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any
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1 // <experimental/any> -*- C++ -*-
2 
3 // Copyright (C) 2014-2018 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 >= 201402L
35 
36 #include <typeinfo>
37 #include <new>
38 #include <utility>
39 #include <type_traits>
40 #include <experimental/bits/lfts_config.h>
41 
42 namespace std _GLIBCXX_VISIBILITY(default)
43 {
44 _GLIBCXX_BEGIN_NAMESPACE_VERSION
45 
46 namespace experimental
47 {
48 inline namespace fundamentals_v1
49 {
50  /**
51  * @defgroup any Type-safe container of any type
52  * @ingroup experimental
53  *
54  * A type-safe container for single values of value types, as
55  * described in n3804 "Any Library Proposal (Revision 3)".
56  *
57  * @{
58  */
59 
60 #define __cpp_lib_experimental_any 201411
61 
62  /**
63  * @brief Exception class thrown by a failed @c any_cast
64  * @ingroup exceptions
65  */
66  class bad_any_cast : public bad_cast
67  {
68  public:
69  virtual const char* what() const noexcept { return "bad any_cast"; }
70  };
71 
72  [[gnu::noreturn]] inline void __throw_bad_any_cast()
73  {
74 #if __cpp_exceptions
75  throw bad_any_cast{};
76 #else
77  __builtin_abort();
78 #endif
79  }
80 
81  /**
82  * @brief A type-safe container of any type.
83  *
84  * An @c any object's state is either empty or it stores a contained object
85  * of CopyConstructible type.
86  */
87  class any
88  {
89  // Holds either pointer to a heap object or the contained object itself.
90  union _Storage
91  {
92  // This constructor intentionally doesn't initialize anything.
93  _Storage() = default;
94 
95  // Prevent trivial copies of this type, buffer might hold a non-POD.
96  _Storage(const _Storage&) = delete;
97  _Storage& operator=(const _Storage&) = delete;
98 
99  void* _M_ptr;
100  aligned_storage<sizeof(_M_ptr), alignof(void*)>::type _M_buffer;
101  };
102 
103  template<typename _Tp, typename _Safe = is_nothrow_move_constructible<_Tp>,
104  bool _Fits = (sizeof(_Tp) <= sizeof(_Storage))
105  && (alignof(_Tp) <= alignof(_Storage))>
106  using _Internal = std::integral_constant<bool, _Safe::value && _Fits>;
107 
108  template<typename _Tp>
109  struct _Manager_internal; // uses small-object optimization
110 
111  template<typename _Tp>
112  struct _Manager_external; // creates contained object on the heap
113 
114  template<typename _Tp>
115  using _Manager = conditional_t<_Internal<_Tp>::value,
116  _Manager_internal<_Tp>,
117  _Manager_external<_Tp>>;
118 
119  template<typename _Tp, typename _Decayed = decay_t<_Tp>>
120  using _Decay = enable_if_t<!is_same<_Decayed, any>::value, _Decayed>;
121 
122  public:
123  // construct/destruct
124 
125  /// Default constructor, creates an empty object.
126  any() noexcept : _M_manager(nullptr) { }
127 
128  /// Copy constructor, copies the state of @p __other
129  any(const any& __other)
130  {
131  if (__other.empty())
132  _M_manager = nullptr;
133  else
134  {
135  _Arg __arg;
136  __arg._M_any = this;
137  __other._M_manager(_Op_clone, &__other, &__arg);
138  }
139  }
140 
141  /**
142  * @brief Move constructor, transfer the state from @p __other
143  *
144  * @post @c __other.empty() (this postcondition is a GNU extension)
145  */
146  any(any&& __other) noexcept
147  {
148  if (__other.empty())
149  _M_manager = nullptr;
150  else
151  {
152  _Arg __arg;
153  __arg._M_any = this;
154  __other._M_manager(_Op_xfer, &__other, &__arg);
155  }
156  }
157 
158  /// Construct with a copy of @p __value as the contained object.
159  template <typename _ValueType, typename _Tp = _Decay<_ValueType>,
160  typename _Mgr = _Manager<_Tp>,
161  typename enable_if<is_constructible<_Tp, _ValueType&&>::value,
162  bool>::type = true>
163  any(_ValueType&& __value)
164  : _M_manager(&_Mgr::_S_manage)
165  {
166  _Mgr::_S_create(_M_storage, std::forward<_ValueType>(__value));
167  static_assert(is_copy_constructible<_Tp>::value,
168  "The contained object must be CopyConstructible");
169  }
170 
171  /// Construct with a copy of @p __value as the contained object.
172  template <typename _ValueType, typename _Tp = _Decay<_ValueType>,
173  typename _Mgr = _Manager<_Tp>,
174  typename enable_if<!is_constructible<_Tp, _ValueType&&>::value,
175  bool>::type = false>
176  any(_ValueType&& __value)
177  : _M_manager(&_Mgr::_S_manage)
178  {
179  _Mgr::_S_create(_M_storage, __value);
180  static_assert(is_copy_constructible<_Tp>::value,
181  "The contained object must be CopyConstructible");
182  }
183 
184  /// Destructor, calls @c clear()
185  ~any() { clear(); }
186 
187  // assignments
188 
189  /// Copy the state of another object.
