _M_empty() { }
255 template<typename... _Args>
257 _Storage(in_place_t, _Args&&... __args)
258 : _M_value(std::forward<_Args>(__args)...)
261 template<typename _Vp, typename... _Args>
263 _Storage(std::initializer_list<_Vp> __il, _Args&&... __args)
264 : _M_value(__il, std::forward<_Args>(__args)...)
267 #if __cplusplus >= 202002L
268 template<typename _Fn, typename _Arg>
270 _Storage(_Optional_func<_Fn> __f, _Arg&& __arg)
271 : _M_value(std::__invoke(std::forward<_Fn>(__f._M_f),
272 std::forward<_Arg>(__arg)))
276 // User-provided destructor is needed when _Up has non-trivial dtor.
277 _GLIBCXX20_CONSTEXPR ~_Storage() { }
279 _Storage(const _Storage&) = default;
280 _Storage(_Storage&&) = default;
281 _Storage& operator=(const _Storage&) = default;
282 _Storage& operator=(_Storage&&) = default;
284 _Empty_byte _M_empty;
289 _Storage<_Stored_type> _M_payload;
291 bool _M_engaged = false;
293 template<typename... _Args>
295 _M_construct(_Args&&... __args)
296 noexcept(is_nothrow_constructible_v<_Stored_type, _Args...>)
298 std::_Construct(std::__addressof(this->_M_payload._M_value),
299 std::forward<_Args>(__args)...);
300 this->_M_engaged = true;
304 _M_destroy() noexcept
307 _M_payload._M_value.~_Stored_type();
310 #if __cplusplus >= 202002L
311 template<typename _Fn, typename _Up>
313 _M_apply(_Optional_func<_Fn> __f, _Up&& __x)
315 std::construct_at(std::__addressof(this->_M_payload),
316 __f, std::forward<_Up>(__x));
321 // The _M_get() operations have _M_engaged as a precondition.
322 // They exist to access the contained value with the appropriate
323 // const-qualification, because _M_payload has had the const removed.
327 { return this->_M_payload._M_value; }
330 _M_get() const noexcept
331 { return this->_M_payload._M_value; }
333 // _M_reset is a 'safe' operation with no precondition.
337 if (this->_M_engaged)
339 else // This seems redundant but improves codegen, see PR 112480.
340 this->_M_engaged = false;
344 // Class template that manages the payload for optionals.
345 template <typename _Tp,
346 bool /*_HasTrivialDestructor*/ =
347 is_trivially_destructible_v<_Tp>,
348 bool /*_HasTrivialCopy */ =
349 is_trivially_copy_assignable_v<_Tp>
350 && is_trivially_copy_constructible_v<_Tp>,
351 bool /*_HasTrivialMove */ =
352 is_trivially_move_assignable_v<_Tp>
353 && is_trivially_move_constructible_v<_Tp>>
354 struct _Optional_payload;
356 // Payload for potentially-constexpr optionals (trivial copy/move/destroy).
357 template <typename _Tp>
358 struct _Optional_payload<_Tp, true, true, true>
359 : _Optional_payload_base<_Tp>
361 using _Optional_payload_base<_Tp>::_Optional_payload_base;
363 _Optional_payload() = default;
366 // Payload for optionals with non-trivial copy construction/assignment.
367 template <typename _Tp>
368 struct _Optional_payload<_Tp, true, false, true>
369 : _Optional_payload_base<_Tp>
371 using _Optional_payload_base<_Tp>::_Optional_payload_base;
373 _Optional_payload() = default;
374 ~_Optional_payload() = default;
375 _Optional_payload(const _Optional_payload&) = default;
376 _Optional_payload(_Optional_payload&&) = default;
377 _Optional_payload& operator=(_Optional_payload&&) = default;
379 // Non-trivial copy assignment.
382 operator=(const _Optional_payload& __other)
384 this->_M_copy_assign(__other);
389 // Payload for optionals with non-trivial move construction/assignment.
390 template <typename _Tp>
391 struct _Optional_payload<_Tp, true, true, false>
392 : _Optional_payload_base<_Tp>
394 using _Optional_payload_base<_Tp>::_Optional_payload_base;
396 _Optional_payload() = default;
397 ~_Optional_payload() = default;
398 _Optional_payload(const _Optional_payload&) = default;
399 _Optional_payload(_Optional_payload&&) = default;
400 _Optional_payload& operator=(const _Optional_payload&) = default;
402 // Non-trivial move assignment.
405 operator=(_Optional_payload&& __other)
406 noexcept(__and_v<is_nothrow_move_constructible<_Tp>,
407 is_nothrow_move_assignable<_Tp>>)
409 this->_M_move_assign(std::move(__other));
414 // Payload for optionals with non-trivial copy and move assignment.
415 template <typename _Tp>
416 struct _Optional_payload<_Tp, true, false, false>
417 : _Optional_payload_base<_Tp>
419 using _Optional_payload_base<_Tp>::_Optional_payload_base;
421 _Optional_payload() = default;
422 ~_Optional_payload() = default;
423 _Optional_payload(const _Optional_payload&) = default;
424 _Optional_payload(_Optional_payload&&) = default;
426 // Non-trivial copy assignment.
429 operator=(const _Optional_payload& __other)
431 this->_M_copy_assign(__other);
435 // Non-trivial move assignment.
438 operator=(_Optional_payload&& __other)
439 noexcept(__and_v<is_nothrow_move_constructible<_Tp>,
440 is_nothrow_move_assignable<_Tp>>)
442 this->_M_move_assign(std::move(__other));
447 // Payload for optionals with non-trivial destructors.
448 template <typename _Tp, bool _Copy, bool _Move>
449 struct _Optional_payload<_Tp, false, _Copy, _Move>
450 : _Optional_payload<_Tp, true, false, false>
452 // Base class implements all the constructors and assignment operators:
453 using _Optional_payload<_Tp, true, false, false>::_Optional_payload;
454 _Optional_payload() = default;
455 _Optional_payload(const _Optional_payload&) = default;
456 _Optional_payload(_Optional_payload&&) = default;
457 _Optional_payload& operator=(const _Optional_payload&) = default;
458 _Optional_payload& operator=(_Optional_payload&&) = default;
460 // Destructor needs to destroy the contained value:
461 _GLIBCXX20_CONSTEXPR ~_Optional_payload() { this->_M_reset(); }
465 * @brief Class template that provides copy/move constructors of optional.
467 * Such a separate base class template is necessary in order to
468 * conditionally make copy/move constructors trivial.
