libstdc++
any
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1 // <any> -*- C++ -*-
2 
3 // Copyright (C) 2014-2021 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 >= 201703L
35 
36 #include <typeinfo>
37 #include <new>
38 #include <utility>
39 #include <type_traits>
40 
41 namespace std _GLIBCXX_VISIBILITY(default)
42 {
43 _GLIBCXX_BEGIN_NAMESPACE_VERSION
44 
45  /**
46  * @addtogroup utilities
47  * @{
48  */
49 
50  /**
51  * @brief Exception class thrown by a failed @c any_cast
52  * @ingroup exceptions
53  */
54  class bad_any_cast : public bad_cast
55  {
56  public:
57  virtual const char* what() const noexcept { return "bad any_cast"; }
58  };
59 
60  [[gnu::noreturn]] inline void __throw_bad_any_cast()
61  {
62 #if __cpp_exceptions
63  throw bad_any_cast{};
64 #else
65  __builtin_abort();
66 #endif
67  }
68 
69 #define __cpp_lib_any 201606L
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  constexpr _Storage() : _M_ptr{nullptr} {}
83 
84  // Prevent trivial copies of this type, buffer might hold a non-POD.
85  _Storage(const _Storage&) = delete;
86  _Storage& operator=(const _Storage&) = delete;
87 
88  void* _M_ptr;
90  };
91 
92  template<typename _Tp, typename _Safe = is_nothrow_move_constructible<_Tp>,
93  bool _Fits = (sizeof(_Tp) <= sizeof(_Storage))
94  && (alignof(_Tp) <= alignof(_Storage))>
95  using _Internal = std::integral_constant<bool, _Safe::value && _Fits>;
96 
97  template<typename _Tp>
98  struct _Manager_internal; // uses small-object optimization
99 
100  template<typename _Tp>
101  struct _Manager_external; // creates contained object on the heap
102 
103  template<typename _Tp>
104  using _Manager = conditional_t<_Internal<_Tp>::value,
105  _Manager_internal<_Tp>,
106  _Manager_external<_Tp>>;
107 
108  template<typename _Tp, typename _VTp = decay_t<_Tp>>
109  using _Decay_if_not_any = enable_if_t<!is_same_v<_VTp, any>, _VTp>;
110 
111  /// Emplace with an object created from @p __args as the contained object.
112  template <typename _Tp, typename... _Args,
113  typename _Mgr = _Manager<_Tp>>
114  void __do_emplace(_Args&&... __args)
115  {
116  reset();
117  _Mgr::_S_create(_M_storage, std::forward<_Args>(__args)...);
118  _M_manager = &_Mgr::_S_manage;
119  }
120 
121  /// Emplace with an object created from @p __il and @p __args as
122  /// the contained object.
123  template <typename _Tp, typename _Up, typename... _Args,
124  typename _Mgr = _Manager<_Tp>>
125  void __do_emplace(initializer_list<_Up> __il, _Args&&... __args)
126  {
127  reset();
128  _Mgr::_S_create(_M_storage, __il, std::forward<_Args>(__args)...);
129  _M_manager = &_Mgr::_S_manage;
130  }
131 
132  template <typename _Res, typename _Tp, typename... _Args>
133  using __any_constructible
135  is_constructible<_Tp, _Args...>>::value,
136  _Res>;
137 
138  template <typename _Tp, typename... _Args>
139  using __any_constructible_t
140  = typename __any_constructible<bool, _Tp, _Args...>::type;
141 
142  template<typename _VTp, typename... _Args>
143  using __emplace_t
144  = typename __any_constructible<_VTp&, _VTp, _Args...>::type;
145 
146  public:
147  // construct/destruct
148 
149  /// Default constructor, creates an empty object.
150  constexpr any() noexcept : _M_manager(nullptr) { }
151 
152  /// Copy constructor, copies the state of @p __other
153  any(const any& __other)
154  {
155  if (!__other.has_value())
156  _M_manager = nullptr;
157  else
158  {
159  _Arg __arg;
160  __arg._M_any = this;
161  __other._M_manager(_Op_clone, &__other, &__arg);
162  }
163  }
164 
165  /**
166  * @brief Move constructor, transfer the state from @p __other
167  *
168  * @post @c !__other.has_value() (this postcondition is a GNU extension)
169  */
170  any(any&& __other) noexcept
171  {
172  if (!__other.has_value())
173  _M_manager = nullptr;
174  else
175  {
176  _Arg __arg;
177  __arg._M_any = this;
178  __other._M_manager(_Op_xfer, &__other, &__arg);
179  }
180  }
181 
182  /// Construct with a copy of @p __value as the contained object.
