libstdc++
experimental/any
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1 // <experimental/any> -*- C++ -*-
2 
3 // Copyright (C) 2014-2025 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 #ifdef _GLIBCXX_SYSHDR
34 #pragma GCC system_header
35 #endif
36 
37 #include <bits/requires_hosted.h> // experimental is currently omitted
38 
39 #if __cplusplus >= 201402L
40 
41 #include <typeinfo>
42 #include <new>
43 #include <type_traits>
44 #include <bits/move.h>
45 #include <experimental/bits/lfts_config.h>
46 
47 namespace std _GLIBCXX_VISIBILITY(default)
48 {
49 _GLIBCXX_BEGIN_NAMESPACE_VERSION
50 
51 namespace experimental
52 {
53 inline namespace fundamentals_v1
54 {
55  /**
56  * @defgroup any Type-safe container of any type
57  * @ingroup libfund-ts
58  *
59  * A type-safe container for single values of value types, as
60  * described in n3804 "Any Library Proposal (Revision 3)".
61  *
62  * @{
63  */
64 
65 #define __cpp_lib_experimental_any 201411
66 
67  /**
68  * @brief Exception class thrown by a failed @c any_cast
69  * @ingroup exceptions
70  */
71  class bad_any_cast : public bad_cast
72  {
73  public:
74  virtual const char* what() const noexcept { return "bad any_cast"; }
75  };
76 
77  /// @cond undocumented
78  [[gnu::noreturn]] inline void __throw_bad_any_cast()
79  {
80 #if __cpp_exceptions
81  throw bad_any_cast{};
82 #else
83  __builtin_abort();
84 #endif
85  }
86  /// @endcond
87 
88  /**
89  * @brief A type-safe container of any type.
90  *
91  * An @c any object's state is either empty or it stores a contained object
92  * of CopyConstructible type.
93  */
94  class any
95  {
96  // Holds either pointer to a heap object or the contained object itself.
97  union _Storage
98  {
99  // This constructor intentionally doesn't initialize anything.
100  _Storage() = default;
101 
102  // Prevent trivial copies of this type, buffer might hold a non-POD.
103  _Storage(const _Storage&) = delete;
104  _Storage& operator=(const _Storage&) = delete;
105 
106  void* _M_ptr;
107  unsigned char _M_buffer[sizeof(_M_ptr)];
108  };
109 
110  template<typename _Tp, typename _Safe = is_nothrow_move_constructible<_Tp>,
111  bool _Fits = (sizeof(_Tp) <= sizeof(_Storage))
112  && (alignof(_Tp) <= alignof(_Storage))>
113  using _Internal = std::integral_constant<bool, _Safe::value && _Fits>;
114 
115  template<typename _Tp>
116  struct _Manager_internal; // uses small-object optimization
117 
118  template<typename _Tp>
119  struct _Manager_external; // creates contained object on the heap
120 
121  template<typename _Tp>
122  using _Manager = __conditional_t<_Internal<_Tp>::value,
123  _Manager_internal<_Tp>,
124  _Manager_external<_Tp>>;
125 
126  template<typename _Tp, typename _Decayed = decay_t<_Tp>>
127  using _Decay = enable_if_t<!is_same<_Decayed, any>::value, _Decayed>;
128 
129  public:
130  // construct/destruct
131 
132  /// Default constructor, creates an empty object.
133  any() noexcept : _M_manager(nullptr) { }
134 
135  /// Copy constructor, copies the state of @p __other
136  any(const any& __other)
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_clone, &__other, &__arg);
145  }
146  }
147 
148  /**
149  * @brief Move constructor, transfer the state from @p __other
150  *
151  * @post @c __other.empty() (this postcondition is a GNU extension)
152  */
153  any(any&& __other) noexcept
154  {
155  if (__other.empty())
156  _M_manager = nullptr;
157  else
158  {
159  _Arg __arg;
160  __arg._M_any = this;
161  __other._M_manager(_Op_xfer, &__other, &__arg);
162  }
163  }
164 
165  /// Construct with a copy of @p __value as the contained object.
166  template <typename _ValueType, typename _Tp = _Decay<_ValueType>,
167  typename _Mgr = _Manager<_Tp>,
168  typename enable_if<is_constructible<_Tp, _ValueType&&>::value,
169  bool>::type = true>
170  any(_ValueType&& __value)
171  : _M_manager(&_Mgr::_S_manage)
172  {
173  _Mgr::_S_create(_M_storage, std::forward<_ValueType>(__value));
174  static_assert(is_copy_constructible<_Tp>::value,
175  "The contained object must be CopyConstructible");
176  }
177 
178  /// Construct with a copy of @p __value as the contained object.