470 * When the contained value is trivially copy/move constructible,
471 * the copy/move constructors of _Optional_base will invoke the
472 * trivial copy/move constructor of _Optional_payload. Otherwise,
473 * they will invoke _Optional_payload(bool, const _Optional_payload&)
474 * or _Optional_payload(bool, _Optional_payload&&) to initialize
475 * the contained value, if copying/moving an engaged optional.
477 * Whether the other special members are trivial is determined by the
478 * _Optional_payload<_Tp> specialization used for the _M_payload member.
480 * @see optional, _Enable_special_members
482 template<typename _Tp,
483 bool = is_trivially_copy_constructible_v<_Tp>,
484 bool = is_trivially_move_constructible_v<_Tp>>
485 struct _Optional_base
487 // Constructors for disengaged optionals.
488 constexpr _Optional_base() = default;
490 // Constructors for engaged optionals.
491 template<typename... _Args,
492 enable_if_t<is_constructible_v<_Tp, _Args...>, bool> = false>
494 _Optional_base(in_place_t, _Args&&... __args)
495 : _M_payload(in_place, std::forward<_Args>(__args)...)
498 template<typename _Up, typename... _Args,
499 enable_if_t<is_constructible_v<_Tp,
500 initializer_list<_Up>&,
501 _Args...>, bool> = false>
503 _Optional_base(in_place_t,
504 initializer_list<_Up> __il,
506 : _M_payload(in_place, __il, std::forward<_Args>(__args)...)
509 // Copy and move constructors.
511 _Optional_base(const _Optional_base& __other)
512 noexcept(is_nothrow_copy_constructible_v<_Tp>)
513 : _M_payload(__other._M_payload._M_engaged, __other._M_payload)
517 _Optional_base(_Optional_base&& __other)
518 noexcept(is_nothrow_move_constructible_v<_Tp>)
519 : _M_payload(__other._M_payload._M_engaged,
520 std::move(__other._M_payload))
523 #if __cpp_concepts >= 202002L // Conditionally trivial special member functions
524 // Define these in the primary template if possible, so that we don't
525 // need to use partial specializations of this class template.
526 constexpr _Optional_base(const _Optional_base&)
527 requires is_trivially_copy_constructible_v<_Tp> = default;
529 constexpr _Optional_base(_Optional_base&&)
530 requires is_trivially_move_constructible_v<_Tp> = default;
533 // Assignment operators.
534 _Optional_base& operator=(const _Optional_base&) = default;
535 _Optional_base& operator=(_Optional_base&&) = default;
537 _Optional_payload<_Tp> _M_payload;
540 // For the primary template, we define these functions here.
541 using _Stored_type = remove_const_t<_Tp>;
543 // The _M_construct operation has !_M_engaged as a precondition
544 // while _M_destruct has _M_engaged as a precondition.
545 template<typename... _Args>
547 _M_construct(_Args&&... __args)
548 noexcept(is_nothrow_constructible_v<_Stored_type, _Args...>)
550 _M_payload._M_construct(std::forward<_Args>(__args)...);
554 _M_destruct() noexcept
555 { _M_payload._M_destroy(); }
557 // _M_reset is a 'safe' operation with no precondition.
560 { _M_payload._M_reset(); }
562 constexpr bool _M_is_engaged() const noexcept
563 { return _M_payload._M_engaged; }
565 // The _M_get operations have _M_engaged as a precondition.
568 { return _M_payload._M_get(); }
571 _M_get() const noexcept
572 { return _M_payload._M_get(); }
575 #if __cpp_concepts < 202002L
576 // If P0848R3 "Conditionally Trivial Special Member Functions" is not
577 // supported (as determined from the __cpp_concepts macro value), the
578 // _Optional_base primary template only has non-trivial copy and move
579 // constructors. Use partial specializations of _Optional_base<T, C, M>
580 // that have a trivial copy and/or move constructor.
582 // Common base class for _Optional_base<T> to avoid repeating these
583 // member functions in each partial specialization.
584 // Only used if P0848R3 "Conditionally Trivial Special Member Functions"
585 // is not supported, as indicated by the __cpp_concepts value.
586 template<typename _Tp, typename _Dp>
587 class _Optional_base_impl
590 using _Stored_type = remove_const_t<_Tp>;
592 // The _M_construct operation has !_M_engaged as a precondition
593 // while _M_destruct has _M_engaged as a precondition.
594 template<typename... _Args>
596 _M_construct(_Args&&... __args)
597 noexcept(is_nothrow_constructible_v<_Stored_type, _Args...>)
599 static_cast<_Dp*>(this)->_M_payload._M_construct(
600 std::forward<_Args>(__args)...);
604 _M_destruct() noexcept
605 { static_cast<_Dp*>(this)->_M_payload._M_destroy(); }
607 // _M_reset is a 'safe' operation with no precondition.
610 { static_cast<_Dp*>(this)->_M_payload._M_reset(); }
612 constexpr bool _M_is_engaged() const noexcept
613 { return static_cast<const _Dp*>(this)->_M_payload._M_engaged; }
615 // The _M_get operations have _M_engaged as a precondition.
618 { return static_cast<_Dp*>(this)->_M_payload._M_get(); }
621 _M_get() const noexcept
622 { return static_cast<const _Dp*>(this)->_M_payload._M_get(); }
625 template<typename _Tp>
626 struct _Optional_base<_Tp, false, true> // trivial move ctor
627 : _Optional_base_impl<_Tp, _Optional_base<_Tp>>
629 // Constructors for disengaged optionals.
630 constexpr _Optional_base() = default;
632 // Constructors for engaged optionals.
633 template<typename... _Args,
634 enable_if_t<is_constructible_v<_Tp, _Args...>, bool> = false>
636 _Optional_base(in_place_t, _Args&&... __args)
637 : _M_payload(in_place, std::forward<_Args>(__args)...)
640 template<typename _Up, typename... _Args,
641 enable_if_t<is_constructible_v<_Tp,
642 initializer_list<_Up>&,
643 _Args...>, bool> = false>
645 _Optional_base(in_place_t,
646 initializer_list<_Up> __il,
648 : _M_payload(in_place, __il, std::forward<_Args>(__args)...)
651 // Copy and move constructors.
652 constexpr _Optional_base(const _Optional_base& __other)
653 : _M_payload(__other._M_payload._M_engaged, __other._M_payload)
656 constexpr _Optional_base(_Optional_base&& __other) = default;
658 // Assignment operators.
