libstdc++-v3/include/experimental/optional

   1 // <optional> -*- C++ -*-
   2
   3 // Copyright (C) 2013-2018 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  */
  28
  29 #ifndef _GLIBCXX_EXPERIMENTAL_OPTIONAL
  30 #define _GLIBCXX_EXPERIMENTAL_OPTIONAL 1
  31
  32 /**
  33  * @defgroup experimental Experimental
  34  *
  35  * Components specified by various Technical Specifications.
  36  *
  37  * As indicated by the std::experimental namespace and the  header paths,
  38  * the contents of these Technical Specifications are experimental and not
  39  * part of the C++ standard. As such the interfaces and implementations may
  40  * change in the future, and there is <STRONG> no guarantee of compatibility
  41  * between different GCC releases </STRONG> for these features.
  42  */
  43
  44 #if __cplusplus >= 201402L
  45
  46 #include <utility>
  47 #include <type_traits>
  48 #include <stdexcept>
  49 #include <new>
  50 #include <initializer_list>
  51 #include <bits/functexcept.h>
  52 #include <bits/functional_hash.h>
  53 #include <bits/enable_special_members.h>
  54 #include <experimental/bits/lfts_config.h>
  55
  56 namespace std _GLIBCXX_VISIBILITY(default)
  57 {
  58 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  59
  60 namespace experimental
  61 {
  62 inline namespace fundamentals_v1
  63 {
  64   /**
  65    * @defgroup optional Optional values
  66    * @ingroup experimental
  67    *
  68    * Class template for optional values and surrounding facilities, as
  69    * described in n3793 "A proposal to add a utility class to represent
  70    * optional objects (Revision 5)".
  71    *
  72    * @{
  73    */
  74
  75 #define __cpp_lib_experimental_optional 201411
  76
  77   // All subsequent [X.Y.n] references are against n3793.
  78
  79   // [X.Y.4]
  80   template<typename _Tp>
  81     class optional;
  82
  83   // [X.Y.5]
  84   /// Tag type for in-place construction.
  85   struct in_place_t { };
  86
  87   /// Tag for in-place construction.
  88   constexpr in_place_t in_place { };
  89
  90   // [X.Y.6]
  91   /// Tag type to disengage optional objects.
  92   struct nullopt_t
  93   {
  94     // Do not user-declare default constructor at all for
  95     // optional_value = {} syntax to work.
  96     // nullopt_t() = delete;
  97
  98     // Used for constructing nullopt.
  99     enum class _Construct { _Token };
 100
 101     // Must be constexpr for nullopt_t to be literal.
 102     explicit constexpr nullopt_t(_Construct) { }
 103   };
 104
 105   // [X.Y.6]
 106   /// Tag to disengage optional objects.
 107   constexpr nullopt_t nullopt { nullopt_t::_Construct::_Token };
 108
 109   // [X.Y.7]
 110   /**
 111    *  @brief Exception class thrown when a disengaged optional object is
 112    *  dereferenced.
 113    *  @ingroup exceptions
 114    */
 115   class bad_optional_access : public logic_error
 116   {
 117   public:
 118     bad_optional_access() : logic_error("bad optional access") { }
 119
 120     // XXX This constructor is non-standard. Should not be inline
 121     explicit bad_optional_access(const char* __arg) : logic_error(__arg) { }
 122
 123     virtual ~bad_optional_access() noexcept = default;
 124   };
 125
 126   void
 127   __throw_bad_optional_access(const char*)
 128   __attribute__((__noreturn__));
 129
 130   // XXX Does not belong here.
 131   inline void
 132   __throw_bad_optional_access(const char* __s)
 133   { _GLIBCXX_THROW_OR_ABORT(bad_optional_access(__s)); }
 134
 135 #ifndef __cpp_lib_addressof_constexpr
 136   template<typename _Tp, typename = void>
 137     struct _Has_addressof_mem : std::false_type { };
 138
 139   template<typename _Tp>
 140     struct _Has_addressof_mem<_Tp,
 141          __void_t<decltype( std::declval<const _Tp&>().operator&() )>
 142       >
 143     : std::true_type { };
 144
 145   template<typename _Tp, typename = void>
 146     struct _Has_addressof_free : std::false_type { };
 147
 148   template<typename _Tp>
 149     struct _Has_addressof_free<_Tp,
 150          __void_t<decltype( operator&(std::declval<const _Tp&>()) )>
 151       >
 152     : std::true_type { };
 153
 154   /**
 155     * @brief Trait that detects the presence of an overloaded unary operator&.
