1 // <optional> -*- C++ -*-
3 // Copyright (C) 2013-2021 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 #pragma GCC system_header
35 #if __cplusplus >= 201703L
37 #include <type_traits>
40 #include <initializer_list>
41 #include <bits/enable_special_members.h>
42 #include <bits/exception_defines.h>
43 #include <bits/functional_hash.h>
44 #include <bits/stl_construct.h> // _Construct
45 #include <bits/utility.h> // in_place_t
46 #if __cplusplus > 201703L
48 # include <bits/invoke.h> // std::__invoke
50 #if __cplusplus > 202002L
54 namespace std _GLIBCXX_VISIBILITY(default)
56 _GLIBCXX_BEGIN_NAMESPACE_VERSION
59 * @addtogroup utilities
63 #if __cplusplus == 201703L
64 # define __cpp_lib_optional 201606L
66 # define __cpp_lib_optional 202106L
69 template<typename _Tp>
72 /// Tag type to disengage optional objects.
75 // Do not user-declare default constructor at all for
76 // optional_value = {} syntax to work.
77 // nullopt_t() = delete;
79 // Used for constructing nullopt.
80 enum class _Construct { _Token };
82 // Must be constexpr for nullopt_t to be literal.
83 explicit constexpr nullopt_t(_Construct) noexcept { }
86 /// Tag to disengage optional objects.
87 inline constexpr nullopt_t nullopt { nullopt_t::_Construct::_Token };
89 template<typename _Fn> struct _Optional_func { _Fn& _M_f; };
92 * @brief Exception class thrown when a disengaged optional object is
96 class bad_optional_access : public exception
99 bad_optional_access() = default;
100 virtual ~bad_optional_access() = default;
102 const char* what() const noexcept override
103 { return "bad optional access"; }
106 // XXX Does not belong here.
107 [[__noreturn__]] inline void
108 __throw_bad_optional_access()
109 { _GLIBCXX_THROW_OR_ABORT(bad_optional_access()); }
111 // This class template manages construction/destruction of
112 // the contained value for a std::optional.
113 template <typename _Tp>
114 struct _Optional_payload_base
116 using _Stored_type = remove_const_t<_Tp>;
118 _Optional_payload_base() = default;
119 ~_Optional_payload_base() = default;
121 template<typename... _Args>
123 _Optional_payload_base(in_place_t __tag, _Args&&... __args)
124 : _M_payload(__tag, std::forward<_Args>(__args)...),
128 template<typename _Up, typename... _Args>
130 _Optional_payload_base(std::initializer_list<_Up> __il,
132 : _M_payload(__il, std::forward<_Args>(__args)...),
136 // Constructor used by _Optional_base copy constructor when the
137 // contained value is not trivially copy constructible.
139 _Optional_payload_base(bool __engaged,
140 const _Optional_payload_base& __other)
142 if (__other._M_engaged)
143 this->_M_construct(__other._M_get());
146 // Constructor used by _Optional_base move constructor when the
147 // contained value is not trivially move constructible.
149 _Optional_payload_base(bool __engaged,
150 _Optional_payload_base&& __other)
152 if (__other._M_engaged)
153 this->_M_construct(std::move(__other._M_get()));
156 // Copy constructor is only used to when the contained value is
157 // trivially copy constructible.
158 _Optional_payload_base(const _Optional_payload_base&) = default;
160 // Move constructor is only used to when the contained value is
161 // trivially copy constructible.
162 _Optional_payload_base(_Optional_payload_base&&) = default;
164 _Optional_payload_base&
165 operator=(const _Optional_payload_base&) = default;
167 _Optional_payload_base&
168 operator=(_Optional_payload_base&&) = default;
170 // used to perform non-trivial copy assignment.
172 _M_copy_assign(const _Optional_payload_base& __other)
174 if (this->_M_engaged && __other._M_engaged)
175 this->_M_get() = __other._M_get();
178 if (__other._M_engaged)
179 this->_M_construct(__other._M_get());
185 // used to perform non-trivial move assignment.
187 _M_move_assign(_Optional_payload_base&& __other)
188 noexcept(__and_v<is_nothrow_move_constructible<_Tp>,
189 is_nothrow_move_assignable<_Tp>>)
191 if (this->_M_engaged && __other._M_engaged)
192 this->_M_get() = std::move(__other._M_get());
195 if (__other._M_engaged)
196 this->_M_construct(std::move(__other._M_get()));
202 struct _Empty_byte { };
204 template<typename _Up, bool = is_trivially_destructible_v<_Up>>
207 constexpr _Storage() noexcept : _M_empty() { }
209 template<typename... _Args>
211 _Storage(in_place_t, _Args&&... __args)
212 : _M_value(std::forward<_Args>(__args)...)
215 template<typename _Vp, typename... _Args>
217 _Storage(std::initializer_list<_Vp> __il, _Args&&... __args)
218 : _M_value(__il, std::forward<_Args>(__args)...)
221 #if __cplusplus >= 202002L
222 template<typename _Fn, typename _Arg>
224 _Storage(_Optional_func<_Fn> __f, _Arg&& __arg)
225 : _M_value(std::__invoke(std::forward<_Fn>(__f._M_f),
226 std::forward<_Arg>(__arg)))
230 _Empty_byte _M_empty;
234 template<typename _Up>
235 union _Storage<_Up, false>
237 constexpr _Storage() noexcept : _M_empty() { }
239 template<typename... _Args>
241 _Storage(in_place_t, _Args&&... __args)
242 : _M_value(std::forward<_Args>(__args)...)
245 template<typename _Vp, typename... _Args>
247 _Storage(std::initializer_list<_Vp> __il, _Args&&... __args)
248 : _M_value(__il, std::forward<_Args>(__args)...)
