libstdc++-v3/include/experimental/any

   1 // <experimental/any> -*- C++ -*-
   2
   3 // Copyright (C) 2014-2017 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  */
  28
  29 #ifndef _GLIBCXX_EXPERIMENTAL_ANY
  30 #define _GLIBCXX_EXPERIMENTAL_ANY 1
  31
  32 #pragma GCC system_header
  33
  34 #if __cplusplus >= 201402L
  35
  36 #include <typeinfo>
  37 #include <new>
  38 #include <utility>
  39 #include <type_traits>
  40 #include <experimental/bits/lfts_config.h>
  41
  42 namespace std _GLIBCXX_VISIBILITY(default)
  43 {
  44 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  45
  46 namespace experimental
  47 {
  48 inline namespace fundamentals_v1
  49 {
  50   /**
  51    * @defgroup any Type-safe container of any type
  52    * @ingroup experimental
  53    *
  54    * A type-safe container for single values of value types, as
  55    * described in n3804 "Any Library Proposal (Revision 3)".
  56    *
  57    * @{
  58    */
  59
  60 #define __cpp_lib_experimental_any 201411
  61
  62   /**
  63    *  @brief Exception class thrown by a failed @c any_cast
  64    *  @ingroup exceptions
  65    */
  66   class bad_any_cast : public bad_cast
  67   {
  68   public:
  69     virtual const char* what() const noexcept { return "bad any_cast"; }
  70   };
  71
  72   [[gnu::noreturn]] inline void __throw_bad_any_cast()
  73   {
  74 #if __cpp_exceptions
  75     throw bad_any_cast{};
  76 #else
  77     __builtin_abort();
  78 #endif
  79   }
  80
  81   /**
  82    *  @brief A type-safe container of any type.
  83    *
  84    *  An @c any object's state is either empty or it stores a contained object
  85    *  of CopyConstructible type.
  86    */
  87   class any
  88   {
  89     // Holds either pointer to a heap object or the contained object itself.
  90     union _Storage
  91     {
  92       // This constructor intentionally doesn't initialize anything.
  93       _Storage() = default;
  94
  95       // Prevent trivial copies of this type, buffer might hold a non-POD.
  96       _Storage(const _Storage&) = delete;
  97       _Storage& operator=(const _Storage&) = delete;
  98
  99       void* _M_ptr;
 100       aligned_storage<sizeof(_M_ptr), alignof(void*)>::type _M_buffer;
 101     };
 102
 103     template<typename _Tp, typename _Safe = is_nothrow_move_constructible<_Tp>,
 104              bool _Fits = (sizeof(_Tp) <= sizeof(_Storage))
 105                           && (alignof(_Tp) <= alignof(_Storage))>
 106       using _Internal = std::integral_constant<bool, _Safe::value && _Fits>;
 107
 108     template<typename _Tp>
 109       struct _Manager_internal; // uses small-object optimization
 110
 111     template<typename _Tp>
 112       struct _Manager_external; // creates contained object on the heap
 113
 114     template<typename _Tp>
 115       using _Manager = conditional_t<_Internal<_Tp>::value,
 116                                      _Manager_internal<_Tp>,
 117                                      _Manager_external<_Tp>>;
 118
 119     template<typename _Tp, typename _Decayed = decay_t<_Tp>>
 120       using _Decay = enable_if_t<!is_same<_Decayed, any>::value, _Decayed>;
 121
 122   public:
 123     // construct/destruct
 124
 125     /// Default constructor, creates an empty object.
 126     any() noexcept : _M_manager(nullptr) { }
 127
 128     /// Copy constructor, copies the state of @p __other
 129     any(const any& __other)
 130     {
 131       if (__other.empty())
 132         _M_manager = nullptr;
 133       else
 134         {
 135           _Arg __arg;
 136           __arg._M_any = this;
 137           __other._M_manager(_Op_clone, &__other, &__arg);
 138         }
 139     }
 140
 141     /**
 142      * @brief Move constructor, transfer the state from @p __other
 143      *
 144      * @post @c __other.empty() (this postcondition is a GNU extension)
 145      */
 146     any(any&& __other) noexcept
 147     {
 148       if (__other.empty())
 149         _M_manager = nullptr;
 150       else
 151         {
 152           _Arg __arg;
 153           __arg._M_any = this;
 154           __other._M_manager(_Op_xfer, &__other, &__arg);
 155         }
 156     }
 157
 158     /// Construct with a copy of @p __value as the contained object.