659 _Optional_base& operator=(const _Optional_base&) = default;
660 _Optional_base& operator=(_Optional_base&&) = default;
662 _Optional_payload<_Tp> _M_payload;
665 template<typename _Tp>
666 struct _Optional_base<_Tp, true, false> // trivial copy ctor
667 : _Optional_base_impl<_Tp, _Optional_base<_Tp>>
669 // Constructors for disengaged optionals.
670 constexpr _Optional_base() = default;
672 // Constructors for engaged optionals.
673 template<typename... _Args,
674 enable_if_t<is_constructible_v<_Tp, _Args...>, bool> = false>
676 _Optional_base(in_place_t, _Args&&... __args)
677 : _M_payload(in_place, std::forward<_Args>(__args)...)
680 template<typename _Up, typename... _Args,
681 enable_if_t<is_constructible_v<_Tp,
682 initializer_list<_Up>&,
683 _Args...>, bool> = false>
685 _Optional_base(in_place_t,
686 initializer_list<_Up> __il,
688 : _M_payload(in_place, __il, std::forward<_Args>(__args)...)
691 // Copy and move constructors.
692 constexpr _Optional_base(const _Optional_base& __other) = default;
695 _Optional_base(_Optional_base&& __other)
696 noexcept(is_nothrow_move_constructible_v<_Tp>)
697 : _M_payload(__other._M_payload._M_engaged,
698 std::move(__other._M_payload))
701 // Assignment operators.
702 _Optional_base& operator=(const _Optional_base&) = default;
703 _Optional_base& operator=(_Optional_base&&) = default;
705 _Optional_payload<_Tp> _M_payload;
708 template<typename _Tp>
709 struct _Optional_base<_Tp, true, true> // trivial copy and move ctors
710 : _Optional_base_impl<_Tp, _Optional_base<_Tp>>
712 // Constructors for disengaged optionals.
713 constexpr _Optional_base() = default;
715 // Constructors for engaged optionals.
716 template<typename... _Args,
717 enable_if_t<is_constructible_v<_Tp, _Args...>, bool> = false>
719 _Optional_base(in_place_t, _Args&&... __args)
720 : _M_payload(in_place, std::forward<_Args>(__args)...)
723 template<typename _Up, typename... _Args,
724 enable_if_t<is_constructible_v<_Tp,
725 initializer_list<_Up>&,
726 _Args...>, bool> = false>
728 _Optional_base(in_place_t,
729 initializer_list<_Up> __il,
731 : _M_payload(in_place, __il, std::forward<_Args>(__args)...)
734 // Copy and move constructors.
735 constexpr _Optional_base(const _Optional_base& __other) = default;
736 constexpr _Optional_base(_Optional_base&& __other) = default;
738 // Assignment operators.
739 _Optional_base& operator=(const _Optional_base&) = default;
740 _Optional_base& operator=(_Optional_base&&) = default;
742 _Optional_payload<_Tp> _M_payload;
744 #endif // __cpp_concepts
746 template<typename _Tp>
747 inline constexpr bool __is_optional_v = false;
748 template<typename _Tp>
749 inline constexpr bool __is_optional_v<optional<_Tp>> = true;
751 template<typename _Tp, typename _Wp>
752 using __converts_from_any_cvref = __or_<
753 is_constructible<_Tp, _Wp&>, is_convertible<_Wp&, _Tp>,
754 is_constructible<_Tp, _Wp>, is_convertible<_Wp, _Tp>,
755 is_constructible<_Tp, const _Wp&>, is_convertible<const _Wp&, _Tp>,
756 is_constructible<_Tp, const _Wp>, is_convertible<const _Wp, _Tp>
759 template<typename _Tp, typename _Up>
760 using __converts_from_optional
761 = __converts_from_any_cvref<_Tp, optional<_Up>>;
763 template<typename _Tp, typename _Up>
764 using __assigns_from_optional =
765 __or_<is_assignable<_Tp&, const optional<_Up>&>,
766 is_assignable<_Tp&, optional<_Up>&>,
767 is_assignable<_Tp&, const optional<_Up>&&>,
768 is_assignable<_Tp&, optional<_Up>&&>>;
770 #if __cpp_concepts && __cpp_conditional_explicit && __glibcxx_remove_cvref
771 # define _GLIBCXX_USE_CONSTRAINTS_FOR_OPTIONAL 1
775 * @brief Class template for optional values.
777 template<typename _Tp>
779 : private _Optional_base<_Tp>,
780 private _Enable_copy_move<
782 is_copy_constructible_v<_Tp>,
784 __and_v<is_copy_constructible<_Tp>, is_copy_assignable<_Tp>>,
786 is_move_constructible_v<_Tp>,
788 __and_v<is_move_constructible<_Tp>, is_move_assignable<_Tp>>,
792 static_assert(!is_same_v<remove_cv_t<_Tp>, nullopt_t>);
793 static_assert(!is_same_v<remove_cv_t<_Tp>, in_place_t>);
794 static_assert(is_object_v<_Tp> && !is_array_v<_Tp>);
797 using _Base = _Optional_base<_Tp>;
801 // _GLIBCXX_RESOLVE_LIB_DEFECTS
802 // 3836. std::expected<bool, E1> conversion constructor
803 // expected(const expected<U, G>&) should take precedence over
804 // expected(U&&) with operator bool
805 #ifdef _GLIBCXX_USE_CONSTRAINTS_FOR_OPTIONAL
806 template<typename _From, typename = remove_cv_t<_Tp>>
807 static constexpr bool __not_constructing_bool_from_optional
810 // If T is cv bool, remove_cvref_t<U> is not a specialization of optional
811 // i.e. do not initialize a bool from optional<U>::operator bool().
812 template<typename _From>
813 static constexpr bool
814 __not_constructing_bool_from_optional<_From, bool>
815 = !__is_optional_v<remove_cvref_t<_From>>;
817 // If T is not cv bool, converts-from-any-cvref<T, optional<U>> is false.
818 // The constructor that converts from optional<U> is disabled if the
819 // contained value can be initialized from optional<U>, so that the
820 // optional(U&&) constructor can be used instead.
821 template<typename _From, typename = remove_cv_t<_Tp>>
822 static constexpr bool __construct_from_contained_value
823 = !__converts_from_optional<_Tp, _From>::value;
825 // However, optional<U> can always be converted to bool, so don't apply
826 // this constraint when T is cv bool.