251 #if __cplusplus >= 202002L
252 template<typename _Fn, typename _Arg>
254 _Storage(_Optional_func<_Fn> __f, _Arg&& __arg)
255 : _M_value(std::__invoke(std::forward<_Fn>(__f._M_f),
256 std::forward<_Arg>(__arg)))
260 // User-provided destructor is needed when _Up has non-trivial dtor.
261 _GLIBCXX20_CONSTEXPR ~_Storage() { }
263 _Empty_byte _M_empty;
267 _Storage<_Stored_type> _M_payload;
269 bool _M_engaged = false;
271 template<typename... _Args>
273 _M_construct(_Args&&... __args)
274 noexcept(is_nothrow_constructible_v<_Stored_type, _Args...>)
276 std::_Construct(std::__addressof(this->_M_payload._M_value),
277 std::forward<_Args>(__args)...);
278 this->_M_engaged = true;
282 _M_destroy() noexcept
285 _M_payload._M_value.~_Stored_type();
288 #if __cplusplus >= 202002L
289 template<typename _Fn, typename _Up>
291 _M_apply(_Optional_func<_Fn> __f, _Up&& __x)
293 std::construct_at(std::__addressof(this->_M_payload),
294 __f, std::forward<_Up>(__x));
299 // The _M_get() operations have _M_engaged as a precondition.
300 // They exist to access the contained value with the appropriate
301 // const-qualification, because _M_payload has had the const removed.
305 { return this->_M_payload._M_value; }
308 _M_get() const noexcept
309 { return this->_M_payload._M_value; }
311 // _M_reset is a 'safe' operation with no precondition.
315 if (this->_M_engaged)
320 // Class template that manages the payload for optionals.
321 template <typename _Tp,
322 bool /*_HasTrivialDestructor*/ =
323 is_trivially_destructible_v<_Tp>,
324 bool /*_HasTrivialCopy */ =
325 is_trivially_copy_assignable_v<_Tp>
326 && is_trivially_copy_constructible_v<_Tp>,
327 bool /*_HasTrivialMove */ =
328 is_trivially_move_assignable_v<_Tp>
329 && is_trivially_move_constructible_v<_Tp>>
330 struct _Optional_payload;
332 // Payload for potentially-constexpr optionals (trivial copy/move/destroy).
333 template <typename _Tp>
334 struct _Optional_payload<_Tp, true, true, true>
335 : _Optional_payload_base<_Tp>
337 using _Optional_payload_base<_Tp>::_Optional_payload_base;
339 _Optional_payload() = default;
342 // Payload for optionals with non-trivial copy construction/assignment.
343 template <typename _Tp>
344 struct _Optional_payload<_Tp, true, false, true>
345 : _Optional_payload_base<_Tp>
347 using _Optional_payload_base<_Tp>::_Optional_payload_base;
349 _Optional_payload() = default;
350 ~_Optional_payload() = default;
351 _Optional_payload(const _Optional_payload&) = default;
352 _Optional_payload(_Optional_payload&&) = default;
353 _Optional_payload& operator=(_Optional_payload&&) = default;
355 // Non-trivial copy assignment.
358 operator=(const _Optional_payload& __other)
360 this->_M_copy_assign(__other);
365 // Payload for optionals with non-trivial move construction/assignment.
366 template <typename _Tp>
367 struct _Optional_payload<_Tp, true, true, false>
368 : _Optional_payload_base<_Tp>
370 using _Optional_payload_base<_Tp>::_Optional_payload_base;
372 _Optional_payload() = default;
373 ~_Optional_payload() = default;
374 _Optional_payload(const _Optional_payload&) = default;
375 _Optional_payload(_Optional_payload&&) = default;
376 _Optional_payload& operator=(const _Optional_payload&) = default;
378 // Non-trivial move assignment.
381 operator=(_Optional_payload&& __other)
382 noexcept(__and_v<is_nothrow_move_constructible<_Tp>,
383 is_nothrow_move_assignable<_Tp>>)
385 this->_M_move_assign(std::move(__other));
390 // Payload for optionals with non-trivial copy and move assignment.
391 template <typename _Tp>
392 struct _Optional_payload<_Tp, true, false, false>
393 : _Optional_payload_base<_Tp>
395 using _Optional_payload_base<_Tp>::_Optional_payload_base;
397 _Optional_payload() = default;
398 ~_Optional_payload() = default;
399 _Optional_payload(const _Optional_payload&) = default;
400 _Optional_payload(_Optional_payload&&) = default;
402 // Non-trivial copy assignment.
405 operator=(const _Optional_payload& __other)
407 this->_M_copy_assign(__other);
411 // Non-trivial move assignment.
414 operator=(_Optional_payload&& __other)
415 noexcept(__and_v<is_nothrow_move_constructible<_Tp>,
416 is_nothrow_move_assignable<_Tp>>)
418 this->_M_move_assign(std::move(__other));
423 // Payload for optionals with non-trivial destructors.
424 template <typename _Tp, bool _Copy, bool _Move>
425 struct _Optional_payload<_Tp, false, _Copy, _Move>
426 : _Optional_payload<_Tp, true, false, false>
428 // Base class implements all the constructors and assignment operators:
429 using _Optional_payload<_Tp, true, false, false>::_Optional_payload;
430 _Optional_payload() = default;
431 _Optional_payload(const _Optional_payload&) = default;
432 _Optional_payload(_Optional_payload&&) = default;
433 _Optional_payload& operator=(const _Optional_payload&) = default;
434 _Optional_payload& operator=(_Optional_payload&&) = default;
436 // Destructor needs to destroy the contained value:
437 _GLIBCXX20_CONSTEXPR ~_Optional_payload() { this->_M_reset(); }
440 // Common base class for _Optional_base<T> to avoid repeating these
441 // member functions in each specialization.