179  template <typename _ValueType, typename _Tp = _Decay<_ValueType>,
180  typename _Mgr = _Manager<_Tp>,
181  typename enable_if<!is_constructible<_Tp, _ValueType&&>::value,
182  bool>::type = false>
183  any(_ValueType&& __value)
184  : _M_manager(&_Mgr::_S_manage)
185  {
186  _Mgr::_S_create(_M_storage, __value);
187  static_assert(is_copy_constructible<_Tp>::value,
188  "The contained object must be CopyConstructible");
189  }
190 
191  /// Destructor, calls @c clear()
192  ~any() { clear(); }
193 
194  // assignments
195 
196  /// Copy the state of another object.
197  any& operator=(const any& __rhs)
198  {
199  *this = any(__rhs);
200  return *this;
201  }
202 
203  /**
204  * @brief Move assignment operator
205  *
206  * @post @c __rhs.empty() (not guaranteed for other implementations)
207  */
208  any& operator=(any&& __rhs) noexcept
209  {
210  if (__rhs.empty())
211  clear();
212  else if (this != &__rhs)
213  {
214  clear();
215  _Arg __arg;
216  __arg._M_any = this;
217  __rhs._M_manager(_Op_xfer, &__rhs, &__arg);
218  }
219  return *this;
220  }
221 
222  /// Store a copy of @p __rhs as the contained object.
223  template<typename _ValueType>
224  enable_if_t<!is_same<any, decay_t<_ValueType>>::value, any&>
225  operator=(_ValueType&& __rhs)
226  {
227  *this = any(std::forward<_ValueType>(__rhs));
228  return *this;
229  }
230 
231  // modifiers
232 
233  /// If not empty, destroy the contained object.
234  void clear() noexcept
235  {
236  if (!empty())
237  {
238  _M_manager(_Op_destroy, this, nullptr);
239  _M_manager = nullptr;
240  }
241  }
242 
243  /// Exchange state with another object.
244  void swap(any& __rhs) noexcept
245  {
246  if (empty() && __rhs.empty())
247  return;
248 
249  if (!empty() && !__rhs.empty())
250  {
251  if (this == &__rhs)
252  return;
253 
254  any __tmp;
255  _Arg __arg;
256  __arg._M_any = &__tmp;
257  __rhs._M_manager(_Op_xfer, &__rhs, &__arg);
258  __arg._M_any = &__rhs;
259  _M_manager(_Op_xfer, this, &__arg);
260  __arg._M_any = this;
261  __tmp._M_manager(_Op_xfer, &__tmp, &__arg);
262  }
263  else
264  {
265  any* __empty = empty() ? this : &__rhs;
266  any* __full = empty() ? &__rhs : this;
267  _Arg __arg;
268  __arg._M_any = __empty;
269  __full->_M_manager(_Op_xfer, __full, &__arg);
270  }
271  }
272 
273  // observers
274 
275  /// Reports whether there is a contained object or not.
276  _GLIBCXX_NODISCARD bool empty() const noexcept { return _M_manager == nullptr; }
277 
278 #if __cpp_rtti
279  /// The @c typeid of the contained object, or @c typeid(void) if empty.
280  const type_info& type() const noexcept
281  {
282  if (empty())
283  return typeid(void);
284  _Arg __arg;
285  _M_manager(_Op_get_type_info, this, &__arg);
286  return *__arg._M_typeinfo;
287  }
288 #endif
289 
290  template<typename _Tp>
291  static constexpr bool __is_valid_cast()
292  { return __or_<is_reference<_Tp>, is_copy_constructible<_Tp>>::value; }
293 
294  private:
295  enum _Op {
296  _Op_access, _Op_get_type_info, _Op_clone, _Op_destroy, _Op_xfer
297  };
298 
299  union _Arg
300  {
301  void* _M_obj;
302  const std::type_info* _M_typeinfo;
303  any* _M_any;
304  };
305 
306  void (*_M_manager)(_Op, const any*, _Arg*);
307  _Storage _M_storage;
308 
309  template<typename _Tp>
310  friend enable_if_t<is_object<_Tp>::value, void*>
311  __any_caster(const any* __any);
312 
313  // Manage in-place contained object.