183  template <typename _Tp, typename _VTp = _Decay_if_not_any<_Tp>,
184  typename _Mgr = _Manager<_VTp>,
185  enable_if_t<is_copy_constructible<_VTp>::value
186  && !__is_in_place_type<_VTp>::value, bool> = true>
187  any(_Tp&& __value)
188  : _M_manager(&_Mgr::_S_manage)
189  {
190  _Mgr::_S_create(_M_storage, std::forward<_Tp>(__value));
191  }
192 
193  /// Construct with an object created from @p __args as the contained object.
194  template <typename _Tp, typename... _Args, typename _VTp = decay_t<_Tp>,
195  typename _Mgr = _Manager<_VTp>,
196  __any_constructible_t<_VTp, _Args&&...> = false>
197  explicit
198  any(in_place_type_t<_Tp>, _Args&&... __args)
199  : _M_manager(&_Mgr::_S_manage)
200  {
201  _Mgr::_S_create(_M_storage, std::forward<_Args>(__args)...);
202  }
203 
204  /// Construct with an object created from @p __il and @p __args as
205  /// the contained object.
206  template <typename _Tp, typename _Up, typename... _Args,
207  typename _VTp = decay_t<_Tp>, typename _Mgr = _Manager<_VTp>,
208  __any_constructible_t<_VTp, initializer_list<_Up>&,
209  _Args&&...> = false>
210  explicit
211  any(in_place_type_t<_Tp>, initializer_list<_Up> __il, _Args&&... __args)
212  : _M_manager(&_Mgr::_S_manage)
213  {
214  _Mgr::_S_create(_M_storage, __il, std::forward<_Args>(__args)...);
215  }
216 
217  /// Destructor, calls @c reset()
218  ~any() { reset(); }
219 
220  // assignments
221 
222  /// Copy the state of another object.
223  any&
224  operator=(const any& __rhs)
225  {
226  *this = any(__rhs);
227  return *this;
228  }
229 
230  /**
231  * @brief Move assignment operator
232  *
233  * @post @c !__rhs.has_value() (not guaranteed for other implementations)
234  */
235  any&
236  operator=(any&& __rhs) noexcept
237  {
238  if (!__rhs.has_value())
239  reset();
240  else if (this != &__rhs)
241  {
242  reset();
243  _Arg __arg;
244  __arg._M_any = this;
245  __rhs._M_manager(_Op_xfer, &__rhs, &__arg);
246  }
247  return *this;
248  }
249 
250  /// Store a copy of @p __rhs as the contained object.
251  template<typename _Tp>
253  operator=(_Tp&& __rhs)
254  {
255  *this = any(std::forward<_Tp>(__rhs));
256  return *this;
257  }
258 
259  /// Emplace with an object created from @p __args as the contained object.
260  template <typename _Tp, typename... _Args>
261  __emplace_t<decay_t<_Tp>, _Args...>
262  emplace(_Args&&... __args)
263  {
264  using _VTp = decay_t<_Tp>;
265  __do_emplace<_VTp>(std::forward<_Args>(__args)...);
266  any::_Arg __arg;
267  this->_M_manager(any::_Op_access, this, &__arg);
268  return *static_cast<_VTp*>(__arg._M_obj);
269  }
270 
271  /// Emplace with an object created from @p __il and @p __args as
272  /// the contained object.
273  template <typename _Tp, typename _Up, typename... _Args>
274  __emplace_t<decay_t<_Tp>, initializer_list<_Up>&, _Args&&...>
275  emplace(initializer_list<_Up> __il, _Args&&... __args)
276  {
277  using _VTp = decay_t<_Tp>;
278  __do_emplace<_VTp, _Up>(__il, std::forward<_Args>(__args)...);
279  any::_Arg __arg;
280  this->_M_manager(any::_Op_access, this, &__arg);
281  return *static_cast<_VTp*>(__arg._M_obj);
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  template<typename _Tp>
344  static constexpr bool __is_valid_cast()
345  { return __or_<is_reference<_Tp>, is_copy_constructible<_Tp>>::value; }
346 
347  private:
348  enum _Op {
349  _Op_access, _Op_get_type_info, _Op_clone, _Op_destroy, _Op_xfer
350  };
351 
352  union _Arg
353  {
354  void* _M_obj;
355  const std::type_info* _M_typeinfo;
356  any* _M_any;
357  };
358 
359  void (*_M_manager)(_Op, const any*, _Arg*);
360  _Storage _M_storage;
361 
362  template<typename _Tp>
363  friend void* __any_caster(const any* __any);
364 
365  // Manage in-place contained object.