827 template<typename _From>
828 static constexpr bool __construct_from_contained_value<_From, bool>
831 template<typename _From, typename = remove_cv_t<_Tp>>
832 struct __not_constructing_bool_from_optional
836 template<typename _From>
837 struct __not_constructing_bool_from_optional<_From, bool>
838 : bool_constant<!__is_optional_v<__remove_cvref_t<_From>>>
841 template<typename _From, typename = remove_cv_t<_Tp>>
842 struct __construct_from_contained_value
843 : __not_<__converts_from_optional<_Tp, _From>>
846 template<typename _From>
847 struct __construct_from_contained_value<_From, bool>
851 template<typename _Up>
852 using __not_self = __not_<is_same<optional, __remove_cvref_t<_Up>>>;
853 template<typename _Up>
854 using __not_tag = __not_<is_same<in_place_t, __remove_cvref_t<_Up>>>;
855 template<typename... _Cond>
856 using _Requires = enable_if_t<__and_v<_Cond...>, bool>;
860 using value_type = _Tp;
862 constexpr optional() noexcept { }
864 constexpr optional(nullopt_t) noexcept { }
866 // Converting constructors for engaged optionals.
867 #ifdef _GLIBCXX_USE_CONSTRAINTS_FOR_OPTIONAL
868 template<typename _Up = remove_cv_t<_Tp>>
869 requires (!is_same_v<optional, remove_cvref_t<_Up>>)
870 && (!is_same_v<in_place_t, remove_cvref_t<_Up>>)
871 && is_constructible_v<_Tp, _Up>
872 && __not_constructing_bool_from_optional<_Up>
873 constexpr explicit(!is_convertible_v<_Up, _Tp>)
875 noexcept(is_nothrow_constructible_v<_Tp, _Up>)
876 : _Base(std::in_place, std::forward<_Up>(__t)) { }
878 template<typename _Up>
879 requires (!is_same_v<_Tp, _Up>)
880 && is_constructible_v<_Tp, const _Up&>
881 && __construct_from_contained_value<_Up>
882 constexpr explicit(!is_convertible_v<const _Up&, _Tp>)
883 optional(const optional<_Up>& __t)
884 noexcept(is_nothrow_constructible_v<_Tp, const _Up&>)
887 emplace(__t._M_get());
890 template<typename _Up>
891 requires (!is_same_v<_Tp, _Up>)
892 && is_constructible_v<_Tp, _Up>
893 && __construct_from_contained_value<_Up>
894 constexpr explicit(!is_convertible_v<_Up, _Tp>)
895 optional(optional<_Up>&& __t)
896 noexcept(is_nothrow_constructible_v<_Tp, _Up>)
899 emplace(std::move(__t._M_get()));
902 template<typename... _Args>
903 requires is_constructible_v<_Tp, _Args...>
905 optional(in_place_t, _Args&&... __args)
906 noexcept(is_nothrow_constructible_v<_Tp, _Args...>)
907 : _Base(std::in_place, std::forward<_Args>(__args)...)
910 template<typename _Up, typename... _Args>
911 requires is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>
913 optional(in_place_t, initializer_list<_Up> __il, _Args&&... __args)
914 noexcept(is_nothrow_constructible_v<_Tp, initializer_list<_Up>&,
916 : _Base(std::in_place, __il, std::forward<_Args>(__args)...)
919 template<typename _Up = remove_cv_t<_Tp>,
920 _Requires<__not_self<_Up>, __not_tag<_Up>,
921 is_constructible<_Tp, _Up>,
922 is_convertible<_Up, _Tp>,
923 __not_constructing_bool_from_optional<_Up>> = true>
926 noexcept(is_nothrow_constructible_v<_Tp, _Up>)
927 : _Base(std::in_place, std::forward<_Up>(__t)) { }
929 template<typename _Up = remove_cv_t<_Tp>,
930 _Requires<__not_self<_Up>, __not_tag<_Up>,
931 is_constructible<_Tp, _Up>,
932 __not_<is_convertible<_Up, _Tp>>,
933 __not_constructing_bool_from_optional<_Up>> = false>
936 noexcept(is_nothrow_constructible_v<_Tp, _Up>)
937 : _Base(std::in_place, std::forward<_Up>(__t)) { }
939 template<typename _Up,
940 _Requires<__not_<is_same<_Tp, _Up>>,
941 is_constructible<_Tp, const _Up&>,
942 is_convertible<const _Up&, _Tp>,
943 __construct_from_contained_value<_Up>> = true>
945 optional(const optional<_Up>& __t)
946 noexcept(is_nothrow_constructible_v<_Tp, const _Up&>)
949 emplace(__t._M_get());
952 template<typename _Up,
953 _Requires<__not_<is_same<_Tp, _Up>>,
954 is_constructible<_Tp, const _Up&>,
955 __not_<is_convertible<const _Up&, _Tp>>,
956 __construct_from_contained_value<_Up>> = false>
958 optional(const optional<_Up>& __t)
959 noexcept(is_nothrow_constructible_v<_Tp, const _Up&>)
962 emplace(__t._M_get());
965 template<typename _Up,
966 _Requires<__not_<is_same<_Tp, _Up>>,
967 is_constructible<_Tp, _Up>,
968 is_convertible<_Up, _Tp>,
969 __construct_from_contained_value<_Up>> = true>
971 optional(optional<_Up>&& __t)
972 noexcept(is_nothrow_constructible_v<_Tp, _Up>)
975 emplace(std::move(__t._M_get()));
978 template<typename _Up,
979 _Requires<__not_<is_same<_Tp, _Up>>,
980 is_constructible<_Tp, _Up>,
981 __not_<is_convertible<_Up, _Tp>>,
982 __construct_from_contained_value<_Up>> = false>
984 optional(optional<_Up>&& __t)
985 noexcept(is_nothrow_constructible_v<_Tp, _Up>)
988 emplace(std::move(__t._M_get()));
991 template<typename... _Args,
992 _Requires<is_constructible<_Tp, _Args...>> = false>
994 optional(in_place_t, _Args&&... __args)
995 noexcept(is_nothrow_constructible_v<_Tp, _Args...>)
996 : _Base(std::in_place, std::forward<_Args>(__args)...) { }
998 template<typename _Up, typename... _Args,
999 _Requires<is_constructible<_Tp,
1000 initializer_list<_Up>&,
1003 optional(in_place_t, initializer_list<_Up> __il, _Args&&... __args)
1004 noexcept(is_nothrow_constructible_v<_Tp, initializer_list<_Up>&,
1006 : _Base(std::in_place, __il, std::forward<_Args>(__args)...) { }
1009 // Assignment operators.