 159     template <typename _ValueType, typename _Tp = _Decay<_ValueType>,
 160               typename _Mgr = _Manager<_Tp>,
 161               typename enable_if<is_constructible<_Tp, _ValueType&&>::value,
 162                                  bool>::type = true>
 163       any(_ValueType&& __value)
 164       : _M_manager(&_Mgr::_S_manage)
 165       {
 166         _Mgr::_S_create(_M_storage, std::forward<_ValueType>(__value));
 167         static_assert(is_copy_constructible<_Tp>::value,
 168                       "The contained object must be CopyConstructible");
 169       }
 170
 171     /// Construct with a copy of @p __value as the contained object.
 172     template <typename _ValueType, typename _Tp = _Decay<_ValueType>,
 173               typename _Mgr = _Manager<_Tp>,
 174               typename enable_if<!is_constructible<_Tp, _ValueType&&>::value,
 175                                  bool>::type = false>
 176       any(_ValueType&& __value)
 177       : _M_manager(&_Mgr::_S_manage)
 178       {
 179         _Mgr::_S_create(_M_storage, __value);
 180         static_assert(is_copy_constructible<_Tp>::value,
 181                       "The contained object must be CopyConstructible");
 182       }
 183
 184     /// Destructor, calls @c clear()
 185     ~any() { clear(); }
 186
 187     // assignments
 188
 189     /// Copy the state of another object.
 190     any& operator=(const any& __rhs)
 191     {
 192       *this = any(__rhs);
 193       return *this;
 194     }
 195
 196     /**
 197      * @brief Move assignment operator
 198      *
 199      * @post @c __rhs.empty() (not guaranteed for other implementations)
 200      */
 201     any& operator=(any&& __rhs) noexcept
 202     {
 203       if (__rhs.empty())
 204         clear();
 205       else if (this != &__rhs)
 206         {
 207           clear();
 208           _Arg __arg;
 209           __arg._M_any = this;
 210           __rhs._M_manager(_Op_xfer, &__rhs, &__arg);
 211         }
 212       return *this;
 213     }
 214
 215     /// Store a copy of @p __rhs as the contained object.
 216     template<typename _ValueType>
 217       enable_if_t<!is_same<any, decay_t<_ValueType>>::value, any&>
 218       operator=(_ValueType&& __rhs)
 219       {
 220         *this = any(std::forward<_ValueType>(__rhs));
 221         return *this;
 222       }
 223
 224     // modifiers
 225
 226     /// If not empty, destroy the contained object.
 227     void clear() noexcept
 228     {
 229       if (!empty())
 230       {
 231         _M_manager(_Op_destroy, this, nullptr);
 232         _M_manager = nullptr;
 233       }
 234     }
 235
 236     /// Exchange state with another object.
 237     void swap(any& __rhs) noexcept
 238     {
 239       if (empty() && __rhs.empty())
 240         return;
 241
 242       if (!empty() && !__rhs.empty())
 243         {
 244           if (this == &__rhs)
 245             return;
 246
 247           any __tmp;
 248           _Arg __arg;
 249           __arg._M_any = &__tmp;
 250           __rhs._M_manager(_Op_xfer, &__rhs, &__arg);
 251           __arg._M_any = &__rhs;
 252           _M_manager(_Op_xfer, this, &__arg);
 253           __arg._M_any = this;
 254           __tmp._M_manager(_Op_xfer, &__tmp, &__arg);
 255         }
 256       else
 257         {
 258           any* __empty = empty() ? this : &__rhs;
 259           any* __full = empty() ? &__rhs : this;
 260           _Arg __arg;
 261           __arg._M_any = __empty;
 262           __full->_M_manager(_Op_xfer, __full, &__arg);
 263         }
 264     }
 265
 266     // observers
 267
 268     /// Reports whether there is a contained object or not.
 269     bool empty() const noexcept { return _M_manager == nullptr; }
 270
 271 #if __cpp_rtti
 272     /// The @c typeid of the contained object, or @c typeid(void) if empty.
