libstdc++
any
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1 // <any> -*- C++ -*-
2 
3 // Copyright (C) 2014-2024 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 #define __glibcxx_want_any
35 #include <bits/version.h>
36 
37 #ifdef __cpp_lib_any // C++ >= 17
38 
39 #include <initializer_list>
40 #include <typeinfo>
41 #include <new>
42 #include <type_traits>
43 #include <bits/utility.h> // in_place_type_t
44 
45 namespace std _GLIBCXX_VISIBILITY(default)
46 {
47 _GLIBCXX_BEGIN_NAMESPACE_VERSION
48 
49  /**
50  * @addtogroup utilities
51  * @{
52  */
53 
54  /**
55  * @brief Exception class thrown by a failed @c any_cast
56  * @ingroup exceptions
57  */
58  class bad_any_cast : public bad_cast
59  {
60  public:
61  virtual const char* what() const noexcept { return "bad any_cast"; }
62  };
63 
64  [[gnu::noreturn]] inline void __throw_bad_any_cast()
65  {
66 #if __cpp_exceptions
67  throw bad_any_cast{};
68 #else
69  __builtin_abort();
70 #endif
71  }
72 
73  /**
74  * @brief A type-safe container of any type.
75  *
76  * An `any` object's state is either empty or it stores a contained object
77  * of CopyConstructible type.
78  *
79  * @since C++17
80  */
81  class any
82  {
83  // Holds either pointer to a heap object or the contained object itself.
84  union _Storage
85  {
86  constexpr _Storage() : _M_ptr{nullptr} {}
87 
88  // Prevent trivial copies of this type, buffer might hold a non-POD.
89  _Storage(const _Storage&) = delete;
90  _Storage& operator=(const _Storage&) = delete;
91 
92  void* _M_ptr;
93  aligned_storage<sizeof(_M_ptr), alignof(void*)>::type _M_buffer;
94  };
95 
96  template<typename _Tp, typename _Safe = is_nothrow_move_constructible<_Tp>,
97  bool _Fits = (sizeof(_Tp) <= sizeof(_Storage))
98  && (alignof(_Tp) <= alignof(_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 _VTp = decay_t<_Tp>>
113  using _Decay_if_not_any = enable_if_t<!is_same_v<_VTp, any>, _VTp>;
114 
115  /// Emplace with an object created from @p __args as the contained object.
116  template <typename _Tp, typename... _Args,
117  typename _Mgr = _Manager<_Tp>>
118  void __do_emplace(_Args&&... __args)
119  {
120  reset();
121  _Mgr::_S_create(_M_storage, std::forward<_Args>(__args)...);
122  _M_manager = &_Mgr::_S_manage;
123  }
124 
125  /// Emplace with an object created from @p __il and @p __args as
126  /// the contained object.
127  template <typename _Tp, typename _Up, typename... _Args,
128  typename _Mgr = _Manager<_Tp>>
129  void __do_emplace(initializer_list<_Up> __il, _Args&&... __args)
130  {
131  reset();
132  _Mgr::_S_create(_M_storage, __il, std::forward<_Args>(__args)...);
133  _M_manager = &_Mgr::_S_manage;
134  }
135 
136  template <typename _Res, typename _Tp, typename... _Args>
137  using __any_constructible
138  = enable_if<__and_<is_copy_constructible<_Tp>,
139  is_constructible<_Tp, _Args...>>::value,
140  _Res>;
141 
142  template <typename _Tp, typename... _Args>
143  using __any_constructible_t
144  = typename __any_constructible<bool, _Tp, _Args...>::type;
145 
146  template<typename _VTp, typename... _Args>
147  using __emplace_t
148  = typename __any_constructible<_VTp&, _VTp, _Args...>::type;
149 
150  public:
151  // construct/destruct
152 
153  /// Default constructor, creates an empty object.
154  constexpr any() noexcept : _M_manager(nullptr) { }
155 
156  /// Copy constructor, copies the state of @p __other
157  any(const any& __other)
158  {
159  if (!__other.has_value())
160  _M_manager = nullptr;
161  else
162  {
163  _Arg __arg;
164  __arg._M_any = this;
165  __other._M_manager(_Op_clone, &__other, &__arg);
166  }
167  }
168 
169  /**
170  * @brief Move constructor, transfer the state from @p __other
171  *
172  * @post @c !__other.has_value() (this postcondition is a GNU extension)
173  */
174  any(any&& __other) noexcept
175  {
176  if (!__other.has_value())
177  _M_manager = nullptr;
178  else
179  {
180  _Arg __arg;
181  __arg._M_any = this;
182  __other._M_manager(_Op_xfer, &__other, &__arg);
183  }
184  }
185 
186  /// Construct with a copy of @p __value as the contained object.