1010 _GLIBCXX20_CONSTEXPR optional&
1011 operator=(nullopt_t) noexcept
1017 template<typename _Up = remove_cv_t<_Tp>>
1018 #ifdef _GLIBCXX_USE_CONSTRAINTS_FOR_OPTIONAL
1019 requires (!is_same_v<optional, remove_cvref_t<_Up>>)
1020 && (!(is_scalar_v<_Tp> && is_same_v<_Tp, decay_t<_Up>>))
1021 && is_constructible_v<_Tp, _Up>
1022 && is_assignable_v<_Tp&, _Up>
1025 enable_if_t<__and_v<__not_self<_Up>,
1026 __not_<__and_<is_scalar<_Tp>,
1027 is_same<_Tp, decay_t<_Up>>>>,
1028 is_constructible<_Tp, _Up>,
1029 is_assignable<_Tp&, _Up>>,
1032 operator=(_Up&& __u)
1033 noexcept(__and_v<is_nothrow_constructible<_Tp, _Up>,
1034 is_nothrow_assignable<_Tp&, _Up>>)
1036 if (this->_M_is_engaged())
1037 this->_M_get() = std::forward<_Up>(__u);
1039 this->_M_construct(std::forward<_Up>(__u));
1044 template<typename _Up>
1045 #ifdef _GLIBCXX_USE_CONSTRAINTS_FOR_OPTIONAL
1046 requires (!is_same_v<_Tp, _Up>)
1047 && is_constructible_v<_Tp, const _Up&>
1048 && is_assignable_v<_Tp&, const _Up&>
1049 && (!__converts_from_optional<_Tp, _Up>::value)
1050 && (!__assigns_from_optional<_Tp, _Up>::value)
1053 enable_if_t<__and_v<__not_<is_same<_Tp, _Up>>,
1054 is_constructible<_Tp, const _Up&>,
1055 is_assignable<_Tp&, const _Up&>,
1056 __not_<__converts_from_optional<_Tp, _Up>>,
1057 __not_<__assigns_from_optional<_Tp, _Up>>>,
1060 operator=(const optional<_Up>& __u)
1061 noexcept(__and_v<is_nothrow_constructible<_Tp, const _Up&>,
1062 is_nothrow_assignable<_Tp&, const _Up&>>)
1066 if (this->_M_is_engaged())
1067 this->_M_get() = __u._M_get();
1069 this->_M_construct(__u._M_get());
1078 template<typename _Up>
1079 #ifdef _GLIBCXX_USE_CONSTRAINTS_FOR_OPTIONAL
1080 requires (!is_same_v<_Tp, _Up>)
1081 && is_constructible_v<_Tp, _Up>
1082 && is_assignable_v<_Tp&, _Up>
1083 && (!__converts_from_optional<_Tp, _Up>::value)
1084 && (!__assigns_from_optional<_Tp, _Up>::value)
1087 enable_if_t<__and_v<__not_<is_same<_Tp, _Up>>,
1088 is_constructible<_Tp, _Up>,
1089 is_assignable<_Tp&, _Up>,
1090 __not_<__converts_from_optional<_Tp, _Up>>,
1091 __not_<__assigns_from_optional<_Tp, _Up>>>,
1094 operator=(optional<_Up>&& __u)
1095 noexcept(__and_v<is_nothrow_constructible<_Tp, _Up>,
1096 is_nothrow_assignable<_Tp&, _Up>>)
1100 if (this->_M_is_engaged())
1101 this->_M_get() = std::move(__u._M_get());
1103 this->_M_construct(std::move(__u._M_get()));
1113 template<typename... _Args>
1114 _GLIBCXX20_CONSTEXPR
1115 enable_if_t<is_constructible_v<_Tp, _Args...>, _Tp&>
1116 emplace(_Args&&... __args)
1117 noexcept(is_nothrow_constructible_v<_Tp, _Args...>)
1120 this->_M_construct(std::forward<_Args>(__args)...);
1121 return this->_M_get();
1124 template<typename _Up, typename... _Args>
1125 _GLIBCXX20_CONSTEXPR
1126 enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>,
1128 emplace(initializer_list<_Up> __il, _Args&&... __args)
1129 noexcept(is_nothrow_constructible_v<_Tp, initializer_list<_Up>&,
1133 this->_M_construct(__il, std::forward<_Args>(__args)...);
1134 return this->_M_get();
1137 // Destructor is implicit, implemented in _Optional_base.
1140 _GLIBCXX20_CONSTEXPR void
1141 swap(optional& __other)
1142 noexcept(is_nothrow_move_constructible_v<_Tp>
1143 && is_nothrow_swappable_v<_Tp>)
1147 if (this->_M_is_engaged() && __other._M_is_engaged())
1148 swap(this->_M_get(), __other._M_get());
1149 else if (this->_M_is_engaged())
1151 __other._M_construct(std::move(this->_M_get()));
1152 this->_M_destruct();
1154 else if (__other._M_is_engaged())
1156 this->_M_construct(std::move(__other._M_get()));
1157 __other._M_destruct();
1162 constexpr const _Tp*
1163 operator->() const noexcept
1165 __glibcxx_assert(this->_M_is_engaged());
1166 return std::__addressof(this->_M_get());
1170 operator->() noexcept
1172 __glibcxx_assert(this->_M_is_engaged());
1173 return std::__addressof(this->_M_get());
1176 constexpr const _Tp&
1177 operator*() const& noexcept
1179 __glibcxx_assert(this->_M_is_engaged());
1180 return this->_M_get();
1184 operator*()& noexcept
1186 __glibcxx_assert(this->_M_is_engaged());
1187 return this->_M_get();
1191 operator*()&& noexcept
1193 __glibcxx_assert(this->_M_is_engaged());
1194 return std::move(this->_M_get());
1197 constexpr const _Tp&&
1198 operator*() const&& noexcept
1200 __glibcxx_assert(this->_M_is_engaged());
1201 return std::move(this->_M_get());
1204 constexpr explicit operator bool() const noexcept
1205 { return this->_M_is_engaged(); }
1207 constexpr bool has_value() const noexcept
1208 { return this->_M_is_engaged(); }
1210 constexpr const _Tp&
1213 if (this->_M_is_engaged())
1214 return this->_M_get();
1215 __throw_bad_optional_access();
1221 if (this->_M_is_engaged())
1222 return this->_M_get();
1223 __throw_bad_optional_access();
1229 if (this->_M_is_engaged())
1230 return std::move(this->_M_get());
1231 __throw_bad_optional_access();
1234 constexpr const _Tp&&
1237 if (this->_M_is_engaged())
1238 return std::move(this->_M_get());
1239 __throw_bad_optional_access();
1242 template<typename _Up = remove_cv_t<_Tp>>
1244 value_or(_Up&& __u) const&
