libstdc++
any
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1// <experimental/any> -*- C++ -*-
2
3// Copyright (C) 2014-2019 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
42namespace std _GLIBCXX_VISIBILITY(default)
43{
44_GLIBCXX_BEGIN_NAMESPACE_VERSION
45
46namespace experimental
47{
48inline 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 _GLIBCXX_NODISCARD 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