libstdc++
optional
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1 // <optional> -*- C++ -*-
2 
3 // Copyright (C) 2013-2020 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 include/optional
26  * This is a Standard C++ Library header.
27  */
28 
29 #ifndef _GLIBCXX_OPTIONAL
30 #define _GLIBCXX_OPTIONAL 1
31 
32 #pragma GCC system_header
33 
34 #if __cplusplus >= 201703L
35 
36 #include <utility>
37 #include <type_traits>
38 #include <exception>
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 #if __cplusplus > 201703L
45 # include <compare>
46 #endif
47 
48 namespace std _GLIBCXX_VISIBILITY(default)
49 {
50 _GLIBCXX_BEGIN_NAMESPACE_VERSION
51 
52  /**
53  * @addtogroup utilities
54  * @{
55  */
56 
57 #define __cpp_lib_optional 201606L
58 
59  template<typename _Tp>
60  class optional;
61 
62  /// Tag type to disengage optional objects.
63  struct nullopt_t
64  {
65  // Do not user-declare default constructor at all for
66  // optional_value = {} syntax to work.
67  // nullopt_t() = delete;
68 
69  // Used for constructing nullopt.
70  enum class _Construct { _Token };
71 
72  // Must be constexpr for nullopt_t to be literal.
73  explicit constexpr nullopt_t(_Construct) { }
74  };
75 
76  /// Tag to disengage optional objects.
77  inline constexpr nullopt_t nullopt { nullopt_t::_Construct::_Token };
78 
79  /**
80  * @brief Exception class thrown when a disengaged optional object is
81  * dereferenced.
82  * @ingroup exceptions
83  */
84  class bad_optional_access : public exception
85  {
86  public:
87  bad_optional_access() { }
88 
89  virtual const char* what() const noexcept override
90  { return "bad optional access"; }
91 
92  virtual ~bad_optional_access() noexcept = default;
93  };
94 
95  void
96  __throw_bad_optional_access()
97  __attribute__((__noreturn__));
98 
99  // XXX Does not belong here.
100  inline void
101  __throw_bad_optional_access()
102  { _GLIBCXX_THROW_OR_ABORT(bad_optional_access()); }
103 
104  // This class template manages construction/destruction of
105  // the contained value for a std::optional.
106  template <typename _Tp>
107  struct _Optional_payload_base
108  {
109  using _Stored_type = remove_const_t<_Tp>;
110 
111  _Optional_payload_base() = default;
112  ~_Optional_payload_base() = default;
113 
114  template<typename... _Args>
115  constexpr
116  _Optional_payload_base(in_place_t __tag, _Args&&... __args)
117  : _M_payload(__tag, std::forward<_Args>(__args)...),
118  _M_engaged(true)
119  { }
120 
121  template<typename _Up, typename... _Args>
122  constexpr
123  _Optional_payload_base(std::initializer_list<_Up> __il,
124  _Args&&... __args)
125  : _M_payload(__il, std::forward<_Args>(__args)...),
126  _M_engaged(true)
127  { }
128 
129  // Constructor used by _Optional_base copy constructor when the
130  // contained value is not trivially copy constructible.
131  constexpr
132  _Optional_payload_base(bool __engaged,
133  const _Optional_payload_base& __other)
134  {
135  if (__other._M_engaged)
136  this->_M_construct(__other._M_get());
137  }
138 
139  // Constructor used by _Optional_base move constructor when the
140  // contained value is not trivially move constructible.
141  constexpr
142  _Optional_payload_base(bool __engaged,
143  _Optional_payload_base&& __other)
144  {
145  if (__other._M_engaged)
146  this->_M_construct(std::move(__other._M_get()));
147  }
148 
149  // Copy constructor is only used to when the contained value is
150  // trivially copy constructible.
151  _Optional_payload_base(const _Optional_payload_base&) = default;
152 
153  // Move constructor is only used to when the contained value is
154  // trivially copy constructible.
155  _Optional_payload_base(_Optional_payload_base&&) = default;
156 
157  _Optional_payload_base&
158  operator=(const _Optional_payload_base&) = default;
159 
160  _Optional_payload_base&
161  operator=(_Optional_payload_base&&) = default;
162 
163  // used to perform non-trivial copy assignment.
164  constexpr void
165  _M_copy_assign(const _Optional_payload_base& __other)
166  {
167  if (this->_M_engaged && __other._M_engaged)
168  this->_M_get() = __other._M_get();
169  else
170  {
171  if (__other._M_engaged)
172  this->_M_construct(__other._M_get());
173  else
174  this->_M_reset();
175  }
176  }
177 
178  // used to perform non-trivial move assignment.
179  constexpr void
180  _M_move_assign(_Optional_payload_base&& __other)
181  noexcept(__and_v<is_nothrow_move_constructible<_Tp>,
182  is_nothrow_move_assignable<_Tp>>)
183  {
184  if (this->_M_engaged && __other._M_engaged)
185  this->_M_get() = std::move(__other._M_get());
186  else
187  {
188  if (__other._M_engaged)
189  this->_M_construct(std::move(__other._M_get()));
190  else
191  this->_M_reset();
192  }
193  }
194 
195  struct _Empty_byte { };
196 
197  template<typename _Up, bool = is_trivially_destructible_v<_Up>>
198  union _Storage
199  {
200  constexpr _Storage() noexcept : _M_empty() { }
201 
202  template<typename... _Args>
203  constexpr
204  _Storage(in_place_t, _Args&&... __args)
205  : _M_value(std::forward<_Args>(__args)...)
206  { }
207 
208  template<typename _Vp, typename... _Args>
209  constexpr
210  _Storage(std::initializer_list<_Vp> __il, _Args&&... __args)
211  : _M_value(__il, std::forward<_Args>(__args)...)