1246 static_assert(is_copy_constructible_v<_Tp>);
1247 static_assert(is_convertible_v<_Up&&, _Tp>);
1249 if (this->_M_is_engaged())
1250 return this->_M_get();
1252 return static_cast<_Tp>(std::forward<_Up>(__u));
1255 template<typename _Up = remove_cv_t<_Tp>>
1257 value_or(_Up&& __u) &&
1259 static_assert(is_move_constructible_v<_Tp>);
1260 static_assert(is_convertible_v<_Up&&, _Tp>);
1262 if (this->_M_is_engaged())
1263 return std::move(this->_M_get());
1265 return static_cast<_Tp>(std::forward<_Up>(__u));
1268 #if __cpp_lib_optional >= 202110L // C++23
1269 // [optional.monadic]
1271 template<typename _Fn>
1273 and_then(_Fn&& __f) &
1275 using _Up = remove_cvref_t<invoke_result_t<_Fn, _Tp&>>;
1276 static_assert(__is_optional_v<remove_cvref_t<_Up>>,
1277 "the function passed to std::optional<T>::and_then "
1278 "must return a std::optional");
1280 return std::__invoke(std::forward<_Fn>(__f), _M_get());
1285 template<typename _Fn>
1287 and_then(_Fn&& __f) const &
1289 using _Up = remove_cvref_t<invoke_result_t<_Fn, const _Tp&>>;
1290 static_assert(__is_optional_v<_Up>,
1291 "the function passed to std::optional<T>::and_then "
1292 "must return a std::optional");
1294 return std::__invoke(std::forward<_Fn>(__f), _M_get());
1299 template<typename _Fn>
1301 and_then(_Fn&& __f) &&
1303 using _Up = remove_cvref_t<invoke_result_t<_Fn, _Tp>>;
1304 static_assert(__is_optional_v<remove_cvref_t<_Up>>,
1305 "the function passed to std::optional<T>::and_then "
1306 "must return a std::optional");
1308 return std::__invoke(std::forward<_Fn>(__f), std::move(_M_get()));
1313 template<typename _Fn>
1315 and_then(_Fn&& __f) const &&
1317 using _Up = remove_cvref_t<invoke_result_t<_Fn, const _Tp>>;
1318 static_assert(__is_optional_v<remove_cvref_t<_Up>>,
1319 "the function passed to std::optional<T>::and_then "
1320 "must return a std::optional");
1322 return std::__invoke(std::forward<_Fn>(__f), std::move(_M_get()));
1327 template<typename _Fn>
1329 transform(_Fn&& __f) &
1331 using _Up = remove_cv_t<invoke_result_t<_Fn, _Tp&>>;
1333 return optional<_Up>(_Optional_func<_Fn>{__f}, _M_get());
1335 return optional<_Up>();
1338 template<typename _Fn>
1340 transform(_Fn&& __f) const &
1342 using _Up = remove_cv_t<invoke_result_t<_Fn, const _Tp&>>;
1344 return optional<_Up>(_Optional_func<_Fn>{__f}, _M_get());
1346 return optional<_Up>();
1349 template<typename _Fn>
1351 transform(_Fn&& __f) &&
1353 using _Up = remove_cv_t<invoke_result_t<_Fn, _Tp>>;
1355 return optional<_Up>(_Optional_func<_Fn>{__f}, std::move(_M_get()));
1357 return optional<_Up>();
1360 template<typename _Fn>
1362 transform(_Fn&& __f) const &&
1364 using _Up = remove_cv_t<invoke_result_t<_Fn, const _Tp>>;
1366 return optional<_Up>(_Optional_func<_Fn>{__f}, std::move(_M_get()));
1368 return optional<_Up>();
1371 template<typename _Fn> requires invocable<_Fn> && copy_constructible<_Tp>
1373 or_else(_Fn&& __f) const&
1375 using _Up = invoke_result_t<_Fn>;
1376 static_assert(is_same_v<remove_cvref_t<_Up>, optional>,
1377 "the function passed to std::optional<T>::or_else "
1378 "must return a std::optional<T>");
1383 return std::forward<_Fn>(__f)();
1386 template<typename _Fn> requires invocable<_Fn> && move_constructible<_Tp>
1388 or_else(_Fn&& __f) &&
1390 using _Up = invoke_result_t<_Fn>;
1391 static_assert(is_same_v<remove_cvref_t<_Up>, optional>,
1392 "the function passed to std::optional<T>::or_else "
1393 "must return a std::optional<T>");
1396 return std::move(*this);
1398 return std::forward<_Fn>(__f)();
1402 _GLIBCXX20_CONSTEXPR void reset() noexcept { this->_M_reset(); }
1405 using _Base::_M_get;
1407 template<typename _Up> friend class optional;
1409 #if __cpp_lib_optional >= 202110L // C++23
1410 template<typename _Fn, typename _Value>
1412 optional(_Optional_func<_Fn> __f, _Value&& __v)
1414 this->_M_payload._M_apply(__f, std::forward<_Value>(__v));
1419 template<typename _Tp>
1420 using __optional_relop_t =
1421 enable_if_t<is_convertible_v<_Tp, bool>, bool>;
1423 template<typename _Tp, typename _Up>
1424 using __optional_eq_t = __optional_relop_t<
1425 decltype(std::declval<const _Tp&>() == std::declval<const _Up&>())
1428 template<typename _Tp, typename _Up>
1429 using __optional_ne_t = __optional_relop_t<
1430 decltype(std::declval<const _Tp&>() != std::declval<const _Up&>())
1433 template<typename _Tp, typename _Up>
1434 using __optional_lt_t = __optional_relop_t<
1435 decltype(std::declval<const _Tp&>() < std::declval<const _Up&>())
1438 template<typename _Tp, typename _Up>
1439 using __optional_gt_t = __optional_relop_t<
1440 decltype(std::declval<const _Tp&>() > std::declval<const _Up&>())
1443 template<typename _Tp, typename _Up>
1444 using __optional_le_t = __optional_relop_t<
1445 decltype(std::declval<const _Tp&>() <= std::declval<const _Up&>())
1448 template<typename _Tp, typename _Up>
1449 using __optional_ge_t = __optional_relop_t<
1450 decltype(std::declval<const _Tp&>() >= std::declval<const _Up&>())
1453 // Comparisons between optional values.