366  template<typename _Tp>
367  struct _Manager_internal
368  {
369  static void
370  _S_manage(_Op __which, const any* __anyp, _Arg* __arg);
371 
372  template<typename _Up>
373  static void
374  _S_create(_Storage& __storage, _Up&& __value)
375  {
376  void* __addr = &__storage._M_buffer;
377  ::new (__addr) _Tp(std::forward<_Up>(__value));
378  }
379 
380  template<typename... _Args>
381  static void
382  _S_create(_Storage& __storage, _Args&&... __args)
383  {
384  void* __addr = &__storage._M_buffer;
385  ::new (__addr) _Tp(std::forward<_Args>(__args)...);
386  }
387  };
388 
389  // Manage external contained object.
390  template<typename _Tp>
391  struct _Manager_external
392  {
393  static void
394  _S_manage(_Op __which, const any* __anyp, _Arg* __arg);
395 
396  template<typename _Up>
397  static void
398  _S_create(_Storage& __storage, _Up&& __value)
399  {
400  __storage._M_ptr = new _Tp(std::forward<_Up>(__value));
401  }
402  template<typename... _Args>
403  static void
404  _S_create(_Storage& __storage, _Args&&... __args)
405  {
406  __storage._M_ptr = new _Tp(std::forward<_Args>(__args)...);
407  }
408  };
409  };
410 
411  /// Exchange the states of two @c any objects.
412  inline void swap(any& __x, any& __y) noexcept { __x.swap(__y); }
413 
414  /// Create an any holding a @c _Tp constructed from @c __args.
415  template <typename _Tp, typename... _Args>
416  any make_any(_Args&&... __args)
417  {
418  return any(in_place_type<_Tp>, std::forward<_Args>(__args)...);
419  }
420 
421  /// Create an any holding a @c _Tp constructed from @c __il and @c __args.
422  template <typename _Tp, typename _Up, typename... _Args>
423  any make_any(initializer_list<_Up> __il, _Args&&... __args)
424  {
425  return any(in_place_type<_Tp>, __il, std::forward<_Args>(__args)...);
426  }
427 
428  /**
429  * @brief Access the contained object.
430  *
431  * @tparam _ValueType A const-reference or CopyConstructible type.
432  * @param __any The object to access.
433  * @return The contained object.
434  * @throw bad_any_cast If <code>
435  * __any.type() != typeid(remove_reference_t<_ValueType>)
436  * </code>
437  */
438  template<typename _ValueType>
439  inline _ValueType any_cast(const any& __any)
440  {
441  using _Up = __remove_cvref_t<_ValueType>;
442  static_assert(any::__is_valid_cast<_ValueType>(),
443  "Template argument must be a reference or CopyConstructible type");
444  static_assert(is_constructible_v<_ValueType, const _Up&>,
445  "Template argument must be constructible from a const value.");
446  auto __p = any_cast<_Up>(&__any);
447  if (__p)
448  return static_cast<_ValueType>(*__p);
449  __throw_bad_any_cast();
450  }
451 
452  /**
453  * @brief Access the contained object.
454  *
455  * @tparam _ValueType A reference or CopyConstructible type.
456  * @param __any The object to access.
457  * @return The contained object.