187  template <typename _Tp, typename _VTp = _Decay_if_not_any<_Tp>,
188  typename _Mgr = _Manager<_VTp>,
189  enable_if_t<is_copy_constructible_v<_VTp>
190  && !__is_in_place_type_v<_VTp>, bool> = true>
191  any(_Tp&& __value)
192  : _M_manager(&_Mgr::_S_manage)
193  {
194  _Mgr::_S_create(_M_storage, std::forward<_Tp>(__value));
195  }
196 
197  /// Construct with an object created from @p __args as the contained object.
198  template <typename _Tp, typename... _Args, typename _VTp = decay_t<_Tp>,
199  typename _Mgr = _Manager<_VTp>,
200  __any_constructible_t<_VTp, _Args&&...> = false>
201  explicit
202  any(in_place_type_t<_Tp>, _Args&&... __args)
203  : _M_manager(&_Mgr::_S_manage)
204  {
205  _Mgr::_S_create(_M_storage, std::forward<_Args>(__args)...);
206  }
207 
208  /// Construct with an object created from @p __il and @p __args as
209  /// the contained object.
210  template <typename _Tp, typename _Up, typename... _Args,
211  typename _VTp = decay_t<_Tp>, typename _Mgr = _Manager<_VTp>,
212  __any_constructible_t<_VTp, initializer_list<_Up>&,
213  _Args&&...> = false>
214  explicit
215  any(in_place_type_t<_Tp>, initializer_list<_Up> __il, _Args&&... __args)
216  : _M_manager(&_Mgr::_S_manage)
217  {
218  _Mgr::_S_create(_M_storage, __il, std::forward<_Args>(__args)...);
219  }
220 
221  /// Destructor, calls @c reset()
222  ~any() { reset(); }
223 
224  // assignments
225 
226  /// Copy the state of another object.
227  any&
228  operator=(const any& __rhs)
229  {
230  *this = any(__rhs);
231  return *this;
232  }
233 
234  /**
235  * @brief Move assignment operator
236  *
237  * @post @c !__rhs.has_value() (not guaranteed for other implementations)
238  */
239  any&
240  operator=(any&& __rhs) noexcept
241  {
242  if (!__rhs.has_value())
243  reset();
244  else if (this != &__rhs)
245  {
246  reset();
247  _Arg __arg;
248  __arg._M_any = this;
249  __rhs._M_manager(_Op_xfer, &__rhs, &__arg);
250  }
251  return *this;
252  }
253 
254  /// Store a copy of @p __rhs as the contained object.
255  template<typename _Tp>
256  enable_if_t<is_copy_constructible<_Decay_if_not_any<_Tp>>::value, any&>
257  operator=(_Tp&& __rhs)
258  {
259  *this = any(std::forward<_Tp>(__rhs));
260  return *this;
261  }
262 
263  /// Emplace with an object created from @p __args as the contained object.
264  template <typename _Tp, typename... _Args>
265  __emplace_t<decay_t<_Tp>, _Args...>
266  emplace(_Args&&... __args)
267  {
268  using _VTp = decay_t<_Tp>;
269  __do_emplace<_VTp>(std::forward<_Args>(__args)...);
270  return *any::_Manager<_VTp>::_S_access(_M_storage);
271  }
272 
273  /// Emplace with an object created from @p __il and @p __args as
274  /// the contained object.
275  template <typename _Tp, typename _Up, typename... _Args>
276  __emplace_t<decay_t<_Tp>, initializer_list<_Up>&, _Args&&...>
277  emplace(initializer_list<_Up> __il, _Args&&... __args)
278  {
279  using _VTp = decay_t<_Tp>;
280  __do_emplace<_VTp, _Up>(__il, std::forward<_Args>(__args)...);
281  return *any::_Manager<_VTp>::_S_access(_M_storage);
282  }
283 
284  // modifiers
285 
286  /// If not empty, destroy the contained object.