 156     *
 157     * Practically speaking this detects the presence of such an operator when
 158     * called on a const-qualified lvalue (e.g.
 159     * declval<const _Tp&>().operator&()).
 160     */
 161   template<typename _Tp>
 162     struct _Has_addressof
 163     : std::__or_<_Has_addressof_mem<_Tp>, _Has_addressof_free<_Tp>>::type
 164     { };
 165
 166   /**
 167     * @brief An overload that attempts to take the address of an lvalue as a
 168     * constant expression. Falls back to __addressof in the presence of an
 169     * overloaded addressof operator (unary operator&), in which case the call
 170     * will not be a constant expression.
 171     */
 172   template<typename _Tp>
 173     constexpr
 174     enable_if_t<!_Has_addressof<_Tp>::value, _Tp*>
 175     __constexpr_addressof(_Tp& __t)
 176     { return &__t; }
 177
 178   /**
 179     * @brief Fallback overload that defers to __addressof.
 180     */
 181   template<typename _Tp>
 182     inline
 183     enable_if_t<_Has_addressof<_Tp>::value, _Tp*>
 184     __constexpr_addressof(_Tp& __t)
 185     { return std::__addressof(__t); }
 186 #endif // __cpp_lib_addressof_constexpr
 187
 188   /**
 189     * @brief Class template that holds the necessary state for @ref optional
 190     * and that has the responsibility for construction and the special members.
 191     *
 192     * Such a separate base class template is necessary in order to
 193     * conditionally enable the special members (e.g. copy/move constructors).
 194     * Note that this means that @ref _Optional_base implements the
 195     * functionality for copy and move assignment, but not for converting
 196     * assignment.
 197     *
 198     * @see optional, _Enable_special_members
 199     */
 200   template<typename _Tp, bool _ShouldProvideDestructor =
 201            !is_trivially_destructible<_Tp>::value>
 202     class _Optional_base
 203     {
 204     private:
 205       // Remove const to avoid prohibition of reusing object storage for
 206       // const-qualified types in [3.8/9]. This is strictly internal
 207       // and even optional itself is oblivious to it.
 208       using _Stored_type = remove_const_t<_Tp>;
 209
 210     public:
 211       // [X.Y.4.1] Constructors.
 212
 213       // Constructors for disengaged optionals.
 214       constexpr _Optional_base() noexcept
 215       : _M_empty{} { }
 216
 217       constexpr _Optional_base(nullopt_t) noexcept
 218       : _Optional_base{} { }
 219
 220       // Constructors for engaged optionals.
 221       template<typename... _Args>
 222         constexpr explicit _Optional_base(in_place_t, _Args&&... __args)
 223         : _M_payload(std::forward<_Args>(__args)...), _M_engaged(true) { }
 224
 225       template<typename _Up, typename... _Args,
 226                enable_if_t<is_constructible<_Tp,
 227                                             initializer_list<_Up>&,
 228                                             _Args&&...>::value,
 229                            int>...>
 230         constexpr explicit _Optional_base(in_place_t,
 231                                           initializer_list<_Up> __il,
 232                                           _Args&&... __args)
 233         : _M_payload(__il, std::forward<_Args>(__args)...),
 234           _M_engaged(true) { }
 235
 236       // Copy and move constructors.
 237       _Optional_base(const _Optional_base& __other)
 238       {
 239         if (__other._M_engaged)
 240           this->_M_construct(__other._M_get());
 241       }
 242
 243       _Optional_base(_Optional_base&& __other)
 244       noexcept(is_nothrow_move_constructible<_Tp>())
 245       {
 246         if (__other._M_engaged)
 247           this->_M_construct(std::move(__other._M_get()));
 248       }
 249
 250       // [X.Y.4.3] (partly) Assignment.
 251       _Optional_base&
 252       operator=(const _Optional_base& __other)
 253       {
 254         if (this->_M_engaged && __other._M_engaged)
 255           this->_M_get() = __other._M_get();
 256         else
 257           {
 258             if (__other._M_engaged)
 259               this->_M_construct(__other._M_get());
 260             else
 261               this->_M_reset();
 262           }
 263
 264         return *this;
 265       }
 266
 267       _Optional_base&
 268       operator=(_Optional_base&& __other)
 269       noexcept(__and_<is_nothrow_move_constructible<_Tp>,
 270                       is_nothrow_move_assignable<_Tp>>())
 271       {
 272         if (this->_M_engaged && __other._M_engaged)
 273           this->_M_get() = std::move(__other._M_get());
 274         else
 275           {
 276             if (__other._M_engaged)
 277               this->_M_construct(std::move(__other._M_get()));
 278             else
 279               this->_M_reset();
 280           }
 281         return *this;
 282       }
 283
 284       // [X.Y.4.2] Destructor.
