libstdc++
optional
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00001 // <optional> -*- C++ -*-
00002 
00003 // Copyright (C) 2013-2019 Free Software Foundation, Inc.
00004 //
00005 // This file is part of the GNU ISO C++ Library.  This library is free
00006 // software; you can redistribute it and/or modify it under the
00007 // terms of the GNU General Public License as published by the
00008 // Free Software Foundation; either version 3, or (at your option)
00009 // any later version.
00010 
00011 // This library is distributed in the hope that it will be useful,
00012 // but WITHOUT ANY WARRANTY; without even the implied warranty of
00013 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00014 // GNU General Public License for more details.
00015 
00016 // Under Section 7 of GPL version 3, you are granted additional
00017 // permissions described in the GCC Runtime Library Exception, version
00018 // 3.1, as published by the Free Software Foundation.
00019 
00020 // You should have received a copy of the GNU General Public License and
00021 // a copy of the GCC Runtime Library Exception along with this program;
00022 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
00023 // <http://www.gnu.org/licenses/>.
00024 
00025 /** @file experimental/optional
00026  *  This is a TS C++ Library header.
00027  */
00028 
00029 #ifndef _GLIBCXX_EXPERIMENTAL_OPTIONAL
00030 #define _GLIBCXX_EXPERIMENTAL_OPTIONAL 1
00031 
00032 /**
00033  * @defgroup experimental Experimental
00034  *
00035  * Components specified by various Technical Specifications.
00036  *
00037  * As indicated by the std::experimental namespace and the  header paths,
00038  * the contents of these Technical Specifications are experimental and not
00039  * part of the C++ standard. As such the interfaces and implementations may
00040  * change in the future, and there is <STRONG> no guarantee of compatibility
00041  * between different GCC releases </STRONG> for these features.
00042  */
00043 
00044 #if __cplusplus >= 201402L
00045 
00046 #include <utility>
00047 #include <type_traits>
00048 #include <stdexcept>
00049 #include <new>
00050 #include <initializer_list>
00051 #include <bits/functexcept.h>
00052 #include <bits/functional_hash.h>
00053 #include <bits/enable_special_members.h>
00054 #include <experimental/bits/lfts_config.h>
00055 
00056 namespace std _GLIBCXX_VISIBILITY(default)
00057 {
00058 _GLIBCXX_BEGIN_NAMESPACE_VERSION
00059 
00060 namespace experimental
00061 {
00062 inline namespace fundamentals_v1
00063 {
00064   /**
00065    * @defgroup optional Optional values
00066    * @ingroup experimental
00067    *
00068    * Class template for optional values and surrounding facilities, as
00069    * described in n3793 "A proposal to add a utility class to represent
00070    * optional objects (Revision 5)".
00071    *
00072    * @{
00073    */
00074 
00075 #define __cpp_lib_experimental_optional 201411
00076 
00077   // All subsequent [X.Y.n] references are against n3793.
00078 
00079   // [X.Y.4]
00080   template<typename _Tp>
00081     class optional;
00082 
00083   // [X.Y.5]
00084   /// Tag type for in-place construction.
00085   struct in_place_t { };
00086 
00087   /// Tag for in-place construction.
00088   constexpr in_place_t in_place { };
00089 
00090   // [X.Y.6]
00091   /// Tag type to disengage optional objects.
00092   struct nullopt_t
00093   {
00094     // Do not user-declare default constructor at all for
00095     // optional_value = {} syntax to work.
00096     // nullopt_t() = delete;
00097 
00098     // Used for constructing nullopt.
00099     enum class _Construct { _Token };
00100 
00101     // Must be constexpr for nullopt_t to be literal.
00102     explicit constexpr nullopt_t(_Construct) { }
00103   };
00104 
00105   // [X.Y.6]
00106   /// Tag to disengage optional objects.
00107   constexpr nullopt_t nullopt { nullopt_t::_Construct::_Token };
00108 
00109   // [X.Y.7]
00110   /**
00111    *  @brief Exception class thrown when a disengaged optional object is
00112    *  dereferenced.
00113    *  @ingroup exceptions
00114    */
00115   class bad_optional_access : public logic_error
00116   {
00117   public:
00118     bad_optional_access() : logic_error("bad optional access") { }
00119 
00120     // XXX This constructor is non-standard. Should not be inline
00121     explicit bad_optional_access(const char* __arg) : logic_error(__arg) { }
00122 
00123     virtual ~bad_optional_access() noexcept = default;
00124   };
00125 
00126   void
00127   __throw_bad_optional_access(const char*)
00128   __attribute__((__noreturn__));
00129 
00130   // XXX Does not belong here.