190  any& operator=(const any& __rhs)
191  {
192  *this = any(__rhs);
193  return *this;
194  }
195 
196  /**
197  * @brief Move assignment operator
198  *
199  * @post @c __rhs.empty() (not guaranteed for other implementations)
200  */
201  any& operator=(any&& __rhs) noexcept
202  {
203  if (__rhs.empty())
204  clear();
205  else if (this != &__rhs)
206  {
207  clear();
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 enable_if_t<is_object<_Tp>::value, void*>
304  __any_caster(const any* __any);
305 
306  // Manage in-place contained object.
307  template<typename _Tp>
308  struct _Manager_internal
309  {
310  static void
311  _S_manage(_Op __which, const any* __anyp, _Arg* __arg);
312 
313  template<typename _Up>
314  static void
315  _S_create(_Storage& __storage, _Up&& __value)
316  {
317  void* __addr = &__storage._M_buffer;
318  ::new (__addr) _Tp(std::forward<_Up>(__value));
319  }
320  };
321 
322  // Manage external contained object.
323  template<typename _Tp>
324  struct _Manager_external
325  {
326  static void
327  _S_manage(_Op __which, const any* __anyp, _Arg* __arg);
328 
329  template<typename _Up>
330  static void
331  _S_create(_Storage& __storage, _Up&& __value)
332  {
333  __storage._M_ptr = new _Tp(std::forward<_Up>(__value));
334  }
335  };
336  };
337 
338  /// Exchange the states of two @c any objects.
339  inline void swap(any& __x, any& __y) noexcept { __x.swap(__y); }
340 
341  /**
342  * @brief Access the contained object.
343  *
344  * @tparam _ValueType A const-reference or CopyConstructible type.
345  * @param __any The object to access.
346  * @return The contained object.
347  * @throw bad_any_cast If <code>
348  * __any.type() != typeid(remove_reference_t<_ValueType>)
349  * </code>
350  */
351  template<typename _ValueType>
352  inline _ValueType any_cast(const any& __any)
353  {
354  static_assert(any::__is_valid_cast<_ValueType>(),
355  "Template argument must be a reference or CopyConstructible type");
356  auto __p = any_cast<add_const_t<remove_reference_t<_ValueType>>>(&__any);
357  if (__p)
358  return *__p;
359  __throw_bad_any_cast();
360  }
361 
362  /**
363  * @brief Access the contained object.
364  *
365  * @tparam _ValueType A reference or CopyConstructible type.
366  * @param __any The object to access.
367  * @return The contained object.
368  * @throw bad_any_cast If <code>
369  * __any.type() != typeid(remove_reference_t<_ValueType>)
370  * </code>
371  *
372  * @{
373  */
374  template<typename _ValueType>
375  inline _ValueType any_cast(any& __any)
376  {
377  static_assert(any::__is_valid_cast<_ValueType>(),
378  "Template argument must be a reference or CopyConstructible type");
379  auto __p = any_cast<remove_reference_t<_ValueType>>(&__any);
380  if (__p)
381  return *__p;
382  __throw_bad_any_cast();
383  }
384 
385  template<typename _ValueType,
386  typename enable_if<!is_move_constructible<_ValueType>::value
387  || is_lvalue_reference<_ValueType>::value,
388  bool>::type = true>
389  inline _ValueType any_cast(any&& __any)
390  {
391  static_assert(any::__is_valid_cast<_ValueType>(),
392  "Template argument must be a reference or CopyConstructible type");
393  auto __p = any_cast<remove_reference_t<_ValueType>>(&__any);
394  if (__p)
395  return *__p;
396  __throw_bad_any_cast();
397  }
398 
399  template<typename _ValueType,
400  typename enable_if<is_move_constructible<_ValueType>::value
401  && !is_lvalue_reference<_ValueType>::value,
402  bool>::type = false>
403  inline _ValueType any_cast(any&& __any)
404  {
405  static_assert(any::__is_valid_cast<_ValueType>(),
406  "Template argument must be a reference or CopyConstructible type");
407  auto __p = any_cast<remove_reference_t<_ValueType>>(&__any);
408  if (__p)
409  return std::move(*__p);
410  __throw_bad_any_cast();
411  }
412  // @}
413 
414  /// @cond undocumented
415  template<typename _Tp>
416  enable_if_t<is_object<_Tp>::value, void*>
417  __any_caster(const any* __any)
418  {
419  // any_cast<T> returns non-null if __any->type() == typeid(T) and
420  // typeid(T) ignores cv-qualifiers so remove them:
421  using _Up = remove_cv_t<_Tp>;
422  // The contained value has a decayed type, so if decay_t<U> is not U,
423  // then it's not possible to have a contained value of type U.
424  using __does_not_decay = is_same<decay_t<_Up>, _Up>;
425  // Only copy constructible types can be used for contained values.