 285       ~_Optional_base()
 286       {
 287         if (this->_M_engaged)
 288           this->_M_payload.~_Stored_type();
 289       }
 290
 291       // The following functionality is also needed by optional, hence the
 292       // protected accessibility.
 293     protected:
 294       constexpr bool _M_is_engaged() const noexcept
 295       { return this->_M_engaged; }
 296
 297       // The _M_get operations have _M_engaged as a precondition.
 298       constexpr _Tp&
 299       _M_get() noexcept
 300       { return _M_payload; }
 301
 302       constexpr const _Tp&
 303       _M_get() const noexcept
 304       { return _M_payload; }
 305
 306       // The _M_construct operation has !_M_engaged as a precondition
 307       // while _M_destruct has _M_engaged as a precondition.
 308       template<typename... _Args>
 309         void
 310         _M_construct(_Args&&... __args)
 311         noexcept(is_nothrow_constructible<_Stored_type, _Args...>())
 312         {
 313           ::new (std::__addressof(this->_M_payload))
 314             _Stored_type(std::forward<_Args>(__args)...);
 315           this->_M_engaged = true;
 316         }
 317
 318       void
 319       _M_destruct()
 320       {
 321         this->_M_engaged = false;
 322         this->_M_payload.~_Stored_type();
 323       }
 324
 325       // _M_reset is a 'safe' operation with no precondition.
 326       void
 327       _M_reset()
 328       {
 329         if (this->_M_engaged)
 330           this->_M_destruct();
 331       }
 332
 333     private:
 334       struct _Empty_byte { };
 335       union {
 336           _Empty_byte _M_empty;
 337           _Stored_type _M_payload;
 338       };
 339       bool _M_engaged = false;
 340     };
 341
 342   /// Partial specialization that is exactly identical to the primary template
 343   /// save for not providing a destructor, to fulfill triviality requirements.
 344   template<typename _Tp>
 345     class _Optional_base<_Tp, false>
 346     {
 347     private:
 348       using _Stored_type = remove_const_t<_Tp>;
 349
 350     public:
 351       constexpr _Optional_base() noexcept
 352       : _M_empty{} { }
 353
 354       constexpr _Optional_base(nullopt_t) noexcept
 355       : _Optional_base{} { }
 356
 357       template<typename... _Args>
 358         constexpr explicit _Optional_base(in_place_t, _Args&&... __args)
 359         : _M_payload(std::forward<_Args>(__args)...), _M_engaged(true) { }
 360
 361       template<typename _Up, typename... _Args,
 362                enable_if_t<is_constructible<_Tp,
 363                                             initializer_list<_Up>&,
 364                                             _Args&&...>::value,
 365                            int>...>
 366         constexpr explicit _Optional_base(in_place_t,
 367                                           initializer_list<_Up> __il,
 368                                           _Args&&... __args)
 369         : _M_payload(__il, std::forward<_Args>(__args)...),
 370           _M_engaged(true) { }
 371
 372       _Optional_base(const _Optional_base& __other)
 373       {
 374         if (__other._M_engaged)
 375           this->_M_construct(__other._M_get());
 376       }
 377
 378       _Optional_base(_Optional_base&& __other)
 379       noexcept(is_nothrow_move_constructible<_Tp>())
 380       {
 381         if (__other._M_engaged)
 382           this->_M_construct(std::move(__other._M_get()));
 383       }
 384
 385       _Optional_base&
 386       operator=(const _Optional_base& __other)
 387       {
 388         if (this->_M_engaged && __other._M_engaged)
 389           this->_M_get() = __other._M_get();
 390         else
 391           {
 392             if (__other._M_engaged)
 393               this->_M_construct(__other._M_get());
 394             else
 395               this->_M_reset();
 396           }
 397         return *this;
 398       }
 399
 400       _Optional_base&
 401       operator=(_Optional_base&& __other)