00131   inline void
00132   __throw_bad_optional_access(const char* __s)
00133   { _GLIBCXX_THROW_OR_ABORT(bad_optional_access(__s)); }
00134 
00135 #ifndef __cpp_lib_addressof_constexpr
00136   template<typename _Tp, typename = void>
00137     struct _Has_addressof_mem : std::false_type { };
00138 
00139   template<typename _Tp>
00140     struct _Has_addressof_mem<_Tp,
00141          __void_t<decltype( std::declval<const _Tp&>().operator&() )>
00142       >
00143     : std::true_type { };
00144 
00145   template<typename _Tp, typename = void>
00146     struct _Has_addressof_free : std::false_type { };
00147 
00148   template<typename _Tp>
00149     struct _Has_addressof_free<_Tp,
00150          __void_t<decltype( operator&(std::declval<const _Tp&>()) )>
00151       >
00152     : std::true_type { };
00153 
00154   /**
00155     * @brief Trait that detects the presence of an overloaded unary operator&.
00156     *
00157     * Practically speaking this detects the presence of such an operator when
00158     * called on a const-qualified lvalue (e.g.
00159     * declval<const _Tp&>().operator&()).
00160     */
00161   template<typename _Tp>
00162     struct _Has_addressof
00163     : std::__or_<_Has_addressof_mem<_Tp>, _Has_addressof_free<_Tp>>::type
00164     { };
00165 
00166   /**
00167     * @brief An overload that attempts to take the address of an lvalue as a
00168     * constant expression. Falls back to __addressof in the presence of an
00169     * overloaded addressof operator (unary operator&), in which case the call
00170     * will not be a constant expression.
00171     */
00172   template<typename _Tp>
00173     constexpr
00174     enable_if_t<!_Has_addressof<_Tp>::value, _Tp*>
00175     __constexpr_addressof(_Tp& __t)
00176     { return &__t; }
00177 
00178   /**
00179     * @brief Fallback overload that defers to __addressof.
00180     */
00181   template<typename _Tp>
00182     inline
00183     enable_if_t<_Has_addressof<_Tp>::value, _Tp*>
00184     __constexpr_addressof(_Tp& __t)
00185     { return std::__addressof(__t); }
00186 #endif // __cpp_lib_addressof_constexpr
00187 
00188   /**
00189     * @brief Class template that holds the necessary state for @ref optional
00190     * and that has the responsibility for construction and the special members.
00191     *
00192     * Such a separate base class template is necessary in order to
00193     * conditionally enable the special members (e.g. copy/move constructors).
00194     * Note that this means that @ref _Optional_base implements the
00195     * functionality for copy and move assignment, but not for converting
00196     * assignment.
00197     *
00198     * @see optional, _Enable_special_members
00199     */
00200   template<typename _Tp, bool _ShouldProvideDestructor =
00201            !is_trivially_destructible<_Tp>::value>
00202     class _Optional_base
00203     {
00204     private:
00205       // Remove const to avoid prohibition of reusing object storage for
00206       // const-qualified types in [3.8/9]. This is strictly internal
00207       // and even optional itself is oblivious to it.
00208       using _Stored_type = remove_const_t<_Tp>;
00209 
00210     public:
00211       // [X.Y.4.1] Constructors.
00212 
00213       // Constructors for disengaged optionals.
00214       constexpr _Optional_base() noexcept
00215       : _M_empty{} { }
00216 
00217       constexpr _Optional_base(nullopt_t) noexcept
00218       : _Optional_base{} { }
00219 
00220       // Constructors for engaged optionals.
00221       template<typename... _Args>
00222         constexpr explicit _Optional_base(in_place_t, _Args&&... __args)
00223         : _M_payload(std::forward<_Args>(__args)...), _M_engaged(true) { }
00224 
00225       template<typename _Up, typename... _Args,
00226                enable_if_t<is_constructible<_Tp,
00227                                             initializer_list<_Up>&,
00228                                             _Args&&...>::value,
00229                            int>...>
00230         constexpr explicit _Optional_base(in_place_t,
00231                                           initializer_list<_Up> __il,
00232                                           _Args&&... __args)
00233         : _M_payload(__il, std::forward<_Args>(__args)...),
00234           _M_engaged(true) { }
00235 
00236       // Copy and move constructors.
00237       _Optional_base(const _Optional_base& __other)
00238       {
00239         if (__other._M_engaged)
00240           this->_M_construct(__other._M_get());
00241       }
00242 
00243       _Optional_base(_Optional_base&& __other)
00244       noexcept(is_nothrow_move_constructible<_Tp>())
00245       {
00246         if (__other._M_engaged)
00247           this->_M_construct(std::move(__other._M_get()));
00248       }
00249 
00250       // [X.Y.4.3] (partly) Assignment.
