libstdc++: optional Source File

libstdc++

experimental/optional
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1// <experimental/optional> -*- C++ -*-
2
3// Copyright (C) 2013-2026 Free Software Foundation, Inc.
4//
5// This file is part of the GNU ISO C++ Library. This library is free
6// software; you can redistribute it and/or modify it under the
7// terms of the GNU General Public License as published by the
8// Free Software Foundation; either version 3, or (at your option)
9// any later version.
10
11// This library is distributed in the hope that it will be useful,
12// but WITHOUT ANY WARRANTY; without even the implied warranty of
13// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14// GNU General Public License for more details.
15
16// Under Section 7 of GPL version 3, you are granted additional
17// permissions described in the GCC Runtime Library Exception, version
18// 3.1, as published by the Free Software Foundation.
19
20// You should have received a copy of the GNU General Public License and
21// a copy of the GCC Runtime Library Exception along with this program;
22// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23// <http://www.gnu.org/licenses/>.
24
25/** @file experimental/optional
26 * This is a TS C++ Library header.
27 * @ingroup libfund-ts
28 */
29
30#ifndef _GLIBCXX_EXPERIMENTAL_OPTIONAL
31#define _GLIBCXX_EXPERIMENTAL_OPTIONAL 1
32
33#include <bits/requires_hosted.h> // experimental is currently omitted
34
35#if __cplusplus >= 201402L
36
37#include <type_traits>
38#include <stdexcept>
39#include <new>
40#include <initializer_list>
41#include <bits/exception_defines.h>
42#include <bits/functional_hash.h>
43#include <bits/enable_special_members.h>
44#include <bits/move.h>
45#include <experimental/bits/lfts_config.h>
46
47namespace std _GLIBCXX_VISIBILITY(default)
48{
49_GLIBCXX_BEGIN_NAMESPACE_VERSION
50
51namespace experimental
52{
53inline namespace fundamentals_v1
54{
55 /**
56 * @defgroup optional Optional values
57 * @ingroup libfund-ts
58 *
59 * Class template for optional values and surrounding facilities, as
60 * described in n3793 "A proposal to add a utility class to represent
61 * optional objects (Revision 5)".
62 *
63 * @{
64 */
65
66#define __cpp_lib_experimental_optional 201411
67
68 // All subsequent [X.Y.n] references are against n3793.
69
70 // [X.Y.4]
71 template<typename _Tp>
72 class optional;
73
74 // [X.Y.5]
75 /// Tag type for in-place construction.
76 struct in_place_t { };
77
78 /// Tag for in-place construction.
79 constexpr in_place_t in_place { };
80
81 // [X.Y.6]
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) { }
94 };
95
96 // [X.Y.6]
97 /// Tag to disengage optional objects.
98 constexpr nullopt_t nullopt { nullopt_t::_Construct::_Token };
99
100 // [X.Y.7]
101 /**
102 * @brief Exception class thrown when a disengaged optional object is
103 * dereferenced.
104 * @ingroup exceptions
105 */
106 class bad_optional_access : public logic_error
107 {
108 public:
109 bad_optional_access() : logic_error("bad optional access") { }
110
111 // XXX This constructor is non-standard. Should not be inline
112 explicit bad_optional_access(const char* __arg) : logic_error(__arg) { }
113
114 virtual ~bad_optional_access() noexcept = default;
115 };
116
117 /// @cond undocumented
118
119 // XXX Does not belong here.
120 [[noreturn]] inline void
121 __throw_bad_optional_access(const char* __s)
122 { _GLIBCXX_THROW_OR_ABORT(bad_optional_access(__s)); }
123
124 /**
125 * @brief Class template that holds the necessary state for @ref optional
126 * and that has the responsibility for construction and the special members.
127 *
128 * Such a separate base class template is necessary in order to
129 * conditionally enable the special members (e.g. copy/move constructors).
130 * Note that this means that @ref _Optional_base implements the
131 * functionality for copy and move assignment, but not for converting
132 * assignment.