 402       noexcept(__and_<is_nothrow_move_constructible<_Tp>,
 403                       is_nothrow_move_assignable<_Tp>>())
 404       {
 405         if (this->_M_engaged && __other._M_engaged)
 406           this->_M_get() = std::move(__other._M_get());
 407         else
 408           {
 409             if (__other._M_engaged)
 410               this->_M_construct(std::move(__other._M_get()));
 411             else
 412               this->_M_reset();
 413           }
 414         return *this;
 415       }
 416
 417       // Sole difference
 418       // ~_Optional_base() noexcept = default;
 419
 420     protected:
 421       constexpr bool _M_is_engaged() const noexcept
 422       { return this->_M_engaged; }
 423
 424       _Tp&
 425       _M_get() noexcept
 426       { return _M_payload; }
 427
 428       constexpr const _Tp&
 429       _M_get() const noexcept
 430       { return _M_payload; }
 431
 432       template<typename... _Args>
 433         void
 434         _M_construct(_Args&&... __args)
 435         noexcept(is_nothrow_constructible<_Stored_type, _Args...>())
 436         {
 437           ::new (std::__addressof(this->_M_payload))
 438             _Stored_type(std::forward<_Args>(__args)...);
 439           this->_M_engaged = true;
 440         }
 441
 442       void
 443       _M_destruct()
 444       {
 445         this->_M_engaged = false;
 446         this->_M_payload.~_Stored_type();
 447       }
 448
 449       void
 450       _M_reset()
 451       {
 452         if (this->_M_engaged)
 453           this->_M_destruct();
 454       }
 455
 456     private:
 457       struct _Empty_byte { };
 458       union
 459       {
 460         _Empty_byte _M_empty;
 461         _Stored_type _M_payload;
 462       };
 463       bool _M_engaged = false;
 464     };
 465
 466   template<typename _Tp>
 467   class optional;
 468
 469   template<typename _Tp, typename _Up>
 470     using __converts_from_optional =
 471       __or_<is_constructible<_Tp, const optional<_Up>&>,
 472             is_constructible<_Tp, optional<_Up>&>,
 473             is_constructible<_Tp, const optional<_Up>&&>,
 474             is_constructible<_Tp, optional<_Up>&&>,
 475             is_convertible<const optional<_Up>&, _Tp>,
 476             is_convertible<optional<_Up>&, _Tp>,
 477             is_convertible<const optional<_Up>&&, _Tp>,
 478             is_convertible<optional<_Up>&&, _Tp>>;
 479
 480   template<typename _Tp, typename _Up>
 481     using __assigns_from_optional =
 482       __or_<is_assignable<_Tp&, const optional<_Up>&>,
 483             is_assignable<_Tp&, optional<_Up>&>,
 484             is_assignable<_Tp&, const optional<_Up>&&>,
 485             is_assignable<_Tp&, optional<_Up>&&>>;
 486
 487   /**
 488     * @brief Class template for optional values.
 489     */
 490   template<typename _Tp>
 491     class optional
 492     : private _Optional_base<_Tp>,
 493       private _Enable_copy_move<
 494         // Copy constructor.
 495         is_copy_constructible<_Tp>::value,
 496         // Copy assignment.
 497         __and_<is_copy_constructible<_Tp>, is_copy_assignable<_Tp>>::value,
 498         // Move constructor.
 499         is_move_constructible<_Tp>::value,
 500         // Move assignment.
 501         __and_<is_move_constructible<_Tp>, is_move_assignable<_Tp>>::value,
 502         // Unique tag type.
 503         optional<_Tp>>
 504     {
 505       static_assert(__and_<__not_<is_same<remove_cv_t<_Tp>, nullopt_t>>,
 506                            __not_<is_same<remove_cv_t<_Tp>, in_place_t>>,
 507                            __not_<is_reference<_Tp>>>(),
 508                     "Invalid instantiation of optional<T>");
 509
 510     private:
 511       using _Base = _Optional_base<_Tp>;
 512
 513     public:
 514       using value_type = _Tp;
 515
 516       // _Optional_base has the responsibility for construction.
 517       using _Base::_Base;
 518
 519       constexpr optional() = default;
 520       // Converting constructors for engaged optionals.
