libstdc++-v3/include/experimental/any

   1 // <experimental/any> -*- C++ -*-
   2
   3 // Copyright (C) 2014 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 <= 201103L
  35 # include <bits/c++14_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 namespace experimental
  46 {
  47 inline namespace fundamentals_v1
  48 {
  49 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  50
  51   /**
  52    * @defgroup any Type-safe container of any type
  53    * @ingroup experimental
  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   [[gnu::noreturn]] inline void __throw_bad_any_cast()
  74   {
  75 #if __cpp_exceptions
  76     throw bad_any_cast{};
  77 #else
  78     __builtin_abort();
  79 #endif
  80   }
  81
  82   /**
  83    *  @brief A type-safe container of any type.
  84    *
  85    *  An @c any object's state is either empty or it stores a contained object
  86    *  of CopyConstructible type.
  87    */
  88   class any
  89   {
  90     // Holds either pointer to a heap object or the contained object itself.
  91     union _Storage
  92     {
  93       void* _M_ptr;
  94       std::aligned_storage<sizeof(_M_ptr), sizeof(_M_ptr)>::type _M_buffer;
  95     };
  96
  97     template<typename _Tp, typename _Safe = is_nothrow_move_constructible<_Tp>,
  98              bool _Fits = (sizeof(_Tp) <= sizeof(_Storage))>
  99       using _Internal = std::integral_constant<bool, _Safe::value && _Fits>;
 100
 101     template<typename _Tp>
 102       struct _Manager_internal; // uses small-object optimization
 103
 104     template<typename _Tp>
 105       struct _Manager_external; // creates contained object on the heap
 106
 107     template<typename _Tp>
 108       using _Manager = conditional_t<_Internal<_Tp>::value,
 109                                      _Manager_internal<_Tp>,
 110                                      _Manager_external<_Tp>>;
 111
 112     template<typename _Tp, typename _Decayed = decay_t<_Tp>>
 113       using _Decay = enable_if_t<!is_same<_Decayed, any>::value, _Decayed>;
 114
 115   public:
 116     // construct/destruct
 117
 118     /// Default constructor, creates an empty object.
 119     any() noexcept : _M_manager(nullptr) { }
 120
 121     /// Copy constructor, copies the state of @p __other
 122     any(const any& __other) : _M_manager(__other._M_manager)
 123     {
 124       if (!__other.empty())
 125         {
 126           _Arg __arg;
 127           __arg._M_any = this;
 128           _M_manager(_Op_clone, &__other, &__arg);
 129         }
 130     }
 131
 132     /**
 133      * @brief Move constructor, transfer the state from @p __other
 134      *
 135      * @post @c __other.empty() (not guaranteed for other implementations)
 136      */
 137     any(any&& __other) noexcept
 138     : _M_manager(__other._M_manager),
 139       _M_storage(__other._M_storage)
 140     { __other._M_manager = nullptr; }
 141
 142     /// Construct with a copy of @p __value as the contained object.
 143     template <typename _ValueType, typename _Tp = _Decay<_ValueType>,
 144               typename _Mgr = _Manager<_Tp>>
 145       any(_ValueType&& __value)
 146       : _M_manager(&_Mgr::_S_manage),
 147         _M_storage(_Mgr::_S_create(std::forward<_ValueType>(__value)))
 148       {
 149         static_assert(is_copy_constructible<_Tp>::value,
 150                       "The contained object must be CopyConstructible");
 151       }
 152
 153     /// Destructor, calls @c clear()
 154     ~any() { clear(); }
 155
 156     // assignments
 157
 158     /// Copy the state of
 159     any& operator=(const any& __rhs)
 160     {
 161       any(__rhs).swap(*this);
 162       return *this;
 163     }
 164
 165     /**
 166      * @brief Move assignment operator
 167      *
 168      * @post @c __rhs.empty() (not guaranteed for other implementations)
 169      */
 170     any& operator=(any&& __rhs) noexcept
 171     {
 172       any(std::move(__rhs)).swap(*this);
 173       return *this;
 174     }
 175
 176     /// Store a copy of @p __rhs as the contained object.
 177     template<typename _ValueType>
 178       any& operator=(_ValueType&& __rhs)
 179       {
 180         any(std::forward<_ValueType>(__rhs)).swap(*this);
 181         return *this;
 182       }
 183
 184     // modifiers
 185
 186     /// If not empty, destroy the contained object.