458  * @throw bad_any_cast If <code>
459  * __any.type() != typeid(remove_reference_t<_ValueType>)
460  * </code>
461  *
462  * @{
463  */
464  template<typename _ValueType>
465  inline _ValueType any_cast(any& __any)
466  {
467  using _Up = __remove_cvref_t<_ValueType>;
468  static_assert(any::__is_valid_cast<_ValueType>(),
469  "Template argument must be a reference or CopyConstructible type");
470  static_assert(is_constructible_v<_ValueType, _Up&>,
471  "Template argument must be constructible from an lvalue.");
472  auto __p = any_cast<_Up>(&__any);
473  if (__p)
474  return static_cast<_ValueType>(*__p);
475  __throw_bad_any_cast();
476  }
477 
478  template<typename _ValueType>
479  inline _ValueType any_cast(any&& __any)
480  {
481  using _Up = __remove_cvref_t<_ValueType>;
482  static_assert(any::__is_valid_cast<_ValueType>(),
483  "Template argument must be a reference or CopyConstructible type");
484  static_assert(is_constructible_v<_ValueType, _Up>,
485  "Template argument must be constructible from an rvalue.");
486  auto __p = any_cast<_Up>(&__any);
487  if (__p)
488  return static_cast<_ValueType>(std::move(*__p));
489  __throw_bad_any_cast();
490  }
491  /// @}
492 
493  /// @cond undocumented
494  template<typename _Tp>
495  void* __any_caster(const any* __any)
496  {
497  // any_cast<T> returns non-null if __any->type() == typeid(T) and
498  // typeid(T) ignores cv-qualifiers so remove them:
499  using _Up = remove_cv_t<_Tp>;
500  // The contained value has a decayed type, so if decay_t<U> is not U,
501  // then it's not possible to have a contained value of type U:
502  if constexpr (!is_same_v<decay_t<_Up>, _Up>)
503  return nullptr;
504  // Only copy constructible types can be used for contained values:
505  else if constexpr (!is_copy_constructible_v<_Up>)
506  return nullptr;
507  // First try comparing function addresses, which works without RTTI
508  else if (__any->_M_manager == &any::_Manager<_Up>::_S_manage
509 #if __cpp_rtti
510  || __any->type() == typeid(_Tp)
511 #endif
512  )
513  {
514  any::_Arg __arg;
515  __any->_M_manager(any::_Op_access, __any, &__arg);
516  return __arg._M_obj;
517  }
518  return nullptr;
519  }
520  /// @endcond
521 
522  /**
523  * @brief Access the contained object.
524  *
525  * @tparam _ValueType The type of the contained object.
526  * @param __any A pointer to the object to access.
527  * @return The address of the contained object if <code>
528  * __any != nullptr && __any.type() == typeid(_ValueType)
529  * </code>, otherwise a null pointer.
530  *
531  * @{
532  */
533  template<typename _ValueType>
534  inline const _ValueType* any_cast(const any* __any) noexcept
535  {
536  if constexpr (is_object_v<_ValueType>)
537  if (__any)
538  return static_cast<_ValueType*>(__any_caster<_ValueType>(__any));
539  return nullptr;
540  }
541 
542  template<typename _ValueType>
543  inline _ValueType* any_cast(any* __any) noexcept
544  {
545  if constexpr (is_object_v<_ValueType>)
546  if (__any)
547  return static_cast<_ValueType*>(__any_caster<_ValueType>(__any));
548  return nullptr;
549  }
550  /// @}
551 
552  template<typename _Tp>
553  void
554  any::_Manager_internal<_Tp>::
555  _S_manage(_Op __which, const any* __any, _Arg* __arg)
556  {
557  // The contained object is in _M_storage._M_buffer
558  auto __ptr = reinterpret_cast<const _Tp*>(&__any->_M_storage._M_buffer);
559  switch (__which)
560  {
561  case _Op_access:
562  __arg->_M_obj = const_cast<_Tp*>(__ptr);
563  break;
564  case _Op_get_type_info:
565 #if __cpp_rtti
566  __arg->_M_typeinfo = &typeid(_Tp);
567 #endif
568  break;
569  case _Op_clone:
570  ::new(&__arg->_M_any->_M_storage._M_buffer) _Tp(*__ptr);
571  __arg->_M_any->_M_manager = __any->_M_manager;
572  break;
573  case _Op_destroy:
574  __ptr->~_Tp();
575  break;
576  case _Op_xfer:
577  ::new(&__arg->_M_any->_M_storage._M_buffer) _Tp
578  (std::move(*const_cast<_Tp*>(__ptr)));
579  __ptr->~_Tp();
580  __arg->_M_any->_M_manager = __any->_M_manager;
581  const_cast<any*>(__any)->_M_manager = nullptr;
582  break;
583  }
584  }
585 
586  template<typename _Tp>
587  void
588  any::_Manager_external<_Tp>::
589  _S_manage(_Op __which, const any* __any, _Arg* __arg)
590  {
591  // The contained object is *_M_storage._M_ptr
592  auto __ptr = static_cast<const _Tp*>(__any->_M_storage._M_ptr);
593  switch (__which)
594  {
595  case _Op_access:
596  __arg->_M_obj = const_cast<_Tp*>(__ptr);
597  break;
598  case _Op_get_type_info:
599 #if __cpp_rtti
600  __arg->_M_typeinfo = &typeid(_Tp);
601 #endif
602  break;
603  case _Op_clone:
604  __arg->_M_any->_M_storage._M_ptr = new _Tp(*__ptr);
605  __arg->_M_any->_M_manager = __any->_M_manager;
606  break;
607  case _Op_destroy:
608  delete __ptr;
609  break;
610  case _Op_xfer:
611  __arg->_M_any->_M_storage._M_ptr = __any->_M_storage._M_ptr;
612  __arg->_M_any->_M_manager = __any->_M_manager;
613  const_cast<any*>(__any)->_M_manager = nullptr;
614  break;
615  }
616  }
617 
618  /// @}
619 
620  namespace __detail::__variant
621  {
622  template<typename> struct _Never_valueless_alt; // see <variant>
623 
624  // Provide the strong exception-safety guarantee when emplacing an
625  // any into a variant.
