libstdc++-v3/include/std/any

   1 // <any> -*- C++ -*-
   2
   3 // Copyright (C) 2014-2016 Free Software Foundation, Inc.
   4 //
   5 // This file is part of the GNU ISO C++ Library.  This library is free
   6 // software; you can redistribute it and/or modify it under the
   7 // terms of the GNU General Public License as published by the
   8 // Free Software Foundation; either version 3, or (at your option)
   9 // any later version.
  10
  11 // This library is distributed in the hope that it will be useful,
  12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 // GNU General Public License for more details.
  15
  16 // Under Section 7 of GPL version 3, you are granted additional
  17 // permissions described in the GCC Runtime Library Exception, version
  18 // 3.1, as published by the Free Software Foundation.
  19
  20 // You should have received a copy of the GNU General Public License and
  21 // a copy of the GCC Runtime Library Exception along with this program;
  22 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  23 // <http://www.gnu.org/licenses/>.
  24
  25 /** @file include/any
  26  *  This is a Standard C++ Library header.
  27  */
  28
  29 #ifndef _GLIBCXX_ANY
  30 #define _GLIBCXX_ANY 1
  31
  32 #pragma GCC system_header
  33
  34 #if __cplusplus <= 201402L
  35 # include <bits/c++17_warning.h>
  36 #else
  37
  38 #include <typeinfo>
  39 #include <new>
  40 #include <utility>
  41 #include <type_traits>
  42
  43 namespace std _GLIBCXX_VISIBILITY(default)
  44 {
  45 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  46
  47   /**
  48    *  @addtogroup utilities
  49    *  @{
  50    */
  51
  52   /**
  53    *  @brief Exception class thrown by a failed @c any_cast
  54    *  @ingroup exceptions
  55    */
  56   class bad_any_cast : public bad_cast
  57   {
  58   public:
  59     virtual const char* what() const noexcept { return "bad any_cast"; }
  60   };
  61
  62   [[gnu::noreturn]] inline void __throw_bad_any_cast()
  63   {
  64 #if __cpp_exceptions
  65     throw bad_any_cast{};
  66 #else
  67     __builtin_abort();
  68 #endif
  69   }
  70
  71   /**
  72    *  @brief A type-safe container of any type.
  73    *
  74    *  An @c any object's state is either empty or it stores a contained object
  75    *  of CopyConstructible type.
  76    */
  77   class any
  78   {
  79     // Holds either pointer to a heap object or the contained object itself.
  80     union _Storage
  81     {
  82       // This constructor intentionally doesn't initialize anything.
  83       _Storage() = default;
  84
  85       // Prevent trivial copies of this type, buffer might hold a non-POD.
  86       _Storage(const _Storage&) = delete;
  87       _Storage& operator=(const _Storage&) = delete;
  88
  89       void* _M_ptr;
  90       aligned_storage<sizeof(_M_ptr), alignof(void*)>::type _M_buffer;
  91     };
  92
  93     template<typename _Tp, typename _Safe = is_nothrow_move_constructible<_Tp>,
  94              bool _Fits = (sizeof(_Tp) <= sizeof(_Storage))
  95                           && (alignof(_Tp) <= alignof(_Storage))>
  96       using _Internal = std::integral_constant<bool, _Safe::value && _Fits>;
  97
  98     template<typename _Tp>
  99       struct _Manager_internal; // uses small-object optimization
 100
 101     template<typename _Tp>
 102       struct _Manager_external; // creates contained object on the heap
 103
 104     template<typename _Tp>
 105       using _Manager = conditional_t<_Internal<_Tp>::value,
 106                                      _Manager_internal<_Tp>,
 107                                      _Manager_external<_Tp>>;
 108
 109     template<typename _Tp, typename _Decayed = decay_t<_Tp>>
 110       using _Decay = enable_if_t<!is_same<_Decayed, any>::value, _Decayed>;
 111
 112   public:
 113     // construct/destruct
 114
 115     /// Default constructor, creates an empty object.
 116     any() noexcept : _M_manager(nullptr) { }
 117
 118     /// Copy constructor, copies the state of @p __other
 119     any(const any& __other)
 120     {
 121       if (__other.empty())
 122         _M_manager = nullptr;
 123       else
 124         {
 125           _Arg __arg;
 126           __arg._M_any = this;
 127           __other._M_manager(_Op_clone, &__other, &__arg);
 128         }
 129     }
 130
 131     /**
 132      * @brief Move constructor, transfer the state from @p __other
 133      *
 134      * @post @c __other.empty() (this postcondition is a GNU extension)
 135      */
 136     any(any&& __other) noexcept
 137     {
 138       if (__other.empty())
 139         _M_manager = nullptr;
 140       else
 141         {
 142           _Arg __arg;
 143           __arg._M_any = this;
 144           __other._M_manager(_Op_xfer, &__other, &__arg);
 145         }
 146     }
 147
 148     /// Construct with a copy of @p __value as the contained object.