 521       template <typename _Up = _Tp,
 522                 enable_if_t<__and_<
 523                               __not_<is_same<optional<_Tp>, decay_t<_Up>>>,
 524                               is_constructible<_Tp, _Up&&>,
 525                               is_convertible<_Up&&, _Tp>
 526                               >::value, bool> = true>
 527       constexpr optional(_Up&& __t)
 528         : _Base(in_place, std::forward<_Up>(__t)) { }
 529
 530       template <typename _Up = _Tp,
 531                 enable_if_t<__and_<
 532                               __not_<is_same<optional<_Tp>, decay_t<_Up>>>,
 533                               is_constructible<_Tp, _Up&&>,
 534                               __not_<is_convertible<_Up&&, _Tp>>
 535                               >::value, bool> = false>
 536       explicit constexpr optional(_Up&& __t)
 537         : _Base(in_place, std::forward<_Up>(__t)) { }
 538
 539       template <typename _Up,
 540                 enable_if_t<__and_<
 541                             __not_<is_same<_Tp, _Up>>,
 542                             is_constructible<_Tp, const _Up&>,
 543                             is_convertible<const _Up&, _Tp>,
 544                             __not_<__converts_from_optional<_Tp, _Up>>
 545                             >::value, bool> = true>
 546       constexpr optional(const optional<_Up>& __t)
 547       {
 548         if (__t)
 549           emplace(*__t);
 550       }
 551
 552       template <typename _Up,
 553                  enable_if_t<__and_<
 554                                __not_<is_same<_Tp, _Up>>,
 555                                is_constructible<_Tp, const _Up&>,
 556                                __not_<is_convertible<const _Up&, _Tp>>,
 557                                __not_<__converts_from_optional<_Tp, _Up>>
 558                                >::value, bool> = false>
 559       explicit constexpr optional(const optional<_Up>& __t)
 560       {
 561         if (__t)
 562           emplace(*__t);
 563       }
 564
 565       template <typename _Up,
 566                 enable_if_t<__and_<
 567                               __not_<is_same<_Tp, _Up>>,
 568                               is_constructible<_Tp, _Up&&>,
 569                               is_convertible<_Up&&, _Tp>,
 570                               __not_<__converts_from_optional<_Tp, _Up>>
 571                               >::value, bool> = true>
 572       constexpr optional(optional<_Up>&& __t)
 573       {
 574         if (__t)
 575           emplace(std::move(*__t));
 576       }
 577
 578       template <typename _Up,
 579                 enable_if_t<__and_<
 580                             __not_<is_same<_Tp, _Up>>,
 581                             is_constructible<_Tp, _Up&&>,
 582                             __not_<is_convertible<_Up&&, _Tp>>,
 583                             __not_<__converts_from_optional<_Tp, _Up>>
 584                             >::value, bool> = false>
 585       explicit constexpr optional(optional<_Up>&& __t)
 586       {
 587         if (__t)
 588           emplace(std::move(*__t));
 589       }
 590
 591       // [X.Y.4.3] (partly) Assignment.
 592       optional&
 593       operator=(nullopt_t) noexcept
 594       {
 595         this->_M_reset();
 596         return *this;
 597       }
 598
 599       template<typename _Up = _Tp>
 600         enable_if_t<__and_<
 601                       __not_<is_same<optional<_Tp>, decay_t<_Up>>>,
 602                       is_constructible<_Tp, _Up>,
 603                       __not_<__and_<is_scalar<_Tp>,
 604                                     is_same<_Tp, decay_t<_Up>>>>,
 605                       is_assignable<_Tp&, _Up>>::value,
 606                     optional&>
 607         operator=(_Up&& __u)
 608         {
 609           if (this->_M_is_engaged())
 610             this->_M_get() = std::forward<_Up>(__u);
 611           else
 612             this->_M_construct(std::forward<_Up>(__u));
 613
 614           return *this;
 615         }
 616
 617       template<typename _Up>
 618         enable_if_t<__and_<
 619                       __not_<is_same<_Tp, _Up>>,
 620                       is_constructible<_Tp, const _Up&>,
 621                       is_assignable<_Tp&, _Up>,
 622                       __not_<__converts_from_optional<_Tp, _Up>>,
 623                       __not_<__assigns_from_optional<_Tp, _Up>>
 624                       >::value,
 625                     optional&>
 626         operator=(const optional<_Up>& __u)
 627         {
 628           if (__u)
 629             {
 630               if (this->_M_is_engaged())
 631                 this->_M_get() = *__u;
 632               else
 633                 this->_M_construct(*__u);
 634             }
 635           else
 636             {
 637               this->_M_reset();
 638             }
 639           return *this;
 640         }
 641
 642       template<typename _Up>
 643         enable_if_t<__and_<
 644                       __not_<is_same<_Tp, _Up>>,
 645                       is_constructible<_Tp, _Up>,
 646                       is_assignable<_Tp&, _Up>,
 647                       __not_<__converts_from_optional<_Tp, _Up>>,
 648                       __not_<__assigns_from_optional<_Tp, _Up>>
 649                       >::value,
 650                     optional&>