212  { }
213 
214  _Empty_byte _M_empty;
215  _Up _M_value;
216  };
217 
218  template<typename _Up>
219  union _Storage<_Up, false>
220  {
221  constexpr _Storage() noexcept : _M_empty() { }
222 
223  template<typename... _Args>
224  constexpr
225  _Storage(in_place_t, _Args&&... __args)
226  : _M_value(std::forward<_Args>(__args)...)
227  { }
228 
229  template<typename _Vp, typename... _Args>
230  constexpr
231  _Storage(std::initializer_list<_Vp> __il, _Args&&... __args)
232  : _M_value(__il, std::forward<_Args>(__args)...)
233  { }
234 
235  // User-provided destructor is needed when _Up has non-trivial dtor.
236  ~_Storage() { }
237 
238  _Empty_byte _M_empty;
239  _Up _M_value;
240  };
241 
242  _Storage<_Stored_type> _M_payload;
243 
244  bool _M_engaged = false;
245 
246  template<typename... _Args>
247  void
248  _M_construct(_Args&&... __args)
249  noexcept(is_nothrow_constructible_v<_Stored_type, _Args...>)
250  {
251  ::new ((void *) std::__addressof(this->_M_payload))
252  _Stored_type(std::forward<_Args>(__args)...);
253  this->_M_engaged = true;
254  }
255 
256  constexpr void
257  _M_destroy() noexcept
258  {
259  _M_engaged = false;
260  _M_payload._M_value.~_Stored_type();
261  }
262 
263  // The _M_get() operations have _M_engaged as a precondition.
264  // They exist to access the contained value with the appropriate
265  // const-qualification, because _M_payload has had the const removed.
266 
267  constexpr _Tp&
268  _M_get() noexcept
269  { return this->_M_payload._M_value; }
270 
271  constexpr const _Tp&
272  _M_get() const noexcept
273  { return this->_M_payload._M_value; }
274 
275  // _M_reset is a 'safe' operation with no precondition.
276  constexpr void
277  _M_reset() noexcept
278  {
279  if (this->_M_engaged)
280  _M_destroy();
281  }
282  };
283 
284  // Class template that manages the payload for optionals.
285  template <typename _Tp,
286  bool /*_HasTrivialDestructor*/ =
287  is_trivially_destructible_v<_Tp>,
288  bool /*_HasTrivialCopy */ =
289  is_trivially_copy_assignable_v<_Tp>
290  && is_trivially_copy_constructible_v<_Tp>,
291  bool /*_HasTrivialMove */ =
292  is_trivially_move_assignable_v<_Tp>
293  && is_trivially_move_constructible_v<_Tp>>
294  struct _Optional_payload;
295 
296  // Payload for potentially-constexpr optionals (trivial copy/move/destroy).
297  template <typename _Tp>
298  struct _Optional_payload<_Tp, true, true, true>
299  : _Optional_payload_base<_Tp>
300  {
301  using _Optional_payload_base<_Tp>::_Optional_payload_base;
302 
303  _Optional_payload() = default;
304  };
305 
306  // Payload for optionals with non-trivial copy construction/assignment.
307  template <typename _Tp>
308  struct _Optional_payload<_Tp, true, false, true>
309  : _Optional_payload_base<_Tp>
310  {
311  using _Optional_payload_base<_Tp>::_Optional_payload_base;
312 
313  _Optional_payload() = default;
314  ~_Optional_payload() = default;
315  _Optional_payload(const _Optional_payload&) = default;
316  _Optional_payload(_Optional_payload&&) = default;
317  _Optional_payload& operator=(_Optional_payload&&) = default;
318 
319  // Non-trivial copy assignment.
320  constexpr
321  _Optional_payload&
322  operator=(const _Optional_payload& __other)
323  {
324  this->_M_copy_assign(__other);
325  return *this;
326  }
327  };
328 
329  // Payload for optionals with non-trivial move construction/assignment.
330  template <typename _Tp>
331  struct _Optional_payload<_Tp, true, true, false>
332  : _Optional_payload_base<_Tp>
333  {
334  using _Optional_payload_base<_Tp>::_Optional_payload_base;
335 
336  _Optional_payload() = default;
337  ~_Optional_payload() = default;
338  _Optional_payload(const _Optional_payload&) = default;
339  _Optional_payload(_Optional_payload&&) = default;
340  _Optional_payload& operator=(const _Optional_payload&) = default;
341 
342  // Non-trivial move assignment.
343  constexpr
344  _Optional_payload&
345  operator=(_Optional_payload&& __other)
346  noexcept(__and_v<is_nothrow_move_constructible<_Tp>,
347  is_nothrow_move_assignable<_Tp>>)
348  {
349  this->_M_move_assign(std::move(__other));
350  return *this;
351  }
352  };
353 
354  // Payload for optionals with non-trivial copy and move assignment.
355  template <typename _Tp>
356  struct _Optional_payload<_Tp, true, false, false>
357  : _Optional_payload_base<_Tp>
358  {
359  using _Optional_payload_base<_Tp>::_Optional_payload_base;
360 
361  _Optional_payload() = default;
362  ~_Optional_payload() = default;
363  _Optional_payload(const _Optional_payload&) = default;
364  _Optional_payload(_Optional_payload&&) = default;
365 
366  // Non-trivial copy assignment.
367  constexpr
368  _Optional_payload&
369  operator=(const _Optional_payload& __other)
370  {
371  this->_M_copy_assign(__other);
372  return *this;
373  }
374 
375  // Non-trivial move assignment.
376  constexpr
377  _Optional_payload&
378  operator=(_Optional_payload&& __other)
379  noexcept(__and_v<is_nothrow_move_constructible<_Tp>,
380  is_nothrow_move_assignable<_Tp>>)
381  {
382  this->_M_move_assign(std::move(__other));
383  return *this;
384  }
385  };
386 
387  // Payload for optionals with non-trivial destructors.