 273     const type_info& type() const noexcept
 274     {
 275       if (empty())
 276         return typeid(void);
 277       _Arg __arg;
 278       _M_manager(_Op_get_type_info, this, &__arg);
 279       return *__arg._M_typeinfo;
 280     }
 281 #endif
 282
 283     template<typename _Tp>
 284       static constexpr bool __is_valid_cast()
 285       { return __or_<is_reference<_Tp>, is_copy_constructible<_Tp>>::value; }
 286
 287   private:
 288     enum _Op {
 289         _Op_access, _Op_get_type_info, _Op_clone, _Op_destroy, _Op_xfer
 290     };
 291
 292     union _Arg
 293     {
 294         void* _M_obj;
 295         const std::type_info* _M_typeinfo;
 296         any* _M_any;
 297     };
 298
 299     void (*_M_manager)(_Op, const any*, _Arg*);
 300     _Storage _M_storage;
 301
 302     template<typename _Tp>
 303       friend void* __any_caster(const any* __any);
 304
 305     // Manage in-place contained object.
 306     template<typename _Tp>
 307       struct _Manager_internal
 308       {
 309         static void
 310         _S_manage(_Op __which, const any* __anyp, _Arg* __arg);
 311
 312         template<typename _Up>
 313           static void
 314           _S_create(_Storage& __storage, _Up&& __value)
 315           {
 316             void* __addr = &__storage._M_buffer;
 317             ::new (__addr) _Tp(std::forward<_Up>(__value));
 318           }
 319       };
 320
 321     // Manage external contained object.
 322     template<typename _Tp>
 323       struct _Manager_external
 324       {
 325         static void
 326         _S_manage(_Op __which, const any* __anyp, _Arg* __arg);
 327
 328         template<typename _Up>
 329           static void
 330           _S_create(_Storage& __storage, _Up&& __value)
 331           {
 332             __storage._M_ptr = new _Tp(std::forward<_Up>(__value));
 333           }
 334       };
 335   };
 336
 337   /// Exchange the states of two @c any objects.
 338   inline void swap(any& __x, any& __y) noexcept { __x.swap(__y); }
 339
 340   /**
 341    * @brief Access the contained object.
 342    *
 343    * @tparam  _ValueType  A const-reference or CopyConstructible type.
 344    * @param   __any       The object to access.
 345    * @return  The contained object.
 346    * @throw   bad_any_cast If <code>
 347    *          __any.type() != typeid(remove_reference_t<_ValueType>)
 348    *          </code>
 349    */
 350   template<typename _ValueType>
 351     inline _ValueType any_cast(const any& __any)
 352     {
 353       static_assert(any::__is_valid_cast<_ValueType>(),
 354           "Template argument must be a reference or CopyConstructible type");
 355       auto __p = any_cast<add_const_t<remove_reference_t<_ValueType>>>(&__any);
 356       if (__p)
 357         return *__p;
 358       __throw_bad_any_cast();
 359     }
 360
 361   /**
 362    * @brief Access the contained object.
 363    *
 364    * @tparam  _ValueType  A reference or CopyConstructible type.
 365    * @param   __any       The object to access.
 366    * @return  The contained object.
 367    * @throw   bad_any_cast If <code>
 368    *          __any.type() != typeid(remove_reference_t<_ValueType>)
 369    *          </code>
 370    *
 371    * @{
 372    */
 373   template<typename _ValueType>
 374     inline _ValueType any_cast(any& __any)
 375     {
 376       static_assert(any::__is_valid_cast<_ValueType>(),
 377           "Template argument must be a reference or CopyConstructible type");
 378       auto __p = any_cast<remove_reference_t<_ValueType>>(&__any);
 379       if (__p)
 380         return *__p;
 381       __throw_bad_any_cast();
 382     }
 383
 384   template<typename _ValueType,
 385            typename enable_if<!is_move_constructible<_ValueType>::value
 386                               || is_lvalue_reference<_ValueType>::value,
 387                               bool>::type = true>
 388     inline _ValueType any_cast(any&& __any)
 389     {
 390       static_assert(any::__is_valid_cast<_ValueType>(),
 391           "Template argument must be a reference or CopyConstructible type");
 392       auto __p = any_cast<remove_reference_t<_ValueType>>(&__any);
 393       if (__p)
 394         return *__p;
 395       __throw_bad_any_cast();
 396     }
 397
 398   template<typename _ValueType,
 399            typename enable_if<is_move_constructible<_ValueType>::value
 400                               && !is_lvalue_reference<_ValueType>::value,
 401                               bool>::type = false>
 402     inline _ValueType any_cast(any&& __any)
 403     {
 404       static_assert(any::__is_valid_cast<_ValueType>(),
 405           "Template argument must be a reference or CopyConstructible type");
 406       auto __p = any_cast<remove_reference_t<_ValueType>>(&__any);
 407       if (__p)
 408         return std::move(*__p);
 409       __throw_bad_any_cast();
 410     }
 411   // @}
 412
 413   template<typename _Tp>
 414     void* __any_caster(const any* __any)
 415     {
 416       struct _None { };
 417       using _Up = decay_t<_Tp>;
 418       using _Vp = conditional_t<is_copy_constructible<_Up>::value, _Up, _None>;
 419       if (__any->_M_manager != &any::_Manager<_Vp>::_S_manage)
 420         return nullptr;
 421       any::_Arg __arg;
 422       __any->_M_manager(any::_Op_access, __any, &__arg);
 423       return __arg._M_obj;
 424     }
 425
 426   /**
 427    * @brief Access the contained object.
