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optional
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1// <optional> -*- C++ -*-
2
3// Copyright (C) 2013-2026 Free Software Foundation, Inc.
4// Copyright The GNU Toolchain Authors.
5//
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)
10// any later version.
11
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.
16
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.
20
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/>.
25
26/** @file include/optional
27 * This is a Standard C++ Library header.
28 */
29
30#ifndef _GLIBCXX_OPTIONAL
31#define _GLIBCXX_OPTIONAL 1
32
33#ifdef _GLIBCXX_SYSHDR
34#pragma GCC system_header
35#endif
36
37#define __glibcxx_want_freestanding_optional
38#define __glibcxx_want_optional
39#define __glibcxx_want_optional_range_support
40#define __glibcxx_want_constrained_equality
41#define __glibcxx_want_constexpr_exceptions
42#include <bits/version.h>
43
44#ifdef __cpp_lib_optional // C++ >= 17
45
46#include <type_traits>
47#include <exception>
48#include <new>
49#include <initializer_list>
50#include <bits/enable_special_members.h>
51#include <bits/exception_defines.h>
52#include <bits/functional_hash.h>
53#include <bits/stl_construct.h> // _Construct
54#include <bits/utility.h> // in_place_t
55#if __cplusplus > 201703L
56# include <compare>
57# include <bits/invoke.h> // std::__invoke
58#endif
59#if __cplusplus > 202002L
60# include <concepts>
61#endif
62#ifdef __cpp_lib_optional_range_support // C++ >= 26
63# if _GLIBCXX_HOSTED
64# include <bits/formatfwd.h>
65# endif
66# include <bits/ranges_base.h>
67# include <bits/range_access.h>
68#endif
69
70namespace std _GLIBCXX_VISIBILITY(default)
71{
72_GLIBCXX_BEGIN_NAMESPACE_VERSION
73
74 /**
75 * @addtogroup utilities
76 * @{
77 */
78
79 template<typename _Tp>
80 class optional;
81
82 /// Tag type to disengage optional objects.
83 struct nullopt_t
84 {
85 // Do not user-declare default constructor at all for
86 // optional_value = {} syntax to work.
87 // nullopt_t() = delete;
88
89 // Used for constructing nullopt.
90 enum class _Construct { _Token };
91
92 // Must be constexpr for nullopt_t to be literal.
93 explicit constexpr nullopt_t(_Construct) noexcept { }
94 };
95
96 /// Tag to disengage optional objects.
97 inline constexpr nullopt_t nullopt { nullopt_t::_Construct::_Token };
98
99 template<typename _Fn> struct _Optional_func { _Fn& _M_f; };
100
101 /**
102 * @brief Exception class thrown when a disengaged optional object is
103 * dereferenced.
104 * @ingroup exceptions
105 */
106 class bad_optional_access : public exception
107 {
108 public:
109 bad_optional_access() = default;
110 virtual ~bad_optional_access() = default;
111
112#if __cpp_lib_constexpr_exceptions >= 202502L
113 constexpr
114#endif
115 const char* what() const noexcept override
116 { return "bad optional access"; }
117 };
118
119 // XXX Does not belong here.
120 [[__noreturn__]]
121#if __cpp_lib_constexpr_exceptions >= 202502L
122 constexpr
123#else
124 inline
125#endif
126 void
127 __throw_bad_optional_access()
128 { _GLIBCXX_THROW_OR_ABORT(bad_optional_access()); }
129
130 // This class template manages construction/destruction of
131 // the contained value for a std::optional.
132 template <typename _Tp>
133 struct _Optional_payload_base
134 {
135 using _Stored_type = remove_const_t<_Tp>;
136
137 _Optional_payload_base() = default;
138 ~_Optional_payload_base() = default;
139
140 template<typename... _Args>
141 constexpr
142 _Optional_payload_base(in_place_t __tag, _Args&&... __args)
143 : _M_payload(__tag, std::forward<_Args>(__args)...),
144 _M_engaged(true)
145 { }
146
147 template<typename _Up, typename... _Args>
148 constexpr
149 _Optional_payload_base(std::initializer_list<_Up> __il,
150 _Args&&... __args)
151 : _M_payload(__il, std::forward<_Args>(__args)...),
152 _M_engaged(true)
153 { }
154
155 // Constructor used by _Optional_base copy constructor when the
156 // contained value is not trivially copy constructible.
157 constexpr
158 _Optional_payload_base(bool /* __engaged */,
159 const _Optional_payload_base& __other)
160 {
161 if (__other._M_engaged)
162 this->_M_construct(__other._M_get());
163 }
164
165 // Constructor used by _Optional_base move constructor when the
166 // contained value is not trivially move constructible.
167 constexpr
168 _Optional_payload_base(bool /* __engaged */,
169 _Optional_payload_base&& __other)
170 {
171 if (__other._M_engaged)
172 this->_M_construct(std::move(__other._M_get()));
173 }
174
175 // Copy constructor is only used to when the contained value is
176 // trivially copy constructible.
177 _Optional_payload_base(const _Optional_payload_base&) = default;
178
179 // Move constructor is only used to when the contained value is
180 // trivially copy constructible.
181 _Optional_payload_base(_Optional_payload_base&&) = default;
182
183 _Optional_payload_base&
184 operator=(const _Optional_payload_base&) = default;
185
186 _Optional_payload_base&
187 operator=(_Optional_payload_base&&) = default;
188
189 // used to perform non-trivial copy assignment.
190 constexpr void
191 _M_copy_assign(const _Optional_payload_base& __other)
192 {
193 if (this->_M_engaged && __other._M_engaged)
194 this->_M_get() = __other._M_get();
195 else
196 {
197 if (__other._M_engaged)
198 this->_M_construct(__other._M_get());
199 else
200 this->_M_reset();
201 }
202 }
203
204 // used to perform non-trivial move assignment.
205 constexpr void
206 _M_move_assign(_Optional_payload_base&& __other)
207 noexcept(__and_v<is_nothrow_move_constructible<_Tp>,
208 is_nothrow_move_assignable<_Tp>>)
209 {
210 if (this->_M_engaged && __other._M_engaged)
211 this->_M_get() = std::move(__other._M_get());
212 else
213 {
214 if (__other._M_engaged)
215 this->_M_construct(std::move(__other._M_get()));
216 else
217 this->_M_reset();
218 }
219 }
220
221 struct _Empty_byte { };
222
223 template<typename _Up, bool = is_trivially_destructible_v<_Up>>
224 union _Storage
225 {
226 constexpr _Storage() noexcept : _M_empty() { }
227
228 template<typename... _Args>
229 constexpr
230 _Storage(in_place_t, _Args&&... __args)
231 : _M_value(std::forward<_Args>(__args)...)
232 { }
233
234 template<typename _Vp, typename... _Args>
235 constexpr
236 _Storage(std::initializer_list<_Vp> __il, _Args&&... __args)
237 : _M_value(__il, std::forward<_Args>(__args)...)
238 { }
239
240#if __cplusplus >= 202002L
241 template<typename _Fn, typename _Arg>
242 constexpr
243 _Storage(_Optional_func<_Fn> __f, _Arg&& __arg)
244 : _M_value(std::__invoke(std::forward<_Fn>(__f._M_f),
245 std::forward<_Arg>(__arg)))
246 { }
247#endif
248
249#if __cpp_concepts >= 202002L // Conditionally trivial special member functions
250 ~_Storage() = default;
251
252 // User-provided destructor is needed when _Up has non-trivial dtor.
253 _GLIBCXX20_CONSTEXPR
254 ~_Storage() requires (!is_trivially_destructible_v<_Up>)
255 { }
256
257 _Storage(const _Storage&) = default;
258 _Storage(_Storage&&) = default;
259 _Storage& operator=(const _Storage&) = default;
260 _Storage& operator=(_Storage&&) = default;
261#endif
262
263 _Empty_byte _M_empty;
264 _Up _M_value;
265 };
266
267#if __cpp_concepts < 202002L
268 template<typename _Up>
269 union _Storage<_Up, false>
270 {
271 constexpr _Storage() noexcept : _M_empty() { }
272
273 template<typename... _Args>
274 constexpr
275 _Storage(in_place_t, _Args&&... __args)
276 : _M_value(std::forward<_Args>(__args)...)
277 { }
278
279 template<typename _Vp, typename... _Args>
280 constexpr
281 _Storage(std::initializer_list<_Vp> __il, _Args&&... __args)
282 : _M_value(__il, std::forward<_Args>(__args)...)
283 { }
284
285#if __cplusplus >= 202002L
286 template<typename _Fn, typename _Arg>
287 constexpr
288 _Storage(_Optional_func<_Fn> __f, _Arg&& __arg)
289 : _M_value(std::__invoke(std::forward<_Fn>(__f._M_f),
290 std::forward<_Arg>(__arg)))
291 { }
292#endif
293
294 // User-provided destructor is needed when _Up has non-trivial dtor.
295 _GLIBCXX20_CONSTEXPR ~_Storage() { }
296
297 _Storage(const _Storage&) = default;
298 _Storage(_Storage&&) = default;
299 _Storage& operator=(const _Storage&) = default;
300 _Storage& operator=(_Storage&&) = default;
301
302 _Empty_byte _M_empty;
303 _Up _M_value;
304 };
305#endif
306
307 _Storage<_Stored_type> _M_payload;
308
309 bool _M_engaged = false;
310
311 template<typename... _Args>
312 constexpr void
313 _M_construct(_Args&&... __args)
314 noexcept(is_nothrow_constructible_v<_Stored_type, _Args...>)
315 {
316 std::_Construct(std::__addressof(this->_M_payload._M_value),
317 std::forward<_Args>(__args)...);
318 this->_M_engaged = true;
319 }
320
321 constexpr void
322 _M_destroy() noexcept
323 {
324 _M_engaged = false;
325 _M_payload._M_value.~_Stored_type();
326#if defined(__clang__) && __cpp_lib_optional >= 202106L // full constexpr support
327 if (std::is_constant_evaluated())
328 // Work around PR124910 for Clang.
329 std::construct_at(std::__addressof(_M_payload._M_empty));
330#endif
331 }
332
333#if __cplusplus >= 202002L
334 template<typename _Fn, typename _Up>
335 constexpr void
336 _M_apply(_Optional_func<_Fn> __f, _Up&& __x)
337 {
338 std::construct_at(std::__addressof(this->_M_payload),
339 __f, std::forward<_Up>(__x));
340 _M_engaged = true;
341 }
342#endif
343
344 // The _M_get() operations have _M_engaged as a precondition.
345 // They exist to access the contained value with the appropriate
346 // const-qualification, because _M_payload has had the const removed.
347
348 constexpr _Tp&
349 _M_get() noexcept
350 { return this->_M_payload._M_value; }
351
352 constexpr const _Tp&
353 _M_get() const noexcept
354 { return this->_M_payload._M_value; }
355
356 // _M_reset is a 'safe' operation with no precondition.
357 constexpr void
358 _M_reset() noexcept
359 {
360 if (this->_M_engaged)
361 _M_destroy();
362 else // This seems redundant but improves codegen, see PR 112480.