388  template <typename _Tp, bool _Copy, bool _Move>
389  struct _Optional_payload<_Tp, false, _Copy, _Move>
390  : _Optional_payload<_Tp, true, false, false>
391  {
392  // Base class implements all the constructors and assignment operators:
393  using _Optional_payload<_Tp, true, false, false>::_Optional_payload;
394  _Optional_payload() = default;
395  _Optional_payload(const _Optional_payload&) = default;
396  _Optional_payload(_Optional_payload&&) = default;
397  _Optional_payload& operator=(const _Optional_payload&) = default;
398  _Optional_payload& operator=(_Optional_payload&&) = default;
399 
400  // Destructor needs to destroy the contained value:
401  ~_Optional_payload() { this->_M_reset(); }
402  };
403 
404  // Common base class for _Optional_base<T> to avoid repeating these
405  // member functions in each specialization.
406  template<typename _Tp, typename _Dp>
407  class _Optional_base_impl
408  {
409  protected:
410  using _Stored_type = remove_const_t<_Tp>;
411 
412  // The _M_construct operation has !_M_engaged as a precondition
413  // while _M_destruct has _M_engaged as a precondition.
414  template<typename... _Args>
415  void
416  _M_construct(_Args&&... __args)
417  noexcept(is_nothrow_constructible_v<_Stored_type, _Args...>)
418  {
419  ::new
420  (std::__addressof(static_cast<_Dp*>(this)->_M_payload._M_payload))
421  _Stored_type(std::forward<_Args>(__args)...);
422  static_cast<_Dp*>(this)->_M_payload._M_engaged = true;
423  }
424 
425  void
426  _M_destruct() noexcept
427  { static_cast<_Dp*>(this)->_M_payload._M_destroy(); }
428 
429  // _M_reset is a 'safe' operation with no precondition.
430  constexpr void
431  _M_reset() noexcept
432  { static_cast<_Dp*>(this)->_M_payload._M_reset(); }
433 
434  constexpr bool _M_is_engaged() const noexcept
435  { return static_cast<const _Dp*>(this)->_M_payload._M_engaged; }
436 
437  // The _M_get operations have _M_engaged as a precondition.
438  constexpr _Tp&
439  _M_get() noexcept
440  {
441  __glibcxx_assert(this->_M_is_engaged());
442  return static_cast<_Dp*>(this)->_M_payload._M_get();
443  }
444 
445  constexpr const _Tp&
446  _M_get() const noexcept
447  {
448  __glibcxx_assert(this->_M_is_engaged());
449  return static_cast<const _Dp*>(this)->_M_payload._M_get();
450  }
451  };
452 
453  /**
454  * @brief Class template that provides copy/move constructors of optional.
455  *
456  * Such a separate base class template is necessary in order to
457  * conditionally make copy/move constructors trivial.
458  *
459  * When the contained value is trivially copy/move constructible,
460  * the copy/move constructors of _Optional_base will invoke the
461  * trivial copy/move constructor of _Optional_payload. Otherwise,
462  * they will invoke _Optional_payload(bool, const _Optional_payload&)
463  * or _Optional_payload(bool, _Optional_payload&&) to initialize
464  * the contained value, if copying/moving an engaged optional.
465  *
466  * Whether the other special members are trivial is determined by the
467  * _Optional_payload<_Tp> specialization used for the _M_payload member.
468  *
469  * @see optional, _Enable_special_members
470  */
471  template<typename _Tp,
472  bool = is_trivially_copy_constructible_v<_Tp>,
473  bool = is_trivially_move_constructible_v<_Tp>>
474  struct _Optional_base
475  : _Optional_base_impl<_Tp, _Optional_base<_Tp>>
476  {
477  // Constructors for disengaged optionals.
478  constexpr _Optional_base() = default;
479 
480  // Constructors for engaged optionals.
481  template<typename... _Args,
482  enable_if_t<is_constructible_v<_Tp, _Args&&...>, bool> = false>
483  constexpr explicit _Optional_base(in_place_t, _Args&&... __args)
484  : _M_payload(in_place,
485  std::forward<_Args>(__args)...) { }
486 
487  template<typename _Up, typename... _Args,
488  enable_if_t<is_constructible_v<_Tp,
489  initializer_list<_Up>&,
490  _Args&&...>, bool> = false>
491  constexpr explicit _Optional_base(in_place_t,
492  initializer_list<_Up> __il,
493  _Args&&... __args)
494  : _M_payload(in_place,
495  __il, std::forward<_Args>(__args)...)
496  { }
497 
498  // Copy and move constructors.
499  constexpr _Optional_base(const _Optional_base& __other)
500  : _M_payload(__other._M_payload._M_engaged,
501  __other._M_payload)
502  { }
503 
504  constexpr _Optional_base(_Optional_base&& __other)
505  noexcept(is_nothrow_move_constructible_v<_Tp>)
506  : _M_payload(__other._M_payload._M_engaged,
507  std::move(__other._M_payload))
508  { }
509 
510  // Assignment operators.
511  _Optional_base& operator=(const _Optional_base&) = default;
512  _Optional_base& operator=(_Optional_base&&) = default;
513 
514  _Optional_payload<_Tp> _M_payload;
515  };
516 
517  template<typename _Tp>
518  struct _Optional_base<_Tp, false, true>
519  : _Optional_base_impl<_Tp, _Optional_base<_Tp>>
520  {
521  // Constructors for disengaged optionals.
522  constexpr _Optional_base() = default;
523 
524  // Constructors for engaged optionals.