442 template<typename _Tp, typename _Dp>
443 class _Optional_base_impl
446 using _Stored_type = remove_const_t<_Tp>;
448 // The _M_construct operation has !_M_engaged as a precondition
449 // while _M_destruct has _M_engaged as a precondition.
450 template<typename... _Args>
452 _M_construct(_Args&&... __args)
453 noexcept(is_nothrow_constructible_v<_Stored_type, _Args...>)
455 static_cast<_Dp*>(this)->_M_payload._M_construct(
456 std::forward<_Args>(__args)...);
460 _M_destruct() noexcept
461 { static_cast<_Dp*>(this)->_M_payload._M_destroy(); }
463 // _M_reset is a 'safe' operation with no precondition.
466 { static_cast<_Dp*>(this)->_M_payload._M_reset(); }
468 constexpr bool _M_is_engaged() const noexcept
469 { return static_cast<const _Dp*>(this)->_M_payload._M_engaged; }
471 // The _M_get operations have _M_engaged as a precondition.
475 __glibcxx_assert(this->_M_is_engaged());
476 return static_cast<_Dp*>(this)->_M_payload._M_get();
480 _M_get() const noexcept
482 __glibcxx_assert(this->_M_is_engaged());
483 return static_cast<const _Dp*>(this)->_M_payload._M_get();
488 * @brief Class template that provides copy/move constructors of optional.
490 * Such a separate base class template is necessary in order to
491 * conditionally make copy/move constructors trivial.
493 * When the contained value is trivially copy/move constructible,
494 * the copy/move constructors of _Optional_base will invoke the
495 * trivial copy/move constructor of _Optional_payload. Otherwise,
496 * they will invoke _Optional_payload(bool, const _Optional_payload&)
497 * or _Optional_payload(bool, _Optional_payload&&) to initialize
498 * the contained value, if copying/moving an engaged optional.
500 * Whether the other special members are trivial is determined by the
501 * _Optional_payload<_Tp> specialization used for the _M_payload member.
503 * @see optional, _Enable_special_members
505 template<typename _Tp,
506 bool = is_trivially_copy_constructible_v<_Tp>,
507 bool = is_trivially_move_constructible_v<_Tp>>
508 struct _Optional_base
509 : _Optional_base_impl<_Tp, _Optional_base<_Tp>>
511 // Constructors for disengaged optionals.
512 constexpr _Optional_base() = default;
514 // Constructors for engaged optionals.
515 template<typename... _Args,
516 enable_if_t<is_constructible_v<_Tp, _Args...>, bool> = false>
518 _Optional_base(in_place_t, _Args&&... __args)
519 : _M_payload(in_place, std::forward<_Args>(__args)...)
522 template<typename _Up, typename... _Args,
523 enable_if_t<is_constructible_v<_Tp,
524 initializer_list<_Up>&,
525 _Args...>, bool> = false>
527 _Optional_base(in_place_t,
528 initializer_list<_Up> __il,
530 : _M_payload(in_place, __il, std::forward<_Args>(__args)...)
533 // Copy and move constructors.
535 _Optional_base(const _Optional_base& __other)
536 : _M_payload(__other._M_payload._M_engaged, __other._M_payload)
540 _Optional_base(_Optional_base&& __other)
541 noexcept(is_nothrow_move_constructible_v<_Tp>)
542 : _M_payload(__other._M_payload._M_engaged,
543 std::move(__other._M_payload))
546 // Assignment operators.
547 _Optional_base& operator=(const _Optional_base&) = default;
548 _Optional_base& operator=(_Optional_base&&) = default;
550 _Optional_payload<_Tp> _M_payload;
553 template<typename _Tp>
554 struct _Optional_base<_Tp, false, true>
555 : _Optional_base_impl<_Tp, _Optional_base<_Tp>>
557 // Constructors for disengaged optionals.
558 constexpr _Optional_base() = default;
560 // Constructors for engaged optionals.
561 template<typename... _Args,
562 enable_if_t<is_constructible_v<_Tp, _Args...>, bool> = false>
564 _Optional_base(in_place_t, _Args&&... __args)
565 : _M_payload(in_place, std::forward<_Args>(__args)...)
568 template<typename _Up, typename... _Args,
569 enable_if_t<is_constructible_v<_Tp,
570 initializer_list<_Up>&,
571 _Args...>, bool> = false>
573 _Optional_base(in_place_t,
574 initializer_list<_Up> __il,
576 : _M_payload(in_place, __il, std::forward<_Args>(__args)...)
579 // Copy and move constructors.
580 constexpr _Optional_base(const _Optional_base& __other)
581 : _M_payload(__other._M_payload._M_engaged, __other._M_payload)
584 constexpr _Optional_base(_Optional_base&& __other) = default;
586 // Assignment operators.
587 _Optional_base& operator=(const _Optional_base&) = default;
588 _Optional_base& operator=(_Optional_base&&) = default;
590 _Optional_payload<_Tp> _M_payload;
593 template<typename _Tp>
594 struct _Optional_base<_Tp, true, false>
595 : _Optional_base_impl<_Tp, _Optional_base<_Tp>>
597 // Constructors for disengaged optionals.
598 constexpr _Optional_base() = default;
600 // Constructors for engaged optionals.
601 template<typename... _Args,
602 enable_if_t<is_constructible_v<_Tp, _Args...>, bool> = false>
604 _Optional_base(in_place_t, _Args&&... __args)
605 : _M_payload(in_place, std::forward<_Args>(__args)...)