1454 template<typename _Tp, typename _Up>
1456 operator==(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
1457 -> __optional_eq_t<_Tp, _Up>
1459 return static_cast<bool>(__lhs) == static_cast<bool>(__rhs)
1460 && (!__lhs || *__lhs == *__rhs);
1463 template<typename _Tp, typename _Up>
1465 operator!=(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
1466 -> __optional_ne_t<_Tp, _Up>
1468 return static_cast<bool>(__lhs) != static_cast<bool>(__rhs)
1469 || (static_cast<bool>(__lhs) && *__lhs != *__rhs);
1472 template<typename _Tp, typename _Up>
1474 operator<(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
1475 -> __optional_lt_t<_Tp, _Up>
1477 return static_cast<bool>(__rhs) && (!__lhs || *__lhs < *__rhs);
1480 template<typename _Tp, typename _Up>
1482 operator>(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
1483 -> __optional_gt_t<_Tp, _Up>
1485 return static_cast<bool>(__lhs) && (!__rhs || *__lhs > *__rhs);
1488 template<typename _Tp, typename _Up>
1490 operator<=(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
1491 -> __optional_le_t<_Tp, _Up>
1493 return !__lhs || (static_cast<bool>(__rhs) && *__lhs <= *__rhs);
1496 template<typename _Tp, typename _Up>
1498 operator>=(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
1499 -> __optional_ge_t<_Tp, _Up>
1501 return !__rhs || (static_cast<bool>(__lhs) && *__lhs >= *__rhs);
1504 #ifdef __cpp_lib_three_way_comparison
1505 template<typename _Tp, three_way_comparable_with<_Tp> _Up>
1507 constexpr compare_three_way_result_t<_Tp, _Up>
1508 operator<=>(const optional<_Tp>& __x, const optional<_Up>& __y)
1510 return __x && __y ? *__x <=> *__y : bool(__x) <=> bool(__y);
1514 // Comparisons with nullopt.
1515 template<typename _Tp>
1518 operator==(const optional<_Tp>& __lhs, nullopt_t) noexcept
1521 #ifdef __cpp_lib_three_way_comparison
1522 template<typename _Tp>
1524 constexpr strong_ordering
1525 operator<=>(const optional<_Tp>& __x, nullopt_t) noexcept
1526 { return bool(__x) <=> false; }
1528 template<typename _Tp>
1530 operator==(nullopt_t, const optional<_Tp>& __rhs) noexcept
1533 template<typename _Tp>
1535 operator!=(const optional<_Tp>& __lhs, nullopt_t) noexcept
1536 { return static_cast<bool>(__lhs); }
1538 template<typename _Tp>
1540 operator!=(nullopt_t, const optional<_Tp>& __rhs) noexcept
1541 { return static_cast<bool>(__rhs); }
1543 template<typename _Tp>
1545 operator<(const optional<_Tp>& /* __lhs */, nullopt_t) noexcept
1548 template<typename _Tp>
1550 operator<(nullopt_t, const optional<_Tp>& __rhs) noexcept
1551 { return static_cast<bool>(__rhs); }
1553 template<typename _Tp>
1555 operator>(const optional<_Tp>& __lhs, nullopt_t) noexcept
1556 { return static_cast<bool>(__lhs); }
1558 template<typename _Tp>
1560 operator>(nullopt_t, const optional<_Tp>& /* __rhs */) noexcept
1563 template<typename _Tp>
1565 operator<=(const optional<_Tp>& __lhs, nullopt_t) noexcept
1568 template<typename _Tp>
1570 operator<=(nullopt_t, const optional<_Tp>& /* __rhs */) noexcept
1573 template<typename _Tp>
1575 operator>=(const optional<_Tp>& /* __lhs */, nullopt_t) noexcept
1578 template<typename _Tp>
1580 operator>=(nullopt_t, const optional<_Tp>& __rhs) noexcept
1582 #endif // three-way-comparison
1584 #if __cpp_lib_concepts
1585 // _GLIBCXX_RESOLVE_LIB_DEFECTS
1586 // 4072. std::optional comparisons: constrain harder
1587 # define _REQUIRES_NOT_OPTIONAL(T) requires (!__is_optional_v<T>)
1589 # define _REQUIRES_NOT_OPTIONAL(T)
1592 // Comparisons with value type.
1593 template<typename _Tp, typename _Up>
1594 _REQUIRES_NOT_OPTIONAL(_Up)
1596 operator== [[nodiscard]] (const optional<_Tp>& __lhs, const _Up& __rhs)
1597 -> __optional_eq_t<_Tp, _Up>
1598 { return __lhs && *__lhs == __rhs; }
1600 template<typename _Tp, typename _Up>
1601 _REQUIRES_NOT_OPTIONAL(_Tp)
1603 operator== [[nodiscard]] (const _Tp& __lhs, const optional<_Up>& __rhs)
1604 -> __optional_eq_t<_Tp, _Up>
1605 { return __rhs && __lhs == *__rhs; }
1607 template<typename _Tp, typename _Up>
1608 _REQUIRES_NOT_OPTIONAL(_Up)
1610 operator!= [[nodiscard]] (const optional<_Tp>& __lhs, const _Up& __rhs)
1611 -> __optional_ne_t<_Tp, _Up>
1612 { return !__lhs || *__lhs != __rhs; }
1614 template<typename _Tp, typename _Up>
1615 _REQUIRES_NOT_OPTIONAL(_Tp)
1617 operator!= [[nodiscard]] (const _Tp& __lhs, const optional<_Up>& __rhs)
1618 -> __optional_ne_t<_Tp, _Up>
1619 { return !__rhs || __lhs != *__rhs; }
1621 template<typename _Tp, typename _Up>
1622 _REQUIRES_NOT_OPTIONAL(_Up)
1624 operator< [[nodiscard]] (const optional<_Tp>& __lhs, const _Up& __rhs)
1625 -> __optional_lt_t<_Tp, _Up>
1626 { return !__lhs || *__lhs < __rhs; }
1628 template<typename _Tp, typename _Up>
1629 _REQUIRES_NOT_OPTIONAL(_Tp)
1631 operator< [[nodiscard]] (const _Tp& __lhs, const optional<_Up>& __rhs)
1632 -> __optional_lt_t<_Tp, _Up>