363 this->_M_engaged = false;
364 }
365 };
366
367 // Class template that manages the payload for optionals.
368 template <typename _Tp,
369 bool /*_HasTrivialDestructor*/ =
370 is_trivially_destructible_v<_Tp>,
371 bool /*_HasTrivialCopy */ =
372 is_trivially_copy_assignable_v<_Tp>
373 && is_trivially_copy_constructible_v<_Tp>,
374 bool /*_HasTrivialMove */ =
375 is_trivially_move_assignable_v<_Tp>
376 && is_trivially_move_constructible_v<_Tp>>
377 struct _Optional_payload;
378
379 // Payload for potentially-constexpr optionals (trivial copy/move/destroy).
380 template <typename _Tp>
381 struct _Optional_payload<_Tp, true, true, true>
382 : _Optional_payload_base<_Tp>
383 {
384 using _Optional_payload_base<_Tp>::_Optional_payload_base;
385
386 _Optional_payload() = default;
387 };
388
389 // Payload for optionals with non-trivial copy construction/assignment.
390 template <typename _Tp>
391 struct _Optional_payload<_Tp, true, false, true>
392 : _Optional_payload_base<_Tp>
393 {
394 using _Optional_payload_base<_Tp>::_Optional_payload_base;
395
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=(_Optional_payload&&) = default;
401
402 // Non-trivial copy assignment.
403 constexpr
404 _Optional_payload&
405 operator=(const _Optional_payload& __other)
406 {
407 this->_M_copy_assign(__other);
408 return *this;
409 }
410 };
411
412 // Payload for optionals with non-trivial move construction/assignment.
413 template <typename _Tp>
414 struct _Optional_payload<_Tp, true, true, false>
415 : _Optional_payload_base<_Tp>
416 {
417 using _Optional_payload_base<_Tp>::_Optional_payload_base;
418
419 _Optional_payload() = default;
420 ~_Optional_payload() = default;
421 _Optional_payload(const _Optional_payload&) = default;
422 _Optional_payload(_Optional_payload&&) = default;
423 _Optional_payload& operator=(const _Optional_payload&) = default;
424
425 // Non-trivial move assignment.
426 constexpr
427 _Optional_payload&
428 operator=(_Optional_payload&& __other)
429 noexcept(__and_v<is_nothrow_move_constructible<_Tp>,
430 is_nothrow_move_assignable<_Tp>>)
431 {
432 this->_M_move_assign(std::move(__other));
433 return *this;
434 }
435 };
436
437 // Payload for optionals with non-trivial copy and move assignment.
438 template <typename _Tp>
439 struct _Optional_payload<_Tp, true, false, false>
440 : _Optional_payload_base<_Tp>
441 {
442 using _Optional_payload_base<_Tp>::_Optional_payload_base;
443
444 _Optional_payload() = default;
445 ~_Optional_payload() = default;
446 _Optional_payload(const _Optional_payload&) = default;
447 _Optional_payload(_Optional_payload&&) = default;
448
449 // Non-trivial copy assignment.
450 constexpr
451 _Optional_payload&
452 operator=(const _Optional_payload& __other)
453 {
454 this->_M_copy_assign(__other);
455 return *this;
456 }
457
458 // Non-trivial move assignment.
459 constexpr
460 _Optional_payload&
461 operator=(_Optional_payload&& __other)
462 noexcept(__and_v<is_nothrow_move_constructible<_Tp>,
463 is_nothrow_move_assignable<_Tp>>)
464 {
465 this->_M_move_assign(std::move(__other));
466 return *this;
467 }
468 };
469
470 // Payload for optionals with non-trivial destructors.
471 template <typename _Tp, bool _Copy, bool _Move>
472 struct _Optional_payload<_Tp, false, _Copy, _Move>
473 : _Optional_payload<_Tp, true, false, false>
474 {
475 // Base class implements all the constructors and assignment operators:
476 using _Optional_payload<_Tp, true, false, false>::_Optional_payload;
477 _Optional_payload() = default;
478 _Optional_payload(const _Optional_payload&) = default;
479 _Optional_payload(_Optional_payload&&) = default;
480 _Optional_payload& operator=(const _Optional_payload&) = default;
481 _Optional_payload& operator=(_Optional_payload&&) = default;
482
483 // Destructor needs to destroy the contained value:
484 _GLIBCXX20_CONSTEXPR ~_Optional_payload() { this->_M_reset(); }
485 };
486
487 /**
488 * @brief Class template that provides copy/move constructors of optional.
489 *
490 * Such a separate base class template is necessary in order to
491 * conditionally make copy/move constructors trivial.
492 *
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.
499 *
500 * Whether the other special members are trivial is determined by the
501 * _Optional_payload<_Tp> specialization used for the _M_payload member.
502 *
503 * @see optional, _Enable_special_members
504 */
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 {
510 // Constructors for disengaged optionals.
511 constexpr _Optional_base() = default;
512
513 // Constructors for engaged optionals.
514 template<typename... _Args,
515 enable_if_t<is_constructible_v<_Tp, _Args...>, bool> = false>
516 constexpr explicit
517 _Optional_base(in_place_t, _Args&&... __args)
518 : _M_payload(in_place, std::forward<_Args>(__args)...)
519 { }
520
521 template<typename _Up, typename... _Args,
522 enable_if_t<is_constructible_v<_Tp,
523 initializer_list<_Up>&,
524 _Args...>, bool> = false>
525 constexpr explicit
526 _Optional_base(in_place_t,
527 initializer_list<_Up> __il,
528 _Args&&... __args)
529 : _M_payload(in_place, __il, std::forward<_Args>(__args)...)
530 { }
531
532 // Copy and move constructors.
533 constexpr
534 _Optional_base(const _Optional_base& __other)
535 noexcept(is_nothrow_copy_constructible_v<_Tp>)
536 : _M_payload(__other._M_payload._M_engaged, __other._M_payload)
537 { }
538
539 constexpr
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))
544 { }
545
546#if __cpp_concepts >= 202002L // Conditionally trivial special member functions
547 // Define these in the primary template if possible, so that we don't
548 // need to use partial specializations of this class template.
549 constexpr _Optional_base(const _Optional_base&)
550 requires is_trivially_copy_constructible_v<_Tp> = default;
551
552 constexpr _Optional_base(_Optional_base&&)
553 requires is_trivially_move_constructible_v<_Tp> = default;
554#endif
555
556 // Assignment operators.
557 _Optional_base& operator=(const _Optional_base&) = default;
558 _Optional_base& operator=(_Optional_base&&) = default;
559
560 _Optional_payload<_Tp> _M_payload;
561
562 protected:
563 // For the primary template, we define these functions here.
564 using _Stored_type = remove_const_t<_Tp>;
565
566 // The _M_construct operation has !_M_engaged as a precondition
567 // while _M_destruct has _M_engaged as a precondition.
568 template<typename... _Args>
569 constexpr void
570 _M_construct(_Args&&... __args)
571 noexcept(is_nothrow_constructible_v<_Stored_type, _Args...>)
572 {
573 _M_payload._M_construct(std::forward<_Args>(__args)...);
574 }
575
576 constexpr void
577 _M_destruct() noexcept
578 { _M_payload._M_destroy(); }
579
580 // _M_reset is a 'safe' operation with no precondition.
581 constexpr void
582 _M_reset() noexcept
583 { _M_payload._M_reset(); }
584
585 constexpr bool _M_is_engaged() const noexcept
586 { return _M_payload._M_engaged; }
587
588 // The _M_get operations have _M_engaged as a precondition.
589 constexpr _Tp&
590 _M_get() noexcept
591 { return _M_payload._M_get(); }
592
593 constexpr const _Tp&
594 _M_get() const noexcept
595 { return _M_payload._M_get(); }
596 };
597
598#if __cpp_concepts < 202002L
599 // If P0848R3 "Conditionally Trivial Special Member Functions" is not
600 // supported (as determined from the __cpp_concepts macro value), the
601 // _Optional_base primary template only has non-trivial copy and move
602 // constructors. Use partial specializations of _Optional_base<T, C, M>
603 // that have a trivial copy and/or move constructor.
604
605 // Common base class for _Optional_base<T> to avoid repeating these
606 // member functions in each partial specialization.
607 // Only used if P0848R3 "Conditionally Trivial Special Member Functions"
608 // is not supported, as indicated by the __cpp_concepts value.
609 template<typename _Tp, typename _Dp>
610 class _Optional_base_impl
611 {
612 protected:
613 using _Stored_type = remove_const_t<_Tp>;
614
615 // The _M_construct operation has !_M_engaged as a precondition
616 // while _M_destruct has _M_engaged as a precondition.
617 template<typename... _Args>
618 constexpr void
619 _M_construct(_Args&&... __args)
620 noexcept(is_nothrow_constructible_v<_Stored_type, _Args...>)
621 {
622 static_cast<_Dp*>(this)->_M_payload._M_construct(
623 std::forward<_Args>(__args)...);
624 }
625
626 constexpr void
627 _M_destruct() noexcept
628 { static_cast<_Dp*>(this)->_M_payload._M_destroy(); }
629
630 // _M_reset is a 'safe' operation with no precondition.
631 constexpr void
632 _M_reset() noexcept
633 { static_cast<_Dp*>(this)->_M_payload._M_reset(); }
634
635 constexpr bool _M_is_engaged() const noexcept
636 { return static_cast<const _Dp*>(this)->_M_payload._M_engaged; }
637
638 // The _M_get operations have _M_engaged as a precondition.
639 constexpr _Tp&
640 _M_get() noexcept
641 { return static_cast<_Dp*>(this)->_M_payload._M_get(); }
642
643 constexpr const _Tp&
644 _M_get() const noexcept
645 { return static_cast<const _Dp*>(this)->_M_payload._M_get(); }
646 };
647
648 template<typename _Tp>
649 struct _Optional_base<_Tp, false, true> // trivial move ctor
650 : _Optional_base_impl<_Tp, _Optional_base<_Tp>>
651 {
652 // Constructors for disengaged optionals.
653 constexpr _Optional_base() = default;
654
655 // Constructors for engaged optionals.
656 template<typename... _Args,
657 enable_if_t<is_constructible_v<_Tp, _Args...>, bool> = false>
658 constexpr explicit
659 _Optional_base(in_place_t, _Args&&... __args)
660 : _M_payload(in_place, std::forward<_Args>(__args)...)
661 { }
662
663 template<typename _Up, typename... _Args,
664 enable_if_t<is_constructible_v<_Tp,
665 initializer_list<_Up>&,
666 _Args...>, bool> = false>
667 constexpr explicit
668 _Optional_base(in_place_t,
669 initializer_list<_Up> __il,
670 _Args... __args)
671 : _M_payload(in_place, __il, std::forward<_Args>(__args)...)
672 { }
673
674 // Copy and move constructors.
675 constexpr _Optional_base(const _Optional_base& __other)
676 : _M_payload(__other._M_payload._M_engaged, __other._M_payload)
677 { }
678
679 constexpr _Optional_base(_Optional_base&& __other) = default;
680
681 // Assignment operators.