608 template<typename _Up, typename... _Args,
609 enable_if_t<is_constructible_v<_Tp,
610 initializer_list<_Up>&,
611 _Args...>, bool> = false>
613 _Optional_base(in_place_t,
614 initializer_list<_Up> __il,
616 : _M_payload(in_place, __il, std::forward<_Args>(__args)...)
619 // Copy and move constructors.
620 constexpr _Optional_base(const _Optional_base& __other) = default;
623 _Optional_base(_Optional_base&& __other)
624 noexcept(is_nothrow_move_constructible_v<_Tp>)
625 : _M_payload(__other._M_payload._M_engaged,
626 std::move(__other._M_payload))
629 // Assignment operators.
630 _Optional_base& operator=(const _Optional_base&) = default;
631 _Optional_base& operator=(_Optional_base&&) = default;
633 _Optional_payload<_Tp> _M_payload;
636 template<typename _Tp>
637 struct _Optional_base<_Tp, true, true>
638 : _Optional_base_impl<_Tp, _Optional_base<_Tp>>
640 // Constructors for disengaged optionals.
641 constexpr _Optional_base() = default;
643 // Constructors for engaged optionals.
644 template<typename... _Args,
645 enable_if_t<is_constructible_v<_Tp, _Args...>, bool> = false>
647 _Optional_base(in_place_t, _Args&&... __args)
648 : _M_payload(in_place, std::forward<_Args>(__args)...)
651 template<typename _Up, typename... _Args,
652 enable_if_t<is_constructible_v<_Tp,
653 initializer_list<_Up>&,
654 _Args...>, bool> = false>
656 _Optional_base(in_place_t,
657 initializer_list<_Up> __il,
659 : _M_payload(in_place, __il, std::forward<_Args>(__args)...)
662 // Copy and move constructors.
663 constexpr _Optional_base(const _Optional_base& __other) = default;
664 constexpr _Optional_base(_Optional_base&& __other) = default;
666 // Assignment operators.
667 _Optional_base& operator=(const _Optional_base&) = default;
668 _Optional_base& operator=(_Optional_base&&) = default;
670 _Optional_payload<_Tp> _M_payload;
673 template<typename _Tp>
676 template<typename _Tp>
677 inline constexpr bool __is_optional_v = false;
678 template<typename _Tp>
679 inline constexpr bool __is_optional_v<optional<_Tp>> = true;
681 template<typename _Tp, typename _Up>
682 using __converts_from_optional =
683 __or_<is_constructible<_Tp, const optional<_Up>&>,
684 is_constructible<_Tp, optional<_Up>&>,
685 is_constructible<_Tp, const optional<_Up>&&>,
686 is_constructible<_Tp, optional<_Up>&&>,
687 is_convertible<const optional<_Up>&, _Tp>,
688 is_convertible<optional<_Up>&, _Tp>,
689 is_convertible<const optional<_Up>&&, _Tp>,
690 is_convertible<optional<_Up>&&, _Tp>>;
692 template<typename _Tp, typename _Up>
693 using __assigns_from_optional =
694 __or_<is_assignable<_Tp&, const optional<_Up>&>,
695 is_assignable<_Tp&, optional<_Up>&>,
696 is_assignable<_Tp&, const optional<_Up>&&>,
697 is_assignable<_Tp&, optional<_Up>&&>>;
700 * @brief Class template for optional values.
702 template<typename _Tp>
704 : private _Optional_base<_Tp>,
705 private _Enable_copy_move<
707 is_copy_constructible_v<_Tp>,
709 __and_v<is_copy_constructible<_Tp>, is_copy_assignable<_Tp>>,
711 is_move_constructible_v<_Tp>,
713 __and_v<is_move_constructible<_Tp>, is_move_assignable<_Tp>>,
717 static_assert(!is_same_v<remove_cv_t<_Tp>, nullopt_t>);
718 static_assert(!is_same_v<remove_cv_t<_Tp>, in_place_t>);
719 static_assert(!is_reference_v<_Tp>);
722 using _Base = _Optional_base<_Tp>;
725 template<typename _Up>
726 using __not_self = __not_<is_same<optional, __remove_cvref_t<_Up>>>;
727 template<typename _Up>
728 using __not_tag = __not_<is_same<in_place_t, __remove_cvref_t<_Up>>>;
729 template<typename... _Cond>
730 using _Requires = enable_if_t<__and_v<_Cond...>, bool>;
733 using value_type = _Tp;
735 constexpr optional() noexcept { }
737 constexpr optional(nullopt_t) noexcept { }
739 // Converting constructors for engaged optionals.