133 *
134 * @see optional, _Enable_special_members
135 */
136 template<typename _Tp, bool _ShouldProvideDestructor =
137 !is_trivially_destructible<_Tp>::value>
138 class _Optional_base
139 {
140 private:
141 // Remove const to avoid prohibition of reusing object storage for
142 // const-qualified types in [3.8/9]. This is strictly internal
143 // and even optional itself is oblivious to it.
144 using _Stored_type = remove_const_t<_Tp>;
145
146 public:
147 // [X.Y.4.1] Constructors.
148
149 // Constructors for disengaged optionals.
150 constexpr _Optional_base() noexcept
151 : _M_empty{} { }
152
153 constexpr _Optional_base(nullopt_t) noexcept
154 : _Optional_base{} { }
155
156 // Constructors for engaged optionals.
157 template<typename... _Args>
158 constexpr explicit _Optional_base(in_place_t, _Args&&... __args)
159 : _M_payload(std::forward<_Args>(__args)...), _M_engaged(true) { }
160
161 template<typename _Up, typename... _Args,
162 enable_if_t<is_constructible<_Tp,
163 initializer_list<_Up>&,
164 _Args&&...>::value,
165 int>...>
166 constexpr explicit _Optional_base(in_place_t,
167 initializer_list<_Up> __il,
168 _Args&&... __args)
169 : _M_payload(__il, std::forward<_Args>(__args)...),
170 _M_engaged(true) { }
171
172 // Copy and move constructors.
173 _Optional_base(const _Optional_base& __other)
174 {
175 if (__other._M_engaged)
176 this->_M_construct(__other._M_get());
177 }
178
179 _Optional_base(_Optional_base&& __other)
180 noexcept(is_nothrow_move_constructible<_Tp>())
181 {
182 if (__other._M_engaged)
183 this->_M_construct(std::move(__other._M_get()));
184 }
185
186 // [X.Y.4.3] (partly) Assignment.
187 _Optional_base&
188 operator=(const _Optional_base& __other)
189 {
190 if (this->_M_engaged && __other._M_engaged)
191 this->_M_get() = __other._M_get();
192 else
193 {
194 if (__other._M_engaged)
195 this->_M_construct(__other._M_get());
196 else
197 this->_M_reset();
198 }
199
200 return *this;
201 }
202
203 _Optional_base&
204 operator=(_Optional_base&& __other)
205 noexcept(__and_<is_nothrow_move_constructible<_Tp>,
206 is_nothrow_move_assignable<_Tp>>())
207 {
208 if (this->_M_engaged && __other._M_engaged)
209 this->_M_get() = std::move(__other._M_get());
210 else
211 {
212 if (__other._M_engaged)
213 this->_M_construct(std::move(__other._M_get()));
214 else
215 this->_M_reset();
216 }
217 return *this;
218 }
219
220 // [X.Y.4.2] Destructor.
221 ~_Optional_base()
222 {
223 if (this->_M_engaged)
224 this->_M_payload.~_Stored_type();
225 }
226
227 // The following functionality is also needed by optional, hence the
228 // protected accessibility.
229 protected:
230 constexpr bool _M_is_engaged() const noexcept
231 { return this->_M_engaged; }
232
233 // The _M_get operations have _M_engaged as a precondition.
234 constexpr _Tp&
235 _M_get() noexcept
236 { return _M_payload; }
237
238 constexpr const _Tp&
239 _M_get() const noexcept
240 { return _M_payload; }
241
242 // The _M_construct operation has !_M_engaged as a precondition
243 // while _M_destruct has _M_engaged as a precondition.
244 template<typename... _Args>
245 void
246 _M_construct(_Args&&... __args)
247 noexcept(is_nothrow_constructible<_Stored_type, _Args...>())
248 {
249 ::new (std::__addressof(this->_M_payload))
250 _Stored_type(std::forward<_Args>(__args)...);
251 this->_M_engaged = true;
252 }
253
254 void
255 _M_destruct()
256 {
257 this->_M_engaged = false;
258 this->_M_payload.~_Stored_type();
259 }
260
261 // _M_reset is a 'safe' operation with no precondition.