682 _Optional_base& operator=(const _Optional_base&) = default;
683 _Optional_base& operator=(_Optional_base&&) = default;
684
685 _Optional_payload<_Tp> _M_payload;
686 };
687
688 template<typename _Tp>
689 struct _Optional_base<_Tp, true, false> // trivial copy ctor
690 : _Optional_base_impl<_Tp, _Optional_base<_Tp>>
691 {
692 // Constructors for disengaged optionals.
693 constexpr _Optional_base() = default;
694
695 // Constructors for engaged optionals.
696 template<typename... _Args,
697 enable_if_t<is_constructible_v<_Tp, _Args...>, bool> = false>
698 constexpr explicit
699 _Optional_base(in_place_t, _Args&&... __args)
700 : _M_payload(in_place, std::forward<_Args>(__args)...)
701 { }
702
703 template<typename _Up, typename... _Args,
704 enable_if_t<is_constructible_v<_Tp,
705 initializer_list<_Up>&,
706 _Args...>, bool> = false>
707 constexpr explicit
708 _Optional_base(in_place_t,
709 initializer_list<_Up> __il,
710 _Args&&... __args)
711 : _M_payload(in_place, __il, std::forward<_Args>(__args)...)
712 { }
713
714 // Copy and move constructors.
715 constexpr _Optional_base(const _Optional_base& __other) = default;
716
717 constexpr
718 _Optional_base(_Optional_base&& __other)
719 noexcept(is_nothrow_move_constructible_v<_Tp>)
720 : _M_payload(__other._M_payload._M_engaged,
721 std::move(__other._M_payload))
722 { }
723
724 // Assignment operators.
725 _Optional_base& operator=(const _Optional_base&) = default;
726 _Optional_base& operator=(_Optional_base&&) = default;
727
728 _Optional_payload<_Tp> _M_payload;
729 };
730
731 template<typename _Tp>
732 struct _Optional_base<_Tp, true, true> // trivial copy and move ctors
733 : _Optional_base_impl<_Tp, _Optional_base<_Tp>>
734 {
735 // Constructors for disengaged optionals.
736 constexpr _Optional_base() = default;
737
738 // Constructors for engaged optionals.
739 template<typename... _Args,
740 enable_if_t<is_constructible_v<_Tp, _Args...>, bool> = false>
741 constexpr explicit
742 _Optional_base(in_place_t, _Args&&... __args)
743 : _M_payload(in_place, std::forward<_Args>(__args)...)
744 { }
745
746 template<typename _Up, typename... _Args,
747 enable_if_t<is_constructible_v<_Tp,
748 initializer_list<_Up>&,
749 _Args...>, bool> = false>
750 constexpr explicit
751 _Optional_base(in_place_t,
752 initializer_list<_Up> __il,
753 _Args&&... __args)
754 : _M_payload(in_place, __il, std::forward<_Args>(__args)...)
755 { }
756
757 // Copy and move constructors.
758 constexpr _Optional_base(const _Optional_base& __other) = default;
759 constexpr _Optional_base(_Optional_base&& __other) = default;
760
761 // Assignment operators.
762 _Optional_base& operator=(const _Optional_base&) = default;
763 _Optional_base& operator=(_Optional_base&&) = default;
764
765 _Optional_payload<_Tp> _M_payload;
766 };
767#endif // __cpp_concepts
768
769 template<typename _Tp>
770 inline constexpr bool __is_optional_v = false;
771 template<typename _Tp>
772 inline constexpr bool __is_optional_v<optional<_Tp>> = true;
773
774 template<typename _Tp, typename _Wp>
775 using __converts_from_any_cvref = __or_<
776 is_constructible<_Tp, _Wp&>, is_convertible<_Wp&, _Tp>,
777 is_constructible<_Tp, _Wp>, is_convertible<_Wp, _Tp>,
778 is_constructible<_Tp, const _Wp&>, is_convertible<const _Wp&, _Tp>,
779 is_constructible<_Tp, const _Wp>, is_convertible<const _Wp, _Tp>
780 >;
781
782 template<typename _Tp, typename _Up>
783 using __converts_from_optional
784 = __converts_from_any_cvref<_Tp, optional<_Up>>;
785
786 template<typename _Tp, typename _Up>
787 using __assigns_from_optional =
788 __or_<is_assignable<_Tp&, const optional<_Up>&>,
789 is_assignable<_Tp&, optional<_Up>&>,
790 is_assignable<_Tp&, const optional<_Up>&&>,
791 is_assignable<_Tp&, optional<_Up>&&>>;
792
793#if __cpp_concepts && __cpp_conditional_explicit && __glibcxx_remove_cvref
794# define _GLIBCXX_USE_CONSTRAINTS_FOR_OPTIONAL 1
795#endif
796
797 template<typename _Tp>
798 inline constexpr bool __is_valid_contained_type_for_optional =
799 (
800#if __cpp_lib_optional >= 202506L
801 is_lvalue_reference_v<_Tp> ||
802#endif
803 (is_object_v<_Tp> && is_destructible_v<_Tp> && !is_array_v<_Tp>)
804 )
805 && !is_same_v<remove_cv_t<remove_reference_t<_Tp>>, nullopt_t>
806 && !is_same_v<remove_cv_t<remove_reference_t<_Tp>>, in_place_t>;
807
808 /**
809 * @brief Class template for optional values.
810 */
811 template<typename _Tp>
812 class optional
813 : private _Optional_base<_Tp>,
814 private _Enable_copy_move<
815 // Copy constructor.
816 is_copy_constructible_v<_Tp>,
817 // Copy assignment.
818 __and_v<is_copy_constructible<_Tp>, is_copy_assignable<_Tp>>,
819 // Move constructor.
820 is_move_constructible_v<_Tp>,
821 // Move assignment.
822 __and_v<is_move_constructible<_Tp>, is_move_assignable<_Tp>>,
823 // Unique tag type.
824 optional<_Tp>>
825 {
826 static_assert(__is_valid_contained_type_for_optional<_Tp>);
827
828 private:
829 using _Base = _Optional_base<_Tp>;
830
831 // SFINAE helpers
832
833 // _GLIBCXX_RESOLVE_LIB_DEFECTS
834 // 3836. std::expected<bool, E1> conversion constructor
835 // expected(const expected<U, G>&) should take precedence over
836 // expected(U&&) with operator bool
837#ifdef _GLIBCXX_USE_CONSTRAINTS_FOR_OPTIONAL
838 template<typename _From, typename = remove_cv_t<_Tp>>
839 static constexpr bool __not_constructing_bool_from_optional
840 = true;
841
842 // If T is cv bool, remove_cvref_t<U> is not a specialization of optional
843 // i.e. do not initialize a bool from optional<U>::operator bool().
844 template<typename _From>
845 static constexpr bool
846 __not_constructing_bool_from_optional<_From, bool>
847 = !__is_optional_v<remove_cvref_t<_From>>;
848
849 // If T is not cv bool, converts-from-any-cvref<T, optional<U>> is false.
850 // The constructor that converts from optional<U> is disabled if the
851 // contained value can be initialized from optional<U>, so that the
852 // optional(U&&) constructor can be used instead.
853 template<typename _From, typename = remove_cv_t<_Tp>>
854 static constexpr bool __construct_from_contained_value
855 = !__converts_from_optional<_Tp, _From>::value;
856
857 // However, optional<U> can always be converted to bool, so don't apply
858 // this constraint when T is cv bool.
859 template<typename _From>
860 static constexpr bool __construct_from_contained_value<_From, bool>
861 = true;
862#else
863 template<typename _From, typename = remove_cv_t<_Tp>>
864 struct __not_constructing_bool_from_optional
865 : true_type
866 { };
867
868 template<typename _From>
869 struct __not_constructing_bool_from_optional<_From, bool>
870 : bool_constant<!__is_optional_v<__remove_cvref_t<_From>>>
871 { };
872
873 template<typename _From, typename = remove_cv_t<_Tp>>
874 struct __construct_from_contained_value
875 : __not_<__converts_from_optional<_Tp, _From>>
876 { };
877
878 template<typename _From>
879 struct __construct_from_contained_value<_From, bool>
880 : true_type
881 { };
882
883 template<typename _Up>
884 using __not_self = __not_<is_same<optional, __remove_cvref_t<_Up>>>;
885 template<typename _Up>
886 using __not_tag = __not_<is_same<in_place_t, __remove_cvref_t<_Up>>>;
887 template<typename... _Cond>
888 using _Requires = enable_if_t<__and_v<_Cond...>, bool>;
889#endif
890
891 public:
892 using value_type = _Tp;
893#ifdef __cpp_lib_optional_range_support // >= C++26
894 using iterator = __gnu_cxx::__normal_iterator<_Tp*, optional>;
895 using const_iterator = __gnu_cxx::__normal_iterator<const _Tp*, optional>;
896#endif
897
898 constexpr optional() noexcept { }
899
900 constexpr optional(nullopt_t) noexcept { }
901
902 // Converting constructors for engaged optionals.
903#ifdef _GLIBCXX_USE_CONSTRAINTS_FOR_OPTIONAL
904 template<typename _Up = remove_cv_t<_Tp>>
905 requires (!is_same_v<optional, remove_cvref_t<_Up>>)
906 && (!is_same_v<in_place_t, remove_cvref_t<_Up>>)
907 && is_constructible_v<_Tp, _Up>
908 && __not_constructing_bool_from_optional<_Up>
909 constexpr explicit(!is_convertible_v<_Up, _Tp>)
910 optional(_Up&& __t)
911 noexcept(is_nothrow_constructible_v<_Tp, _Up>)
912 : _Base(std::in_place, std::forward<_Up>(__t)) { }
913
914 template<typename _Up>
915 requires (!is_same_v<_Tp, _Up>)
916 && is_constructible_v<_Tp, const _Up&>
917 && __construct_from_contained_value<_Up>
918 constexpr explicit(!is_convertible_v<const _Up&, _Tp>)
919 optional(const optional<_Up>& __t)
920 noexcept(is_nothrow_constructible_v<_Tp, const _Up&>)
921 {
922 if (__t)
923 emplace(__t._M_fwd());
924 }
925
926 template<typename _Up>
927 requires (!is_same_v<_Tp, _Up>)
928 && is_constructible_v<_Tp, _Up>
929 && __construct_from_contained_value<_Up>
930 constexpr explicit(!is_convertible_v<_Up, _Tp>)
931 optional(optional<_Up>&& __t)
932 noexcept(is_nothrow_constructible_v<_Tp, _Up>)
933 {
934 if (__t)
935 emplace(std::move(__t)._M_fwd());
936 }
937
938 template<typename... _Args>
939 requires is_constructible_v<_Tp, _Args...>
940 explicit constexpr
941 optional(in_place_t, _Args&&... __args)
942 noexcept(is_nothrow_constructible_v<_Tp, _Args...>)
943 : _Base(std::in_place, std::forward<_Args>(__args)...)
944 { }
945
946 template<typename _Up, typename... _Args>
947 requires is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>
948 explicit constexpr
949 optional(in_place_t, initializer_list<_Up> __il, _Args&&... __args)
950 noexcept(is_nothrow_constructible_v<_Tp, initializer_list<_Up>&,
951 _Args...>)
952 : _Base(std::in_place, __il, std::forward<_Args>(__args)...)