740 template<typename _Up = _Tp,
741 _Requires<__not_self<_Up>, __not_tag<_Up>,
742 is_constructible<_Tp, _Up>,
743 is_convertible<_Up, _Tp>> = true>
746 noexcept(is_nothrow_constructible_v<_Tp, _Up>)
747 : _Base(std::in_place, std::forward<_Up>(__t)) { }
749 template<typename _Up = _Tp,
750 _Requires<__not_self<_Up>, __not_tag<_Up>,
751 is_constructible<_Tp, _Up>,
752 __not_<is_convertible<_Up, _Tp>>> = false>
755 noexcept(is_nothrow_constructible_v<_Tp, _Up>)
756 : _Base(std::in_place, std::forward<_Up>(__t)) { }
758 template<typename _Up,
759 _Requires<__not_<is_same<_Tp, _Up>>,
760 is_constructible<_Tp, const _Up&>,
761 is_convertible<const _Up&, _Tp>,
762 __not_<__converts_from_optional<_Tp, _Up>>> = true>
764 optional(const optional<_Up>& __t)
765 noexcept(is_nothrow_constructible_v<_Tp, const _Up&>)
771 template<typename _Up,
772 _Requires<__not_<is_same<_Tp, _Up>>,
773 is_constructible<_Tp, const _Up&>,
774 __not_<is_convertible<const _Up&, _Tp>>,
775 __not_<__converts_from_optional<_Tp, _Up>>> = false>
777 optional(const optional<_Up>& __t)
778 noexcept(is_nothrow_constructible_v<_Tp, const _Up&>)
784 template<typename _Up,
785 _Requires<__not_<is_same<_Tp, _Up>>,
786 is_constructible<_Tp, _Up>,
787 is_convertible<_Up, _Tp>,
788 __not_<__converts_from_optional<_Tp, _Up>>> = true>
790 optional(optional<_Up>&& __t)
791 noexcept(is_nothrow_constructible_v<_Tp, _Up>)
794 emplace(std::move(*__t));
797 template<typename _Up,
798 _Requires<__not_<is_same<_Tp, _Up>>,
799 is_constructible<_Tp, _Up>,
800 __not_<is_convertible<_Up, _Tp>>,
801 __not_<__converts_from_optional<_Tp, _Up>>> = false>
803 optional(optional<_Up>&& __t)
804 noexcept(is_nothrow_constructible_v<_Tp, _Up>)
807 emplace(std::move(*__t));
810 template<typename... _Args,
811 _Requires<is_constructible<_Tp, _Args...>> = false>
813 optional(in_place_t, _Args&&... __args)
814 noexcept(is_nothrow_constructible_v<_Tp, _Args...>)
815 : _Base(std::in_place, std::forward<_Args>(__args)...) { }
817 template<typename _Up, typename... _Args,
818 _Requires<is_constructible<_Tp,
819 initializer_list<_Up>&,
822 optional(in_place_t, initializer_list<_Up> __il, _Args&&... __args)
823 noexcept(is_nothrow_constructible_v<_Tp, initializer_list<_Up>&,
825 : _Base(std::in_place, __il, std::forward<_Args>(__args)...) { }
828 // Assignment operators.
829 _GLIBCXX20_CONSTEXPR optional&
830 operator=(nullopt_t) noexcept
836 template<typename _Up = _Tp>
838 enable_if_t<__and_v<__not_self<_Up>,
839 __not_<__and_<is_scalar<_Tp>,
840 is_same<_Tp, decay_t<_Up>>>>,
841 is_constructible<_Tp, _Up>,
842 is_assignable<_Tp&, _Up>>,
845 noexcept(__and_v<is_nothrow_constructible<_Tp, _Up>,
846 is_nothrow_assignable<_Tp&, _Up>>)
848 if (this->_M_is_engaged())
849 this->_M_get() = std::forward<_Up>(__u);
851 this->_M_construct(std::forward<_Up>(__u));
856 template<typename _Up>
858 enable_if_t<__and_v<__not_<is_same<_Tp, _Up>>,
859 is_constructible<_Tp, const _Up&>,
860 is_assignable<_Tp&, const _Up&>,
861 __not_<__converts_from_optional<_Tp, _Up>>,
862 __not_<__assigns_from_optional<_Tp, _Up>>>,
864 operator=(const optional<_Up>& __u)
865 noexcept(__and_v<is_nothrow_constructible<_Tp, const _Up&>,
866 is_nothrow_assignable<_Tp&, const _Up&>>)
870 if (this->_M_is_engaged())
871 this->_M_get() = *__u;
873 this->_M_construct(*__u);
882 template<typename _Up>
884 enable_if_t<__and_v<__not_<is_same<_Tp, _Up>>,
885 is_constructible<_Tp, _Up>,
886 is_assignable<_Tp&, _Up>,
887 __not_<__converts_from_optional<_Tp, _Up>>,
888 __not_<__assigns_from_optional<_Tp, _Up>>>,
890 operator=(optional<_Up>&& __u)
891 noexcept(__and_v<is_nothrow_constructible<_Tp, _Up>,
892 is_nothrow_assignable<_Tp&, _Up>>)
896 if (this->_M_is_engaged())
897 this->_M_get() = std::move(*__u);
899 this->_M_construct(std::move(*__u));
909 template<typename... _Args>
911 enable_if_t<is_constructible_v<_Tp, _Args...>, _Tp&>
912 emplace(_Args&&... __args)
913 noexcept(is_nothrow_constructible_v<_Tp, _Args...>)
916 this->_M_construct(std::forward<_Args>(__args)...);
917 return this->_M_get();
920 template<typename _Up, typename... _Args>
922 enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>,
924 emplace(initializer_list<_Up> __il, _Args&&... __args)
925 noexcept(is_nothrow_constructible_v<_Tp, initializer_list<_Up>&,
929 this->_M_construct(__il, std::forward<_Args>(__args)...);
930 return this->_M_get();
933 // Destructor is implicit, implemented in _Optional_base.