287  void reset() noexcept
288  {
289  if (has_value())
290  {
291  _M_manager(_Op_destroy, this, nullptr);
292  _M_manager = nullptr;
293  }
294  }
295 
296  /// Exchange state with another object.
297  void swap(any& __rhs) noexcept
298  {
299  if (!has_value() && !__rhs.has_value())
300  return;
301 
302  if (has_value() && __rhs.has_value())
303  {
304  if (this == &__rhs)
305  return;
306 
307  any __tmp;
308  _Arg __arg;
309  __arg._M_any = &__tmp;
310  __rhs._M_manager(_Op_xfer, &__rhs, &__arg);
311  __arg._M_any = &__rhs;
312  _M_manager(_Op_xfer, this, &__arg);
313  __arg._M_any = this;
314  __tmp._M_manager(_Op_xfer, &__tmp, &__arg);
315  }
316  else
317  {
318  any* __empty = !has_value() ? this : &__rhs;
319  any* __full = !has_value() ? &__rhs : this;
320  _Arg __arg;
321  __arg._M_any = __empty;
322  __full->_M_manager(_Op_xfer, __full, &__arg);
323  }
324  }
325 
326  // observers
327 
328  /// Reports whether there is a contained object or not.
329  bool has_value() const noexcept { return _M_manager != nullptr; }
330 
331 #if __cpp_rtti
332  /// The @c typeid of the contained object, or @c typeid(void) if empty.
333  const type_info& type() const noexcept
334  {
335  if (!has_value())
336  return typeid(void);
337  _Arg __arg;
338  _M_manager(_Op_get_type_info, this, &__arg);
339  return *__arg._M_typeinfo;
340  }
341 #endif
342 
343  /// @cond undocumented
344  template<typename _Tp>
345  static constexpr bool __is_valid_cast()
346  { return __or_<is_reference<_Tp>, is_copy_constructible<_Tp>>::value; }
347  /// @endcond
348 
349  private:
350  enum _Op {
351  _Op_access, _Op_get_type_info, _Op_clone, _Op_destroy, _Op_xfer
352  };
353 
354  union _Arg
355  {
356  void* _M_obj;
357  const std::type_info* _M_typeinfo;
358  any* _M_any;
359  };
360 
361  void (*_M_manager)(_Op, const any*, _Arg*);
362  _Storage _M_storage;
363 
364  /// @cond undocumented
365  template<typename _Tp>
366  friend void* __any_caster(const any* __any);
367  /// @endcond
368 
369  // Manage in-place contained object.
370  template<typename _Tp>
371  struct _Manager_internal
372  {
373  static void
374  _S_manage(_Op __which, const any* __anyp, _Arg* __arg);
375 
376  template<typename _Up>
377  static void
378  _S_create(_Storage& __storage, _Up&& __value)
379  {
380  void* __addr = &__storage._M_buffer;
381  ::new (__addr) _Tp(std::forward<_Up>(__value));
382  }
383 
384  template<typename... _Args>
385  static void
386  _S_create(_Storage& __storage, _Args&&... __args)
387  {
388  void* __addr = &__storage._M_buffer;
389  ::new (__addr) _Tp(std::forward<_Args>(__args)...);
390  }
391 
392  static _Tp*
393  _S_access(const _Storage& __storage)
394  {
395  // The contained object is in __storage._M_buffer
396  const void* __addr = &__storage._M_buffer;
397  return static_cast<_Tp*>(const_cast<void*>(__addr));
398  }
399  };
400 
401  // Manage external contained object.
402  template<typename _Tp>
403  struct _Manager_external
404  {
405  static void
406  _S_manage(_Op __which, const any* __anyp, _Arg* __arg);
407 
408  template<typename _Up>
409  static void
410  _S_create(_Storage& __storage, _Up&& __value)
411  {
412  __storage._M_ptr = new _Tp(std::forward<_Up>(__value));
413  }
414  template<typename... _Args>
415  static void
416  _S_create(_Storage& __storage, _Args&&... __args)
417  {
418  __storage._M_ptr = new _Tp(std::forward<_Args>(__args)...);
419  }
420  static _Tp*
421  _S_access(const _Storage& __storage)
422  {
423  // The contained object is in *__storage._M_ptr
424  return static_cast<_Tp*>(__storage._M_ptr);
425  }
426  };
427  };
428 
429  /// Exchange the states of two @c any objects.
