libstdc++-v3/include/experimental/any

   1 // <experimental/any> -*- C++ -*-
   2
   3 // Copyright (C) 2014-2021 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/any
  26  *  This is a TS C++ Library header.
  27  *  @ingroup libfund-ts
  28  */
  29
  30 #ifndef _GLIBCXX_EXPERIMENTAL_ANY
  31 #define _GLIBCXX_EXPERIMENTAL_ANY 1
  32
  33 #pragma GCC system_header
  34
  35 #if __cplusplus >= 201402L
  36
  37 #include <typeinfo>
  38 #include <new>
  39 #include <utility>
  40 #include <type_traits>
  41 #include <experimental/bits/lfts_config.h>
  42
  43 namespace std _GLIBCXX_VISIBILITY(default)
  44 {
  45 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  46
  47 namespace experimental
  48 {
  49 inline namespace fundamentals_v1
  50 {
  51   /**
  52    * @defgroup any Type-safe container of any type
  53    * @ingroup libfund-ts
  54    *
  55    * A type-safe container for single values of value types, as
  56    * described in n3804 "Any Library Proposal (Revision 3)".
  57    *
  58    * @{
  59    */
  60
  61 #define __cpp_lib_experimental_any 201411
  62
  63   /**
  64    *  @brief Exception class thrown by a failed @c any_cast
  65    *  @ingroup exceptions
  66    */
  67   class bad_any_cast : public bad_cast
  68   {
  69   public:
  70     virtual const char* what() const noexcept { return "bad any_cast"; }
  71   };
  72
  73   /// @cond undocumented
  74   [[gnu::noreturn]] inline void __throw_bad_any_cast()
  75   {
  76 #if __cpp_exceptions
  77     throw bad_any_cast{};
  78 #else
  79     __builtin_abort();
  80 #endif
  81   }
  82   /// @endcond
  83
  84   /**
  85    *  @brief A type-safe container of any type.
  86    *
  87    *  An @c any object's state is either empty or it stores a contained object
  88    *  of CopyConstructible type.
  89    */
  90   class any
  91   {
  92     // Holds either pointer to a heap object or the contained object itself.
  93     union _Storage
  94     {
  95       // This constructor intentionally doesn't initialize anything.
  96       _Storage() = default;
  97
  98       // Prevent trivial copies of this type, buffer might hold a non-POD.
  99       _Storage(const _Storage&) = delete;
 100       _Storage& operator=(const _Storage&) = delete;
 101
 102       void* _M_ptr;
 103       aligned_storage<sizeof(_M_ptr), alignof(void*)>::type _M_buffer;
 104     };
 105
 106     template<typename _Tp, typename _Safe = is_nothrow_move_constructible<_Tp>,
 107              bool _Fits = (sizeof(_Tp) <= sizeof(_Storage))
 108                           && (alignof(_Tp) <= alignof(_Storage))>
 109       using _Internal = std::integral_constant<bool, _Safe::value && _Fits>;
 110
 111     template<typename _Tp>
 112       struct _Manager_internal; // uses small-object optimization
 113
 114     template<typename _Tp>
 115       struct _Manager_external; // creates contained object on the heap
 116
 117     template<typename _Tp>
 118       using _Manager = conditional_t<_Internal<_Tp>::value,
 119                                      _Manager_internal<_Tp>,
 120                                      _Manager_external<_Tp>>;
 121
 122     template<typename _Tp, typename _Decayed = decay_t<_Tp>>
 123       using _Decay = enable_if_t<!is_same<_Decayed, any>::value, _Decayed>;
 124
 125   public:
 126     // construct/destruct
 127
 128     /// Default constructor, creates an empty object.