262 void
263 _M_reset()
264 {
265 if (this->_M_engaged)
266 this->_M_destruct();
267 }
268
269 private:
270 struct _Empty_byte { };
271 union {
272 _Empty_byte _M_empty;
273 _Stored_type _M_payload;
274 };
275 bool _M_engaged = false;
276 };
277
278 /// Partial specialization that is exactly identical to the primary template
279 /// save for not providing a destructor, to fulfill triviality requirements.
280 template<typename _Tp>
281 class _Optional_base<_Tp, false>
282 {
283 private:
284 using _Stored_type = remove_const_t<_Tp>;
285
286 public:
287 constexpr _Optional_base() noexcept
288 : _M_empty{} { }
289
290 constexpr _Optional_base(nullopt_t) noexcept
291 : _Optional_base{} { }
292
293 template<typename... _Args>
294 constexpr explicit _Optional_base(in_place_t, _Args&&... __args)
295 : _M_payload(std::forward<_Args>(__args)...), _M_engaged(true) { }
296
297 template<typename _Up, typename... _Args,
298 enable_if_t<is_constructible<_Tp,
299 initializer_list<_Up>&,
300 _Args&&...>::value,
301 int>...>
302 constexpr explicit _Optional_base(in_place_t,
303 initializer_list<_Up> __il,
304 _Args&&... __args)
305 : _M_payload(__il, std::forward<_Args>(__args)...),
306 _M_engaged(true) { }
307
308 _Optional_base(const _Optional_base& __other)
309 {
310 if (__other._M_engaged)
311 this->_M_construct(__other._M_get());
312 }
313
314 _Optional_base(_Optional_base&& __other)
315 noexcept(is_nothrow_move_constructible<_Tp>())
316 {
317 if (__other._M_engaged)
318 this->_M_construct(std::move(__other._M_get()));
319 }
320
321 _Optional_base&
322 operator=(const _Optional_base& __other)
323 {
324 if (this->_M_engaged && __other._M_engaged)
325 this->_M_get() = __other._M_get();
326 else
327 {
328 if (__other._M_engaged)
329 this->_M_construct(__other._M_get());
330 else
331 this->_M_reset();
332 }
333 return *this;
334 }
335
336 _Optional_base&
337 operator=(_Optional_base&& __other)
338 noexcept(__and_<is_nothrow_move_constructible<_Tp>,
339 is_nothrow_move_assignable<_Tp>>())
340 {
341 if (this->_M_engaged && __other._M_engaged)
342 this->_M_get() = std::move(__other._M_get());
343 else
344 {
345 if (__other._M_engaged)
346 this->_M_construct(std::move(__other._M_get()));
347 else
348 this->_M_reset();
349 }
350 return *this;
351 }
352
353 // Sole difference
354 // ~_Optional_base() noexcept = default;
355
356 protected:
357 constexpr bool _M_is_engaged() const noexcept
358 { return this->_M_engaged; }
359
360 _Tp&
361 _M_get() noexcept
362 { return _M_payload; }
363
364 constexpr const _Tp&
365 _M_get() const noexcept
366 { return _M_payload; }
367
368 template<typename... _Args>
369 void
370 _M_construct(_Args&&... __args)
371 noexcept(is_nothrow_constructible<_Stored_type, _Args...>())
372 {
373 ::new (std::__addressof(this->_M_payload))
374 _Stored_type(std::forward<_Args>(__args)...);
375 this->_M_engaged = true;
376 }
377
378 void
379 _M_destruct()
380 {
381 this->_M_engaged = false;
382 this->_M_payload.~_Stored_type();
383 }
384
385 void
386 _M_reset()
387 {
388 if (this->_M_engaged)
389 this->_M_destruct();
390 }
391
392 private:
393 struct _Empty_byte { };
394 union
395 {
396 _Empty_byte _M_empty;
397 _Stored_type _M_payload;
398 };
399 bool _M_engaged = false;
400 };
401
402 template<typename _Tp, typename _Up>
403 using __converts_from_optional =
404 __or_<is_constructible<_Tp, const optional<_Up>&>,
405 is_constructible<_Tp, optional<_Up>&>,
406 is_constructible<_Tp, const optional<_Up>&&>,
407 is_constructible<_Tp, optional<_Up>&&>,
408 is_convertible<const optional<_Up>&, _Tp>,
409 is_convertible<optional<_Up>&, _Tp>,
410 is_convertible<const optional<_Up>&&, _Tp>,
411 is_convertible<optional<_Up>&&, _Tp>>;
412
413 template<typename _Tp, typename _Up>
414 using __assigns_from_optional =
415 __or_<is_assignable<_Tp&, const optional<_Up>&>,
416 is_assignable<_Tp&, optional<_Up>&>,
417 is_assignable<_Tp&, const optional<_Up>&&>,
418 is_assignable<_Tp&, optional<_Up>&&>>;
419
420 /// @endcond
421
422 /**
423 * @brief Class template for optional values.