936 _GLIBCXX20_CONSTEXPR void
937 swap(optional& __other)
938 noexcept(is_nothrow_move_constructible_v<_Tp>
939 && is_nothrow_swappable_v<_Tp>)
943 if (this->_M_is_engaged() && __other._M_is_engaged())
944 swap(this->_M_get(), __other._M_get());
945 else if (this->_M_is_engaged())
947 __other._M_construct(std::move(this->_M_get()));
950 else if (__other._M_is_engaged())
952 this->_M_construct(std::move(__other._M_get()));
953 __other._M_destruct();
959 operator->() const noexcept
960 { return std::__addressof(this->_M_get()); }
963 operator->() noexcept
964 { return std::__addressof(this->_M_get()); }
967 operator*() const& noexcept
968 { return this->_M_get(); }
971 operator*()& noexcept
972 { return this->_M_get(); }
975 operator*()&& noexcept
976 { return std::move(this->_M_get()); }
978 constexpr const _Tp&&
979 operator*() const&& noexcept
980 { return std::move(this->_M_get()); }
982 constexpr explicit operator bool() const noexcept
983 { return this->_M_is_engaged(); }
985 constexpr bool has_value() const noexcept
986 { return this->_M_is_engaged(); }
991 if (this->_M_is_engaged())
992 return this->_M_get();
993 __throw_bad_optional_access();
999 if (this->_M_is_engaged())
1000 return this->_M_get();
1001 __throw_bad_optional_access();
1007 if (this->_M_is_engaged())
1008 return std::move(this->_M_get());
1009 __throw_bad_optional_access();
1012 constexpr const _Tp&&
1015 if (this->_M_is_engaged())
1016 return std::move(this->_M_get());
1017 __throw_bad_optional_access();
1020 template<typename _Up>
1022 value_or(_Up&& __u) const&
1024 static_assert(is_copy_constructible_v<_Tp>);
1025 static_assert(is_convertible_v<_Up&&, _Tp>);
1027 if (this->_M_is_engaged())
1028 return this->_M_get();
1030 return static_cast<_Tp>(std::forward<_Up>(__u));
1033 template<typename _Up>
1035 value_or(_Up&& __u) &&
1037 static_assert(is_move_constructible_v<_Tp>);
1038 static_assert(is_convertible_v<_Up&&, _Tp>);
1040 if (this->_M_is_engaged())
1041 return std::move(this->_M_get());
1043 return static_cast<_Tp>(std::forward<_Up>(__u));
1046 #if __cplusplus > 202002L && __cpp_lib_concepts
1047 #define __cpp_lib_monadic_optional 202110L
1049 // [optional.monadic]
1051 template<typename _Fn>
1053 and_then(_Fn&& __f) &
1055 using _Up = remove_cvref_t<invoke_result_t<_Fn, _Tp&>>;
1056 static_assert(__is_optional_v<remove_cvref_t<_Up>>);
1058 return std::__invoke(std::forward<_Fn>(__f), **this);
1063 template<typename _Fn>
1065 and_then(_Fn&& __f) const &
1067 using _Up = remove_cvref_t<invoke_result_t<_Fn, const _Tp&>>;
1068 static_assert(__is_optional_v<_Up>);
1070 return std::__invoke(std::forward<_Fn>(__f), **this);
1075 template<typename _Fn>
1077 and_then(_Fn&& __f) &&
1079 using _Up = remove_cvref_t<invoke_result_t<_Fn, _Tp>>;
1080 static_assert(__is_optional_v<remove_cvref_t<_Up>>);
1082 return std::__invoke(std::forward<_Fn>(__f), std::move(**this));
1087 template<typename _Fn>
1089 and_then(_Fn&& __f) const &&
1091 using _Up = remove_cvref_t<invoke_result_t<_Fn, const _Tp>>;
1092 static_assert(__is_optional_v<remove_cvref_t<_Up>>);
1094 return std::__invoke(std::forward<_Fn>(__f), std::move(**this));
1099 template<typename _Fn>
1101 transform(_Fn&& __f) &
1103 using _Up = invoke_result_t<_Fn, _Tp&>;
1105 return optional<_Up>(_Optional_func<_Fn>{__f}, **this);
1107 return optional<_Up>();
1110 template<typename _Fn>
1112 transform(_Fn&& __f) const &
1114 using _Up = invoke_result_t<_Fn, const _Tp&>;
1116 return optional<_Up>(_Optional_func<_Fn>{__f}, **this);
1118 return optional<_Up>();
1121 template<typename _Fn>
1123 transform(_Fn&& __f) &&
1125 using _Up = invoke_result_t<_Fn, _Tp>;
1127 return optional<_Up>(_Optional_func<_Fn>{__f}, std::move(**this));
1129 return optional<_Up>();
1132 template<typename _Fn>
1134 transform(_Fn&& __f) const &&
1136 using _Up = invoke_result_t<_Fn, const _Tp>;
1138 return optional<_Up>(_Optional_func<_Fn>{__f}, std::move(**this));
1140 return optional<_Up>();
1143 template<typename _Fn> requires invocable<_Fn> && copy_constructible<_Tp>
1145 or_else(_Fn&& __f) const&
1147 using _Up = invoke_result_t<_Fn>;
1148 static_assert( is_same_v<remove_cvref_t<_Up>, optional> );
1153 return std::forward<_Fn>(__f)();
1156 template<typename _Fn> requires invocable<_Fn> && move_constructible<_Tp>
1158 or_else(_Fn&& __f) &&
1160 using _Up = invoke_result_t<_Fn>;
1161 static_assert( is_same_v<remove_cvref_t<_Up>, optional> );
1164 return std::move(*this);
1166 return std::forward<_Fn>(__f)();
1170 _GLIBCXX20_CONSTEXPR void reset() noexcept { this->_M_reset(); }
1173 #if __cplusplus >= 202002L
1174 template<typename _Up> friend class optional;
1176 template<typename _Fn, typename _Value>
1178 optional(_Optional_func<_Fn> __f, _Value&& __v)
1180 this->_M_payload._M_apply(__f, std::forward<_Value>(__v));
1185 template<typename _Tp>
1186 using __optional_relop_t =
1187 enable_if_t<is_convertible<_Tp, bool>::value, bool>;
1189 template<typename _Tp, typename _Up>
1190 using __optional_eq_t = __optional_relop_t<
1191 decltype(std::declval<const _Tp&>() == std::declval<const _Up&>())
1194 template<typename _Tp, typename _Up>
1195 using __optional_ne_t = __optional_relop_t<
1196 decltype(std::declval<const _Tp&>() != std::declval<const _Up&>())
1199 template<typename _Tp, typename _Up>
1200 using __optional_lt_t = __optional_relop_t<
1201 decltype(std::declval<const _Tp&>() < std::declval<const _Up&>())
1204 template<typename _Tp, typename _Up>
1205 using __optional_gt_t = __optional_relop_t<
1206 decltype(std::declval<const _Tp&>() > std::declval<const _Up&>())
1209 template<typename _Tp, typename _Up>
1210 using __optional_le_t = __optional_relop_t<
1211 decltype(std::declval<const _Tp&>() <= std::declval<const _Up&>())
1214 template<typename _Tp, typename _Up>
1215 using __optional_ge_t = __optional_relop_t<
1216 decltype(std::declval<const _Tp&>() >= std::declval<const _Up&>())
1219 // Comparisons between optional values.