1633 { return __rhs && __lhs < *__rhs; }
1635 template<typename _Tp, typename _Up>
1636 _REQUIRES_NOT_OPTIONAL(_Up)
1638 operator> [[nodiscard]] (const optional<_Tp>& __lhs, const _Up& __rhs)
1639 -> __optional_gt_t<_Tp, _Up>
1640 { return __lhs && *__lhs > __rhs; }
1642 template<typename _Tp, typename _Up>
1643 _REQUIRES_NOT_OPTIONAL(_Tp)
1645 operator> [[nodiscard]] (const _Tp& __lhs, const optional<_Up>& __rhs)
1646 -> __optional_gt_t<_Tp, _Up>
1647 { return !__rhs || __lhs > *__rhs; }
1649 template<typename _Tp, typename _Up>
1650 _REQUIRES_NOT_OPTIONAL(_Up)
1652 operator<= [[nodiscard]] (const optional<_Tp>& __lhs, const _Up& __rhs)
1653 -> __optional_le_t<_Tp, _Up>
1654 { return !__lhs || *__lhs <= __rhs; }
1656 template<typename _Tp, typename _Up>
1657 _REQUIRES_NOT_OPTIONAL(_Tp)
1659 operator<= [[nodiscard]] (const _Tp& __lhs, const optional<_Up>& __rhs)
1660 -> __optional_le_t<_Tp, _Up>
1661 { return __rhs && __lhs <= *__rhs; }
1663 template<typename _Tp, typename _Up>
1664 _REQUIRES_NOT_OPTIONAL(_Up)
1666 operator>= [[nodiscard]] (const optional<_Tp>& __lhs, const _Up& __rhs)
1667 -> __optional_ge_t<_Tp, _Up>
1668 { return __lhs && *__lhs >= __rhs; }
1670 template<typename _Tp, typename _Up>
1671 _REQUIRES_NOT_OPTIONAL(_Tp)
1673 operator>= [[nodiscard]] (const _Tp& __lhs, const optional<_Up>& __rhs)
1674 -> __optional_ge_t<_Tp, _Up>
1675 { return !__rhs || __lhs >= *__rhs; }
1677 #ifdef __cpp_lib_three_way_comparison
1678 // _GLIBCXX_RESOLVE_LIB_DEFECTS
1679 // 3746. optional's spaceship with U with a type derived from optional
1680 // causes infinite constraint meta-recursion
1681 template<typename _Tp>
1682 concept __is_derived_from_optional = requires (const _Tp& __t) {
1683 []<typename _Up>(const optional<_Up>&){ }(__t);
1686 template<typename _Tp, typename _Up>
1687 requires (!__is_derived_from_optional<_Up>)
1688 && requires { typename compare_three_way_result_t<_Tp, _Up>; }
1689 && three_way_comparable_with<_Tp, _Up>
1690 constexpr compare_three_way_result_t<_Tp, _Up>
1691 operator<=> [[nodiscard]] (const optional<_Tp>& __x, const _Up& __v)
1692 { return bool(__x) ? *__x <=> __v : strong_ordering::less; }
1695 // Swap and creation functions.
1697 // _GLIBCXX_RESOLVE_LIB_DEFECTS
1698 // 2748. swappable traits for optionals
1699 template<typename _Tp>
1700 _GLIBCXX20_CONSTEXPR
1701 inline enable_if_t<is_move_constructible_v<_Tp> && is_swappable_v<_Tp>>
1702 swap(optional<_Tp>& __lhs, optional<_Tp>& __rhs)
1703 noexcept(noexcept(__lhs.swap(__rhs)))
1704 { __lhs.swap(__rhs); }
1706 template<typename _Tp>
1707 enable_if_t<!(is_move_constructible_v<_Tp> && is_swappable_v<_Tp>)>
1708 swap(optional<_Tp>&, optional<_Tp>&) = delete;
1710 template<typename _Tp>
1712 enable_if_t<is_constructible_v<decay_t<_Tp>, _Tp>,
1713 optional<decay_t<_Tp>>>
1714 make_optional(_Tp&& __t)
1715 noexcept(is_nothrow_constructible_v<optional<decay_t<_Tp>>, _Tp>)
1716 { return optional<decay_t<_Tp>>{ std::forward<_Tp>(__t) }; }
1718 template<typename _Tp, typename... _Args>
1720 enable_if_t<is_constructible_v<_Tp, _Args...>,
1722 make_optional(_Args&&... __args)
1723 noexcept(is_nothrow_constructible_v<_Tp, _Args...>)
1724 { return optional<_Tp>{ in_place, std::forward<_Args>(__args)... }; }
1726 template<typename _Tp, typename _Up, typename... _Args>
1728 enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>,
1730 make_optional(initializer_list<_Up> __il, _Args&&... __args)
1731 noexcept(is_nothrow_constructible_v<_Tp, initializer_list<_Up>&, _Args...>)
1732 { return optional<_Tp>{ in_place, __il, std::forward<_Args>(__args)... }; }
1736 template<typename _Tp, typename _Up = remove_const_t<_Tp>>
1737 struct __optional_hash
1738 #if ! _GLIBCXX_INLINE_VERSION
1739 : public __hash_empty_base<_Up>
1742 #if __cplusplus < 202002L
1743 using result_type [[__deprecated__]] = size_t;
1744 using argument_type [[__deprecated__]] = optional<_Tp>;
1748 operator()(const optional<_Tp>& __t) const
1749 noexcept(noexcept(hash<_Up>{}(*__t)))
1751 // We pick an arbitrary hash for disengaged optionals which hopefully
1752 // usual values of _Tp won't typically hash to.
1753 constexpr size_t __magic_disengaged_hash = static_cast<size_t>(-3333);
1754 return __t ? hash<_Up>{}(*__t) : __magic_disengaged_hash;
1758 template<typename _Tp>
1759 struct hash<optional<_Tp>>
1760 : public __conditional_t<__is_hash_enabled_for<remove_const_t<_Tp>>,
1761 __optional_hash<_Tp>,
1762 __hash_not_enabled<_Tp>>
1765 template<typename _Tp>
1766 struct __is_fast_hash<hash<optional<_Tp>>> : __is_fast_hash<hash<_Tp>>
1771 #if __cpp_deduction_guides >= 201606
1772 template <typename _Tp> optional(_Tp) -> optional<_Tp>;
1775 #undef _GLIBCXX_USE_CONSTRAINTS_FOR_OPTIONAL
1777 _GLIBCXX_END_NAMESPACE_VERSION
1780 #endif // __cpp_lib_optional
1782 #endif // _GLIBCXX_OPTIONAL