424 */
425 template<typename _Tp>
426 class optional
427 : private _Optional_base<_Tp>,
428 private _Enable_copy_move<
429 // Copy constructor.
430 is_copy_constructible<_Tp>::value,
431 // Copy assignment.
432 __and_<is_copy_constructible<_Tp>, is_copy_assignable<_Tp>>::value,
433 // Move constructor.
434 is_move_constructible<_Tp>::value,
435 // Move assignment.
436 __and_<is_move_constructible<_Tp>, is_move_assignable<_Tp>>::value,
437 // Unique tag type.
438 optional<_Tp>>
439 {
440 static_assert(__and_<__not_<is_same<remove_cv_t<_Tp>, nullopt_t>>,
441 __not_<is_same<remove_cv_t<_Tp>, in_place_t>>,
442 __not_<is_reference<_Tp>>>(),
443 "Invalid instantiation of optional<T>");
444
445 private:
446 using _Base = _Optional_base<_Tp>;
447
448 public:
449 using value_type = _Tp;
450
451 // _Optional_base has the responsibility for construction.
452 using _Base::_Base;
453
454 constexpr optional() = default;
455 // Converting constructors for engaged optionals.
456 template <typename _Up = _Tp,
457 enable_if_t<__and_<
458 __not_<is_same<optional<_Tp>, decay_t<_Up>>>,
459 is_constructible<_Tp, _Up&&>,
460 is_convertible<_Up&&, _Tp>
461 >::value, bool> = true>
462 constexpr optional(_Up&& __t)
463 : _Base(in_place, std::forward<_Up>(__t)) { }
464
465 template <typename _Up = _Tp,
466 enable_if_t<__and_<
467 __not_<is_same<optional<_Tp>, decay_t<_Up>>>,
468 is_constructible<_Tp, _Up&&>,
469 __not_<is_convertible<_Up&&, _Tp>>
470 >::value, bool> = false>
471 explicit constexpr optional(_Up&& __t)
472 : _Base(in_place, std::forward<_Up>(__t)) { }
473
474 template <typename _Up,
475 enable_if_t<__and_<
476 __not_<is_same<_Tp, _Up>>,
477 is_constructible<_Tp, const _Up&>,
478 is_convertible<const _Up&, _Tp>,
479 __not_<__converts_from_optional<_Tp, _Up>>
480 >::value, bool> = true>
481 constexpr optional(const optional<_Up>& __t)
482 {
483 if (__t)
484 emplace(*__t);
485 }
486
487 template <typename _Up,
488 enable_if_t<__and_<
489 __not_<is_same<_Tp, _Up>>,
490 is_constructible<_Tp, const _Up&>,
491 __not_<is_convertible<const _Up&, _Tp>>,
492 __not_<__converts_from_optional<_Tp, _Up>>
493 >::value, bool> = false>
494 explicit constexpr optional(const optional<_Up>& __t)
495 {
496 if (__t)
497 emplace(*__t);
498 }
499
500 template <typename _Up,
501 enable_if_t<__and_<
502 __not_<is_same<_Tp, _Up>>,
503 is_constructible<_Tp, _Up&&>,
504 is_convertible<_Up&&, _Tp>,
505 __not_<__converts_from_optional<_Tp, _Up>>
506 >::value, bool> = true>
507 constexpr optional(optional<_Up>&& __t)
508 {
509 if (__t)
510 emplace(std::move(*__t));
511 }
512
513 template <typename _Up,
514 enable_if_t<__and_<
515 __not_<is_same<_Tp, _Up>>,
516 is_constructible<_Tp, _Up&&>,
517 __not_<is_convertible<_Up&&, _Tp>>,
518 __not_<__converts_from_optional<_Tp, _Up>>
519 >::value, bool> = false>
520 explicit constexpr optional(optional<_Up>&& __t)
521 {
522 if (__t)
523 emplace(std::move(*__t));
524 }
525
526 // [X.Y.4.3] (partly) Assignment.