430  inline void swap(any& __x, any& __y) noexcept { __x.swap(__y); }
431 
432  /// Create an `any` holding a `_Tp` constructed from `__args...`.
433  template <typename _Tp, typename... _Args>
434  inline
435  enable_if_t<is_constructible_v<any, in_place_type_t<_Tp>, _Args...>, any>
436  make_any(_Args&&... __args)
437  {
438  return any(in_place_type<_Tp>, std::forward<_Args>(__args)...);
439  }
440 
441  /// Create an `any` holding a `_Tp` constructed from `__il` and `__args...`.
442  template <typename _Tp, typename _Up, typename... _Args>
443  inline
444  enable_if_t<is_constructible_v<any, in_place_type_t<_Tp>,
445  initializer_list<_Up>&, _Args...>, any>
446  make_any(initializer_list<_Up> __il, _Args&&... __args)
447  {
448  return any(in_place_type<_Tp>, __il, std::forward<_Args>(__args)...);
449  }
450 
451  /**
452  * @brief Access the contained object.
453  *
454  * @tparam _ValueType A const-reference or CopyConstructible type.
455  * @param __any The object to access.
456  * @return The contained object.
457  * @throw bad_any_cast If <code>
458  * __any.type() != typeid(remove_reference_t<_ValueType>)
459  * </code>
460  */
461  template<typename _ValueType>
462  inline _ValueType any_cast(const any& __any)
463  {
464  using _Up = __remove_cvref_t<_ValueType>;
465  static_assert(any::__is_valid_cast<_ValueType>(),
466  "Template argument must be a reference or CopyConstructible type");
467  static_assert(is_constructible_v<_ValueType, const _Up&>,
468  "Template argument must be constructible from a const value.");
469  auto __p = any_cast<_Up>(&__any);
470  if (__p)
471  return static_cast<_ValueType>(*__p);
472  __throw_bad_any_cast();
473  }
474 
475  /**
476  * @brief Access the contained object.
477  *
478  * @tparam _ValueType A reference or CopyConstructible type.
479  * @param __any The object to access.
480  * @return The contained object.
481  * @throw bad_any_cast If <code>
482  * __any.type() != typeid(remove_reference_t<_ValueType>)
483  * </code>
484  *
485  * @{
486  */
487  template<typename _ValueType>
488  inline _ValueType any_cast(any& __any)
489  {
490  using _Up = __remove_cvref_t<_ValueType>;
491  static_assert(any::__is_valid_cast<_ValueType>(),
492  "Template argument must be a reference or CopyConstructible type");
493  static_assert(is_constructible_v<_ValueType, _Up&>,
494  "Template argument must be constructible from an lvalue.");
495  auto __p = any_cast<_Up>(&__any);
496  if (__p)
497  return static_cast<_ValueType>(*__p);
498  __throw_bad_any_cast();
499  }
500 
501  template<typename _ValueType>
502  inline _ValueType any_cast(any&& __any)
503  {
504  using _Up = __remove_cvref_t<_ValueType>;
505  static_assert(any::__is_valid_cast<_ValueType>(),
506  "Template argument must be a reference or CopyConstructible type");
507  static_assert(is_constructible_v<_ValueType, _Up>,
508  "Template argument must be constructible from an rvalue.");
509  auto __p = any_cast<_Up>(&__any);
510  if (__p)
511  return static_cast<_ValueType>(std::move(*__p));
512  __throw_bad_any_cast();
513  }
514  /// @}
515 
516  /// @cond undocumented
517  template<typename _Tp>
518  void* __any_caster(const any* __any)
519  {
520  // any_cast<T> returns non-null if __any->type() == typeid(T) and
521  // typeid(T) ignores cv-qualifiers so remove them:
522  using _Up = remove_cv_t<_Tp>;
523  // The contained value has a decayed type, so if decay_t<U> is not U,
524  // then it's not possible to have a contained value of type U:
525  if constexpr (!is_same_v<decay_t<_Up>, _Up>)
526  return nullptr;
527  // Only copy constructible types can be used for contained values:
528  else if constexpr (!is_copy_constructible_v<_Up>)
529  return nullptr;
530  // First try comparing function addresses, which works without RTTI
531  else if (__any->_M_manager == &any::_Manager<_Up>::_S_manage
532 #if __cpp_rtti
533  || __any->type() == typeid(_Tp)
534 #endif
535  )
536  {
537  return any::_Manager<_Up>::_S_access(__any->_M_storage);
538  }
539  return nullptr;
540  }
541  /// @endcond
542 
543  /**
544  * @brief Access the contained object.