 651         operator=(optional<_Up>&& __u)
 652         {
 653           if (__u)
 654             {
 655               if (this->_M_is_engaged())
 656                 this->_M_get() = std::move(*__u);
 657               else
 658                 this->_M_construct(std::move(*__u));
 659             }
 660           else
 661             {
 662               this->_M_reset();
 663             }
 664
 665           return *this;
 666         }
 667
 668       template<typename... _Args>
 669         enable_if_t<is_constructible<_Tp, _Args&&...>::value>
 670         emplace(_Args&&... __args)
 671         {
 672           this->_M_reset();
 673           this->_M_construct(std::forward<_Args>(__args)...);
 674         }
 675
 676       template<typename _Up, typename... _Args>
 677         enable_if_t<is_constructible<_Tp, initializer_list<_Up>&,
 678                                      _Args&&...>::value>
 679         emplace(initializer_list<_Up> __il, _Args&&... __args)
 680         {
 681           this->_M_reset();
 682           this->_M_construct(__il, std::forward<_Args>(__args)...);
 683         }
 684
 685       // [X.Y.4.2] Destructor is implicit, implemented in _Optional_base.
 686
 687       // [X.Y.4.4] Swap.
 688       void
 689       swap(optional& __other)
 690       noexcept(is_nothrow_move_constructible<_Tp>()
 691                && __is_nothrow_swappable<_Tp>::value)
 692       {
 693         using std::swap;
 694
 695         if (this->_M_is_engaged() && __other._M_is_engaged())
 696           swap(this->_M_get(), __other._M_get());
 697         else if (this->_M_is_engaged())
 698           {
 699             __other._M_construct(std::move(this->_M_get()));
 700             this->_M_destruct();
 701           }
 702         else if (__other._M_is_engaged())
 703           {
 704             this->_M_construct(std::move(__other._M_get()));
 705             __other._M_destruct();
 706           }
 707       }
 708
 709       // [X.Y.4.5] Observers.
 710       constexpr const _Tp*
 711       operator->() const
 712       {
 713 #ifndef __cpp_lib_addressof_constexpr
 714         return __constexpr_addressof(this->_M_get());
 715 #else
 716         return std::__addressof(this->_M_get());
 717 #endif
 718       }
 719
 720       _Tp*
 721       operator->()
 722       { return std::__addressof(this->_M_get()); }
 723
 724       constexpr const _Tp&
 725       operator*() const&
 726       { return this->_M_get(); }
 727
 728       constexpr _Tp&
 729       operator*()&
 730       { return this->_M_get(); }
 731
 732       constexpr _Tp&&
 733       operator*()&&
 734       { return std::move(this->_M_get()); }
 735
 736       constexpr const _Tp&&
 737       operator*() const&&
 738       { return std::move(this->_M_get()); }
 739
 740       constexpr explicit operator bool() const noexcept
 741       { return this->_M_is_engaged(); }
 742
 743       constexpr const _Tp&
 744       value() const&
 745       {
 746         return this->_M_is_engaged()
 747           ?  this->_M_get()
 748           : (__throw_bad_optional_access("Attempt to access value of a "
 749                                          "disengaged optional object"),
 750              this->_M_get());
 751       }
 752
 753       constexpr _Tp&
 754       value()&
 755       {
 756         return this->_M_is_engaged()
 757           ?  this->_M_get()
 758           : (__throw_bad_optional_access("Attempt to access value of a "
 759                                          "disengaged optional object"),
 760              this->_M_get());
 761       }
 762
 763       constexpr _Tp&&
 764       value()&&
 765       {
 766         return this->_M_is_engaged()
 767           ?  std::move(this->_M_get())
 768           : (__throw_bad_optional_access("Attempt to access value of a "
 769                                          "disengaged optional object"),
 770              std::move(this->_M_get()));
 771       }
 772
 773       constexpr const _Tp&&
 774       value() const&&
 775       {
 776         return this->_M_is_engaged()
 777           ?  std::move(this->_M_get())
 778           : (__throw_bad_optional_access("Attempt to access value of a "
 779                                          "disengaged optional object"),
 780              std::move(this->_M_get()));
 781       }
 782
 783       template<typename _Up>
 784         constexpr _Tp
 785         value_or(_Up&& __u) const&
 786         {
 787           static_assert(__and_<is_copy_constructible<_Tp>,
 788                                is_convertible<_Up&&, _Tp>>(),
 789                         "Cannot return value");
 790
 791           return this->_M_is_engaged()
 792             ? this->_M_get()
 793             : static_cast<_Tp>(std::forward<_Up>(__u));
 794         }
 795
 796       template<typename _Up>
 797         _Tp
 798         value_or(_Up&& __u) &&
 799         {
 800           static_assert(__and_<is_move_constructible<_Tp>,
 801                                is_convertible<_Up&&, _Tp>>(),
 802                         "Cannot return value" );
 803
 804           return this->_M_is_engaged()
 805             ? std::move(this->_M_get())
 806             : static_cast<_Tp>(std::forward<_Up>(__u));
 807         }
 808     };
 809
 810   // [X.Y.8] Comparisons between optional values.