 129     any() noexcept : _M_manager(nullptr) { }
 130
 131     /// Copy constructor, copies the state of @p __other
 132     any(const any& __other)
 133     {
 134       if (__other.empty())
 135         _M_manager = nullptr;
 136       else
 137         {
 138           _Arg __arg;
 139           __arg._M_any = this;
 140           __other._M_manager(_Op_clone, &__other, &__arg);
 141         }
 142     }
 143
 144     /**
 145      * @brief Move constructor, transfer the state from @p __other
 146      *
 147      * @post @c __other.empty() (this postcondition is a GNU extension)
 148      */
 149     any(any&& __other) noexcept
 150     {
 151       if (__other.empty())
 152         _M_manager = nullptr;
 153       else
 154         {
 155           _Arg __arg;
 156           __arg._M_any = this;
 157           __other._M_manager(_Op_xfer, &__other, &__arg);
 158         }
 159     }
 160
 161     /// Construct with a copy of @p __value as the contained object.
 162     template <typename _ValueType, typename _Tp = _Decay<_ValueType>,
 163               typename _Mgr = _Manager<_Tp>,
 164               typename enable_if<is_constructible<_Tp, _ValueType&&>::value,
 165                                  bool>::type = true>
 166       any(_ValueType&& __value)
 167       : _M_manager(&_Mgr::_S_manage)
 168       {
 169         _Mgr::_S_create(_M_storage, std::forward<_ValueType>(__value));
 170         static_assert(is_copy_constructible<_Tp>::value,
 171                       "The contained object must be CopyConstructible");
 172       }
 173
 174     /// Construct with a copy of @p __value as the contained object.
 175     template <typename _ValueType, typename _Tp = _Decay<_ValueType>,
 176               typename _Mgr = _Manager<_Tp>,
 177               typename enable_if<!is_constructible<_Tp, _ValueType&&>::value,
 178                                  bool>::type = false>
 179       any(_ValueType&& __value)
 180       : _M_manager(&_Mgr::_S_manage)
 181       {
 182         _Mgr::_S_create(_M_storage, __value);
 183         static_assert(is_copy_constructible<_Tp>::value,
 184                       "The contained object must be CopyConstructible");
 185       }
 186
 187     /// Destructor, calls @c clear()
 188     ~any() { clear(); }
 189
 190     // assignments
 191
 192     /// Copy the state of another object.
 193     any& operator=(const any& __rhs)
 194     {
 195       *this = any(__rhs);
 196       return *this;
 197     }
 198
 199     /**
 200      * @brief Move assignment operator
 201      *
 202      * @post @c __rhs.empty() (not guaranteed for other implementations)
 203      */
 204     any& operator=(any&& __rhs) noexcept
 205     {
 206       if (__rhs.empty())
 207         clear();
 208       else if (this != &__rhs)
 209         {
 210           clear();
 211           _Arg __arg;
 212           __arg._M_any = this;
 213           __rhs._M_manager(_Op_xfer, &__rhs, &__arg);
 214         }
 215       return *this;
 216     }
 217
 218     /// Store a copy of @p __rhs as the contained object.
 219     template<typename _ValueType>
 220       enable_if_t<!is_same<any, decay_t<_ValueType>>::value, any&>
 221       operator=(_ValueType&& __rhs)
 222       {
 223         *this = any(std::forward<_ValueType>(__rhs));
 224         return *this;
 225       }
 226
 227     // modifiers
 228
 229     /// If not empty, destroy the contained object.
 230     void clear() noexcept
 231     {
 232       if (!empty())
 233       {
 234         _M_manager(_Op_destroy, this, nullptr);
 235         _M_manager = nullptr;
 236       }
 237     }
 238
 239     /// Exchange state with another object.