527 optional&
528 operator=(nullopt_t) noexcept
529 {
530 this->_M_reset();
531 return *this;
532 }
533
534 template<typename _Up = _Tp>
535 enable_if_t<__and_<
536 __not_<is_same<optional<_Tp>, decay_t<_Up>>>,
537 is_constructible<_Tp, _Up>,
538 __not_<__and_<is_scalar<_Tp>,
539 is_same<_Tp, decay_t<_Up>>>>,
540 is_assignable<_Tp&, _Up>>::value,
541 optional&>
542 operator=(_Up&& __u)
543 {
544 if (this->_M_is_engaged())
545 this->_M_get() = std::forward<_Up>(__u);
546 else
547 this->_M_construct(std::forward<_Up>(__u));
548
549 return *this;
550 }
551
552 template<typename _Up>
553 enable_if_t<__and_<
554 __not_<is_same<_Tp, _Up>>,
555 is_constructible<_Tp, const _Up&>,
556 is_assignable<_Tp&, _Up>,
557 __not_<__converts_from_optional<_Tp, _Up>>,
558 __not_<__assigns_from_optional<_Tp, _Up>>
559 >::value,
560 optional&>
561 operator=(const optional<_Up>& __u)
562 {
563 if (__u)
564 {
565 if (this->_M_is_engaged())
566 this->_M_get() = *__u;
567 else
568 this->_M_construct(*__u);
569 }
570 else
571 {
572 this->_M_reset();
573 }
574 return *this;
575 }
576
577 template<typename _Up>
578 enable_if_t<__and_<
579 __not_<is_same<_Tp, _Up>>,
580 is_constructible<_Tp, _Up>,
581 is_assignable<_Tp&, _Up>,
582 __not_<__converts_from_optional<_Tp, _Up>>,
583 __not_<__assigns_from_optional<_Tp, _Up>>
584 >::value,
585 optional&>
586 operator=(optional<_Up>&& __u)
587 {
588 if (__u)
589 {
590 if (this->_M_is_engaged())
591 this->_M_get() = std::move(*__u);
592 else
593 this->_M_construct(std::move(*__u));
594 }
595 else
596 {
597 this->_M_reset();
598 }
599
600 return *this;
601 }
602
603 template<typename... _Args>
604 enable_if_t<is_constructible<_Tp, _Args&&...>::value>
605 emplace(_Args&&... __args)
606 {
607 this->_M_reset();
608 this->_M_construct(std::forward<_Args>(__args)...);
609 }
610
611 template<typename _Up, typename... _Args>
612 enable_if_t<is_constructible<_Tp, initializer_list<_Up>&,
613 _Args&&...>::value>
614 emplace(initializer_list<_Up> __il, _Args&&... __args)
615 {
616 this->_M_reset();
617 this->_M_construct(__il, std::forward<_Args>(__args)...);
618 }
619
620 // [X.Y.4.2] Destructor is implicit, implemented in _Optional_base.
621
622 // [X.Y.4.4] Swap.
623 void
624 swap(optional& __other)
625 noexcept(is_nothrow_move_constructible<_Tp>()
626 && __is_nothrow_swappable<_Tp>::value)
627 {
628 using std::swap;
629
630 if (this->_M_is_engaged() && __other._M_is_engaged())
631 swap(this->_M_get(), __other._M_get());
632 else if (this->_M_is_engaged())
633 {
634 __other._M_construct(std::move(this->_M_get()));
635 this->_M_destruct();
636 }
637 else if (__other._M_is_engaged())
638 {
639 this->_M_construct(std::move(__other._M_get()));
640 __other._M_destruct();
641 }
642 }
643
644 // [X.Y.4.5] Observers.