626  template<>
627  struct _Never_valueless_alt<std::any>
629  { };
630  } // namespace __detail::__variant
631 
632 _GLIBCXX_END_NAMESPACE_VERSION
633 } // namespace std
634 
635 #endif // C++17
636 #endif // _GLIBCXX_ANY
virtual const char * what() const noexcept
Definition: any:57
Part of RTTI.
Definition: typeinfo:88
constexpr std::remove_reference< _Tp >::type && move(_Tp &&__t) noexcept
Convert a value to an rvalue.
Definition: move.h:104
_ValueType any_cast(const any &__any)
Access the contained object.
Definition: any:439
is_constructible
Definition: type_traits:911
any make_any(_Args &&...__args)
Create an any holding a _Tp constructed from __args.
Definition: any:416
constexpr any() noexcept
Default constructor, creates an empty object.
Definition: any:150
any(any &&__other) noexcept
Move constructor, transfer the state from __other.
Definition: any:170
enable_if_t< is_copy_constructible< _Decay_if_not_any< _Tp > >::value, any & > operator=(_Tp &&__rhs)
Store a copy of __rhs as the contained object.
Definition: any:253
typename enable_if< _Cond, _Tp >::type enable_if_t
Alias template for enable_if.
Definition: type_traits:2514
bool has_value() const noexcept
Reports whether there is a contained object or not.
Definition: any:329
typename decay< _Tp >::type decay_t
Alias template for decay.
Definition: type_traits:2510
any(_Tp &&__value)
Construct with a copy of __value as the contained object.
Definition: any:187
is_copy_constructible
Definition: type_traits:941
any(in_place_type_t< _Tp >, _Args &&...__args)
Construct with an object created from __args as the contained object.
Definition: any:198
void reset() noexcept
If not empty, destroy the contained object.
Definition: any:287
__emplace_t< decay_t< _Tp >, _Args...> emplace(_Args &&...__args)
Emplace with an object created from __args as the contained object.
Definition: any:262
any & operator=(const any &__rhs)
Copy the state of another object.
Definition: any:224
void swap(any &__rhs) noexcept
Exchange state with another object.
Definition: any:297
constexpr _Tp && forward(typename std::remove_reference< _Tp >::type &__t) noexcept
Forward an lvalue.
Definition: move.h:77
Exception class thrown by a failed any_cast.
Definition: any:54
typename conditional< _Cond, _Iftrue, _Iffalse >::type conditional_t
Alias template for conditional.
Definition: type_traits:2518
A type-safe container of any type.
Definition: any:77
Alignment type.
Definition: type_traits:2029
any & operator=(any &&__rhs) noexcept
Move assignment operator.
Definition: any:236
any(const any &__other)
Copy constructor, copies the state of __other.
Definition: any:153
~any()
Destructor, calls reset()
Definition: any:218
const type_info & type() const noexcept
The typeid of the contained object, or typeid(void) if empty.
Definition: any:333
Define a member typedef type only if a boolean constant is true.
Definition: type_traits:2142
any(in_place_type_t< _Tp >, initializer_list< _Up > __il, _Args &&...__args)
Construct with an object created from __il and __args as the contained object.
Definition: any:211
__emplace_t< decay_t< _Tp >, initializer_list< _Up > &, _Args &&...> emplace(initializer_list< _Up > __il, _Args &&...__args)
Emplace with an object created from __il and __args as the contained object.
Definition: any:275
initializer_list
integral_constant
Definition: type_traits:57
Thrown during incorrect typecasting.If you attempt an invalid dynamic_cast expression, an instance of this class (or something derived from this class) is thrown.
Definition: typeinfo:190