00251       _Optional_base&
00252       operator=(const _Optional_base& __other)
00253       {
00254         if (this->_M_engaged && __other._M_engaged)
00255           this->_M_get() = __other._M_get();
00256         else
00257           {
00258             if (__other._M_engaged)
00259               this->_M_construct(__other._M_get());
00260             else
00261               this->_M_reset();
00262           }
00263 
00264         return *this;
00265       }
00266 
00267       _Optional_base&
00268       operator=(_Optional_base&& __other)
00269       noexcept(__and_<is_nothrow_move_constructible<_Tp>,
00270                       is_nothrow_move_assignable<_Tp>>())
00271       {
00272         if (this->_M_engaged && __other._M_engaged)
00273           this->_M_get() = std::move(__other._M_get());
00274         else
00275           {
00276             if (__other._M_engaged)
00277               this->_M_construct(std::move(__other._M_get()));
00278             else
00279               this->_M_reset();
00280           }
00281         return *this;
00282       }
00283 
00284       // [X.Y.4.2] Destructor.
00285       ~_Optional_base()
00286       {
00287         if (this->_M_engaged)
00288           this->_M_payload.~_Stored_type();
00289       }
00290 
00291       // The following functionality is also needed by optional, hence the
00292       // protected accessibility.
00293     protected:
00294       constexpr bool _M_is_engaged() const noexcept
00295       { return this->_M_engaged; }
00296 
00297       // The _M_get operations have _M_engaged as a precondition.
00298       constexpr _Tp&
00299       _M_get() noexcept
00300       { return _M_payload; }
00301 
00302       constexpr const _Tp&
00303       _M_get() const noexcept
00304       { return _M_payload; }
00305 
00306       // The _M_construct operation has !_M_engaged as a precondition
00307       // while _M_destruct has _M_engaged as a precondition.
00308       template<typename... _Args>
00309         void
00310         _M_construct(_Args&&... __args)
00311         noexcept(is_nothrow_constructible<_Stored_type, _Args...>())
00312         {
00313           ::new (std::__addressof(this->_M_payload))
00314             _Stored_type(std::forward<_Args>(__args)...);
00315           this->_M_engaged = true;
00316         }
00317 
00318       void
00319       _M_destruct()
00320       {
00321         this->_M_engaged = false;
00322         this->_M_payload.~_Stored_type();
00323       }
00324 
00325       // _M_reset is a 'safe' operation with no precondition.
00326       void
00327       _M_reset()
00328       {
00329         if (this->_M_engaged)
00330           this->_M_destruct();
00331       }
00332 
00333     private:
00334       struct _Empty_byte { };
00335       union {
00336           _Empty_byte _M_empty;
00337           _Stored_type _M_payload;
00338       };
00339       bool _M_engaged = false;
00340     };
00341 
00342   /// Partial specialization that is exactly identical to the primary template
00343   /// save for not providing a destructor, to fulfill triviality requirements.
00344   template<typename _Tp>
00345     class _Optional_base<_Tp, false>
00346     {
00347     private:
00348       using _Stored_type = remove_const_t<_Tp>;
00349 
00350     public:
00351       constexpr _Optional_base() noexcept
00352       : _M_empty{} { }
00353 
00354       constexpr _Optional_base(nullopt_t) noexcept
00355       : _Optional_base{} { }
00356 
00357       template<typename... _Args>
00358         constexpr explicit _Optional_base(in_place_t, _Args&&... __args)
00359         : _M_payload(std::forward<_Args>(__args)...), _M_engaged(true) { }
00360 
00361       template<typename _Up, typename... _Args,
00362                enable_if_t<is_constructible<_Tp,
00363                                             initializer_list<_Up>&,
00364                                             _Args&&...>::value,
00365                            int>...>
00366         constexpr explicit _Optional_base(in_place_t,
00367                                           initializer_list<_Up> __il,
00368                                           _Args&&... __args)
00369         : _M_payload(__il, std::forward<_Args>(__args)...),
00370           _M_engaged(true) { }
00371 
00372       _Optional_base(const _Optional_base& __other)
00373       {
00374         if (__other._M_engaged)
00375           this->_M_construct(__other._M_get());
00376       }
00377 
00378       _Optional_base(_Optional_base&& __other)
00379       noexcept(is_nothrow_move_constructible<_Tp>())
00380       {
00381         if (__other._M_engaged)