545  *
546  * @tparam _ValueType The type of the contained object.
547  * @param __any A pointer to the object to access.
548  * @return The address of the contained object if <code>
549  * __any != nullptr && __any.type() == typeid(_ValueType)
550  * </code>, otherwise a null pointer.
551  *
552  * @{
553  */
554  template<typename _ValueType>
555  inline const _ValueType* any_cast(const any* __any) noexcept
556  {
557  if constexpr (is_object_v<_ValueType>)
558  if (__any)
559  return static_cast<_ValueType*>(__any_caster<_ValueType>(__any));
560  return nullptr;
561  }
562 
563  template<typename _ValueType>
564  inline _ValueType* any_cast(any* __any) noexcept
565  {
566  if constexpr (is_object_v<_ValueType>)
567  if (__any)
568  return static_cast<_ValueType*>(__any_caster<_ValueType>(__any));
569  return nullptr;
570  }
571  /// @}
572 
573  template<typename _Tp>
574  void
575  any::_Manager_internal<_Tp>::
576  _S_manage(_Op __which, const any* __any, _Arg* __arg)
577  {
578  // The contained object is in _M_storage._M_buffer
579  auto __ptr = reinterpret_cast<const _Tp*>(&__any->_M_storage._M_buffer);
580  switch (__which)
581  {
582  case _Op_access:
583  __arg->_M_obj = const_cast<_Tp*>(__ptr);
584  break;
585  case _Op_get_type_info:
586 #if __cpp_rtti
587  __arg->_M_typeinfo = &typeid(_Tp);
588 #endif
589  break;
590  case _Op_clone:
591  ::new(&__arg->_M_any->_M_storage._M_buffer) _Tp(*__ptr);
592  __arg->_M_any->_M_manager = __any->_M_manager;
593  break;
594  case _Op_destroy:
595  __ptr->~_Tp();
596  break;
597  case _Op_xfer:
598  ::new(&__arg->_M_any->_M_storage._M_buffer) _Tp
599  (std::move(*const_cast<_Tp*>(__ptr)));
600  __ptr->~_Tp();
601  __arg->_M_any->_M_manager = __any->_M_manager;
602  const_cast<any*>(__any)->_M_manager = nullptr;
603  break;
604  }
605  }
606 
607  template<typename _Tp>
608  void
609  any::_Manager_external<_Tp>::
610  _S_manage(_Op __which, const any* __any, _Arg* __arg)
611  {
612  // The contained object is *_M_storage._M_ptr
613  auto __ptr = static_cast<const _Tp*>(__any->_M_storage._M_ptr);
614  switch (__which)
615  {
616  case _Op_access:
617  __arg->_M_obj = const_cast<_Tp*>(__ptr);
618  break;
619  case _Op_get_type_info:
620 #if __cpp_rtti
621  __arg->_M_typeinfo = &typeid(_Tp);
622 #endif
623  break;
624  case _Op_clone:
625  __arg->_M_any->_M_storage._M_ptr = new _Tp(*__ptr);
626  __arg->_M_any->_M_manager = __any->_M_manager;
627  break;
628  case _Op_destroy:
629  delete __ptr;
630  break;
631  case _Op_xfer:
632  __arg->_M_any->_M_storage._M_ptr = __any->_M_storage._M_ptr;
633  __arg->_M_any->_M_manager = __any->_M_manager;
634  const_cast<any*>(__any)->_M_manager = nullptr;
635  break;
636  }
637  }
638 
639  /// @}
640 
641  namespace __detail::__variant
642  {
643  template<typename> struct _Never_valueless_alt; // see <variant>
644 
645  // Provide the strong exception-safety guarantee when emplacing an
646  // any into a variant.
647  template<>
648  struct _Never_valueless_alt<std::any>
649  : std::true_type
650  { };
651  } // namespace __detail::__variant
652 
653 _GLIBCXX_END_NAMESPACE_VERSION
654 } // namespace std
655 
656 #endif // __cpp_lib_any
657 #endif // _GLIBCXX_ANY