1220 template<typename _Tp, typename _Up>
1222 operator==(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
1223 -> __optional_eq_t<_Tp, _Up>
1225 return static_cast<bool>(__lhs) == static_cast<bool>(__rhs)
1226 && (!__lhs || *__lhs == *__rhs);
1229 template<typename _Tp, typename _Up>
1231 operator!=(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
1232 -> __optional_ne_t<_Tp, _Up>
1234 return static_cast<bool>(__lhs) != static_cast<bool>(__rhs)
1235 || (static_cast<bool>(__lhs) && *__lhs != *__rhs);
1238 template<typename _Tp, typename _Up>
1240 operator<(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
1241 -> __optional_lt_t<_Tp, _Up>
1243 return static_cast<bool>(__rhs) && (!__lhs || *__lhs < *__rhs);
1246 template<typename _Tp, typename _Up>
1248 operator>(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
1249 -> __optional_gt_t<_Tp, _Up>
1251 return static_cast<bool>(__lhs) && (!__rhs || *__lhs > *__rhs);
1254 template<typename _Tp, typename _Up>
1256 operator<=(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
1257 -> __optional_le_t<_Tp, _Up>
1259 return !__lhs || (static_cast<bool>(__rhs) && *__lhs <= *__rhs);
1262 template<typename _Tp, typename _Up>
1264 operator>=(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
1265 -> __optional_ge_t<_Tp, _Up>
1267 return !__rhs || (static_cast<bool>(__lhs) && *__lhs >= *__rhs);
1270 #ifdef __cpp_lib_three_way_comparison
1271 template<typename _Tp, three_way_comparable_with<_Tp> _Up>
1272 constexpr compare_three_way_result_t<_Tp, _Up>
1273 operator<=>(const optional<_Tp>& __x, const optional<_Up>& __y)
1275 return __x && __y ? *__x <=> *__y : bool(__x) <=> bool(__y);
1279 // Comparisons with nullopt.
1280 template<typename _Tp>
1282 operator==(const optional<_Tp>& __lhs, nullopt_t) noexcept
1285 #ifdef __cpp_lib_three_way_comparison
1286 template<typename _Tp>
1287 constexpr strong_ordering
1288 operator<=>(const optional<_Tp>& __x, nullopt_t) noexcept
1289 { return bool(__x) <=> false; }
1291 template<typename _Tp>
1293 operator==(nullopt_t, const optional<_Tp>& __rhs) noexcept
1296 template<typename _Tp>
1298 operator!=(const optional<_Tp>& __lhs, nullopt_t) noexcept
1299 { return static_cast<bool>(__lhs); }
1301 template<typename _Tp>
1303 operator!=(nullopt_t, const optional<_Tp>& __rhs) noexcept
1304 { return static_cast<bool>(__rhs); }
1306 template<typename _Tp>
1308 operator<(const optional<_Tp>& /* __lhs */, nullopt_t) noexcept
1311 template<typename _Tp>
1313 operator<(nullopt_t, const optional<_Tp>& __rhs) noexcept
1314 { return static_cast<bool>(__rhs); }
1316 template<typename _Tp>
1318 operator>(const optional<_Tp>& __lhs, nullopt_t) noexcept
1319 { return static_cast<bool>(__lhs); }
1321 template<typename _Tp>
1323 operator>(nullopt_t, const optional<_Tp>& /* __rhs */) noexcept
1326 template<typename _Tp>
1328 operator<=(const optional<_Tp>& __lhs, nullopt_t) noexcept
1331 template<typename _Tp>
1333 operator<=(nullopt_t, const optional<_Tp>& /* __rhs */) noexcept
1336 template<typename _Tp>
1338 operator>=(const optional<_Tp>& /* __lhs */, nullopt_t) noexcept
1341 template<typename _Tp>
1343 operator>=(nullopt_t, const optional<_Tp>& __rhs) noexcept
1345 #endif // three-way-comparison
1347 // Comparisons with value type.