953 { }
954#else
955 template<typename _Up = remove_cv_t<_Tp>,
956 _Requires<__not_self<_Up>, __not_tag<_Up>,
957 is_constructible<_Tp, _Up>,
958 is_convertible<_Up, _Tp>,
959 __not_constructing_bool_from_optional<_Up>> = true>
960 constexpr
961 optional(_Up&& __t)
962 noexcept(is_nothrow_constructible_v<_Tp, _Up>)
963 : _Base(std::in_place, std::forward<_Up>(__t)) { }
964
965 template<typename _Up = remove_cv_t<_Tp>,
966 _Requires<__not_self<_Up>, __not_tag<_Up>,
967 is_constructible<_Tp, _Up>,
968 __not_<is_convertible<_Up, _Tp>>,
969 __not_constructing_bool_from_optional<_Up>> = false>
970 explicit constexpr
971 optional(_Up&& __t)
972 noexcept(is_nothrow_constructible_v<_Tp, _Up>)
973 : _Base(std::in_place, std::forward<_Up>(__t)) { }
974
975 template<typename _Up,
976 _Requires<__not_<is_same<_Tp, _Up>>,
977 is_constructible<_Tp, const _Up&>,
978 is_convertible<const _Up&, _Tp>,
979 __construct_from_contained_value<_Up>> = true>
980 constexpr
981 optional(const optional<_Up>& __t)
982 noexcept(is_nothrow_constructible_v<_Tp, const _Up&>)
983 {
984 if (__t)
985 emplace(__t._M_fwd());
986 }
987
988 template<typename _Up,
989 _Requires<__not_<is_same<_Tp, _Up>>,
990 is_constructible<_Tp, const _Up&>,
991 __not_<is_convertible<const _Up&, _Tp>>,
992 __construct_from_contained_value<_Up>> = false>
993 explicit constexpr
994 optional(const optional<_Up>& __t)
995 noexcept(is_nothrow_constructible_v<_Tp, const _Up&>)
996 {
997 if (__t)
998 emplace(__t._M_fwd());
999 }
1000
1001 template<typename _Up,
1002 _Requires<__not_<is_same<_Tp, _Up>>,
1003 is_constructible<_Tp, _Up>,
1004 is_convertible<_Up, _Tp>,
1005 __construct_from_contained_value<_Up>> = true>
1006 constexpr
1007 optional(optional<_Up>&& __t)
1008 noexcept(is_nothrow_constructible_v<_Tp, _Up>)
1009 {
1010 if (__t)
1011 emplace(std::move(__t)._M_fwd());
1012 }
1013
1014 template<typename _Up,
1015 _Requires<__not_<is_same<_Tp, _Up>>,
1016 is_constructible<_Tp, _Up>,
1017 __not_<is_convertible<_Up, _Tp>>,
1018 __construct_from_contained_value<_Up>> = false>
1019 explicit constexpr
1020 optional(optional<_Up>&& __t)
1021 noexcept(is_nothrow_constructible_v<_Tp, _Up>)
1022 {
1023 if (__t)
1024 emplace(std::move(__t)._M_fwd());
1025 }
1026
1027 template<typename... _Args,
1028 _Requires<is_constructible<_Tp, _Args...>> = false>
1029 explicit constexpr
1030 optional(in_place_t, _Args&&... __args)
1031 noexcept(is_nothrow_constructible_v<_Tp, _Args...>)
1032 : _Base(std::in_place, std::forward<_Args>(__args)...) { }
1033
1034 template<typename _Up, typename... _Args,
1035 _Requires<is_constructible<_Tp,
1036 initializer_list<_Up>&,
1037 _Args...>> = false>
1038 explicit constexpr
1039 optional(in_place_t, initializer_list<_Up> __il, _Args&&... __args)
1040 noexcept(is_nothrow_constructible_v<_Tp, initializer_list<_Up>&,
1041 _Args...>)
1042 : _Base(std::in_place, __il, std::forward<_Args>(__args)...) { }
1043#endif
1044
1045 // Assignment operators.
1046 _GLIBCXX20_CONSTEXPR optional&
1047 operator=(nullopt_t) noexcept
1048 {
1049 this->_M_reset();
1050 return *this;
1051 }
1052
1053 template<typename _Up = remove_cv_t<_Tp>>
1054#ifdef _GLIBCXX_USE_CONSTRAINTS_FOR_OPTIONAL
1055 requires (!is_same_v<optional, remove_cvref_t<_Up>>)
1056 && (!(is_scalar_v<_Tp> && is_same_v<_Tp, decay_t<_Up>>))
1057 && is_constructible_v<_Tp, _Up>
1058 && is_assignable_v<_Tp&, _Up>
1059 constexpr optional&
1060#else
1061 enable_if_t<__and_v<__not_self<_Up>,
1062 __not_<__and_<is_scalar<_Tp>,
1063 is_same<_Tp, decay_t<_Up>>>>,
1064 is_constructible<_Tp, _Up>,
1065 is_assignable<_Tp&, _Up>>,
1066 optional&>
1067#endif
1068 operator=(_Up&& __u)
1069 noexcept(__and_v<is_nothrow_constructible<_Tp, _Up>,
1070 is_nothrow_assignable<_Tp&, _Up>>)
1071 {
1072 if (this->_M_is_engaged())
1073 this->_M_get() = std::forward<_Up>(__u);
1074 else
1075 this->_M_construct(std::forward<_Up>(__u));
1076
1077 return *this;
1078 }
1079
1080 template<typename _Up>
1081#ifdef _GLIBCXX_USE_CONSTRAINTS_FOR_OPTIONAL
1082 requires (!is_same_v<_Tp, _Up>)
1083 && is_constructible_v<_Tp, const _Up&>
1084 && is_assignable_v<_Tp&, const _Up&>
1085 && (!__converts_from_optional<_Tp, _Up>::value)
1086 && (!__assigns_from_optional<_Tp, _Up>::value)
1087 constexpr optional&
1088#else
1089 enable_if_t<__and_v<__not_<is_same<_Tp, _Up>>,
1090 is_constructible<_Tp, const _Up&>,
1091 is_assignable<_Tp&, const _Up&>,
1092 __not_<__converts_from_optional<_Tp, _Up>>,
1093 __not_<__assigns_from_optional<_Tp, _Up>>>,
1094 optional&>
1095#endif
1096 operator=(const optional<_Up>& __u)
1097 noexcept(__and_v<is_nothrow_constructible<_Tp, const _Up&>,
1098 is_nothrow_assignable<_Tp&, const _Up&>>)
1099 {
1100 if (__u)
1101 {
1102 if (this->_M_is_engaged())
1103 this->_M_get() = __u._M_fwd();
1104 else
1105 this->_M_construct(__u._M_fwd());
1106 }
1107 else
1108 {
1109 this->_M_reset();
1110 }
1111 return *this;
1112 }
1113
1114 template<typename _Up>
1115#ifdef _GLIBCXX_USE_CONSTRAINTS_FOR_OPTIONAL
1116 requires (!is_same_v<_Tp, _Up>)
1117 && is_constructible_v<_Tp, _Up>
1118 && is_assignable_v<_Tp&, _Up>
1119 && (!__converts_from_optional<_Tp, _Up>::value)
1120 && (!__assigns_from_optional<_Tp, _Up>::value)
1121 constexpr optional&
1122#else
1123 enable_if_t<__and_v<__not_<is_same<_Tp, _Up>>,
1124 is_constructible<_Tp, _Up>,
1125 is_assignable<_Tp&, _Up>,
1126 __not_<__converts_from_optional<_Tp, _Up>>,
1127 __not_<__assigns_from_optional<_Tp, _Up>>>,
1128 optional&>
1129#endif
1130 operator=(optional<_Up>&& __u)
1131 noexcept(__and_v<is_nothrow_constructible<_Tp, _Up>,
1132 is_nothrow_assignable<_Tp&, _Up>>)
1133 {
1134 if (__u)
1135 {
1136 if (this->_M_is_engaged())
1137 this->_M_get() = std::move(__u)._M_fwd();
1138 else
1139 this->_M_construct(std::move(__u)._M_fwd());
1140 }
1141 else
1142 {
1143 this->_M_reset();
1144 }
1145
1146 return *this;
1147 }
1148
1149 // _GLIBCXX_RESOLVE_LIB_DEFECTS
1150 // 2746. Inconsistency between requirements for emplace between optional and variant
1151 template<typename... _Args>
1152 _GLIBCXX20_CONSTEXPR
1153 enable_if_t<is_constructible_v<_Tp, _Args...>, _Tp&>
1154 emplace(_Args&&... __args)
1155 noexcept(is_nothrow_constructible_v<_Tp, _Args...>)
1156 {
1157 this->_M_reset();
1158 this->_M_construct(std::forward<_Args>(__args)...);
1159 return this->_M_get();
1160 }
1161
1162 template<typename _Up, typename... _Args>
1163 _GLIBCXX20_CONSTEXPR
1164 enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>,
1165 _Tp&>
1166 emplace(initializer_list<_Up> __il, _Args&&... __args)
1167 noexcept(is_nothrow_constructible_v<_Tp, initializer_list<_Up>&,
1168 _Args...>)
1169 {
1170 this->_M_reset();
1171 this->_M_construct(__il, std::forward<_Args>(__args)...);
1172 return this->_M_get();
1173 }
1174
1175 // Destructor is implicit, implemented in _Optional_base.
1176
1177 // Swap.
1178 _GLIBCXX20_CONSTEXPR void
1179 swap(optional& __other)
1180 noexcept(is_nothrow_move_constructible_v<_Tp>
1181 && is_nothrow_swappable_v<_Tp>)
1182 {
1183 using std::swap;
1184
1185 if (this->_M_is_engaged() && __other._M_is_engaged())
1186 swap(this->_M_get(), __other._M_get());
1187 else if (this->_M_is_engaged())
1188 {
1189 __other._M_construct(std::move(this->_M_get()));
1190 this->_M_destruct();
1191 }
1192 else if (__other._M_is_engaged())
1193 {
1194 this->_M_construct(std::move(__other._M_get()));
1195 __other._M_destruct();
1196 }
1197 }
1198
1199#ifdef __cpp_lib_optional_range_support // >= C++26
1200 // Iterator support.
1201 constexpr iterator begin() noexcept
1202 {
1203 return iterator(
1204 this->_M_is_engaged() ? std::addressof(this->_M_get()) : nullptr
1205 );
1206 }
1207
1208 constexpr const_iterator begin() const noexcept
1209 {
1210 return const_iterator(
1211 this->_M_is_engaged() ? std::addressof(this->_M_get()) : nullptr
1212 );
1213 }
1214
1215 constexpr iterator end() noexcept
1216 {
1217 return begin() + has_value();
1218 }
1219
1220 constexpr const_iterator end() const noexcept
1221 {
1222 return begin() + has_value();
1223 }
1224#endif // __cpp_lib_optional_range_support
1225
1226 // Observers.