 149     template <typename _ValueType, typename _Tp = _Decay<_ValueType>,
 150               typename _Mgr = _Manager<_Tp>,
 151               typename enable_if<is_constructible<_Tp, _ValueType&&>::value,
 152                                  bool>::type = true>
 153       any(_ValueType&& __value)
 154       : _M_manager(&_Mgr::_S_manage)
 155       {
 156         _Mgr::_S_create(_M_storage, std::forward<_ValueType>(__value));
 157         static_assert(is_copy_constructible<_Tp>::value,
 158                       "The contained object must be CopyConstructible");
 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 = false>
 166       any(_ValueType&& __value)
 167       : _M_manager(&_Mgr::_S_manage)
 168       {
 169         _Mgr::_S_create(_M_storage, __value);
 170         static_assert(is_copy_constructible<_Tp>::value,
 171                       "The contained object must be CopyConstructible");
 172       }
 173
 174     /// Destructor, calls @c clear()
 175     ~any() { clear(); }
 176
 177     // assignments
 178
 179     /// Copy the state of another object.
 180     any& operator=(const any& __rhs)
 181     {
 182       if (__rhs.empty())
 183         clear();
 184       else if (this != &__rhs)
 185         {
 186           if (!empty())
 187             _M_manager(_Op_destroy, this, nullptr);
 188           _Arg __arg;
 189           __arg._M_any = this;
 190           __rhs._M_manager(_Op_clone, &__rhs, &__arg);
 191         }
 192       return *this;
 193     }
 194
 195     /**
 196      * @brief Move assignment operator
 197      *
 198      * @post @c __rhs.empty() (not guaranteed for other implementations)
 199      */
 200     any& operator=(any&& __rhs) noexcept
 201     {
 202       if (__rhs.empty())
 203         clear();
 204       else if (this != &__rhs)
 205         {
 206           if (!empty())
 207             _M_manager(_Op_destroy, this, nullptr);
 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       if (__any->_M_manager != &any::_Manager<decay_t<_Tp>>::_S_manage)
 417         return nullptr;
 418       any::_Arg __arg;
 419       __any->_M_manager(any::_Op_access, __any, &__arg);
 420       return __arg._M_obj;
 421     }
 422
 423   /**
 424    * @brief Access the contained object.
 425    *
 426    * @tparam  _ValueType  The type of the contained object.
 427    * @param   __any       A pointer to the object to access.
 428    * @return  The address of the contained object if <code>
 429    *          __any != nullptr && __any.type() == typeid(_ValueType)
 430    *          </code>, otherwise a null pointer.
 431    *
 432    * @{
 433    */
 434   template<typename _ValueType>
 435     inline const _ValueType* any_cast(const any* __any) noexcept
 436     {
 437       if (__any)
 438         return static_cast<_ValueType*>(__any_caster<_ValueType>(__any));
 439       return nullptr;
 440     }
 441
 442   template<typename _ValueType>
 443     inline _ValueType* any_cast(any* __any) noexcept
 444     {
 445       if (__any)
 446         return static_cast<_ValueType*>(__any_caster<_ValueType>(__any));
 447       return nullptr;
 448     }
 449   // @}
 450
 451   template<typename _Tp>
 452     void
 453     any::_Manager_internal<_Tp>::
 454     _S_manage(_Op __which, const any* __any, _Arg* __arg)
 455     {
 456       // The contained object is in _M_storage._M_buffer
 457       auto __ptr = reinterpret_cast<const _Tp*>(&__any->_M_storage._M_buffer);
 458       switch (__which)
 459       {
 460       case _Op_access:
 461         __arg->_M_obj = const_cast<_Tp*>(__ptr);
 462         break;
 463       case _Op_get_type_info:
 464 #if __cpp_rtti
 465         __arg->_M_typeinfo = &typeid(_Tp);
 466 #endif
 467         break;
 468       case _Op_clone:
 469         ::new(&__arg->_M_any->_M_storage._M_buffer) _Tp(*__ptr);
 470         __arg->_M_any->_M_manager = __any->_M_manager;
 471         break;
 472       case _Op_destroy:
 473         __ptr->~_Tp();
 474         break;
 475       case _Op_xfer:
 476         ::new(&__arg->_M_any->_M_storage._M_buffer) _Tp(*__ptr);
 477         __ptr->~_Tp();
 478         __arg->_M_any->_M_manager = __any->_M_manager;
 479         const_cast<any*>(__any)->_M_manager = nullptr;
 480         break;
 481       }
 482     }
 483
 484   template<typename _Tp>
 485     void
 486     any::_Manager_external<_Tp>::
 487     _S_manage(_Op __which, const any* __any, _Arg* __arg)
 488     {
 489       // The contained object is *_M_storage._M_ptr
 490       auto __ptr = static_cast<const _Tp*>(__any->_M_storage._M_ptr);
 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         __arg->_M_any->_M_storage._M_ptr = new _Tp(*__ptr);
 503         __arg->_M_any->_M_manager = __any->_M_manager;
 504         break;
 505       case _Op_destroy:
 506         delete __ptr;
 507         break;
 508       case _Op_xfer:
 509         __arg->_M_any->_M_storage._M_ptr = __any->_M_storage._M_ptr;
 510         __arg->_M_any->_M_manager = __any->_M_manager;
 511         const_cast<any*>(__any)->_M_manager = nullptr;
 512         break;
 513       }
 514     }
 515
 516   /// @}
 517
 518 _GLIBCXX_END_NAMESPACE_VERSION
 519 } // namespace std
 520
 521 #endif // C++14
 522
 523 #endif // _GLIBCXX_ANY