 187     void clear() noexcept
 188     {
 189       if (!empty())
 190       {
 191         _M_manager(_Op_destroy, this, nullptr);
 192         _M_manager = nullptr;
 193       }
 194     }
 195
 196     /// Exchange state with another object.
 197     void swap(any& __rhs) noexcept
 198     {
 199       std::swap(_M_manager, __rhs._M_manager);
 200       std::swap(_M_storage, __rhs._M_storage);
 201     }
 202
 203     // observers
 204
 205     /// Reports whether there is a contained object or not.
 206     bool empty() const noexcept { return _M_manager == nullptr; }
 207
 208 #if __cpp_rtti
 209     /// The @c typeid of the contained object, or @c typeid(void) if empty.
 210     const type_info& type() const noexcept
 211     {
 212       if (empty())
 213         return typeid(void);
 214       _Arg __arg;
 215       _M_manager(_Op_get_type_info, this, &__arg);
 216       return *__arg._M_typeinfo;
 217     }
 218 #endif
 219
 220     template<typename _Tp>
 221       static constexpr bool __is_valid_cast()
 222       { return __or_<is_reference<_Tp>, is_copy_constructible<_Tp>>::value; }
 223
 224   private:
 225     enum _Op { _Op_access, _Op_get_type_info, _Op_clone, _Op_destroy };
 226
 227     union _Arg
 228     {
 229         void* _M_obj;
 230         const std::type_info* _M_typeinfo;
 231         any* _M_any;
 232     };
 233
 234     void (*_M_manager)(_Op, const any*, _Arg*);
 235     _Storage _M_storage;
 236
 237     template<typename _Tp>
 238       friend void* __any_caster(const any* __any)
 239       {
 240         if (__any->_M_manager != &_Manager<decay_t<_Tp>>::_S_manage)
 241           return nullptr;
 242         _Arg __arg;
 243         __any->_M_manager(_Op_access, __any, &__arg);
 244         return __arg._M_obj;
 245       }
 246
 247     // Manage in-place contained object.
 248     template<typename _Tp>
 249       struct _Manager_internal
 250       {
 251         static void
 252         _S_manage(_Op __which, const any* __anyp, _Arg* __arg);
 253
 254         template<typename _Up>
 255           static _Storage
 256           _S_create(_Up&& __value)
 257           {
 258             _Storage __storage;
 259             void* __addr = &__storage._M_buffer;
 260             ::new (__addr) _Tp(std::forward<_Up>(__value));
 261             return __storage;
 262           }
 263
 264         template<typename _Alloc, typename _Up>
 265           static _Storage
 266           _S_alloc(const _Alloc&, _Up&& __value)
 267           {
 268             return _S_create(std::forward<_Up>(__value));
 269           }
 270       };
 271
 272     // Manage external contained object.
 273     template<typename _Tp>
 274       struct _Manager_external
 275       {
 276         static void
 277         _S_manage(_Op __which, const any* __anyp, _Arg* __arg);
 278
 279         template<typename _Up>
 280           static _Storage
 281           _S_create(_Up&& __value)
 282           {
 283             _Storage __storage;
 284             __storage._M_ptr = new _Tp(std::forward<_Up>(__value));
 285             return __storage;
 286           }
 287       };
 288   };
 289
 290   /// Exchange the states of two @c any objects.
 291   inline void swap(any& __x, any& __y) noexcept { __x.swap(__y); }
 292
 293   /**
 294    * @brief Access the contained object.
 295    *
 296    * @tparam  _ValueType  A const-reference or CopyConstructible type.
 297    * @param   __any       The object to access.
 298    * @return  The contained object.
 299    * @throw   bad_any_cast If <code>
 300    *          __any.type() != typeid(remove_reference_t<_ValueType>)
 301    *          </code>
 302    */
 303   template<typename _ValueType>
 304     inline _ValueType any_cast(const any& __any)
 305     {
 306       static_assert(any::__is_valid_cast<_ValueType>(),
 307           "Template argument must be a reference or CopyConstructible type");
 308       auto __p = any_cast<add_const_t<remove_reference_t<_ValueType>>>(&__any);
 309       if (__p)
 310         return *__p;
 311       __throw_bad_any_cast();
 312     }
 313
 314   /**
 315    * @brief Access the contained object.