1227 constexpr const _Tp*
1228 operator->() const noexcept
1229 {
1230 __glibcxx_assert(this->_M_is_engaged());
1231 return std::__addressof(this->_M_get());
1232 }
1233
1234 constexpr _Tp*
1235 operator->() noexcept
1236 {
1237 __glibcxx_assert(this->_M_is_engaged());
1238 return std::__addressof(this->_M_get());
1239 }
1240
1241 constexpr const _Tp&
1242 operator*() const& noexcept
1243 {
1244 __glibcxx_assert(this->_M_is_engaged());
1245 return this->_M_get();
1246 }
1247
1248 constexpr _Tp&
1249 operator*()& noexcept
1250 {
1251 __glibcxx_assert(this->_M_is_engaged());
1252 return this->_M_get();
1253 }
1254
1255 constexpr _Tp&&
1256 operator*()&& noexcept
1257 {
1258 __glibcxx_assert(this->_M_is_engaged());
1259 return std::move(this->_M_get());
1260 }
1261
1262 constexpr const _Tp&&
1263 operator*() const&& noexcept
1264 {
1265 __glibcxx_assert(this->_M_is_engaged());
1266 return std::move(this->_M_get());
1267 }
1268
1269 constexpr explicit operator bool() const noexcept
1270 { return this->_M_is_engaged(); }
1271
1272 constexpr bool has_value() const noexcept
1273 { return this->_M_is_engaged(); }
1274
1275 constexpr const _Tp&
1276 value() const&
1277 {
1278 if (this->_M_is_engaged())
1279 return this->_M_get();
1280 __throw_bad_optional_access();
1281 }
1282
1283 constexpr _Tp&
1284 value()&
1285 {
1286 if (this->_M_is_engaged())
1287 return this->_M_get();
1288 __throw_bad_optional_access();
1289 }
1290
1291 constexpr _Tp&&
1292 value()&&
1293 {
1294 if (this->_M_is_engaged())
1295 return std::move(this->_M_get());
1296 __throw_bad_optional_access();
1297 }
1298
1299 constexpr const _Tp&&
1300 value() const&&
1301 {
1302 if (this->_M_is_engaged())
1303 return std::move(this->_M_get());
1304 __throw_bad_optional_access();
1305 }
1306
1307 // _GLIBCXX_RESOLVE_LIB_DEFECTS
1308 // 4406. value_or return statement is inconsistent with Mandates
1309 template<typename _Up = remove_cv_t<_Tp>>
1310 constexpr remove_cv_t<_Tp>
1311 value_or(_Up&& __u) const&
1312 {
1313 using _Xp = remove_cv_t<_Tp>;
1314 static_assert(is_convertible_v<const _Tp&, _Xp>);
1315 static_assert(is_convertible_v<_Up, _Xp>);
1316
1317 if (this->_M_is_engaged())
1318 return this->_M_get();
1319 return std::forward<_Up>(__u);
1320 }
1321
1322 template<typename _Up = remove_cv_t<_Tp>>
1323 constexpr remove_cv_t<_Tp>
1324 value_or(_Up&& __u) &&
1325 {
1326 using _Xp = remove_cv_t<_Tp>;
1327 static_assert(is_convertible_v<_Tp, _Xp>);
1328 static_assert(is_convertible_v<_Up, _Xp>);
1329
1330 if (this->_M_is_engaged())
1331 return std::move(this->_M_get());
1332 return std::forward<_Up>(__u);
1333 }
1334
1335#if __cpp_lib_optional >= 202110L // C++23
1336 // [optional.monadic]
1337
1338 template<typename _Fn>
1339 constexpr auto
1340 and_then(_Fn&& __f) &
1341 {
1342 using _Up = remove_cvref_t<invoke_result_t<_Fn, _Tp&>>;
1343 static_assert(__is_optional_v<_Up>,
1344 "the function passed to std::optional<T>::and_then "
1345 "must return a std::optional");
1346 if (has_value())
1347 return std::__invoke(std::forward<_Fn>(__f), _M_get());
1348 else
1349 return _Up();
1350 }
1351
1352 template<typename _Fn>
1353 constexpr auto
1354 and_then(_Fn&& __f) const &
1355 {
1356 using _Up = remove_cvref_t<invoke_result_t<_Fn, const _Tp&>>;
1357 static_assert(__is_optional_v<_Up>,
1358 "the function passed to std::optional<T>::and_then "
1359 "must return a std::optional");
1360 if (has_value())
1361 return std::__invoke(std::forward<_Fn>(__f), _M_get());
1362 else
1363 return _Up();
1364 }
1365
1366 template<typename _Fn>
1367 constexpr auto
1368 and_then(_Fn&& __f) &&
1369 {
1370 using _Up = remove_cvref_t<invoke_result_t<_Fn, _Tp>>;
1371 static_assert(__is_optional_v<_Up>,
1372 "the function passed to std::optional<T>::and_then "
1373 "must return a std::optional");
1374 if (has_value())
1375 return std::__invoke(std::forward<_Fn>(__f), std::move(_M_get()));
1376 else
1377 return _Up();
1378 }
1379
1380 template<typename _Fn>
1381 constexpr auto
1382 and_then(_Fn&& __f) const &&
1383 {
1384 using _Up = remove_cvref_t<invoke_result_t<_Fn, const _Tp>>;
1385 static_assert(__is_optional_v<_Up>,
1386 "the function passed to std::optional<T>::and_then "
1387 "must return a std::optional");
1388 if (has_value())
1389 return std::__invoke(std::forward<_Fn>(__f), std::move(_M_get()));
1390 else
1391 return _Up();
1392 }
1393
1394 template<typename _Fn>
1395 constexpr auto
1396 transform(_Fn&& __f) &
1397 {
1398 using _Up = remove_cv_t<invoke_result_t<_Fn, _Tp&>>;
1399 if (has_value())
1400 return optional<_Up>(_Optional_func<_Fn>{__f}, _M_get());
1401 else
1402 return optional<_Up>();
1403 }
1404
1405 template<typename _Fn>
1406 constexpr auto
1407 transform(_Fn&& __f) const &
1408 {
1409 using _Up = remove_cv_t<invoke_result_t<_Fn, const _Tp&>>;
1410 if (has_value())
1411 return optional<_Up>(_Optional_func<_Fn>{__f}, _M_get());
1412 else
1413 return optional<_Up>();
1414 }
1415
1416 template<typename _Fn>
1417 constexpr auto
1418 transform(_Fn&& __f) &&
1419 {
1420 using _Up = remove_cv_t<invoke_result_t<_Fn, _Tp>>;
1421 if (has_value())
1422 return optional<_Up>(_Optional_func<_Fn>{__f}, std::move(_M_get()));
1423 else
1424 return optional<_Up>();
1425 }
1426
1427 template<typename _Fn>
1428 constexpr auto
1429 transform(_Fn&& __f) const &&
1430 {
1431 using _Up = remove_cv_t<invoke_result_t<_Fn, const _Tp>>;
1432 if (has_value())
1433 return optional<_Up>(_Optional_func<_Fn>{__f}, std::move(_M_get()));
1434 else
1435 return optional<_Up>();
1436 }
1437
1438 template<typename _Fn> requires invocable<_Fn> && copy_constructible<_Tp>
1439 constexpr optional
1440 or_else(_Fn&& __f) const&
1441 {
1442 using _Up = invoke_result_t<_Fn>;
1443 static_assert(is_same_v<remove_cvref_t<_Up>, optional>,
1444 "the function passed to std::optional<T>::or_else "
1445 "must return a std::optional<T>");
1446
1447 if (has_value())
1448 return *this;
1449 else
1450 return std::forward<_Fn>(__f)();
1451 }
1452
1453 template<typename _Fn> requires invocable<_Fn> && move_constructible<_Tp>
1454 constexpr optional
1455 or_else(_Fn&& __f) &&
1456 {
1457 using _Up = invoke_result_t<_Fn>;
1458 static_assert(is_same_v<remove_cvref_t<_Up>, optional>,
1459 "the function passed to std::optional<T>::or_else "
1460 "must return a std::optional<T>");
1461
1462 if (has_value())
1463 return std::move(*this);
1464 else
1465 return std::forward<_Fn>(__f)();
1466 }
1467#endif
1468
1469 _GLIBCXX20_CONSTEXPR void reset() noexcept { this->_M_reset(); }
1470
1471 private:
1472 using _Base::_M_get;
1473
1474 [[__gnu__::__always_inline__]]
1475 constexpr _Tp&
1476 _M_fwd() & noexcept
1477 { return _M_get(); }
1478
1479 [[__gnu__::__always_inline__]]
1480 constexpr _Tp&&
1481 _M_fwd() && noexcept
1482 { return std::move(_M_get()); }
1483
1484 [[__gnu__::__always_inline__]]
1485 constexpr const _Tp&
1486 _M_fwd() const& noexcept
1487 { return _M_get(); }
1488
1489 [[__gnu__::__always_inline__]]
1490 constexpr const _Tp&&
1491 _M_fwd() const&& noexcept
1492 { return std::move(_M_get()); }
1493
1494 template<typename _Up> friend class optional;
1495
1496#if __cpp_lib_optional >= 202110L // C++23
1497 template<typename _Fn, typename _Value>
1498 explicit constexpr
1499 optional(_Optional_func<_Fn> __f, _Value&& __v)
1500 {
1501 this->_M_payload._M_apply(__f, std::forward<_Value>(__v));
1502 }
1503#endif
1504 };
1505
1506#if __cpp_lib_optional >= 202506L // C++26
1507 template<typename _Tp>
1508 class optional<_Tp&>;
1509
1510 template<typename _Tp>
1511 constexpr bool __is_optional_ref_v = false;
1512
1513 template<typename _Tp>
1514 constexpr bool __is_optional_ref_v<optional<_Tp&>> = true;
1515
1516 template<typename _Tp>
1517 struct __optional_ref_base
1518 {};
1519
1520#ifdef __cpp_lib_optional_range_support // >= C++26
1521 template<typename _Tp>
1522 struct __optional_ref_base<_Tp[]>
1523 {};
1524
1525 template<typename _Tp>
1526 requires is_object_v<_Tp>
1527 struct __optional_ref_base<_Tp>
1528 {
1529 using iterator = __gnu_cxx::__normal_iterator<_Tp*, optional<_Tp&>>;
1530 };
1531#endif // __cpp_lib_optional_range_support
1532
1533 template<typename _Tp>
1534 class optional<_Tp&> : public __optional_ref_base<_Tp>
1535 {
1536 static_assert(__is_valid_contained_type_for_optional<_Tp&>);
1537
1538 public:
1539 using value_type = _Tp;
1540
1541 // Constructors.