 428    *
 429    * @tparam  _ValueType  The type of the contained object.
 430    * @param   __any       A pointer to the object to access.
 431    * @return  The address of the contained object if <code>
 432    *          __any != nullptr && __any.type() == typeid(_ValueType)
 433    *          </code>, otherwise a null pointer.
 434    *
 435    * @{
 436    */
 437   template<typename _ValueType>
 438     inline const _ValueType* any_cast(const any* __any) noexcept
 439     {
 440       if (__any)
 441         return static_cast<_ValueType*>(__any_caster<_ValueType>(__any));
 442       return nullptr;
 443     }
 444
 445   template<typename _ValueType>
 446     inline _ValueType* any_cast(any* __any) noexcept
 447     {
 448       if (__any)
 449         return static_cast<_ValueType*>(__any_caster<_ValueType>(__any));
 450       return nullptr;
 451     }
 452   // @}
 453
 454   template<typename _Tp>
 455     void
 456     any::_Manager_internal<_Tp>::
 457     _S_manage(_Op __which, const any* __any, _Arg* __arg)
 458     {
 459       // The contained object is in _M_storage._M_buffer
 460       auto __ptr = reinterpret_cast<const _Tp*>(&__any->_M_storage._M_buffer);
 461       switch (__which)
 462       {
 463       case _Op_access:
 464         __arg->_M_obj = const_cast<_Tp*>(__ptr);
 465         break;
 466       case _Op_get_type_info:
 467 #if __cpp_rtti
 468         __arg->_M_typeinfo = &typeid(_Tp);
 469 #endif
 470         break;
 471       case _Op_clone:
 472         ::new(&__arg->_M_any->_M_storage._M_buffer) _Tp(*__ptr);
 473         __arg->_M_any->_M_manager = __any->_M_manager;
 474         break;
 475       case _Op_destroy:
 476         __ptr->~_Tp();
 477         break;
 478       case _Op_xfer:
 479         ::new(&__arg->_M_any->_M_storage._M_buffer) _Tp
 480           (std::move(*const_cast<_Tp*>(__ptr)));
 481         __ptr->~_Tp();
 482         __arg->_M_any->_M_manager = __any->_M_manager;
 483         const_cast<any*>(__any)->_M_manager = nullptr;
 484         break;
 485       }
 486     }
 487
 488   template<typename _Tp>
 489     void
 490     any::_Manager_external<_Tp>::
 491     _S_manage(_Op __which, const any* __any, _Arg* __arg)
 492     {
 493       // The contained object is *_M_storage._M_ptr
 494       auto __ptr = static_cast<const _Tp*>(__any->_M_storage._M_ptr);
 495       switch (__which)
 496       {
 497       case _Op_access:
 498         __arg->_M_obj = const_cast<_Tp*>(__ptr);
 499         break;
 500       case _Op_get_type_info:
 501 #if __cpp_rtti
 502         __arg->_M_typeinfo = &typeid(_Tp);
 503 #endif
 504         break;
 505       case _Op_clone:
 506         __arg->_M_any->_M_storage._M_ptr = new _Tp(*__ptr);
 507         __arg->_M_any->_M_manager = __any->_M_manager;
 508         break;
 509       case _Op_destroy:
 510         delete __ptr;
 511         break;
 512       case _Op_xfer:
 513         __arg->_M_any->_M_storage._M_ptr = __any->_M_storage._M_ptr;
 514         __arg->_M_any->_M_manager = __any->_M_manager;
 515         const_cast<any*>(__any)->_M_manager = nullptr;
 516         break;
 517       }
 518     }
 519
 520   // @} group any
 521 } // namespace fundamentals_v1
 522 } // namespace experimental
 523
 524 _GLIBCXX_END_NAMESPACE_VERSION
 525 } // namespace std
 526
 527 #endif // C++14
 528
 529 #endif // _GLIBCXX_EXPERIMENTAL_ANY