645 constexpr const _Tp*
646 operator->() const
647 { return std::__addressof(this->_M_get()); }
648
649 _Tp*
650 operator->()
651 { return std::__addressof(this->_M_get()); }
652
653 constexpr const _Tp&
654 operator*() const&
655 { return this->_M_get(); }
656
657 constexpr _Tp&
658 operator*()&
659 { return this->_M_get(); }
660
661 constexpr _Tp&&
662 operator*()&&
663 { return std::move(this->_M_get()); }
664
665 constexpr const _Tp&&
666 operator*() const&&
667 { return std::move(this->_M_get()); }
668
669 constexpr explicit operator bool() const noexcept
670 { return this->_M_is_engaged(); }
671
672 constexpr const _Tp&
673 value() const&
674 {
675 if (this->_M_is_engaged())
676 return this->_M_get();
677 __throw_bad_optional_access("Attempt to access value of a "
678 "disengaged optional object");
679 }
680
681 constexpr _Tp&
682 value()&
683 {
684 if (this->_M_is_engaged())
685 return this->_M_get();
686 __throw_bad_optional_access("Attempt to access value of a "
687 "disengaged optional object");
688 }
689
690 constexpr _Tp&&
691 value()&&
692 {
693 if (this->_M_is_engaged())
694 return std::move(this->_M_get());
695 __throw_bad_optional_access("Attempt to access value of a "
696 "disengaged optional object");
697 }
698
699 constexpr const _Tp&&
700 value() const&&
701 {
702 if (this->_M_is_engaged())
703 return std::move(this->_M_get());
704 __throw_bad_optional_access("Attempt to access value of a "
705 "disengaged optional object");
706 }
707
708 template<typename _Up>
709 constexpr _Tp
710 value_or(_Up&& __u) const&
711 {
712 static_assert(__and_<is_copy_constructible<_Tp>,
713 is_convertible<_Up&&, _Tp>>(),
714 "Cannot return value");
715
716 if (this->_M_is_engaged())
717 return this->_M_get();
718 else
719 return static_cast<_Tp>(std::forward<_Up>(__u));
720 }
721
722 template<typename _Up>
723 _Tp
724 value_or(_Up&& __u) &&
725 {
726 static_assert(__and_<is_move_constructible<_Tp>,
727 is_convertible<_Up&&, _Tp>>(),
728 "Cannot return value" );
729
730 if (this->_M_is_engaged())
731 return std::move(this->_M_get());
732 else
733 return static_cast<_Tp>(std::forward<_Up>(__u));
734 }
735 };
736
737 /// @relates experimental::optional @{
738
739 // [X.Y.8] Comparisons between optional values.
740 template<typename _Tp>
741 constexpr bool
742 operator==(const optional<_Tp>& __lhs, const optional<_Tp>& __rhs)
743 {
744 return static_cast<bool>(__lhs) == static_cast<bool>(__rhs)
745 && (!__lhs || *__lhs == *__rhs);
746 }
747
748 template<typename _Tp>
749 constexpr bool
750 operator!=(const optional<_Tp>& __lhs, const optional<_Tp>& __rhs)
751 { return !(__lhs == __rhs); }
752
753 template<typename _Tp>
754 constexpr bool
755 operator<(const optional<_Tp>& __lhs, const optional<_Tp>& __rhs)
756 {
757 return static_cast<bool>(__rhs) && (!__lhs || *__lhs < *__rhs);
758 }
759
760 template<typename _Tp>
761 constexpr bool
762 operator>(const optional<_Tp>& __lhs, const optional<_Tp>& __rhs)
763 { return __rhs < __lhs; }
764
765 template<typename _Tp>
766 constexpr bool
767 operator<=(const optional<_Tp>& __lhs, const optional<_Tp>& __rhs)
768 { return !(__rhs < __lhs); }
769
770 template<typename _Tp>
771 constexpr bool
772 operator>=(const optional<_Tp>& __lhs, const optional<_Tp>& __rhs)
773 { return !(__lhs < __rhs); }
774
775 // [X.Y.9] Comparisons with nullopt.