 240     void swap(any& __rhs) noexcept
 241     {
 242       if (empty() && __rhs.empty())
 243         return;
 244
 245       if (!empty() && !__rhs.empty())
 246         {
 247           if (this == &__rhs)
 248             return;
 249
 250           any __tmp;
 251           _Arg __arg;
 252           __arg._M_any = &__tmp;
 253           __rhs._M_manager(_Op_xfer, &__rhs, &__arg);
 254           __arg._M_any = &__rhs;
 255           _M_manager(_Op_xfer, this, &__arg);
 256           __arg._M_any = this;
 257           __tmp._M_manager(_Op_xfer, &__tmp, &__arg);
 258         }
 259       else
 260         {
 261           any* __empty = empty() ? this : &__rhs;
 262           any* __full = empty() ? &__rhs : this;
 263           _Arg __arg;
 264           __arg._M_any = __empty;
 265           __full->_M_manager(_Op_xfer, __full, &__arg);
 266         }
 267     }
 268
 269     // observers
 270
 271     /// Reports whether there is a contained object or not.
 272     _GLIBCXX_NODISCARD bool empty() const noexcept { return _M_manager == nullptr; }
 273
 274 #if __cpp_rtti
 275     /// The @c typeid of the contained object, or @c typeid(void) if empty.
 276     const type_info& type() const noexcept
 277     {
 278       if (empty())
 279         return typeid(void);
 280       _Arg __arg;
 281       _M_manager(_Op_get_type_info, this, &__arg);
 282       return *__arg._M_typeinfo;
 283     }
 284 #endif
 285
 286     template<typename _Tp>
 287       static constexpr bool __is_valid_cast()
 288       { return __or_<is_reference<_Tp>, is_copy_constructible<_Tp>>::value; }
 289
 290   private:
 291     enum _Op {
 292         _Op_access, _Op_get_type_info, _Op_clone, _Op_destroy, _Op_xfer
 293     };
 294
 295     union _Arg
 296     {
 297         void* _M_obj;
 298         const std::type_info* _M_typeinfo;
 299         any* _M_any;
 300     };
 301
 302     void (*_M_manager)(_Op, const any*, _Arg*);
 303     _Storage _M_storage;
 304
 305     template<typename _Tp>
 306       friend enable_if_t<is_object<_Tp>::value, void*>
 307       __any_caster(const any* __any);
 308
 309     // Manage in-place contained object.
 310     template<typename _Tp>
 311       struct _Manager_internal
 312       {
 313         static void
 314         _S_manage(_Op __which, const any* __anyp, _Arg* __arg);
 315
 316         template<typename _Up>
 317           static void
 318           _S_create(_Storage& __storage, _Up&& __value)
 319           {
 320             void* __addr = &__storage._M_buffer;
 321             ::new (__addr) _Tp(std::forward<_Up>(__value));
 322           }
 323       };
 324
 325     // Manage external contained object.
 326     template<typename _Tp>
 327       struct _Manager_external
 328       {
 329         static void
 330         _S_manage(_Op __which, const any* __anyp, _Arg* __arg);
 331
 332         template<typename _Up>
 333           static void
 334           _S_create(_Storage& __storage, _Up&& __value)
 335           {
 336             __storage._M_ptr = new _Tp(std::forward<_Up>(__value));
 337           }
 338       };
 339   };
 340
 341   /// Exchange the states of two @c any objects.
 342   inline void swap(any& __x, any& __y) noexcept { __x.swap(__y); }
 343
 344   /**
 345    * @brief Access the contained object.
 346    *
 347    * @tparam  _ValueType  A const-reference or CopyConstructible type.
 348    * @param   __any       The object to access.
 349    * @return  The contained object.
 350    * @throw   bad_any_cast If <code>
 351    *          __any.type() != typeid(remove_reference_t<_ValueType>)
 352    *          </code>
 353    */
 354   template<typename _ValueType>
 355     inline _ValueType any_cast(const any& __any)
 356     {
 357       static_assert(any::__is_valid_cast<_ValueType>(),
 358           "Template argument must be a reference or CopyConstructible type");
 359       auto __p = any_cast<add_const_t<remove_reference_t<_ValueType>>>(&__any);
 360       if (__p)
 361         return *__p;
 362       __throw_bad_any_cast();
 363     }
 364
 365   /**
 366    * @brief Access the contained object.
 367    *
 368    * @tparam  _ValueType  A reference or CopyConstructible type.
 369    * @param   __any       The object to access.