1542 constexpr optional() noexcept = default;
1543 constexpr optional(nullopt_t) noexcept : optional() {}
1544 constexpr optional(const optional&) noexcept = default;
1545
1546 template<typename _Arg>
1547 requires is_constructible_v<_Tp&, _Arg>
1548 && (!reference_constructs_from_temporary_v<_Tp&, _Arg>)
1549 explicit constexpr
1550 optional(in_place_t, _Arg&& __arg)
1551 {
1552 __convert_ref_init_val(std::forward<_Arg>(__arg));
1553 }
1554
1555 template<typename _Up>
1556 requires (!is_same_v<remove_cvref_t<_Up>, optional>)
1557 && (!is_same_v<remove_cvref_t<_Up>, in_place_t>)
1558 && is_constructible_v<_Tp&, _Up>
1559 && (!reference_constructs_from_temporary_v<_Tp&, _Up>)
1560 explicit(!is_convertible_v<_Up, _Tp&>)
1561 constexpr
1562 optional(_Up&& __u)
1563 noexcept(is_nothrow_constructible_v<_Tp&, _Up>)
1564 {
1565 __convert_ref_init_val(std::forward<_Up>(__u));
1566 }
1567
1568 template<typename _Up>
1569 requires (!is_same_v<remove_cvref_t<_Up>, optional>)
1570 && (!is_same_v<remove_cvref_t<_Up>, in_place_t>)
1571 && is_constructible_v<_Tp&, _Up>
1572 && reference_constructs_from_temporary_v<_Tp&, _Up>
1573 explicit(!is_convertible_v<_Up, _Tp&>)
1574 constexpr
1575 optional(_Up&& __u) = delete;
1576
1577 // optional<U> &
1578 template<typename _Up>
1579 requires (!is_same_v<remove_cv_t<_Tp>, optional<_Up>>)
1580 && (!is_same_v<_Tp&, _Up>)
1581 && is_constructible_v<_Tp&, _Up&>
1582 && (!reference_constructs_from_temporary_v<_Tp&, _Up&>)
1583 explicit(!is_convertible_v<_Up&, _Tp&>)
1584 constexpr
1585 optional(optional<_Up>& __rhs)
1586 noexcept(is_nothrow_constructible_v<_Tp&, _Up&>)
1587 {
1588 if (__rhs)
1589 __convert_ref_init_val(__rhs._M_fwd());
1590 }
1591
1592 template<typename _Up>
1593 requires (!is_same_v<remove_cv_t<_Tp>, optional<_Up>>)
1594 && (!is_same_v<_Tp&, _Up>)
1595 && is_constructible_v<_Tp&, _Up&>
1596 && reference_constructs_from_temporary_v<_Tp&, _Up&>
1597 explicit(!is_convertible_v<_Up&, _Tp&>)
1598 constexpr
1599 optional(optional<_Up>& __rhs) = delete;
1600
1601 // const optional<U>&
1602 template<typename _Up>
1603 requires (!is_same_v<remove_cv_t<_Tp>, optional<_Up>>)
1604 && (!is_same_v<_Tp&, _Up>)
1605 && is_constructible_v<_Tp&, const _Up&>
1606 && (!reference_constructs_from_temporary_v<_Tp&, const _Up&>)
1607 explicit(!is_convertible_v<const _Up&, _Tp&>)
1608 constexpr
1609 optional(const optional<_Up>& __rhs)
1610 noexcept(is_nothrow_constructible_v<_Tp&, _Up&>)
1611 {
1612 if (__rhs)
1613 __convert_ref_init_val(__rhs._M_fwd());
1614 }
1615
1616 template<typename _Up>
1617 requires (!is_same_v<remove_cv_t<_Tp>, optional<_Up>>)
1618 && (!is_same_v<_Tp&, _Up>)
1619 && is_constructible_v<_Tp&, const _Up&>
1620 && reference_constructs_from_temporary_v<_Tp&, const _Up&>
1621 explicit(!is_convertible_v<const _Up&, _Tp&>)
1622 constexpr
1623 optional(const optional<_Up>& __rhs) = delete;
1624
1625 // optional<U>&&
1626 template<typename _Up>
1627 requires (!is_same_v<remove_cv_t<_Tp>, optional<_Up>>)
1628 && (!is_same_v<_Tp&, _Up>)
1629 && is_constructible_v<_Tp&, _Up>
1630 && (!reference_constructs_from_temporary_v<_Tp&, _Up>)
1631 explicit(!is_convertible_v<_Up, _Tp&>)
1632 constexpr
1633 optional(optional<_Up>&& __rhs)
1634 noexcept(is_nothrow_constructible_v<_Tp&, _Up>)
1635 {
1636 if (__rhs)
1637 __convert_ref_init_val(std::move(__rhs)._M_fwd());
1638 }
1639
1640 template<typename _Up>
1641 requires (!is_same_v<remove_cv_t<_Tp>, optional<_Up>>)
1642 && (!is_same_v<_Tp&, _Up>)
1643 && is_constructible_v<_Tp&, _Up>
1644 && reference_constructs_from_temporary_v<_Tp&, _Up>
1645 explicit(!is_convertible_v<_Up, _Tp&>)
1646 constexpr
1647 optional(optional<_Up>&& __rhs) = delete;
1648
1649 // const optional<U>&&
1650 template<typename _Up>
1651 requires (!is_same_v<remove_cv_t<_Tp>, optional<_Up>>)
1652 && (!is_same_v<_Tp&, _Up>)
1653 && is_constructible_v<_Tp&, const _Up>
1654 && (!reference_constructs_from_temporary_v<_Tp&, _Up>)
1655 explicit(!is_convertible_v<const _Up, _Tp&>)
1656 constexpr
1657 optional(const optional<_Up>&& __rhs)
1658 noexcept(is_nothrow_constructible_v<_Tp&, const _Up>)
1659 {
1660 if (__rhs)
1661 __convert_ref_init_val(std::move(__rhs)._M_fwd());
1662 }
1663
1664 template<typename _Up>
1665 requires (!is_same_v<remove_cv_t<_Tp>, optional<_Up>>)
1666 && (!is_same_v<_Tp&, _Up>)
1667 && is_constructible_v<_Tp&, const _Up>
1668 && reference_constructs_from_temporary_v<_Tp&, const _Up>
1669 explicit(!is_convertible_v<const _Up, _Tp&>)
1670 constexpr
1671 optional(const optional<_Up>&& __rhs) = delete;
1672
1673 constexpr ~optional() = default;
1674
1675 // Assignment.
1676 constexpr optional& operator=(nullopt_t) noexcept
1677 {
1678 _M_val = nullptr;
1679 return *this;
1680 }
1681
1682 constexpr optional& operator=(const optional&) noexcept = default;
1683
1684 template<typename _Up>
1685 requires is_constructible_v<_Tp&, _Up>
1686 && (!reference_constructs_from_temporary_v<_Tp&, _Up>)
1687 constexpr _Tp&
1688 emplace(_Up&& __u)
1689 noexcept(is_nothrow_constructible_v<_Tp&, _Up>)
1690 {
1691 __convert_ref_init_val(std::forward<_Up>(__u));
1692 // _GLIBCXX_RESOLVE_LIB_DEFECTS
1693 // 4300. Missing Returns: element in optional<T&>::emplace
1694 return *_M_val;
1695 }
1696
1697 // Swap.
1698 constexpr void swap(optional& __rhs) noexcept
1699 { std::swap(_M_val, __rhs._M_val); }
1700
1701#ifdef __cpp_lib_optional_range_support // >= C++26
1702 // Iterator support.
1703 constexpr auto begin() const noexcept
1704 requires is_object_v<_Tp> && (!is_unbounded_array_v<_Tp>)
1705 { return __gnu_cxx::__normal_iterator<_Tp*, optional>(_M_val); }
1706
1707 constexpr auto end() const noexcept
1708 requires is_object_v<_Tp> && (!is_unbounded_array_v<_Tp>)
1709 { return begin() + has_value(); }
1710#endif // __cpp_lib_optional_range_support
1711
1712 // Observers.
1713 constexpr _Tp* operator->() const noexcept
1714 {
1715 __glibcxx_assert(_M_val); // hardened precondition
1716 return _M_val;
1717 }
1718
1719 constexpr _Tp& operator*() const noexcept
1720 {
1721 __glibcxx_assert(_M_val); // hardened precondition
1722 return *_M_val;
1723 }
1724
1725 constexpr explicit operator bool() const noexcept
1726 {
1727 return _M_val;
1728 }
1729
1730 constexpr bool has_value() const noexcept
1731 {
1732 return _M_val;
1733 }
1734
1735 constexpr _Tp& value() const
1736 {
1737 if (_M_val)
1738 return *_M_val;
1739 __throw_bad_optional_access();
1740 }
1741
1742 // _GLIBCXX_RESOLVE_LIB_DEFECTS
1743 // 4304. std::optional<NonReturnable&> is ill-formed due to value_or
1744 template<typename _Up = remove_cv_t<_Tp>>
1745 requires is_object_v<_Tp> && (!is_array_v<_Tp>)
1746 constexpr decay_t<_Tp>
1747 value_or(_Up&& __u) const
1748 {
1749 using _Xp = remove_cv_t<_Tp>;
1750 static_assert(is_convertible_v<_Tp&, _Xp>);
1751 static_assert(is_convertible_v<_Up, _Xp>);
1752 if (_M_val)
1753 return *_M_val;
1754 return std::forward<_Up>(__u);
1755 }
1756
1757 // Monadic operations.
1758 template<typename _Fn>
1759 constexpr auto
1760 and_then(_Fn&& __f) const
1761 {
1762 using _Up = remove_cvref_t<invoke_result_t<_Fn, _Tp&>>;
1763 static_assert(__is_optional_v<_Up>,
1764 "the function passed to std::optional<T&>::and_then "
1765 "must return a std::optional");
1766 if (has_value())
1767 return std::__invoke(std::forward<_Fn>(__f), *_M_val);
1768 else
1769 return _Up();
1770 }
1771
1772 template<typename _Fn>
1773 constexpr
1774 optional<remove_cv_t<invoke_result_t<_Fn, _Tp&>>>
1775 transform(_Fn&& __f) const
1776 {
1777 using _Up = remove_cv_t<invoke_result_t<_Fn, _Tp&>>;
1778 if (has_value())
1779 return optional<_Up>(_Optional_func<_Fn>{__f}, *_M_val);
1780 else
1781 return optional<_Up>();
1782 }
1783
1784 template<typename _Fn>
1785 requires invocable<_Fn>
1786 constexpr
1787 optional
1788 or_else(_Fn&& __f) const
1789 {
1790 static_assert(is_same_v<remove_cvref_t<invoke_result_t<_Fn>>, optional>,
1791 "the function passed to std::optional<T&>::or_else "
1792 "must return a std::optional<T&>");
1793 // _GLIBCXX_RESOLVE_LIB_DEFECTS
1794 // 4367. Improve optional<T&>::or_else
1795 if (has_value())
1796 return *this;
1797 else
1798 return std::forward<_Fn>(__f)();
1799 }
1800
1801 // Modifiers.