776 template<typename _Tp>
777 constexpr bool
778 operator==(const optional<_Tp>& __lhs, nullopt_t) noexcept
779 { return !__lhs; }
780
781 template<typename _Tp>
782 constexpr bool
783 operator==(nullopt_t, const optional<_Tp>& __rhs) noexcept
784 { return !__rhs; }
785
786 template<typename _Tp>
787 constexpr bool
788 operator!=(const optional<_Tp>& __lhs, nullopt_t) noexcept
789 { return static_cast<bool>(__lhs); }
790
791 template<typename _Tp>
792 constexpr bool
793 operator!=(nullopt_t, const optional<_Tp>& __rhs) noexcept
794 { return static_cast<bool>(__rhs); }
795
796 template<typename _Tp>
797 constexpr bool
798 operator<(const optional<_Tp>& /* __lhs */, nullopt_t) noexcept
799 { return false; }
800
801 template<typename _Tp>
802 constexpr bool
803 operator<(nullopt_t, const optional<_Tp>& __rhs) noexcept
804 { return static_cast<bool>(__rhs); }
805
806 template<typename _Tp>
807 constexpr bool
808 operator>(const optional<_Tp>& __lhs, nullopt_t) noexcept
809 { return static_cast<bool>(__lhs); }
810
811 template<typename _Tp>
812 constexpr bool
813 operator>(nullopt_t, const optional<_Tp>& /* __rhs */) noexcept
814 { return false; }
815
816 template<typename _Tp>
817 constexpr bool
818 operator<=(const optional<_Tp>& __lhs, nullopt_t) noexcept
819 { return !__lhs; }
820
821 template<typename _Tp>
822 constexpr bool
823 operator<=(nullopt_t, const optional<_Tp>& /* __rhs */) noexcept
824 { return true; }
825
826 template<typename _Tp>
827 constexpr bool
828 operator>=(const optional<_Tp>& /* __lhs */, nullopt_t) noexcept
829 { return true; }
830
831 template<typename _Tp>
832 constexpr bool
833 operator>=(nullopt_t, const optional<_Tp>& __rhs) noexcept
834 { return !__rhs; }
835
836 // [X.Y.10] Comparisons with value type.
837 template<typename _Tp>
838 constexpr bool
839 operator==(const optional<_Tp>& __lhs, const _Tp& __rhs)
840 { return __lhs && *__lhs == __rhs; }
841
842 template<typename _Tp>
843 constexpr bool
844 operator==(const _Tp& __lhs, const optional<_Tp>& __rhs)
845 { return __rhs && __lhs == *__rhs; }
846
847 template<typename _Tp>
848 constexpr bool
849 operator!=(const optional<_Tp>& __lhs, _Tp const& __rhs)
850 { return !__lhs || !(*__lhs == __rhs); }
851
852 template<typename _Tp>
853 constexpr bool
854 operator!=(const _Tp& __lhs, const optional<_Tp>& __rhs)
855 { return !__rhs || !(__lhs == *__rhs); }
856
857 template<typename _Tp>
858 constexpr bool
859 operator<(const optional<_Tp>& __lhs, const _Tp& __rhs)
860 { return !__lhs || *__lhs < __rhs; }
861
862 template<typename _Tp>
863 constexpr bool
864 operator<(const _Tp& __lhs, const optional<_Tp>& __rhs)
865 { return __rhs && __lhs < *__rhs; }
866
867 template<typename _Tp>
868 constexpr bool
869 operator>(const optional<_Tp>& __lhs, const _Tp& __rhs)
870 { return __lhs && __rhs < *__lhs; }
871
872 template<typename _Tp>
873 constexpr bool
874 operator>(const _Tp& __lhs, const optional<_Tp>& __rhs)
875 { return !__rhs || *__rhs < __lhs; }
876
877 template<typename _Tp>
878 constexpr bool
879 operator<=(const optional<_Tp>& __lhs, const _Tp& __rhs)
880 { return !__lhs || !(__rhs < *__lhs); }
881
882 template<typename _Tp>
883 constexpr bool
884 operator<=(const _Tp& __lhs, const optional<_Tp>& __rhs)
885 { return __rhs && !(*__rhs < __lhs); }
886
887 template<typename _Tp>
888 constexpr bool
889 operator>=(const optional<_Tp>& __lhs, const _Tp& __rhs)
890 { return __lhs && !(*__lhs < __rhs); }
891
892 template<typename _Tp>
893 constexpr bool
894 operator>=(const _Tp& __lhs, const optional<_Tp>& __rhs)