 370    * @return  The contained object.
 371    * @throw   bad_any_cast If <code>
 372    *          __any.type() != typeid(remove_reference_t<_ValueType>)
 373    *          </code>
 374    *
 375    * @{
 376    */
 377   template<typename _ValueType>
 378     inline _ValueType any_cast(any& __any)
 379     {
 380       static_assert(any::__is_valid_cast<_ValueType>(),
 381           "Template argument must be a reference or CopyConstructible type");
 382       auto __p = any_cast<remove_reference_t<_ValueType>>(&__any);
 383       if (__p)
 384         return *__p;
 385       __throw_bad_any_cast();
 386     }
 387
 388   template<typename _ValueType,
 389            typename enable_if<!is_move_constructible<_ValueType>::value
 390                               || is_lvalue_reference<_ValueType>::value,
 391                               bool>::type = true>
 392     inline _ValueType any_cast(any&& __any)
 393     {
 394       static_assert(any::__is_valid_cast<_ValueType>(),
 395           "Template argument must be a reference or CopyConstructible type");
 396       auto __p = any_cast<remove_reference_t<_ValueType>>(&__any);
 397       if (__p)
 398         return *__p;
 399       __throw_bad_any_cast();
 400     }
 401
 402   template<typename _ValueType,
 403            typename enable_if<is_move_constructible<_ValueType>::value
 404                               && !is_lvalue_reference<_ValueType>::value,
 405                               bool>::type = false>
 406     inline _ValueType any_cast(any&& __any)
 407     {
 408       static_assert(any::__is_valid_cast<_ValueType>(),
 409           "Template argument must be a reference or CopyConstructible type");
 410       auto __p = any_cast<remove_reference_t<_ValueType>>(&__any);
 411       if (__p)
 412         return std::move(*__p);
 413       __throw_bad_any_cast();
 414     }
 415   // @}
 416
 417   /// @cond undocumented
 418   template<typename _Tp>
 419     enable_if_t<is_object<_Tp>::value, void*>
 420     __any_caster(const any* __any)
 421     {
 422       // any_cast<T> returns non-null if __any->type() == typeid(T) and
 423       // typeid(T) ignores cv-qualifiers so remove them:
 424       using _Up = remove_cv_t<_Tp>;
 425       // The contained value has a decayed type, so if decay_t<U> is not U,
 426       // then it's not possible to have a contained value of type U.
 427       using __does_not_decay = is_same<decay_t<_Up>, _Up>;
 428       // Only copy constructible types can be used for contained values.
 429       using __is_copyable = is_copy_constructible<_Up>;
 430       // If the type _Tp could never be stored in an any we don't want to
 431       // instantiate _Manager<_Tp>, so use _Manager<any::_Op> instead, which
 432       // is explicitly specialized and has a no-op _S_manage function.
 433       using _Vp = conditional_t<__and_<__does_not_decay, __is_copyable>::value,
 434                                 _Up, any::_Op>;
 435       // First try comparing function addresses, which works without RTTI
 436       if (__any->_M_manager == &any::_Manager<_Vp>::_S_manage
 437 #if __cpp_rtti
 438           || __any->type() == typeid(_Tp)
 439 #endif
 440           )
 441         {
 442           any::_Arg __arg;
 443           __any->_M_manager(any::_Op_access, __any, &__arg);
 444           return __arg._M_obj;
 445         }
 446       return nullptr;
 447     }
 448
 449   // This overload exists so that std::any_cast<void(*)()>(a) is well-formed.
 450   template<typename _Tp>
 451     enable_if_t<!is_object<_Tp>::value, _Tp*>
 452     __any_caster(const any*) noexcept
 453     { return nullptr; }
 454   /// @endcond
 455
 456   /**
 457    * @brief Access the contained object.
 458    *
 459    * @tparam  _ValueType  The type of the contained object.
 460    * @param   __any       A pointer to the object to access.