00382           this->_M_construct(std::move(__other._M_get()));
00383       }
00384 
00385       _Optional_base&
00386       operator=(const _Optional_base& __other)
00387       {
00388         if (this->_M_engaged && __other._M_engaged)
00389           this->_M_get() = __other._M_get();
00390         else
00391           {
00392             if (__other._M_engaged)
00393               this->_M_construct(__other._M_get());
00394             else
00395               this->_M_reset();
00396           }
00397         return *this;
00398       }
00399 
00400       _Optional_base&
00401       operator=(_Optional_base&& __other)
00402       noexcept(__and_<is_nothrow_move_constructible<_Tp>,
00403                       is_nothrow_move_assignable<_Tp>>())
00404       {
00405         if (this->_M_engaged && __other._M_engaged)
00406           this->_M_get() = std::move(__other._M_get());
00407         else
00408           {
00409             if (__other._M_engaged)
00410               this->_M_construct(std::move(__other._M_get()));
00411             else
00412               this->_M_reset();
00413           }
00414         return *this;
00415       }
00416 
00417       // Sole difference
00418       // ~_Optional_base() noexcept = default;
00419 
00420     protected:
00421       constexpr bool _M_is_engaged() const noexcept
00422       { return this->_M_engaged; }
00423 
00424       _Tp&
00425       _M_get() noexcept
00426       { return _M_payload; }
00427 
00428       constexpr const _Tp&
00429       _M_get() const noexcept
00430       { return _M_payload; }
00431 
00432       template<typename... _Args>
00433         void
00434         _M_construct(_Args&&... __args)
00435         noexcept(is_nothrow_constructible<_Stored_type, _Args...>())
00436         {
00437           ::new (std::__addressof(this->_M_payload))
00438             _Stored_type(std::forward<_Args>(__args)...);
00439           this->_M_engaged = true;
00440         }
00441 
00442       void
00443       _M_destruct()
00444       {
00445         this->_M_engaged = false;
00446         this->_M_payload.~_Stored_type();
00447       }
00448 
00449       void
00450       _M_reset()
00451       {
00452         if (this->_M_engaged)
00453           this->_M_destruct();
00454       }
00455 
00456     private:
00457       struct _Empty_byte { };
00458       union
00459       {
00460         _Empty_byte _M_empty;
00461         _Stored_type _M_payload;
00462       };
00463       bool _M_engaged = false;
00464     };
00465 
00466   template<typename _Tp>
00467   class optional;
00468 
00469   template<typename _Tp, typename _Up>
00470     using __converts_from_optional =
00471       __or_<is_constructible<_Tp, const optional<_Up>&>,
00472             is_constructible<_Tp, optional<_Up>&>,
00473             is_constructible<_Tp, const optional<_Up>&&>,
00474             is_constructible<_Tp, optional<_Up>&&>,
00475             is_convertible<const optional<_Up>&, _Tp>,
00476             is_convertible<optional<_Up>&, _Tp>,
00477             is_convertible<const optional<_Up>&&, _Tp>,
00478             is_convertible<optional<_Up>&&, _Tp>>;
00479 
00480   template<typename _Tp, typename _Up>
00481     using __assigns_from_optional =
00482       __or_<is_assignable<_Tp&, const optional<_Up>&>,
00483             is_assignable<_Tp&, optional<_Up>&>,
00484             is_assignable<_Tp&, const optional<_Up>&&>,
00485             is_assignable<_Tp&, optional<_Up>&&>>;
00486 
00487   /**
00488     * @brief Class template for optional values.
00489     */
00490   template<typename _Tp>
00491     class optional
00492     : private _Optional_base<_Tp>,
00493       private _Enable_copy_move<
00494         // Copy constructor.
00495         is_copy_constructible<_Tp>::value,
00496         // Copy assignment.
00497         __and_<is_copy_constructible<_Tp>, is_copy_assignable<_Tp>>::value,
00498         // Move constructor.
00499         is_move_constructible<_Tp>::value,
00500         // Move assignment.
00501         __and_<is_move_constructible<_Tp>, is_move_assignable<_Tp>>::value,
00502         // Unique tag type.
00503         optional<_Tp>>
00504     {
00505       static_assert(__and_<__not_<is_same<remove_cv_t<_Tp>, nullopt_t>>,
00506                            __not_<is_same<remove_cv_t<_Tp>, in_place_t>>,
00507                            __not_<is_reference<_Tp>>>(),
00508                     "Invalid instantiation of optional<T>");
00509 
00510     private:
00511       using _Base = _Optional_base<_Tp>;
00512 
00513     public:
00514       using value_type = _Tp;
00515 
00516       // _Optional_base has the responsibility for construction.