1802 constexpr void reset() noexcept
1803 {
1804 _M_val = nullptr;
1805 }
1806
1807 private:
1808 _Tp *_M_val = nullptr;
1809
1810 [[__gnu__::__always_inline__]]
1811 constexpr _Tp&
1812 _M_fwd() const noexcept
1813 { return *_M_val; }
1814
1815 template<typename _Up> friend class optional;
1816
1817 template<typename _Up>
1818 constexpr
1819 void
1820 __convert_ref_init_val(_Up&& __u)
1821 noexcept
1822 {
1823 _Tp& __r(std::forward<_Up>(__u));
1824 _M_val = std::addressof(__r);
1825 }
1826
1827 template<typename _Fn, typename _Value>
1828 explicit constexpr
1829 optional(_Optional_func<_Fn> __f, _Value&& __v)
1830 {
1831 _Tp& __r = std::__invoke(std::forward<_Fn>(__f._M_f), std::forward<_Value>(__v));
1832 _M_val = std::addressof(__r);
1833 }
1834 };
1835#endif // __cpp_lib_optional >= 202506L
1836
1837 template<typename _Tp>
1838 using __optional_relop_t =
1839 enable_if_t<is_convertible_v<_Tp, bool>, bool>;
1840
1841 template<typename _Tp, typename _Up>
1842 using __optional_eq_t = __optional_relop_t<
1843 decltype(std::declval<const _Tp&>() == std::declval<const _Up&>())
1844 >;
1845
1846 template<typename _Tp, typename _Up>
1847 using __optional_ne_t = __optional_relop_t<
1848 decltype(std::declval<const _Tp&>() != std::declval<const _Up&>())
1849 >;
1850
1851 template<typename _Tp, typename _Up>
1852 using __optional_lt_t = __optional_relop_t<
1853 decltype(std::declval<const _Tp&>() < std::declval<const _Up&>())
1854 >;
1855
1856 template<typename _Tp, typename _Up>
1857 using __optional_gt_t = __optional_relop_t<
1858 decltype(std::declval<const _Tp&>() > std::declval<const _Up&>())
1859 >;
1860
1861 template<typename _Tp, typename _Up>
1862 using __optional_le_t = __optional_relop_t<
1863 decltype(std::declval<const _Tp&>() <= std::declval<const _Up&>())
1864 >;
1865
1866 template<typename _Tp, typename _Up>
1867 using __optional_ge_t = __optional_relop_t<
1868 decltype(std::declval<const _Tp&>() >= std::declval<const _Up&>())
1869 >;
1870
1871 // Comparisons between optional values.
1872 template<typename _Tp, typename _Up>
1873 constexpr auto
1874 operator==(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
1875 -> __optional_eq_t<_Tp, _Up>
1876 {
1877 if (__lhs.has_value() != __rhs.has_value())
1878 return false;
1879 if (!__lhs.has_value())
1880 return true;
1881 return *__lhs == *__rhs;
1882 }
1883
1884 template<typename _Tp, typename _Up>
1885 constexpr auto
1886 operator!=(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
1887 -> __optional_ne_t<_Tp, _Up>
1888 {
1889 if (__lhs.has_value() != __rhs.has_value())
1890 return true;
1891 if (!__lhs.has_value())
1892 return false;
1893 return *__lhs != *__rhs;
1894 }
1895
1896 template<typename _Tp, typename _Up>
1897 constexpr auto
1898 operator<(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
1899 -> __optional_lt_t<_Tp, _Up>
1900 {
1901 if (!__rhs.has_value())
1902 return false;
1903 if (!__lhs.has_value())
1904 return true;
1905 return *__lhs < *__rhs;
1906 }
1907
1908 template<typename _Tp, typename _Up>
1909 constexpr auto
1910 operator>(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
1911 -> __optional_gt_t<_Tp, _Up>
1912 {
1913 if (!__lhs.has_value())
1914 return false;
1915 if (!__rhs.has_value())
1916 return true;
1917 return *__lhs > *__rhs;
1918 }
1919
1920 template<typename _Tp, typename _Up>
1921 constexpr auto
1922 operator<=(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
1923 -> __optional_le_t<_Tp, _Up>
1924 {
1925 if (!__lhs.has_value())
1926 return true;
1927 if (!__rhs.has_value())
1928 return false;
1929 return *__lhs <= *__rhs;
1930 }
1931
1932 template<typename _Tp, typename _Up>
1933 constexpr auto
1934 operator>=(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
1935 -> __optional_ge_t<_Tp, _Up>
1936 {
1937 if (!__rhs.has_value())
1938 return true;
1939 if (!__lhs.has_value())
1940 return false;
1941 return *__lhs >= *__rhs;
1942 }
1943
1944#ifdef __cpp_lib_three_way_comparison
1945 template<typename _Tp, three_way_comparable_with<_Tp> _Up>
1946 [[nodiscard]]
1947 constexpr compare_three_way_result_t<_Tp, _Up>
1948 operator<=>(const optional<_Tp>& __x, const optional<_Up>& __y)
1949 {
1950 return __x && __y ? *__x <=> *__y : bool(__x) <=> bool(__y);
1951 }
1952#endif
1953
1954 // Comparisons with nullopt.
1955 template<typename _Tp>
1956 [[nodiscard]]
1957 constexpr bool
1958 operator==(const optional<_Tp>& __lhs, nullopt_t) noexcept
1959 { return !__lhs; }
1960
1961#ifdef __cpp_lib_three_way_comparison
1962 template<typename _Tp>
1963 [[nodiscard]]
1964 constexpr strong_ordering
1965 operator<=>(const optional<_Tp>& __x, nullopt_t) noexcept
1966 { return bool(__x) <=> false; }
1967#else
1968 template<typename _Tp>
1969 constexpr bool
1970 operator==(nullopt_t, const optional<_Tp>& __rhs) noexcept
1971 { return !__rhs; }
1972
1973 template<typename _Tp>
1974 constexpr bool
1975 operator!=(const optional<_Tp>& __lhs, nullopt_t) noexcept
1976 { return static_cast<bool>(__lhs); }
1977
1978 template<typename _Tp>
1979 constexpr bool
1980 operator!=(nullopt_t, const optional<_Tp>& __rhs) noexcept
1981 { return static_cast<bool>(__rhs); }
1982
1983 template<typename _Tp>
1984 constexpr bool
1985 operator<(const optional<_Tp>& /* __lhs */, nullopt_t) noexcept
1986 { return false; }
1987
1988 template<typename _Tp>
1989 constexpr bool
1990 operator<(nullopt_t, const optional<_Tp>& __rhs) noexcept
1991 { return static_cast<bool>(__rhs); }
1992
1993 template<typename _Tp>
1994 constexpr bool
1995 operator>(const optional<_Tp>& __lhs, nullopt_t) noexcept
1996 { return static_cast<bool>(__lhs); }
1997
1998 template<typename _Tp>
1999 constexpr bool
2000 operator>(nullopt_t, const optional<_Tp>& /* __rhs */) noexcept
2001 { return false; }
2002
2003 template<typename _Tp>
2004 constexpr bool
2005 operator<=(const optional<_Tp>& __lhs, nullopt_t) noexcept
2006 { return !__lhs; }
2007
2008 template<typename _Tp>
2009 constexpr bool
2010 operator<=(nullopt_t, const optional<_Tp>& /* __rhs */) noexcept
2011 { return true; }
2012
2013 template<typename _Tp>
2014 constexpr bool
2015 operator>=(const optional<_Tp>& /* __lhs */, nullopt_t) noexcept
2016 { return true; }
2017
2018 template<typename _Tp>
2019 constexpr bool
2020 operator>=(nullopt_t, const optional<_Tp>& __rhs) noexcept
2021 { return !__rhs; }
2022#endif // three-way-comparison
2023
2024#if __cpp_lib_concepts
2025 // _GLIBCXX_RESOLVE_LIB_DEFECTS
2026 // 4072. std::optional comparisons: constrain harder
2027# define _REQUIRES_NOT_OPTIONAL(T) requires (!__is_optional_v<T>)
2028#else
2029# define _REQUIRES_NOT_OPTIONAL(T)
2030#endif
2031
2032 // Comparisons with value type.
2033 template<typename _Tp, typename _Up>
2034 _REQUIRES_NOT_OPTIONAL(_Up)
2035 constexpr auto
2036 operator== [[nodiscard]] (const optional<_Tp>& __lhs, const _Up& __rhs)
2037 -> __optional_eq_t<_Tp, _Up>
2038 {
2039 if (__lhs.has_value())
2040 return *__lhs == __rhs;
2041 return false;
2042 }
2043
2044 template<typename _Tp, typename _Up>
2045 _REQUIRES_NOT_OPTIONAL(_Tp)
2046 constexpr auto
2047 operator== [[nodiscard]] (const _Tp& __lhs, const optional<_Up>& __rhs)
2048 -> __optional_eq_t<_Tp, _Up>
2049 {
2050 if (__rhs.has_value())
2051 return __lhs == *__rhs;
2052 return false;
2053 }
2054
2055 template<typename _Tp, typename _Up>
2056 _REQUIRES_NOT_OPTIONAL(_Up)
2057 constexpr auto
2058 operator!= [[nodiscard]] (const optional<_Tp>& __lhs, const _Up& __rhs)
2059 -> __optional_ne_t<_Tp, _Up>
2060 {
2061 if (__lhs.has_value())
2062 return *__lhs != __rhs;
2063 return true;
2064 }
2065
2066 template<typename _Tp, typename _Up>
2067 _REQUIRES_NOT_OPTIONAL(_Tp)
2068 constexpr auto
2069 operator!= [[nodiscard]] (const _Tp& __lhs, const optional<_Up>& __rhs)
2070 -> __optional_ne_t<_Tp, _Up>
2071 {
2072 if (__rhs.has_value())
2073 return __lhs != *__rhs;
2074 return true;
2075 }
2076
2077 template<typename _Tp, typename _Up>
2078 _REQUIRES_NOT_OPTIONAL(_Up)
2079 constexpr auto
2080 operator< [[nodiscard]] (const optional<_Tp>& __lhs, const _Up& __rhs)
2081 -> __optional_lt_t<_Tp, _Up>
2082 {
2083 if (__lhs.has_value())
2084 return *__lhs < __rhs;
2085 return true;
2086 }
2087
2088 template<typename _Tp, typename _Up>
2089 _REQUIRES_NOT_OPTIONAL(_Tp)
2090 constexpr auto
2091 operator< [[nodiscard]] (const _Tp& __lhs, const optional<_Up>& __rhs)
2092 -> __optional_lt_t<_Tp, _Up>
2093 {
2094 if (__rhs.has_value())
2095 return __lhs < *__rhs;
2096 return false;
2097 }
2098
2099 template<typename _Tp, typename _Up>
2100 _REQUIRES_NOT_OPTIONAL(_Up)
2101 constexpr auto
2102 operator> [[nodiscard]] (const optional<_Tp>& __lhs, const _Up& __rhs)
2103 -> __optional_gt_t<_Tp, _Up>
2104 {
2105 if (__lhs.has_value())
2106 return *__lhs > __rhs;
2107 return false;
2108 }
2109
2110 template<typename _Tp, typename _Up>
2111 _REQUIRES_NOT_OPTIONAL(_Tp)
2112 constexpr auto
2113 operator> [[nodiscard]] (const _Tp& __lhs, const optional<_Up>& __rhs)
2114 -> __optional_gt_t<_Tp, _Up>
2115 {
2116 if (__rhs.has_value())
2117 return __lhs > *__rhs;
2118 return true;
2119 }
2120
2121 template<typename _Tp, typename _Up>
2122 _REQUIRES_NOT_OPTIONAL(_Up)
2123 constexpr auto
2124 operator<= [[nodiscard]] (const optional<_Tp>& __lhs, const _Up& __rhs)
2125 -> __optional_le_t<_Tp, _Up>
2126 {
2127 if (__lhs.has_value())
2128 return *__lhs <= __rhs;
2129 return true;
2130 }
2131
2132 template<typename _Tp, typename _Up>
2133 _REQUIRES_NOT_OPTIONAL(_Tp)
2134 constexpr auto
2135 operator<= [[nodiscard]] (const _Tp& __lhs, const optional<_Up>& __rhs)
2136 -> __optional_le_t<_Tp, _Up>
2137 {
2138 if (__rhs.has_value())
2139 return __lhs <= *__rhs;
2140 return false;
2141 }
2142
2143 template<typename _Tp, typename _Up>
2144 _REQUIRES_NOT_OPTIONAL(_Up)
2145 constexpr auto
2146 operator>= [[nodiscard]] (const optional<_Tp>& __lhs, const _Up& __rhs)
2147 -> __optional_ge_t<_Tp, _Up>
2148 {
2149 if (__lhs.has_value())
2150 return *__lhs >= __rhs;
2151 return false;
2152 }
2153
2154 template<typename _Tp, typename _Up>
2155 _REQUIRES_NOT_OPTIONAL(_Tp)
2156 constexpr auto
2157 operator>= [[nodiscard]] (const _Tp& __lhs, const optional<_Up>& __rhs)
2158 -> __optional_ge_t<_Tp, _Up>
2159 {
2160 if (__rhs.has_value())
2161 return __lhs >= *__rhs;
2162 return true;
2163 }
2164
2165#ifdef __cpp_lib_three_way_comparison
2166 // _GLIBCXX_RESOLVE_LIB_DEFECTS
2167 // 3746. optional's spaceship with U with a type derived from optional
2168 // causes infinite constraint meta-recursion
2169 template<typename _Tp>
2170 concept __is_derived_from_optional = requires (const _Tp& __t) {
2171 []<typename _Up>(const optional<_Up>&){ }(__t);
2172 };
2173
2174 template<typename _Tp, typename _Up>
2175 requires (!__is_derived_from_optional<_Up>)
2176 && requires { typename compare_three_way_result_t<_Tp, _Up>; }
2177 && three_way_comparable_with<_Tp, _Up>
2178 constexpr compare_three_way_result_t<_Tp, _Up>
2179 operator<=> [[nodiscard]] (const optional<_Tp>& __x, const _Up& __v)
2180 { return bool(__x) ? *__x <=> __v : strong_ordering::less; }
2181#endif
2182
2183 // Swap and creation functions.