 811   template<typename _Tp>
 812     constexpr bool
 813     operator==(const optional<_Tp>& __lhs, const optional<_Tp>& __rhs)
 814     {
 815       return static_cast<bool>(__lhs) == static_cast<bool>(__rhs)
 816              && (!__lhs || *__lhs == *__rhs);
 817     }
 818
 819   template<typename _Tp>
 820     constexpr bool
 821     operator!=(const optional<_Tp>& __lhs, const optional<_Tp>& __rhs)
 822     { return !(__lhs == __rhs); }
 823
 824   template<typename _Tp>
 825     constexpr bool
 826     operator<(const optional<_Tp>& __lhs, const optional<_Tp>& __rhs)
 827     {
 828       return static_cast<bool>(__rhs) && (!__lhs || *__lhs < *__rhs);
 829     }
 830
 831   template<typename _Tp>
 832     constexpr bool
 833     operator>(const optional<_Tp>& __lhs, const optional<_Tp>& __rhs)
 834     { return __rhs < __lhs; }
 835
 836   template<typename _Tp>
 837     constexpr bool
 838     operator<=(const optional<_Tp>& __lhs, const optional<_Tp>& __rhs)
 839     { return !(__rhs < __lhs); }
 840
 841   template<typename _Tp>
 842     constexpr bool
 843     operator>=(const optional<_Tp>& __lhs, const optional<_Tp>& __rhs)
 844     { return !(__lhs < __rhs); }
 845
 846   // [X.Y.9] Comparisons with nullopt.
 847   template<typename _Tp>
 848     constexpr bool
 849     operator==(const optional<_Tp>& __lhs, nullopt_t) noexcept
 850     { return !__lhs; }
 851
 852   template<typename _Tp>
 853     constexpr bool
 854     operator==(nullopt_t, const optional<_Tp>& __rhs) noexcept
 855     { return !__rhs; }
 856
 857   template<typename _Tp>
 858     constexpr bool
 859     operator!=(const optional<_Tp>& __lhs, nullopt_t) noexcept
 860     { return static_cast<bool>(__lhs); }
 861
 862   template<typename _Tp>
 863     constexpr bool
 864     operator!=(nullopt_t, const optional<_Tp>& __rhs) noexcept
 865     { return static_cast<bool>(__rhs); }
 866
 867   template<typename _Tp>
 868     constexpr bool
 869     operator<(const optional<_Tp>& /* __lhs */, nullopt_t) noexcept
 870     { return false; }
 871
 872   template<typename _Tp>
 873     constexpr bool
 874     operator<(nullopt_t, const optional<_Tp>& __rhs) noexcept
 875     { return static_cast<bool>(__rhs); }
 876
 877   template<typename _Tp>
 878     constexpr bool
 879     operator>(const optional<_Tp>& __lhs, nullopt_t) noexcept
 880     { return static_cast<bool>(__lhs); }
 881
 882   template<typename _Tp>
 883     constexpr bool
 884     operator>(nullopt_t, const optional<_Tp>& /* __rhs */) noexcept
 885     { return false; }
 886
 887   template<typename _Tp>
 888     constexpr bool
 889     operator<=(const optional<_Tp>& __lhs, nullopt_t) noexcept
 890     { return !__lhs; }
 891
 892   template<typename _Tp>
 893     constexpr bool
 894     operator<=(nullopt_t, const optional<_Tp>& /* __rhs */) noexcept
 895     { return true; }
 896
 897   template<typename _Tp>
 898     constexpr bool
 899     operator>=(const optional<_Tp>& /* __lhs */, nullopt_t) noexcept
 900     { return true; }
 901
 902   template<typename _Tp>
 903     constexpr bool
 904     operator>=(nullopt_t, const optional<_Tp>& __rhs) noexcept
 905     { return !__rhs; }
 906
 907   // [X.Y.10] Comparisons with value type.