1348 template<typename _Tp, typename _Up>
1350 operator==(const optional<_Tp>& __lhs, const _Up& __rhs)
1351 -> __optional_eq_t<_Tp, _Up>
1352 { return __lhs && *__lhs == __rhs; }
1354 template<typename _Tp, typename _Up>
1356 operator==(const _Up& __lhs, const optional<_Tp>& __rhs)
1357 -> __optional_eq_t<_Up, _Tp>
1358 { return __rhs && __lhs == *__rhs; }
1360 template<typename _Tp, typename _Up>
1362 operator!=(const optional<_Tp>& __lhs, const _Up& __rhs)
1363 -> __optional_ne_t<_Tp, _Up>
1364 { return !__lhs || *__lhs != __rhs; }
1366 template<typename _Tp, typename _Up>
1368 operator!=(const _Up& __lhs, const optional<_Tp>& __rhs)
1369 -> __optional_ne_t<_Up, _Tp>
1370 { return !__rhs || __lhs != *__rhs; }
1372 template<typename _Tp, typename _Up>
1374 operator<(const optional<_Tp>& __lhs, const _Up& __rhs)
1375 -> __optional_lt_t<_Tp, _Up>
1376 { return !__lhs || *__lhs < __rhs; }
1378 template<typename _Tp, typename _Up>
1380 operator<(const _Up& __lhs, const optional<_Tp>& __rhs)
1381 -> __optional_lt_t<_Up, _Tp>
1382 { return __rhs && __lhs < *__rhs; }
1384 template<typename _Tp, typename _Up>
1386 operator>(const optional<_Tp>& __lhs, const _Up& __rhs)
1387 -> __optional_gt_t<_Tp, _Up>
1388 { return __lhs && *__lhs > __rhs; }
1390 template<typename _Tp, typename _Up>
1392 operator>(const _Up& __lhs, const optional<_Tp>& __rhs)
1393 -> __optional_gt_t<_Up, _Tp>
1394 { return !__rhs || __lhs > *__rhs; }
1396 template<typename _Tp, typename _Up>
1398 operator<=(const optional<_Tp>& __lhs, const _Up& __rhs)
1399 -> __optional_le_t<_Tp, _Up>
1400 { return !__lhs || *__lhs <= __rhs; }
1402 template<typename _Tp, typename _Up>
1404 operator<=(const _Up& __lhs, const optional<_Tp>& __rhs)
1405 -> __optional_le_t<_Up, _Tp>
1406 { return __rhs && __lhs <= *__rhs; }
1408 template<typename _Tp, typename _Up>
1410 operator>=(const optional<_Tp>& __lhs, const _Up& __rhs)
1411 -> __optional_ge_t<_Tp, _Up>
1412 { return __lhs && *__lhs >= __rhs; }
1414 template<typename _Tp, typename _Up>
1416 operator>=(const _Up& __lhs, const optional<_Tp>& __rhs)
1417 -> __optional_ge_t<_Up, _Tp>
1418 { return !__rhs || __lhs >= *__rhs; }
1420 #ifdef __cpp_lib_three_way_comparison
1421 template<typename _Tp, typename _Up>
1422 requires (!__is_optional_v<_Up>)
1423 && three_way_comparable_with<_Tp, _Up>
1424 constexpr compare_three_way_result_t<_Tp, _Up>
1425 operator<=>(const optional<_Tp>& __x, const _Up& __v)
1426 { return bool(__x) ? *__x <=> __v : strong_ordering::less; }
1429 // Swap and creation functions.
1431 // _GLIBCXX_RESOLVE_LIB_DEFECTS
1432 // 2748. swappable traits for optionals
1433 template<typename _Tp>
1434 _GLIBCXX20_CONSTEXPR
1435 inline enable_if_t<is_move_constructible_v<_Tp> && is_swappable_v<_Tp>>
1436 swap(optional<_Tp>& __lhs, optional<_Tp>& __rhs)
1437 noexcept(noexcept(__lhs.swap(__rhs)))
1438 { __lhs.swap(__rhs); }
1440 template<typename _Tp>
1441 enable_if_t<!(is_move_constructible_v<_Tp> && is_swappable_v<_Tp>)>
1442 swap(optional<_Tp>&, optional<_Tp>&) = delete;
1444 template<typename _Tp>
1446 enable_if_t<is_constructible_v<decay_t<_Tp>, _Tp>,
1447 optional<decay_t<_Tp>>>
1448 make_optional(_Tp&& __t)
1449 noexcept(is_nothrow_constructible_v<optional<decay_t<_Tp>>, _Tp>)
1450 { return optional<decay_t<_Tp>>{ std::forward<_Tp>(__t) }; }
1452 template<typename _Tp, typename... _Args>
1454 enable_if_t<is_constructible_v<_Tp, _Args...>,
1456 make_optional(_Args&&... __args)
1457 noexcept(is_nothrow_constructible_v<_Tp, _Args...>)
1458 { return optional<_Tp>{ in_place, std::forward<_Args>(__args)... }; }
1460 template<typename _Tp, typename _Up, typename... _Args>
1462 enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>,
1464 make_optional(initializer_list<_Up> __il, _Args&&... __args)
1465 noexcept(is_nothrow_constructible_v<_Tp, initializer_list<_Up>&, _Args...>)
1466 { return optional<_Tp>{ in_place, __il, std::forward<_Args>(__args)... }; }
1470 template<typename _Tp, typename _Up = remove_const_t<_Tp>,
1471 bool = __poison_hash<_Up>::__enable_hash_call>
1472 struct __optional_hash_call_base
1475 operator()(const optional<_Tp>& __t) const
1476 noexcept(noexcept(hash<_Up>{}(*__t)))
1478 // We pick an arbitrary hash for disengaged optionals which hopefully
1479 // usual values of _Tp won't typically hash to.
1480 constexpr size_t __magic_disengaged_hash = static_cast<size_t>(-3333);
1481 return __t ? hash<_Up>{}(*__t) : __magic_disengaged_hash;
1485 template<typename _Tp, typename _Up>
1486 struct __optional_hash_call_base<_Tp, _Up, false> {};
1488 template<typename _Tp>
1489 struct hash<optional<_Tp>>
1490 : private __poison_hash<remove_const_t<_Tp>>,
1491 public __optional_hash_call_base<_Tp>
1493 using result_type [[__deprecated__]] = size_t;
1494 using argument_type [[__deprecated__]] = optional<_Tp>;
1497 template<typename _Tp>
1498 struct __is_fast_hash<hash<optional<_Tp>>> : __is_fast_hash<hash<_Tp>>
1503 #if __cpp_deduction_guides >= 201606
1504 template <typename _Tp> optional(_Tp) -> optional<_Tp>;
1507 _GLIBCXX_END_NAMESPACE_VERSION
1512 #endif // _GLIBCXX_OPTIONAL