426  using __is_copyable = is_copy_constructible<_Up>;
427  // If the type _Tp could never be stored in an any we don't want to
428  // instantiate _Manager<_Tp>, so use _Manager<any::_Op> instead, which
429  // is explicitly specialized and has a no-op _S_manage function.
430  using _Vp = conditional_t<__and_<__does_not_decay, __is_copyable>::value,
431  _Up, any::_Op>;
432  // First try comparing function addresses, which works without RTTI
433  if (__any->_M_manager == &any::_Manager<_Vp>::_S_manage
434 #if __cpp_rtti
435  || __any->type() == typeid(_Tp)
436 #endif
437  )
438  {
439  any::_Arg __arg;
440  __any->_M_manager(any::_Op_access, __any, &__arg);
441  return __arg._M_obj;
442  }
443  return nullptr;
444  }
445 
446  // This overload exists so that std::any_cast<void(*)()>(a) is well-formed.
447  template<typename _Tp>
448  enable_if_t<!is_object<_Tp>::value, _Tp*>
449  __any_caster(const any*) noexcept
450  { return nullptr; }
451  /// @endcond
452 
453  /**
454  * @brief Access the contained object.
455  *
456  * @tparam _ValueType The type of the contained object.
457  * @param __any A pointer to the object to access.
458  * @return The address of the contained object if <code>
459  * __any != nullptr && __any.type() == typeid(_ValueType)
460  * </code>, otherwise a null pointer.
461  *
462  * @{
463  */
464  template<typename _ValueType>
465  inline const _ValueType* any_cast(const any* __any) noexcept
466  {
467  if (__any)
468  return static_cast<_ValueType*>(__any_caster<_ValueType>(__any));
469  return nullptr;
470  }
471 
472  template<typename _ValueType>
473  inline _ValueType* any_cast(any* __any) noexcept
474  {
475  if (__any)
476  return static_cast<_ValueType*>(__any_caster<_ValueType>(__any));
477  return nullptr;
478  }
479  // @}
480 
481  template<typename _Tp>
482  void
483  any::_Manager_internal<_Tp>::
484  _S_manage(_Op __which, const any* __any, _Arg* __arg)
485  {
486  // The contained object is in _M_storage._M_buffer
487  auto __ptr = reinterpret_cast<const _Tp*>(&__any->_M_storage._M_buffer);
488  switch (__which)
489  {
490  case _Op_access:
491  __arg->_M_obj = const_cast<_Tp*>(__ptr);
492  break;
493  case _Op_get_type_info:
494 #if __cpp_rtti
495  __arg->_M_typeinfo = &typeid(_Tp);
496 #endif
497  break;
498  case _Op_clone:
499  ::new(&__arg->_M_any->_M_storage._M_buffer) _Tp(*__ptr);
500  __arg->_M_any->_M_manager = __any->_M_manager;
501  break;
502  case _Op_destroy:
503  __ptr->~_Tp();
504  break;
505  case _Op_xfer:
506  ::new(&__arg->_M_any->_M_storage._M_buffer) _Tp
507  (std::move(*const_cast<_Tp*>(__ptr)));
508  __ptr->~_Tp();
509  __arg->_M_any->_M_manager = __any->_M_manager;
510  const_cast<any*>(__any)->_M_manager = nullptr;
511  break;
512  }
513  }
514 
515  template<typename _Tp>
516  void
517  any::_Manager_external<_Tp>::
518  _S_manage(_Op __which, const any* __any, _Arg* __arg)
519  {
520  // The contained object is *_M_storage._M_ptr
521  auto __ptr = static_cast<const _Tp*>(__any->_M_storage._M_ptr);
522  switch (__which)
523  {
524  case _Op_access:
525  __arg->_M_obj = const_cast<_Tp*>(__ptr);
526  break;
527  case _Op_get_type_info:
528 #if __cpp_rtti
529  __arg->_M_typeinfo = &typeid(_Tp);
530 #endif
531  break;
532  case _Op_clone:
533  __arg->_M_any->_M_storage._M_ptr = new _Tp(*__ptr);
534  __arg->_M_any->_M_manager = __any->_M_manager;
535  break;
536  case _Op_destroy:
537  delete __ptr;
538  break;
539  case _Op_xfer:
540  __arg->_M_any->_M_storage._M_ptr = __any->_M_storage._M_ptr;
541  __arg->_M_any->_M_manager = __any->_M_manager;
542  const_cast<any*>(__any)->_M_manager = nullptr;
543  break;
544  }
545  }
546 
547  // Dummy specialization used by __any_caster.
548  template<>
549  struct any::_Manager_internal<any::_Op>
550  {
551  static void
552  _S_manage(_Op, const any*, _Arg*) { }
553  };
554 
555  // @} group any
556 } // namespace fundamentals_v1
557 } // namespace experimental
558 
559 _GLIBCXX_END_NAMESPACE_VERSION
560 } // namespace std
561 
562 #endif // C++14
563 
564 #endif // _GLIBCXX_EXPERIMENTAL_ANY