00517       using _Base::_Base;
00518 
00519       constexpr optional() = default;
00520       // Converting constructors for engaged optionals.
00521       template <typename _Up = _Tp,
00522                 enable_if_t<__and_<
00523                               __not_<is_same<optional<_Tp>, decay_t<_Up>>>,
00524                               is_constructible<_Tp, _Up&&>,
00525                               is_convertible<_Up&&, _Tp>
00526                               >::value, bool> = true>
00527       constexpr optional(_Up&& __t)
00528         : _Base(in_place, std::forward<_Up>(__t)) { }
00529 
00530       template <typename _Up = _Tp,
00531                 enable_if_t<__and_<
00532                               __not_<is_same<optional<_Tp>, decay_t<_Up>>>,
00533                               is_constructible<_Tp, _Up&&>,
00534                               __not_<is_convertible<_Up&&, _Tp>>
00535                               >::value, bool> = false>
00536       explicit constexpr optional(_Up&& __t)
00537         : _Base(in_place, std::forward<_Up>(__t)) { }
00538 
00539       template <typename _Up,
00540                 enable_if_t<__and_<
00541                             __not_<is_same<_Tp, _Up>>,
00542                             is_constructible<_Tp, const _Up&>,
00543                             is_convertible<const _Up&, _Tp>,
00544                             __not_<__converts_from_optional<_Tp, _Up>>
00545                             >::value, bool> = true>
00546       constexpr optional(const optional<_Up>& __t)
00547       {
00548         if (__t)
00549           emplace(*__t);
00550       }
00551 
00552       template <typename _Up,
00553                  enable_if_t<__and_<
00554                                __not_<is_same<_Tp, _Up>>,
00555                                is_constructible<_Tp, const _Up&>,
00556                                __not_<is_convertible<const _Up&, _Tp>>,
00557                                __not_<__converts_from_optional<_Tp, _Up>>
00558                                >::value, bool> = false>
00559       explicit constexpr optional(const optional<_Up>& __t)
00560       {
00561         if (__t)
00562           emplace(*__t);
00563       }
00564 
00565       template <typename _Up,
00566                 enable_if_t<__and_<
00567                               __not_<is_same<_Tp, _Up>>,
00568                               is_constructible<_Tp, _Up&&>,
00569                               is_convertible<_Up&&, _Tp>,
00570                               __not_<__converts_from_optional<_Tp, _Up>>
00571                               >::value, bool> = true>
00572       constexpr optional(optional<_Up>&& __t)
00573       {
00574         if (__t)
00575           emplace(std::move(*__t));
00576       }
00577 
00578       template <typename _Up,
00579                 enable_if_t<__and_<
00580                             __not_<is_same<_Tp, _Up>>,
00581                             is_constructible<_Tp, _Up&&>,
00582                             __not_<is_convertible<_Up&&, _Tp>>,
00583                             __not_<__converts_from_optional<_Tp, _Up>>
00584                             >::value, bool> = false>
00585       explicit constexpr optional(optional<_Up>&& __t)
00586       {
00587         if (__t)
00588           emplace(std::move(*__t));
00589       }
00590 
00591       // [X.Y.4.3] (partly) Assignment.
00592       optional&
00593       operator=(nullopt_t) noexcept
00594       {
00595         this->_M_reset();
00596         return *this;
00597       }
00598 
00599       template<typename _Up = _Tp>
00600         enable_if_t<__and_<
00601                       __not_<is_same<optional<_Tp>, decay_t<_Up>>>,
00602                       is_constructible<_Tp, _Up>,
00603                       __not_<__and_<is_scalar<_Tp>,
00604                                     is_same<_Tp, decay_t<_Up>>>>,
00605                       is_assignable<_Tp&, _Up>>::value,
00606                     optional&>
00607         operator=(_Up&& __u)
00608         {
00609           if (this->_M_is_engaged())
00610             this->_M_get() = std::forward<_Up>(__u);
00611           else
00612             this->_M_construct(std::forward<_Up>(__u));
00613 
00614           return *this;
00615         }
00616 
00617       template<typename _Up>
00618         enable_if_t<__and_<
00619                       __not_<is_same<_Tp, _Up>>,
00620                       is_constructible<_Tp, const _Up&>,
00621                       is_assignable<_Tp&, _Up>,
00622                       __not_<__converts_from_optional<_Tp, _Up>>,
00623                       __not_<__assigns_from_optional<_Tp, _Up>>
00624                       >::value,
00625                     optional&>
00626         operator=(const optional<_Up>& __u)
00627         {
00628           if (__u)
00629             {
00630               if (this->_M_is_engaged())
00631                 this->_M_get() = *__u;
00632               else
00633                 this->_M_construct(*__u);
00634             }
00635           else
00636             {
00637               this->_M_reset();
00638             }
00639           return *this;
00640         }
00641 
00642       template<typename _Up>
00643         enable_if_t<__and_<
00644                       __not_<is_same<_Tp, _Up>>,
00645                       is_constructible<_Tp, _Up>,
00646                       is_assignable<_Tp&, _Up>,
00647                       __not_<__converts_from_optional<_Tp, _Up>>,
00648                       __not_<__assigns_from_optional<_Tp, _Up>>