 908   template<typename _Tp>
 909     constexpr bool
 910     operator==(const optional<_Tp>& __lhs, const _Tp& __rhs)
 911     { return __lhs && *__lhs == __rhs; }
 912
 913   template<typename _Tp>
 914     constexpr bool
 915     operator==(const _Tp& __lhs, const optional<_Tp>& __rhs)
 916     { return __rhs && __lhs == *__rhs; }
 917
 918   template<typename _Tp>
 919     constexpr bool
 920     operator!=(const optional<_Tp>& __lhs, _Tp const& __rhs)
 921     { return !__lhs || !(*__lhs == __rhs); }
 922
 923   template<typename _Tp>
 924     constexpr bool
 925     operator!=(const _Tp& __lhs, const optional<_Tp>& __rhs)
 926     { return !__rhs || !(__lhs == *__rhs); }
 927
 928   template<typename _Tp>
 929     constexpr bool
 930     operator<(const optional<_Tp>& __lhs, const _Tp& __rhs)
 931     { return !__lhs || *__lhs < __rhs; }
 932
 933   template<typename _Tp>
 934     constexpr bool
 935     operator<(const _Tp& __lhs, const optional<_Tp>& __rhs)
 936     { return __rhs && __lhs < *__rhs; }
 937
 938   template<typename _Tp>
 939     constexpr bool
 940     operator>(const optional<_Tp>& __lhs, const _Tp& __rhs)
 941     { return __lhs && __rhs < *__lhs; }
 942
 943   template<typename _Tp>
 944     constexpr bool
 945     operator>(const _Tp& __lhs, const optional<_Tp>& __rhs)
 946     { return !__rhs || *__rhs < __lhs; }
 947
 948   template<typename _Tp>
 949     constexpr bool
 950     operator<=(const optional<_Tp>& __lhs, const _Tp& __rhs)
 951     { return !__lhs || !(__rhs < *__lhs); }
 952
 953   template<typename _Tp>
 954     constexpr bool
 955     operator<=(const _Tp& __lhs, const optional<_Tp>& __rhs)
 956     { return __rhs && !(*__rhs < __lhs); }
 957
 958   template<typename _Tp>
 959     constexpr bool
 960     operator>=(const optional<_Tp>& __lhs, const _Tp& __rhs)
 961     { return __lhs && !(*__lhs < __rhs); }
 962
 963   template<typename _Tp>
 964     constexpr bool
 965     operator>=(const _Tp& __lhs, const optional<_Tp>& __rhs)
 966     { return !__rhs || !(__lhs < *__rhs); }
 967
 968   // [X.Y.11]
 969   template<typename _Tp>
 970     inline void
 971     swap(optional<_Tp>& __lhs, optional<_Tp>& __rhs)
 972     noexcept(noexcept(__lhs.swap(__rhs)))
 973     { __lhs.swap(__rhs); }
 974
 975   template<typename _Tp>
 976     constexpr optional<decay_t<_Tp>>
 977     make_optional(_Tp&& __t)
 978     { return optional<decay_t<_Tp>> { std::forward<_Tp>(__t) }; }
 979
 980   // @} group optional
 981 } // namespace fundamentals_v1
 982 } // namespace experimental
 983
 984   // [X.Y.12]
 985   template<typename _Tp>
 986     struct hash<experimental::optional<_Tp>>
 987     {
 988       using result_type = size_t;
 989       using argument_type = experimental::optional<_Tp>;
 990
 991       size_t
 992       operator()(const experimental::optional<_Tp>& __t) const
 993       noexcept(noexcept(hash<_Tp> {}(*__t)))
 994       {
 995         // We pick an arbitrary hash for disengaged optionals which hopefully
 996         // usual values of _Tp won't typically hash to.
 997         constexpr size_t __magic_disengaged_hash = static_cast<size_t>(-3333);
 998         return __t ? hash<_Tp> {}(*__t) : __magic_disengaged_hash;
 999       }
1000     };
1001
1002 _GLIBCXX_END_NAMESPACE_VERSION
1003 } // namespace std
1004
1005 #endif // C++14
1006
1007 #endif // _GLIBCXX_EXPERIMENTAL_OPTIONAL