314  template<typename _Tp>
315  struct _Manager_internal
316  {
317  static void
318  _S_manage(_Op __which, const any* __anyp, _Arg* __arg);
319 
320  template<typename _Up>
321  static void
322  _S_create(_Storage& __storage, _Up&& __value)
323  {
324  void* __addr = &__storage._M_buffer;
325  ::new (__addr) _Tp(std::forward<_Up>(__value));
326  }
327  };
328 
329  // Manage external contained object.
330  template<typename _Tp>
331  struct _Manager_external
332  {
333  static void
334  _S_manage(_Op __which, const any* __anyp, _Arg* __arg);
335 
336  template<typename _Up>
337  static void
338  _S_create(_Storage& __storage, _Up&& __value)
339  {
340  __storage._M_ptr = new _Tp(std::forward<_Up>(__value));
341  }
342  };
343  };
344 
345  /// Exchange the states of two @c any objects.
346  inline void swap(any& __x, any& __y) noexcept { __x.swap(__y); }
347 
348  /**
349  * @brief Access the contained object.
350  *
351  * @tparam _ValueType A const-reference or CopyConstructible type.
352  * @param __any The object to access.
353  * @return The contained object.
354  * @throw bad_any_cast If <code>
355  * __any.type() != typeid(remove_reference_t<_ValueType>)
356  * </code>
357  */
358  template<typename _ValueType>
359  inline _ValueType any_cast(const any& __any)
360  {
361  static_assert(any::__is_valid_cast<_ValueType>(),
362  "Template argument must be a reference or CopyConstructible type");
363  auto __p = any_cast<add_const_t<remove_reference_t<_ValueType>>>(&__any);
364  if (__p)
365  return *__p;
366  __throw_bad_any_cast();
367  }
368 
369  /**
370  * @brief Access the contained object.
371  *
372  * @tparam _ValueType A reference or CopyConstructible type.
373  * @param __any The object to access.
374  * @return The contained object.
375  * @throw bad_any_cast If <code>
376  * __any.type() != typeid(remove_reference_t<_ValueType>)
377  * </code>
378  *
379  * @{
380  */
381  template<typename _ValueType>
382  inline _ValueType any_cast(any& __any)
383  {
384  static_assert(any::__is_valid_cast<_ValueType>(),
385  "Template argument must be a reference or CopyConstructible type");
386  auto __p = any_cast<remove_reference_t<_ValueType>>(&__any);
387  if (__p)
388  return *__p;
389  __throw_bad_any_cast();
390  }
391 
392  template<typename _ValueType,
393  typename enable_if<!is_move_constructible<_ValueType>::value
394  || is_lvalue_reference<_ValueType>::value,
395  bool>::type = true>
396  inline _ValueType any_cast(any&& __any)
397  {
398  static_assert(any::__is_valid_cast<_ValueType>(),
399  "Template argument must be a reference or CopyConstructible type");
400  auto __p = any_cast<remove_reference_t<_ValueType>>(&__any);
401  if (__p)
402  return *__p;
403  __throw_bad_any_cast();
404  }
405 
406  template<typename _ValueType,
407  typename enable_if<is_move_constructible<_ValueType>::value
408  && !is_lvalue_reference<_ValueType>::value,
409  bool>::type = false>
410  inline _ValueType any_cast(any&& __any)
411  {
412  static_assert(any::__is_valid_cast<_ValueType>(),
413  "Template argument must be a reference or CopyConstructible type");
414  auto __p = any_cast<remove_reference_t<_ValueType>>(&__any);
415  if (__p)
416  return std::move(*__p);
417  __throw_bad_any_cast();
418  }
419  /// @}
420 
421  /// @cond undocumented
422  template<typename _Tp>
423  enable_if_t<is_object<_Tp>::value, void*>
424  __any_caster(const any* __any)
425  {
426  // any_cast<T> returns non-null if __any->type() == typeid(T) and
427  // typeid(T) ignores cv-qualifiers so remove them:
428  using _Up = remove_cv_t<_Tp>;
429  // The contained value has a decayed type, so if decay_t<U> is not U,
430  // then it's not possible to have a contained value of type U.
431  using __does_not_decay = is_same<decay_t<_Up>, _Up>;
432  // Only copy constructible types can be used for contained values.
433  using __is_copyable = is_copy_constructible<_Up>;
434  // If the type _Tp could never be stored in an any we don't want to
435  // instantiate _Manager<_Tp>, so use _Manager<any::_Op> instead, which
436  // is explicitly specialized and has a no-op _S_manage function.