525  template<typename... _Args,
526  enable_if_t<is_constructible_v<_Tp, _Args&&...>, bool> = false>
527  constexpr explicit _Optional_base(in_place_t, _Args&&... __args)
528  : _M_payload(in_place,
529  std::forward<_Args>(__args)...) { }
530 
531  template<typename _Up, typename... _Args,
532  enable_if_t<is_constructible_v<_Tp,
533  initializer_list<_Up>&,
534  _Args&&...>, bool> = false>
535  constexpr explicit _Optional_base(in_place_t,
536  initializer_list<_Up> __il,
537  _Args&&... __args)
538  : _M_payload(in_place,
539  __il, std::forward<_Args>(__args)...)
540  { }
541 
542  // Copy and move constructors.
543  constexpr _Optional_base(const _Optional_base& __other)
544  : _M_payload(__other._M_payload._M_engaged,
545  __other._M_payload)
546  { }
547 
548  constexpr _Optional_base(_Optional_base&& __other) = default;
549 
550  // Assignment operators.
551  _Optional_base& operator=(const _Optional_base&) = default;
552  _Optional_base& operator=(_Optional_base&&) = default;
553 
554  _Optional_payload<_Tp> _M_payload;
555  };
556 
557  template<typename _Tp>
558  struct _Optional_base<_Tp, true, false>
559  : _Optional_base_impl<_Tp, _Optional_base<_Tp>>
560  {
561  // Constructors for disengaged optionals.
562  constexpr _Optional_base() = default;
563 
564  // Constructors for engaged optionals.
565  template<typename... _Args,
566  enable_if_t<is_constructible_v<_Tp, _Args&&...>, bool> = false>
567  constexpr explicit _Optional_base(in_place_t, _Args&&... __args)
568  : _M_payload(in_place,
569  std::forward<_Args>(__args)...) { }
570 
571  template<typename _Up, typename... _Args,
572  enable_if_t<is_constructible_v<_Tp,
573  initializer_list<_Up>&,
574  _Args&&...>, bool> = false>
575  constexpr explicit _Optional_base(in_place_t,
576  initializer_list<_Up> __il,
577  _Args&&... __args)
578  : _M_payload(in_place,
579  __il, std::forward<_Args>(__args)...)
580  { }
581 
582  // Copy and move constructors.
583  constexpr _Optional_base(const _Optional_base& __other) = default;
584 
585  constexpr _Optional_base(_Optional_base&& __other)
586  noexcept(is_nothrow_move_constructible_v<_Tp>)
587  : _M_payload(__other._M_payload._M_engaged,
588  std::move(__other._M_payload))
589  { }
590 
591  // Assignment operators.
592  _Optional_base& operator=(const _Optional_base&) = default;
593  _Optional_base& operator=(_Optional_base&&) = default;
594 
595  _Optional_payload<_Tp> _M_payload;
596  };
597 
598  template<typename _Tp>
599  struct _Optional_base<_Tp, true, true>
600  : _Optional_base_impl<_Tp, _Optional_base<_Tp>>
601  {
602  // Constructors for disengaged optionals.
603  constexpr _Optional_base() = default;
604 
605  // Constructors for engaged optionals.
606  template<typename... _Args,
607  enable_if_t<is_constructible_v<_Tp, _Args&&...>, bool> = false>
608  constexpr explicit _Optional_base(in_place_t, _Args&&... __args)
609  : _M_payload(in_place,
610  std::forward<_Args>(__args)...) { }
611 
612  template<typename _Up, typename... _Args,
613  enable_if_t<is_constructible_v<_Tp,
614  initializer_list<_Up>&,
615  _Args&&...>, bool> = false>
616  constexpr explicit _Optional_base(in_place_t,
617  initializer_list<_Up> __il,
618  _Args&&... __args)
619  : _M_payload(in_place,
620  __il, std::forward<_Args>(__args)...)
621  { }
622 
623  // Copy and move constructors.
624  constexpr _Optional_base(const _Optional_base& __other) = default;
625  constexpr _Optional_base(_Optional_base&& __other) = default;
626 
627  // Assignment operators.
628  _Optional_base& operator=(const _Optional_base&) = default;
629  _Optional_base& operator=(_Optional_base&&) = default;
630 
631  _Optional_payload<_Tp> _M_payload;
632  };
633 
634  template<typename _Tp>
635  class optional;
636 
637  template<typename _Tp, typename _Up>
638  using __converts_from_optional =
639  __or_<is_constructible<_Tp, const optional<_Up>&>,
640  is_constructible<_Tp, optional<_Up>&>,
641  is_constructible<_Tp, const optional<_Up>&&>,
642  is_constructible<_Tp, optional<_Up>&&>,
643  is_convertible<const optional<_Up>&, _Tp>,
644  is_convertible<optional<_Up>&, _Tp>,
645  is_convertible<const optional<_Up>&&, _Tp>,
646  is_convertible<optional<_Up>&&, _Tp>>;
647 
648  template<typename _Tp, typename _Up>
649  using __assigns_from_optional =
650  __or_<is_assignable<_Tp&, const optional<_Up>&>,
651  is_assignable<_Tp&, optional<_Up>&>,
652  is_assignable<_Tp&, const optional<_Up>&&>,
653  is_assignable<_Tp&, optional<_Up>&&>>;
654 
655  /**
656  * @brief Class template for optional values.
657  */
658  template<typename _Tp>
659  class optional
660  : private _Optional_base<_Tp>,
661  private _Enable_copy_move<
662  // Copy constructor.
663  is_copy_constructible_v<_Tp>,
664  // Copy assignment.
665  __and_v<is_copy_constructible<_Tp>, is_copy_assignable<_Tp>>,
666  // Move constructor.
667  is_move_constructible_v<_Tp>,
668  // Move assignment.
669  __and_v<is_move_constructible<_Tp>, is_move_assignable<_Tp>>,
670  // Unique tag type.