 461    * @return  The address of the contained object if <code>
 462    *          __any != nullptr && __any.type() == typeid(_ValueType)
 463    *          </code>, otherwise a null pointer.
 464    *
 465    * @{
 466    */
 467   template<typename _ValueType>
 468     inline const _ValueType* any_cast(const any* __any) noexcept
 469     {
 470       if (__any)
 471         return static_cast<_ValueType*>(__any_caster<_ValueType>(__any));
 472       return nullptr;
 473     }
 474
 475   template<typename _ValueType>
 476     inline _ValueType* any_cast(any* __any) noexcept
 477     {
 478       if (__any)
 479         return static_cast<_ValueType*>(__any_caster<_ValueType>(__any));
 480       return nullptr;
 481     }
 482   // @}
 483
 484   template<typename _Tp>
 485     void
 486     any::_Manager_internal<_Tp>::
 487     _S_manage(_Op __which, const any* __any, _Arg* __arg)
 488     {
 489       // The contained object is in _M_storage._M_buffer
 490       auto __ptr = reinterpret_cast<const _Tp*>(&__any->_M_storage._M_buffer);
 491       switch (__which)
 492       {
 493       case _Op_access:
 494         __arg->_M_obj = const_cast<_Tp*>(__ptr);
 495         break;
 496       case _Op_get_type_info:
 497 #if __cpp_rtti
 498         __arg->_M_typeinfo = &typeid(_Tp);
 499 #endif
 500         break;
 501       case _Op_clone:
 502         ::new(&__arg->_M_any->_M_storage._M_buffer) _Tp(*__ptr);
 503         __arg->_M_any->_M_manager = __any->_M_manager;
 504         break;
 505       case _Op_destroy:
 506         __ptr->~_Tp();
 507         break;
 508       case _Op_xfer:
 509         ::new(&__arg->_M_any->_M_storage._M_buffer) _Tp
 510           (std::move(*const_cast<_Tp*>(__ptr)));
 511         __ptr->~_Tp();
 512         __arg->_M_any->_M_manager = __any->_M_manager;
 513         const_cast<any*>(__any)->_M_manager = nullptr;
 514         break;
 515       }
 516     }
 517
 518   template<typename _Tp>
 519     void
 520     any::_Manager_external<_Tp>::
 521     _S_manage(_Op __which, const any* __any, _Arg* __arg)
 522     {
 523       // The contained object is *_M_storage._M_ptr
 524       auto __ptr = static_cast<const _Tp*>(__any->_M_storage._M_ptr);
 525       switch (__which)
 526       {
 527       case _Op_access:
 528         __arg->_M_obj = const_cast<_Tp*>(__ptr);
 529         break;
 530       case _Op_get_type_info:
 531 #if __cpp_rtti
 532         __arg->_M_typeinfo = &typeid(_Tp);
 533 #endif
 534         break;
 535       case _Op_clone:
 536         __arg->_M_any->_M_storage._M_ptr = new _Tp(*__ptr);
 537         __arg->_M_any->_M_manager = __any->_M_manager;
 538         break;
 539       case _Op_destroy:
 540         delete __ptr;
 541         break;
 542       case _Op_xfer:
 543         __arg->_M_any->_M_storage._M_ptr = __any->_M_storage._M_ptr;
 544         __arg->_M_any->_M_manager = __any->_M_manager;
 545         const_cast<any*>(__any)->_M_manager = nullptr;
 546         break;
 547       }
 548     }
 549
 550   // Dummy specialization used by __any_caster.
 551   template<>
 552     struct any::_Manager_internal<any::_Op>
 553     {
 554       static void
 555       _S_manage(_Op, const any*, _Arg*) { }
 556     };
 557
 558   // @} group any
 559 } // namespace fundamentals_v1
 560 } // namespace experimental
 561
 562 _GLIBCXX_END_NAMESPACE_VERSION
 563 } // namespace std
 564
 565 #endif // C++14
 566
 567 #endif // _GLIBCXX_EXPERIMENTAL_ANY