00649                       >::value,
00650                     optional&>
00651         operator=(optional<_Up>&& __u)
00652         {
00653           if (__u)
00654             {
00655               if (this->_M_is_engaged())
00656                 this->_M_get() = std::move(*__u);
00657               else
00658                 this->_M_construct(std::move(*__u));
00659             }
00660           else
00661             {
00662               this->_M_reset();
00663             }
00664 
00665           return *this;
00666         }
00667 
00668       template<typename... _Args>
00669         enable_if_t<is_constructible<_Tp, _Args&&...>::value>
00670         emplace(_Args&&... __args)
00671         {
00672           this->_M_reset();
00673           this->_M_construct(std::forward<_Args>(__args)...);
00674         }
00675 
00676       template<typename _Up, typename... _Args>
00677         enable_if_t<is_constructible<_Tp, initializer_list<_Up>&,
00678                                      _Args&&...>::value>
00679         emplace(initializer_list<_Up> __il, _Args&&... __args)
00680         {
00681           this->_M_reset();
00682           this->_M_construct(__il, std::forward<_Args>(__args)...);
00683         }
00684 
00685       // [X.Y.4.2] Destructor is implicit, implemented in _Optional_base.
00686 
00687       // [X.Y.4.4] Swap.
00688       void
00689       swap(optional& __other)
00690       noexcept(is_nothrow_move_constructible<_Tp>()
00691                && __is_nothrow_swappable<_Tp>::value)
00692       {
00693         using std::swap;
00694 
00695         if (this->_M_is_engaged() && __other._M_is_engaged())
00696           swap(this->_M_get(), __other._M_get());
00697         else if (this->_M_is_engaged())
00698           {
00699             __other._M_construct(std::move(this->_M_get()));
00700             this->_M_destruct();
00701           }
00702         else if (__other._M_is_engaged())
00703           {
00704             this->_M_construct(std::move(__other._M_get()));
00705             __other._M_destruct();
00706           }
00707       }
00708 
00709       // [X.Y.4.5] Observers.
00710       constexpr const _Tp*
00711       operator->() const
00712       {
00713 #ifndef __cpp_lib_addressof_constexpr
00714         return __constexpr_addressof(this->_M_get());
00715 #else
00716         return std::__addressof(this->_M_get());
00717 #endif
00718       }
00719 
00720       _Tp*
00721       operator->()
00722       { return std::__addressof(this->_M_get()); }
00723 
00724       constexpr const _Tp&
00725       operator*() const&
00726       { return this->_M_get(); }
00727 
00728       constexpr _Tp&
00729       operator*()&
00730       { return this->_M_get(); }
00731 
00732       constexpr _Tp&&
00733       operator*()&&
00734       { return std::move(this->_M_get()); }
00735 
00736       constexpr const _Tp&&
00737       operator*() const&&
00738       { return std::move(this->_M_get()); }
00739 
00740       constexpr explicit operator bool() const noexcept
00741       { return this->_M_is_engaged(); }
00742 
00743       constexpr const _Tp&
00744       value() const&
00745       {
00746         return this->_M_is_engaged()
00747           ?  this->_M_get()
00748           : (__throw_bad_optional_access("Attempt to access value of a "
00749                                          "disengaged optional object"),
00750              this->_M_get());
00751       }
00752 
00753       constexpr _Tp&
00754       value()&
00755       {
00756         return this->_M_is_engaged()
00757           ?  this->_M_get()
00758           : (__throw_bad_optional_access("Attempt to access value of a "
00759                                          "disengaged optional object"),
00760              this->_M_get());
00761       }
00762 
00763       constexpr _Tp&&
00764       value()&&
00765       {
00766         return this->_M_is_engaged()
00767           ?  std::move(this->_M_get())
00768           : (__throw_bad_optional_access("Attempt to access value of a "
00769                                          "disengaged optional object"),
00770              std::move(this->_M_get()));
00771       }
00772 
00773       constexpr const _Tp&&
00774       value() const&&
00775       {
00776         return this->_M_is_engaged()
00777           ?  std::move(this->_M_get())
00778           : (__throw_bad_optional_access("Attempt to access value of a "
00779                                          "disengaged optional object"),
00780              std::move(this->_M_get()));
00781       }
00782 
00783       template<typename _Up>
00784         constexpr _Tp
00785         value_or(_Up&& __u) const&
00786         {
00787           static_assert(__and_<is_copy_constructible<_Tp>,
00788                                is_convertible<_Up&&, _Tp>>(),
00789                         "Cannot return value");
00790 
00791           return this->_M_is_engaged()
00792             ? this->_M_get()
00793             : static_cast<_Tp>(std::forward<_Up>(__u));
00794         }
00795 
00796       template<typename _Up>
00797         _Tp
00798         value_or(_Up&& __u) &&
00799         {
00800           static_assert(__and_<is_move_constructible<_Tp>,
00801                                is_convertible<_Up&&, _Tp>>(),
00802                         "Cannot return value" );
00803 
00804           return this->_M_is_engaged()
00805             ? std::move(this->_M_get())
00806             : static_cast<_Tp>(std::forward<_Up>(__u));
00807         }
00808     };
00809 
00810   // [X.Y.8] Comparisons between optional values.