671  optional<_Tp>>
672  {
673  static_assert(!is_same_v<remove_cv_t<_Tp>, nullopt_t>);
674  static_assert(!is_same_v<remove_cv_t<_Tp>, in_place_t>);
675  static_assert(!is_reference_v<_Tp>);
676 
677  private:
678  using _Base = _Optional_base<_Tp>;
679 
680  // SFINAE helpers
681  template<typename _Up>
682  using __not_self = __not_<is_same<optional, __remove_cvref_t<_Up>>>;
683  template<typename _Up>
684  using __not_tag = __not_<is_same<in_place_t, __remove_cvref_t<_Up>>>;
685  template<typename... _Cond>
686  using _Requires = enable_if_t<__and_v<_Cond...>, bool>;
687 
688  public:
689  using value_type = _Tp;
690 
691  constexpr optional() = default;
692 
693  constexpr optional(nullopt_t) noexcept { }
694 
695  // Converting constructors for engaged optionals.
696  template<typename _Up = _Tp,
697  _Requires<__not_self<_Up>, __not_tag<_Up>,
698  is_constructible<_Tp, _Up&&>,
699  is_convertible<_Up&&, _Tp>> = true>
700  constexpr
701  optional(_Up&& __t)
702  : _Base(std::in_place, std::forward<_Up>(__t)) { }
703 
704  template<typename _Up = _Tp,
705  _Requires<__not_self<_Up>, __not_tag<_Up>,
706  is_constructible<_Tp, _Up&&>,
707  __not_<is_convertible<_Up&&, _Tp>>> = false>
708  explicit constexpr
709  optional(_Up&& __t)
710  : _Base(std::in_place, std::forward<_Up>(__t)) { }
711 
712  template<typename _Up,
713  _Requires<__not_<is_same<_Tp, _Up>>,
714  is_constructible<_Tp, const _Up&>,
715  is_convertible<const _Up&, _Tp>,
716  __not_<__converts_from_optional<_Tp, _Up>>> = true>
717  constexpr
718  optional(const optional<_Up>& __t)
719  {
720  if (__t)
721  emplace(*__t);
722  }
723 
724  template<typename _Up,
725  _Requires<__not_<is_same<_Tp, _Up>>,
726  is_constructible<_Tp, const _Up&>,
727  __not_<is_convertible<const _Up&, _Tp>>,
728  __not_<__converts_from_optional<_Tp, _Up>>> = false>
729  explicit constexpr
730  optional(const optional<_Up>& __t)
731  {
732  if (__t)
733  emplace(*__t);
734  }
735 
736  template <typename _Up,
737  _Requires<__not_<is_same<_Tp, _Up>>,
738  is_constructible<_Tp, _Up&&>,
739  is_convertible<_Up&&, _Tp>,
740  __not_<__converts_from_optional<_Tp, _Up>>> = true>
741  constexpr
742  optional(optional<_Up>&& __t)
743  {
744  if (__t)
745  emplace(std::move(*__t));
746  }
747 
748  template <typename _Up,
749  _Requires<__not_<is_same<_Tp, _Up>>,
750  is_constructible<_Tp, _Up&&>,
751  __not_<is_convertible<_Up&&, _Tp>>,
752  __not_<__converts_from_optional<_Tp, _Up>>> = false>
753  explicit constexpr
754  optional(optional<_Up>&& __t)
755  {
756  if (__t)
757  emplace(std::move(*__t));
758  }
759 
760  template<typename... _Args,
761  _Requires<is_constructible<_Tp, _Args&&...>> = false>
762  explicit constexpr
763  optional(in_place_t, _Args&&... __args)
764  : _Base(std::in_place, std::forward<_Args>(__args)...) { }
765 
766  template<typename _Up, typename... _Args,
767  _Requires<is_constructible<_Tp,
768  initializer_list<_Up>&,
769  _Args&&...>> = false>
770  explicit constexpr
771  optional(in_place_t, initializer_list<_Up> __il, _Args&&... __args)
772  : _Base(std::in_place, __il, std::forward<_Args>(__args)...) { }
773 
774  // Assignment operators.
775  optional&
776  operator=(nullopt_t) noexcept
777  {
778  this->_M_reset();
779  return *this;
780  }
781 
782  template<typename _Up = _Tp>
783  enable_if_t<__and_v<__not_self<_Up>,
784  __not_<__and_<is_scalar<_Tp>,
785  is_same<_Tp, decay_t<_Up>>>>,
786  is_constructible<_Tp, _Up>,
787  is_assignable<_Tp&, _Up>>,
788  optional&>
789  operator=(_Up&& __u)
790  {
791  if (this->_M_is_engaged())
792  this->_M_get() = std::forward<_Up>(__u);
793  else
794  this->_M_construct(std::forward<_Up>(__u));
795 
796  return *this;
797  }
798 
799  template<typename _Up>
800  enable_if_t<__and_v<__not_<is_same<_Tp, _Up>>,
801  is_constructible<_Tp, const _Up&>,
802  is_assignable<_Tp&, _Up>,
803  __not_<__converts_from_optional<_Tp, _Up>>,
804  __not_<__assigns_from_optional<_Tp, _Up>>>,
805  optional&>
806  operator=(const optional<_Up>& __u)
807  {
808  if (__u)
809  {
810  if (this->_M_is_engaged())
811  this->_M_get() = *__u;
812  else
813  this->_M_construct(*__u);
814  }
815  else
816  {
817  this->_M_reset();
818  }
819  return *this;
820  }
821 
822  template<typename _Up>
823  enable_if_t<__and_v<__not_<is_same<_Tp, _Up>>,
824  is_constructible<_Tp, _Up>,
825  is_assignable<_Tp&, _Up>,
826  __not_<__converts_from_optional<_Tp, _Up>>,
827  __not_<__assigns_from_optional<_Tp, _Up>>>,
828  optional&>
829  operator=(optional<_Up>&& __u)
830  {
831  if (__u)
832  {
833  if (this->_M_is_engaged())
834  this->_M_get() = std::move(*__u);
835  else
836  this->_M_construct(std::move(*__u));
837  }
838  else
839  {
840  this->_M_reset();
841  }
842 
843  return *this;
844  }
845 
846  template<typename... _Args>
847  enable_if_t<is_constructible_v<_Tp, _Args&&...>, _Tp&>
848  emplace(_Args&&... __args)
849  {
850  this->_M_reset();
851  this->_M_construct(std::forward<_Args>(__args)...);
852  return this->_M_get();
853  }
854 
855  template<typename _Up, typename... _Args>
856  enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&,
857  _Args&&...>, _Tp&>
858  emplace(initializer_list<_Up> __il, _Args&&... __args)
859  {
860  this->_M_reset();
861  this->_M_construct(__il, std::forward<_Args>(__args)...);
862  return this->_M_get();
863  }
864 
865  // Destructor is implicit, implemented in _Optional_base.