 316    *
 317    * @tparam  _ValueType  A reference or CopyConstructible type.
 318    * @param   __any       The object to access.
 319    * @return  The contained object.
 320    * @throw   bad_any_cast If <code>
 321    *          __any.type() != typeid(remove_reference_t<_ValueType>)
 322    *          </code>
 323    *
 324    * @{
 325    */
 326   template<typename _ValueType>
 327     inline _ValueType any_cast(any& __any)
 328     {
 329       static_assert(any::__is_valid_cast<_ValueType>(),
 330           "Template argument must be a reference or CopyConstructible type");
 331       auto __p = any_cast<remove_reference_t<_ValueType>>(&__any);
 332       if (__p)
 333         return *__p;
 334       __throw_bad_any_cast();
 335     }
 336
 337   template<typename _ValueType>
 338     inline _ValueType any_cast(any&& __any)
 339     {
 340       static_assert(any::__is_valid_cast<_ValueType>(),
 341           "Template argument must be a reference or CopyConstructible type");
 342       auto __p = any_cast<remove_reference_t<_ValueType>>(&__any);
 343       if (__p)
 344         return *__p;
 345       __throw_bad_any_cast();
 346     }
 347   // @}
 348
 349   /**
 350    * @brief Access the contained object.
 351    *
 352    * @tparam  _ValueType  The type of the contained object.
 353    * @param   __any       A pointer to the object to access.
 354    * @return  The address of the contained object if <code>
 355    *          __any != nullptr && __any.type() == typeid(_ValueType)
 356    *          </code>, otherwise a null pointer.
 357    *
 358    * @{
 359    */
 360   template<typename _ValueType>
 361     inline const _ValueType* any_cast(const any* __any) noexcept
 362     {
 363       if (__any)
 364         return static_cast<_ValueType*>(__any_caster<_ValueType>(__any));
 365       return nullptr;
 366     }
 367
 368   template<typename _ValueType>
 369     inline _ValueType* any_cast(any* __any) noexcept
 370     {
 371       if (__any)
 372         return static_cast<_ValueType*>(__any_caster<_ValueType>(__any));
 373       return nullptr;
 374     }
 375   // @}
 376
 377   template<typename _Tp>
 378     void
 379     any::_Manager_internal<_Tp>::
 380     _S_manage(_Op __which, const any* __any, _Arg* __arg)
 381     {
 382       // The contained object is in _M_storage._M_buffer
 383       auto __ptr = reinterpret_cast<const _Tp*>(&__any->_M_storage._M_buffer);
 384       switch (__which)
 385       {
 386       case _Op_access:
 387         __arg->_M_obj = const_cast<_Tp*>(__ptr);
 388         break;
 389       case _Op_get_type_info:
 390 #if __cpp_rtti
 391         __arg->_M_typeinfo = &typeid(_Tp);
 392 #endif
 393         break;
 394       case _Op_clone:
 395         ::new(&__arg->_M_any->_M_storage._M_buffer) _Tp(*__ptr);
 396         break;
 397       case _Op_destroy:
 398         __ptr->~_Tp();
 399         break;
 400       }
 401     }
 402
 403   template<typename _Tp>
 404     void
 405     any::_Manager_external<_Tp>::
 406     _S_manage(_Op __which, const any* __any, _Arg* __arg)
 407     {
 408       // The contained object is *_M_storage._M_ptr
 409       auto __ptr = static_cast<const _Tp*>(__any->_M_storage._M_ptr);
 410       switch (__which)
 411       {
 412       case _Op_access:
 413         __arg->_M_obj = const_cast<_Tp*>(__ptr);
 414         break;
 415       case _Op_get_type_info:
 416 #if __cpp_rtti
 417         __arg->_M_typeinfo = &typeid(_Tp);
 418 #endif
 419         break;
 420       case _Op_clone:
 421         __arg->_M_any->_M_storage._M_ptr = new _Tp(*__ptr);
 422         break;
 423       case _Op_destroy:
 424         delete __ptr;
 425         break;
 426       }
 427     }
 428
 429   // @} group any
 430 _GLIBCXX_END_NAMESPACE_VERSION
 431 } // namespace fundamentals_v1
 432 } // namespace experimental
 433 } // namespace std
 434
 435 #endif // C++14
 436
 437 #endif // _GLIBCXX_EXPERIMENTAL_ANY