437  using _Vp = __conditional_t<__and_<__does_not_decay, __is_copyable>{},
438  _Up, any::_Op>;
439  // First try comparing function addresses, which works without RTTI
440  if (__any->_M_manager == &any::_Manager<_Vp>::_S_manage
441 #if __cpp_rtti
442  || __any->type() == typeid(_Tp)
443 #endif
444  )
445  {
446  any::_Arg __arg;
447  __any->_M_manager(any::_Op_access, __any, &__arg);
448  return __arg._M_obj;
449  }
450  return nullptr;
451  }
452 
453  // This overload exists so that std::any_cast<void(*)()>(a) is well-formed.
454  template<typename _Tp>
455  enable_if_t<!is_object<_Tp>::value, _Tp*>
456  __any_caster(const any*) noexcept
457  { return nullptr; }
458  /// @endcond
459 
460  /**
461  * @brief Access the contained object.
462  *
463  * @tparam _ValueType The type of the contained object.
464  * @param __any A pointer to the object to access.
465  * @return The address of the contained object if <code>
466  * __any != nullptr && __any.type() == typeid(_ValueType)
467  * </code>, otherwise a null pointer.
468  *
469  * @{
470  */
471  template<typename _ValueType>
472  inline const _ValueType* any_cast(const any* __any) noexcept
473  {
474  if (__any)
475  return static_cast<_ValueType*>(__any_caster<_ValueType>(__any));
476  return nullptr;
477  }
478 
479  template<typename _ValueType>
480  inline _ValueType* any_cast(any* __any) noexcept
481  {
482  if (__any)
483  return static_cast<_ValueType*>(__any_caster<_ValueType>(__any));
484  return nullptr;
485  }
486  /// @}
487 
488  template<typename _Tp>
489  void
490  any::_Manager_internal<_Tp>::
491  _S_manage(_Op __which, const any* __any, _Arg* __arg)
492  {
493  // The contained object is in _M_storage._M_buffer
494  auto __ptr = reinterpret_cast<const _Tp*>(&__any->_M_storage._M_buffer);
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  ::new(&__arg->_M_any->_M_storage._M_buffer) _Tp(*__ptr);
507  __arg->_M_any->_M_manager = __any->_M_manager;
508  break;
509  case _Op_destroy:
510  __ptr->~_Tp();
511  break;
512  case _Op_xfer:
513  ::new(&__arg->_M_any->_M_storage._M_buffer) _Tp
514  (std::move(*const_cast<_Tp*>(__ptr)));
515  __ptr->~_Tp();
516  __arg->_M_any->_M_manager = __any->_M_manager;
517  const_cast<any*>(__any)->_M_manager = nullptr;
518  break;
519  }
520  }
521 
522  template<typename _Tp>
523  void
524  any::_Manager_external<_Tp>::
525  _S_manage(_Op __which, const any* __any, _Arg* __arg)
526  {
527  // The contained object is *_M_storage._M_ptr
528  auto __ptr = static_cast<const _Tp*>(__any->_M_storage._M_ptr);
529  switch (__which)
530  {
531  case _Op_access:
532  __arg->_M_obj = const_cast<_Tp*>(__ptr);
533  break;
534  case _Op_get_type_info:
535 #if __cpp_rtti
536  __arg->_M_typeinfo = &typeid(_Tp);
537 #endif
538  break;
539  case _Op_clone:
540  __arg->_M_any->_M_storage._M_ptr = new _Tp(*__ptr);
541  __arg->_M_any->_M_manager = __any->_M_manager;
542  break;
543  case _Op_destroy:
544  delete __ptr;
545  break;
546  case _Op_xfer:
547  __arg->_M_any->_M_storage._M_ptr = __any->_M_storage._M_ptr;
548  __arg->_M_any->_M_manager = __any->_M_manager;
549  const_cast<any*>(__any)->_M_manager = nullptr;
550  break;
551  }
552  }
553 
554  // Dummy specialization used by __any_caster.
555  template<>
556  struct any::_Manager_internal<any::_Op>
557  {
558  static void
559  _S_manage(_Op, const any*, _Arg*) { }
560  };
561 
562  /// @} group any
563 } // namespace fundamentals_v1
564 } // namespace experimental
565 
566 _GLIBCXX_END_NAMESPACE_VERSION
567 } // namespace std
568 
569 #endif // C++14
570 
571 #endif // _GLIBCXX_EXPERIMENTAL_ANY