2184
2185 // _GLIBCXX_RESOLVE_LIB_DEFECTS
2186 // 2748. swappable traits for optionals
2187 template<typename _Tp>
2188 _GLIBCXX20_CONSTEXPR
2189 inline enable_if_t<is_move_constructible_v<_Tp> && is_swappable_v<_Tp>>
2190 swap(optional<_Tp>& __lhs, optional<_Tp>& __rhs)
2191 noexcept(noexcept(__lhs.swap(__rhs)))
2192 { __lhs.swap(__rhs); }
2193
2194#if __cpp_lib_optional >= 202506L
2195 // We deviate from standard, that do not declared separate swap overload
2196 // from optional<T&>.
2197 template<typename _Tp>
2198 constexpr void
2199 swap(optional<_Tp&>& __lhs, optional<_Tp&>& __rhs) noexcept
2200 { __lhs.swap(__rhs); }
2201#endif
2202
2203 // _GLIBCXX_RESOLVE_LIB_DEFECTS
2204 // 2766. Swapping non-swappable types
2205 template<typename _Tp>
2206 enable_if_t<!(is_move_constructible_v<_Tp> && is_swappable_v<_Tp>)>
2207 swap(optional<_Tp>&, optional<_Tp>&) = delete;
2208
2209#if __cpp_lib_optional >= 202506L
2210 template<int = 0, typename _Tp>
2211#else
2212 template<typename _Tp>
2213#endif
2214 constexpr
2215 enable_if_t<is_constructible_v<decay_t<_Tp>, _Tp>,
2216 optional<decay_t<_Tp>>>
2217 make_optional(_Tp&& __t)
2218 noexcept(is_nothrow_constructible_v<optional<decay_t<_Tp>>, _Tp>)
2219 { return optional<decay_t<_Tp>>( std::forward<_Tp>(__t) ); }
2220
2221 template<typename _Tp, typename... _Args>
2222 constexpr
2223 enable_if_t<is_constructible_v<_Tp, _Args...>,
2224 optional<_Tp>>
2225 make_optional(_Args&&... __args)
2226 noexcept(is_nothrow_constructible_v<_Tp, _Args...>)
2227 { return optional<_Tp>( in_place, std::forward<_Args>(__args)... ); }
2228
2229 template<typename _Tp, typename _Up, typename... _Args>
2230 constexpr
2231 enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>,
2232 optional<_Tp>>
2233 make_optional(initializer_list<_Up> __il, _Args&&... __args)
2234 noexcept(is_nothrow_constructible_v<_Tp, initializer_list<_Up>&, _Args...>)
2235 { return optional<_Tp>( in_place, __il, std::forward<_Args>(__args)... ); }
2236
2237 // Hash.
2238
2239 template<typename _Tp, typename _Up = remove_const_t<_Tp>>
2240 struct __optional_hash
2241#if ! _GLIBCXX_INLINE_VERSION
2242 : public __hash_empty_base<_Up>
2243#endif
2244 {
2245#if __cplusplus < 202002L
2246 using result_type [[__deprecated__]] = size_t;
2247 using argument_type [[__deprecated__]] = optional<_Tp>;
2248#endif
2249
2250 size_t
2251 operator()(const optional<_Tp>& __t) const
2252 noexcept(noexcept(hash<_Up>{}(*__t)))
2253 {
2254 // We pick an arbitrary hash for disengaged optionals which hopefully
2255 // usual values of _Tp won't typically hash to.
2256 constexpr size_t __magic_disengaged_hash = static_cast<size_t>(-3333);
2257 return __t ? hash<_Up>{}(*__t) : __magic_disengaged_hash;
2258 }
2259 };
2260
2261 template<typename _Tp>
2262 struct hash<optional<_Tp>>
2263 // hash for optional<T&> is disabled because is_hash_enabled_for<T&> is false
2264 : public __conditional_t<__is_hash_enabled_for<remove_const_t<_Tp>>,
2265 __optional_hash<_Tp>,
2266 __hash_not_enabled<_Tp>>
2267 { };
2268
2269 template<typename _Tp>
2270 struct __is_fast_hash<hash<optional<_Tp>>> : __is_fast_hash<hash<_Tp>>
2271 { };
2272
2273 /// @}
2274
2275#if __cpp_deduction_guides >= 201606
2276 template <typename _Tp> optional(_Tp) -> optional<_Tp>;
2277#endif
2278
2279#ifdef __cpp_lib_optional_range_support // >= C++26
2280 template<typename _Tp>
2281 inline constexpr bool
2282 ranges::enable_view<optional<_Tp>> = true;
2283
2284#if __cpp_lib_optional >= 202506L // C++26
2285 template<typename _Tp>
2286 constexpr bool
2287 ranges::enable_borrowed_range<optional<_Tp&>> = true;
2288#endif
2289
2290#if _GLIBCXX_HOSTED
2291 template<typename _Tp>
2292 inline constexpr range_format
2293 format_kind<optional<_Tp>> = range_format::disabled;
2294#endif
2295#endif // __cpp_lib_optional_range_support
2296
2297#undef _GLIBCXX_USE_CONSTRAINTS_FOR_OPTIONAL
2298
2299_GLIBCXX_END_NAMESPACE_VERSION
2300} // namespace std
2301
2302#endif // __cpp_lib_optional
2303
2304#endif // _GLIBCXX_OPTIONAL
std::ranges::enable_view
constexpr bool enable_view
[range.view] The ranges::enable_view boolean.
Definition ranges_base.h:602
std::operator*
constexpr complex< _Tp > operator*(const complex< _Tp > &__x, const complex< _Tp > &__y)
Return new complex value x times y.
Definition complex:434
std::true_type
__bool_constant< true > true_type
The type used as a compile-time boolean with true value.
Definition type_traits:119
std::remove_reference_t
typename remove_reference< _Tp >::type remove_reference_t
Alias template for remove_reference.
Definition type_traits:1913
std::enable_if_t
typename enable_if< _Cond, _Tp >::type enable_if_t
Alias template for enable_if.
Definition type_traits:2967
std::decay_t
typename decay< _Tp >::type decay_t
Alias template for decay.
Definition type_traits:2963
std::declval
auto declval() noexcept -> decltype(__declval< _Tp >(0))
Definition type_traits:2741
std::addressof
constexpr _Tp * addressof(_Tp &__r) noexcept
Returns the actual address of the object or function referenced by r, even in the presence of an over...
Definition move.h:176
std::move
constexpr std::remove_reference< _Tp >::type && move(_Tp &&__t) noexcept
Convert a value to an rvalue.
Definition move.h:138
std::__invoke
constexpr __invoke_result< _Callable, _Args... >::type __invoke(_Callable &&__fn, _Args &&... __args) noexcept(__is_nothrow_invocable< _Callable, _Args... >::value)
Invoke a callable object.
Definition invoke.h:92
std::__addressof
constexpr _Tp * __addressof(_Tp &__r) noexcept
Same as C++11 std::addressof.
Definition move.h:52
std::forward
constexpr _Tp && forward(typename std::remove_reference< _Tp >::type &__t) noexcept
Forward an lvalue.
Definition move.h:72
std::experimental::fundamentals_v1::nullopt
constexpr nullopt_t nullopt
Tag to disengage optional objects.
Definition experimental/optional:98
std
ISO C++ entities toplevel namespace is std.
std::end
constexpr auto end(_Container &__cont) noexcept(noexcept(__cont.end())) -> decltype(__cont.end())
Return an iterator pointing to one past the last element of the container.
Definition range_access.h:80
std::compare_three_way_result_t
typename __detail::__cmp3way_res_impl< _Tp, _Up >::type compare_three_way_result_t
[cmp.result], result of three-way comparison
Definition compare:547
std::_Construct
constexpr void _Construct(_Tp *__p, _Args &&... __args)
Definition stl_construct.h:123
std::begin
constexpr auto begin(_Container &__cont) noexcept(noexcept(__cont.begin())) -> decltype(__cont.begin())
Return an iterator pointing to the first element of the container.
Definition range_access.h:55
std::initializer_list
initializer_list
Definition initializer_list:51
std::hash
Primary class template hash.
Definition functional_hash.h:106
std::is_constructible
is_constructible
Definition type_traits:1265
std::is_assignable
is_assignable
Definition type_traits:1384
std::exception
Base class for all library exceptions.
Definition exception.h:62
std::invocable
[concept.invocable], concept invocable
Definition concepts:383