866 
867  // Swap.
868  void
869  swap(optional& __other)
870  noexcept(is_nothrow_move_constructible_v<_Tp>
871  && is_nothrow_swappable_v<_Tp>)
872  {
873  using std::swap;
874 
875  if (this->_M_is_engaged() && __other._M_is_engaged())
876  swap(this->_M_get(), __other._M_get());
877  else if (this->_M_is_engaged())
878  {
879  __other._M_construct(std::move(this->_M_get()));
880  this->_M_destruct();
881  }
882  else if (__other._M_is_engaged())
883  {
884  this->_M_construct(std::move(__other._M_get()));
885  __other._M_destruct();
886  }
887  }
888 
889  // Observers.
890  constexpr const _Tp*
891  operator->() const
892  { return std::__addressof(this->_M_get()); }
893 
894  constexpr _Tp*
895  operator->()
896  { return std::__addressof(this->_M_get()); }
897 
898  constexpr const _Tp&
899  operator*() const&
900  { return this->_M_get(); }
901 
902  constexpr _Tp&
903  operator*()&
904  { return this->_M_get(); }
905 
906  constexpr _Tp&&
907  operator*()&&
908  { return std::move(this->_M_get()); }
909 
910  constexpr const _Tp&&
911  operator*() const&&
912  { return std::move(this->_M_get()); }
913 
914  constexpr explicit operator bool() const noexcept
915  { return this->_M_is_engaged(); }
916 
917  constexpr bool has_value() const noexcept
918  { return this->_M_is_engaged(); }
919 
920  constexpr const _Tp&
921  value() const&
922  {
923  return this->_M_is_engaged()
924  ? this->_M_get()
925  : (__throw_bad_optional_access(), this->_M_get());
926  }
927 
928  constexpr _Tp&
929  value()&
930  {
931  return this->_M_is_engaged()
932  ? this->_M_get()
933  : (__throw_bad_optional_access(), this->_M_get());
934  }
935 
936  constexpr _Tp&&
937  value()&&
938  {
939  return this->_M_is_engaged()
940  ? std::move(this->_M_get())
941  : (__throw_bad_optional_access(), std::move(this->_M_get()));
942  }
943 
944  constexpr const _Tp&&
945  value() const&&
946  {
947  return this->_M_is_engaged()
948  ? std::move(this->_M_get())
949  : (__throw_bad_optional_access(), std::move(this->_M_get()));
950  }
951 
952  template<typename _Up>
953  constexpr _Tp
954  value_or(_Up&& __u) const&
955  {
956  static_assert(is_copy_constructible_v<_Tp>);
957  static_assert(is_convertible_v<_Up&&, _Tp>);
958 
959  return this->_M_is_engaged()
960  ? this->_M_get() : static_cast<_Tp>(std::forward<_Up>(__u));
961  }
962 
963  template<typename _Up>
964  constexpr _Tp
965  value_or(_Up&& __u) &&
966  {
967  static_assert(is_move_constructible_v<_Tp>);
968  static_assert(is_convertible_v<_Up&&, _Tp>);
969 
970  return this->_M_is_engaged()
971  ? std::move(this->_M_get())
972  : static_cast<_Tp>(std::forward<_Up>(__u));
973  }
974 
975  void reset() noexcept { this->_M_reset(); }
976  };
977 
978  template<typename _Tp>
979  using __optional_relop_t =
980  enable_if_t<is_convertible<_Tp, bool>::value, bool>;
981 
982  // Comparisons between optional values.