895 { return !__rhs || !(__lhs < *__rhs); }
896
897 // [X.Y.11]
898 template<typename _Tp>
899 inline void
900 swap(optional<_Tp>& __lhs, optional<_Tp>& __rhs)
901 noexcept(noexcept(__lhs.swap(__rhs)))
902 { __lhs.swap(__rhs); }
903
904 template<typename _Tp>
905 constexpr optional<decay_t<_Tp>>
906 make_optional(_Tp&& __t)
907 { return optional<decay_t<_Tp>> { std::forward<_Tp>(__t) }; }
908
909 /// @} relates experimental::optional
910 /// @} group optional
911} // namespace fundamentals_v1
912} // namespace experimental
913
914 // [X.Y.12]
915 /// std::hash partial specialization for experimental::optional
916 /// @relates experimental::optional
917 template<typename _Tp>
918 struct hash<experimental::optional<_Tp>>
919 {
920 using result_type = size_t;
921 using argument_type = experimental::optional<_Tp>;
922
923 size_t
924 operator()(const experimental::optional<_Tp>& __t) const
925 noexcept(noexcept(hash<_Tp> {}(*__t)))
926 {
927 // We pick an arbitrary hash for disengaged optionals which hopefully
928 // usual values of _Tp won't typically hash to.
929 constexpr size_t __magic_disengaged_hash = static_cast<size_t>(-3333);
930 return __t ? hash<_Tp> {}(*__t) : __magic_disengaged_hash;
931 }
932 };
933
934_GLIBCXX_END_NAMESPACE_VERSION
935} // namespace std
936
937#endif // C++14
938
939#endif // _GLIBCXX_EXPERIMENTAL_OPTIONAL
initializer_list
new
stdexcept
enable_special_members.h
functional_hash.h
move.h
requires_hosted.h
exception_defines.h
lfts_config.h
std::enable_if_t
typename enable_if< _Cond, _Tp >::type enable_if_t
Alias template for enable_if.
Definition type_traits:2940
std::decay_t
typename decay< _Tp >::type decay_t
Alias template for decay.
Definition type_traits:2936
std::move
constexpr std::remove_reference< _Tp >::type && move(_Tp &&__t) noexcept
Convert a value to an rvalue.
Definition move.h:138
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::swap
void swap(any &__x, any &__y) noexcept
Exchange the states of two any objects.
Definition experimental/any:346
std::experimental::fundamentals_v1::nullopt
constexpr nullopt_t nullopt
Tag to disengage optional objects.
Definition experimental/optional:98
std::experimental::fundamentals_v1::in_place
constexpr in_place_t in_place
Tag for in-place construction.
Definition experimental/optional:79
std
ISO C++ entities toplevel namespace is std.
std::experimental
Namespace for features defined in ISO Technical Specifications.
std::initializer_list
initializer_list
Definition initializer_list:48
std::hash
Primary class template hash.
Definition functional_hash.h:106
std::is_same
is_same
Definition type_traits:1622
std::is_constructible
is_constructible
Definition type_traits:1238
std::is_nothrow_move_constructible
is_nothrow_move_constructible
Definition type_traits:1343
std::is_assignable
is_assignable
Definition type_traits:1357
std::is_trivially_destructible
is_trivially_destructible
Definition type_traits:1539
std::logic_error::logic_error
logic_error(const string &__arg)
std::experimental::fundamentals_v1::optional
Class template for optional values.
Definition experimental/optional:439
std::experimental::fundamentals_v1::in_place_t
Tag type for in-place construction.
Definition experimental/optional:76
std::experimental::fundamentals_v1::nullopt_t
Tag type to disengage optional objects.
Definition experimental/optional:84
std::experimental::bad_optional_access
Exception class thrown when a disengaged optional object is dereferenced.
Definition experimental/optional:107
type_traits