00811   template<typename _Tp>
00812     constexpr bool
00813     operator==(const optional<_Tp>& __lhs, const optional<_Tp>& __rhs)
00814     {
00815       return static_cast<bool>(__lhs) == static_cast<bool>(__rhs)
00816              && (!__lhs || *__lhs == *__rhs);
00817     }
00818 
00819   template<typename _Tp>
00820     constexpr bool
00821     operator!=(const optional<_Tp>& __lhs, const optional<_Tp>& __rhs)
00822     { return !(__lhs == __rhs); }
00823 
00824   template<typename _Tp>
00825     constexpr bool
00826     operator<(const optional<_Tp>& __lhs, const optional<_Tp>& __rhs)
00827     {
00828       return static_cast<bool>(__rhs) && (!__lhs || *__lhs < *__rhs);
00829     }
00830 
00831   template<typename _Tp>
00832     constexpr bool
00833     operator>(const optional<_Tp>& __lhs, const optional<_Tp>& __rhs)
00834     { return __rhs < __lhs; }
00835 
00836   template<typename _Tp>
00837     constexpr bool
00838     operator<=(const optional<_Tp>& __lhs, const optional<_Tp>& __rhs)
00839     { return !(__rhs < __lhs); }
00840 
00841   template<typename _Tp>
00842     constexpr bool
00843     operator>=(const optional<_Tp>& __lhs, const optional<_Tp>& __rhs)
00844     { return !(__lhs < __rhs); }
00845 
00846   // [X.Y.9] Comparisons with nullopt.
00847   template<typename _Tp>
00848     constexpr bool
00849     operator==(const optional<_Tp>& __lhs, nullopt_t) noexcept
00850     { return !__lhs; }
00851 
00852   template<typename _Tp>
00853     constexpr bool
00854     operator==(nullopt_t, const optional<_Tp>& __rhs) noexcept
00855     { return !__rhs; }
00856 
00857   template<typename _Tp>
00858     constexpr bool
00859     operator!=(const optional<_Tp>& __lhs, nullopt_t) noexcept
00860     { return static_cast<bool>(__lhs); }
00861 
00862   template<typename _Tp>
00863     constexpr bool
00864     operator!=(nullopt_t, const optional<_Tp>& __rhs) noexcept
00865     { return static_cast<bool>(__rhs); }
00866 
00867   template<typename _Tp>
00868     constexpr bool
00869     operator<(const optional<_Tp>& /* __lhs */, nullopt_t) noexcept
00870     { return false; }
00871 
00872   template<typename _Tp>
00873     constexpr bool
00874     operator<(nullopt_t, const optional<_Tp>& __rhs) noexcept
00875     { return static_cast<bool>(__rhs); }
00876 
00877   template<typename _Tp>
00878     constexpr bool
00879     operator>(const optional<_Tp>& __lhs, nullopt_t) noexcept
00880     { return static_cast<bool>(__lhs); }
00881 
00882   template<typename _Tp>
00883     constexpr bool
00884     operator>(nullopt_t, const optional<_Tp>& /* __rhs */) noexcept
00885     { return false; }
00886 
00887   template<typename _Tp>
00888     constexpr bool
00889     operator<=(const optional<_Tp>& __lhs, nullopt_t) noexcept
00890     { return !__lhs; }
00891 
00892   template<typename _Tp>
00893     constexpr bool
00894     operator<=(nullopt_t, const optional<_Tp>& /* __rhs */) noexcept
00895     { return true; }
00896 
00897   template<typename _Tp>
00898     constexpr bool
00899     operator>=(const optional<_Tp>& /* __lhs */, nullopt_t) noexcept
00900     { return true; }
00901 
00902   template<typename _Tp>
00903     constexpr bool
00904     operator>=(nullopt_t, const optional<_Tp>& __rhs) noexcept
00905     { return !__rhs; }
00906 
00907   // [X.Y.10] Comparisons with value type.