983  template<typename _Tp, typename _Up>
984  constexpr auto
985  operator==(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
986  -> __optional_relop_t<decltype(declval<_Tp>() == declval<_Up>())>
987  {
988  return static_cast<bool>(__lhs) == static_cast<bool>(__rhs)
989  && (!__lhs || *__lhs == *__rhs);
990  }
991 
992  template<typename _Tp, typename _Up>
993  constexpr auto
994  operator!=(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
995  -> __optional_relop_t<decltype(declval<_Tp>() != declval<_Up>())>
996  {
997  return static_cast<bool>(__lhs) != static_cast<bool>(__rhs)
998  || (static_cast<bool>(__lhs) && *__lhs != *__rhs);
999  }
1000 
1001  template<typename _Tp, typename _Up>
1002  constexpr auto
1003  operator<(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
1004  -> __optional_relop_t<decltype(declval<_Tp>() < declval<_Up>())>
1005  {
1006  return static_cast<bool>(__rhs) && (!__lhs || *__lhs < *__rhs);
1007  }
1008 
1009  template<typename _Tp, typename _Up>
1010  constexpr auto
1011  operator>(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
1012  -> __optional_relop_t<decltype(declval<_Tp>() > declval<_Up>())>
1013  {
1014  return static_cast<bool>(__lhs) && (!__rhs || *__lhs > *__rhs);
1015  }
1016 
1017  template<typename _Tp, typename _Up>
1018  constexpr auto
1019  operator<=(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
1020  -> __optional_relop_t<decltype(declval<_Tp>() <= declval<_Up>())>
1021  {
1022  return !__lhs || (static_cast<bool>(__rhs) && *__lhs <= *__rhs);
1023  }
1024 
1025  template<typename _Tp, typename _Up>
1026  constexpr auto
1027  operator>=(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
1028  -> __optional_relop_t<decltype(declval<_Tp>() >= declval<_Up>())>
1029  {
1030  return !__rhs || (static_cast<bool>(__lhs) && *__lhs >= *__rhs);
1031  }
1032 
1033 #ifdef __cpp_lib_three_way_comparison
1034  template<typename _Tp, three_way_comparable_with<_Tp> _Up>
1035  constexpr compare_three_way_result_t<_Tp, _Up>
1036  operator<=>(const optional<_Tp>& __x, const optional<_Up>& __y)
1037  {
1038  return __x && __y ? *__x <=> *__y : bool(__x) <=> bool(__y);
1039  }
1040 #endif
1041 
1042  // Comparisons with nullopt.
1043  template<typename _Tp>
1044  constexpr bool
1045  operator==(const optional<_Tp>& __lhs, nullopt_t) noexcept
1046  { return !__lhs; }
1047 
1048 #ifdef __cpp_lib_three_way_comparison
1049  template<typename _Tp>
1050  constexpr strong_ordering
1051  operator<=>(const optional<_Tp>& __x, nullopt_t) noexcept
1052  { return bool(__x) <=> false; }
1053 #else
1054  template<typename _Tp>
1055  constexpr bool
1056  operator==(nullopt_t, const optional<_Tp>& __rhs) noexcept
1057  { return !__rhs; }
1058 
1059  template<typename _Tp>
1060  constexpr bool
1061  operator!=(const optional<_Tp>& __lhs, nullopt_t) noexcept
1062  { return static_cast<bool>(__lhs); }
1063 
1064  template<typename _Tp>
1065  constexpr bool
1066  operator!=(nullopt_t, const optional<_Tp>& __rhs) noexcept
1067  { return static_cast<bool>(__rhs); }
1068 
1069  template<typename _Tp>
1070  constexpr bool
1071  operator<(const optional<_Tp>& /* __lhs */, nullopt_t) noexcept
1072  { return false; }
1073 
1074  template<typename _Tp>
1075  constexpr bool
1076  operator<(nullopt_t, const optional<_Tp>& __rhs) noexcept
1077  { return static_cast<bool>(__rhs); }
1078 
1079  template<typename _Tp>
1080  constexpr bool
1081  operator>(const optional<_Tp>& __lhs, nullopt_t) noexcept
1082  { return static_cast<bool>(__lhs); }
1083 
1084  template<typename _Tp>
1085  constexpr bool
1086  operator>(nullopt_t, const optional<_Tp>& /* __rhs */) noexcept
1087  { return false; }
1088 
1089  template<typename _Tp>
1090  constexpr bool
1091  operator<=(const optional<_Tp>& __lhs, nullopt_t) noexcept
1092  { return !__lhs; }
1093 
1094  template<typename _Tp>
1095  constexpr bool
1096  operator<=(nullopt_t, const optional<_Tp>& /* __rhs */) noexcept
1097  { return true; }
1098 
1099  template<typename _Tp>
1100  constexpr bool
1101  operator>=(const optional<_Tp>& /* __lhs */, nullopt_t) noexcept
1102  { return true; }
1103 
1104  template<typename _Tp>
1105  constexpr bool
1106  operator>=(nullopt_t, const optional<_Tp>& __rhs) noexcept
1107  { return !__rhs; }
1108 #endif // three-way-comparison
1109 
1110  // Comparisons with value type.
1111  template<typename _Tp, typename _Up>
1112  constexpr auto
1113  operator==(const optional<_Tp>& __lhs, const _Up& __rhs)
1114  -> __optional_relop_t<decltype(declval<_Tp>() == declval<_Up>())>
1115  { return __lhs && *__lhs == __rhs; }
1116 
1117  template<typename _Tp, typename _Up>
1118  constexpr auto
1119  operator==(const _Up& __lhs, const optional<_Tp>& __rhs)
1120  -> __optional_relop_t<decltype(declval<_Up>() == declval<_Tp>())>
1121  { return __rhs && __lhs == *__rhs; }
1122 
1123  template<typename _Tp, typename _Up>
1124  constexpr auto
1125  operator!=(const optional<_Tp>& __lhs, const _Up& __rhs)
1126  -> __optional_relop_t<decltype(declval<_Tp>() != declval<_Up>())>
1127  { return !__lhs || *__lhs != __rhs; }