00908   template<typename _Tp>
00909     constexpr bool
00910     operator==(const optional<_Tp>& __lhs, const _Tp& __rhs)
00911     { return __lhs && *__lhs == __rhs; }
00912 
00913   template<typename _Tp>
00914     constexpr bool
00915     operator==(const _Tp& __lhs, const optional<_Tp>& __rhs)
00916     { return __rhs && __lhs == *__rhs; }
00917 
00918   template<typename _Tp>
00919     constexpr bool
00920     operator!=(const optional<_Tp>& __lhs, _Tp const& __rhs)
00921     { return !__lhs || !(*__lhs == __rhs); }
00922 
00923   template<typename _Tp>
00924     constexpr bool
00925     operator!=(const _Tp& __lhs, const optional<_Tp>& __rhs)
00926     { return !__rhs || !(__lhs == *__rhs); }
00927 
00928   template<typename _Tp>
00929     constexpr bool
00930     operator<(const optional<_Tp>& __lhs, const _Tp& __rhs)
00931     { return !__lhs || *__lhs < __rhs; }
00932 
00933   template<typename _Tp>
00934     constexpr bool
00935     operator<(const _Tp& __lhs, const optional<_Tp>& __rhs)
00936     { return __rhs && __lhs < *__rhs; }
00937 
00938   template<typename _Tp>
00939     constexpr bool
00940     operator>(const optional<_Tp>& __lhs, const _Tp& __rhs)
00941     { return __lhs && __rhs < *__lhs; }
00942 
00943   template<typename _Tp>
00944     constexpr bool
00945     operator>(const _Tp& __lhs, const optional<_Tp>& __rhs)
00946     { return !__rhs || *__rhs < __lhs; }
00947 
00948   template<typename _Tp>
00949     constexpr bool
00950     operator<=(const optional<_Tp>& __lhs, const _Tp& __rhs)
00951     { return !__lhs || !(__rhs < *__lhs); }
00952 
00953   template<typename _Tp>
00954     constexpr bool
00955     operator<=(const _Tp& __lhs, const optional<_Tp>& __rhs)
00956     { return __rhs && !(*__rhs < __lhs); }
00957 
00958   template<typename _Tp>
00959     constexpr bool
00960     operator>=(const optional<_Tp>& __lhs, const _Tp& __rhs)
00961     { return __lhs && !(*__lhs < __rhs); }
00962 
00963   template<typename _Tp>
00964     constexpr bool
00965     operator>=(const _Tp& __lhs, const optional<_Tp>& __rhs)
00966     { return !__rhs || !(__lhs < *__rhs); }
00967 
00968   // [X.Y.11]
00969   template<typename _Tp>
00970     inline void
00971     swap(optional<_Tp>& __lhs, optional<_Tp>& __rhs)
00972     noexcept(noexcept(__lhs.swap(__rhs)))
00973     { __lhs.swap(__rhs); }
00974 
00975   template<typename _Tp>
00976     constexpr optional<decay_t<_Tp>>
00977     make_optional(_Tp&& __t)
00978     { return optional<decay_t<_Tp>> { std::forward<_Tp>(__t) }; }
00979 
00980   // @} group optional
00981 } // namespace fundamentals_v1
00982 } // namespace experimental
00983 
00984   // [X.Y.12]
00985   template<typename _Tp>
00986     struct hash<experimental::optional<_Tp>>
00987     {
00988       using result_type = size_t;
00989       using argument_type = experimental::optional<_Tp>;
00990 
00991       size_t
00992       operator()(const experimental::optional<_Tp>& __t) const
00993       noexcept(noexcept(hash<_Tp> {}(*__t)))
00994       {
00995         // We pick an arbitrary hash for disengaged optionals which hopefully
00996         // usual values of _Tp won't typically hash to.
00997         constexpr size_t __magic_disengaged_hash = static_cast<size_t>(-3333);
00998         return __t ? hash<_Tp> {}(*__t) : __magic_disengaged_hash;
00999       }
01000     };
01001 
01002 _GLIBCXX_END_NAMESPACE_VERSION
01003 } // namespace std
01004 
01005 #endif // C++14
01006 
01007 #endif // _GLIBCXX_EXPERIMENTAL_OPTIONAL