1128 
1129  template<typename _Tp, typename _Up>
1130  constexpr auto
1131  operator!=(const _Up& __lhs, const optional<_Tp>& __rhs)
1132  -> __optional_relop_t<decltype(declval<_Up>() != declval<_Tp>())>
1133  { return !__rhs || __lhs != *__rhs; }
1134 
1135  template<typename _Tp, typename _Up>
1136  constexpr auto
1137  operator<(const optional<_Tp>& __lhs, const _Up& __rhs)
1138  -> __optional_relop_t<decltype(declval<_Tp>() < declval<_Up>())>
1139  { return !__lhs || *__lhs < __rhs; }
1140 
1141  template<typename _Tp, typename _Up>
1142  constexpr auto
1143  operator<(const _Up& __lhs, const optional<_Tp>& __rhs)
1144  -> __optional_relop_t<decltype(declval<_Up>() < declval<_Tp>())>
1145  { return __rhs && __lhs < *__rhs; }
1146 
1147  template<typename _Tp, typename _Up>
1148  constexpr auto
1149  operator>(const optional<_Tp>& __lhs, const _Up& __rhs)
1150  -> __optional_relop_t<decltype(declval<_Tp>() > declval<_Up>())>
1151  { return __lhs && *__lhs > __rhs; }
1152 
1153  template<typename _Tp, typename _Up>
1154  constexpr auto
1155  operator>(const _Up& __lhs, const optional<_Tp>& __rhs)
1156  -> __optional_relop_t<decltype(declval<_Up>() > declval<_Tp>())>
1157  { return !__rhs || __lhs > *__rhs; }
1158 
1159  template<typename _Tp, typename _Up>
1160  constexpr auto
1161  operator<=(const optional<_Tp>& __lhs, const _Up& __rhs)
1162  -> __optional_relop_t<decltype(declval<_Tp>() <= declval<_Up>())>
1163  { return !__lhs || *__lhs <= __rhs; }
1164 
1165  template<typename _Tp, typename _Up>
1166  constexpr auto
1167  operator<=(const _Up& __lhs, const optional<_Tp>& __rhs)
1168  -> __optional_relop_t<decltype(declval<_Up>() <= declval<_Tp>())>
1169  { return __rhs && __lhs <= *__rhs; }
1170 
1171  template<typename _Tp, typename _Up>
1172  constexpr auto
1173  operator>=(const optional<_Tp>& __lhs, const _Up& __rhs)
1174  -> __optional_relop_t<decltype(declval<_Tp>() >= declval<_Up>())>
1175  { return __lhs && *__lhs >= __rhs; }
1176 
1177  template<typename _Tp, typename _Up>
1178  constexpr auto
1179  operator>=(const _Up& __lhs, const optional<_Tp>& __rhs)
1180  -> __optional_relop_t<decltype(declval<_Up>() >= declval<_Tp>())>
1181  { return !__rhs || __lhs >= *__rhs; }
1182 
1183 #ifdef __cpp_lib_three_way_comparison
1184  template<typename _Tp, typename _Up>
1185  constexpr compare_three_way_result_t<_Tp, _Up>
1186  operator<=>(const optional<_Tp>& __x, const _Up& __v)
1187  { return bool(__x) ? *__x <=> __v : strong_ordering::less; }
1188 #endif
1189 
1190  // Swap and creation functions.
1191 
1192  // _GLIBCXX_RESOLVE_LIB_DEFECTS
1193  // 2748. swappable traits for optionals
1194  template<typename _Tp>
1195  inline enable_if_t<is_move_constructible_v<_Tp> && is_swappable_v<_Tp>>
1196  swap(optional<_Tp>& __lhs, optional<_Tp>& __rhs)
1197  noexcept(noexcept(__lhs.swap(__rhs)))
1198  { __lhs.swap(__rhs); }
1199 
1200  template<typename _Tp>
1201  enable_if_t<!(is_move_constructible_v<_Tp> && is_swappable_v<_Tp>)>
1202  swap(optional<_Tp>&, optional<_Tp>&) = delete;
1203 
1204  template<typename _Tp>
1205  constexpr optional<decay_t<_Tp>>
1206  make_optional(_Tp&& __t)
1207  { return optional<decay_t<_Tp>> { std::forward<_Tp>(__t) }; }
1208 
1209  template<typename _Tp, typename ..._Args>
1210  constexpr optional<_Tp>
1211  make_optional(_Args&&... __args)
1212  { return optional<_Tp> { in_place, std::forward<_Args>(__args)... }; }
1213 
1214  template<typename _Tp, typename _Up, typename ..._Args>
1215  constexpr optional<_Tp>
1216  make_optional(initializer_list<_Up> __il, _Args&&... __args)
1217  { return optional<_Tp> { in_place, __il, std::forward<_Args>(__args)... }; }
1218 
1219  // Hash.
1220 
1221  template<typename _Tp, typename _Up = remove_const_t<_Tp>,
1222  bool = __poison_hash<_Up>::__enable_hash_call>
1223  struct __optional_hash_call_base
1224  {
1225  size_t
1226  operator()(const optional<_Tp>& __t) const
1227  noexcept(noexcept(hash<_Up>{}(*__t)))
1228  {
1229  // We pick an arbitrary hash for disengaged optionals which hopefully
1230  // usual values of _Tp won't typically hash to.
1231  constexpr size_t __magic_disengaged_hash = static_cast<size_t>(-3333);
1232  return __t ? hash<_Up>{}(*__t) : __magic_disengaged_hash;
1233  }
1234  };
1235 
1236  template<typename _Tp, typename _Up>
1237  struct __optional_hash_call_base<_Tp, _Up, false> {};
1238 
1239  template<typename _Tp>
1240  struct hash<optional<_Tp>>
1241  : private __poison_hash<remove_const_t<_Tp>>,
1242  public __optional_hash_call_base<_Tp>
1243  {
1244  using result_type [[__deprecated__]] = size_t;
1245  using argument_type [[__deprecated__]] = optional<_Tp>;
1246  };
1247 
1248  template<typename _Tp>
1249  struct __is_fast_hash<hash<optional<_Tp>>> : __is_fast_hash<hash<_Tp>>
1250  { };
1251 
1252  /// @}
1253 
1254 #if __cpp_deduction_guides >= 201606
1255  template <typename _Tp> optional(_Tp) -> optional<_Tp>;
1256 #endif
1257 
1258 _GLIBCXX_END_NAMESPACE_VERSION
1259 } // namespace std
1260 
1261 #endif // C++17
1262 
1263 #endif // _GLIBCXX_OPTIONAL