libstdc++
any
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1// <any> -*- C++ -*-
2
3// Copyright (C) 2014-2022 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 <initializer_list>
37#include <typeinfo>
38#include <new>
39#include <type_traits>
40#include <bits/utility.h> // in_place_type_t
41
42namespace std _GLIBCXX_VISIBILITY(default)
43{
44_GLIBCXX_BEGIN_NAMESPACE_VERSION
45
46 /**
47 * @addtogroup utilities
48 * @{
49 */
50
51 /**
52 * @brief Exception class thrown by a failed @c any_cast
53 * @ingroup exceptions
54 */
55 class bad_any_cast : public bad_cast
56 {
57 public:
58 virtual const char* what() const noexcept { return "bad any_cast"; }
59 };
60
61 [[gnu::noreturn]] inline void __throw_bad_any_cast()
62 {
63#if __cpp_exceptions
64 throw bad_any_cast{};
65#else
66 __builtin_abort();
67#endif
68 }
69
70#define __cpp_lib_any 201606L
71
72 /**
73 * @brief A type-safe container of any type.
74 *
75 * An `any` object's state is either empty or it stores a contained object
76 * of CopyConstructible type.
77 *
78 * @since C++17
79 */
80 class any
81 {
82 // Holds either pointer to a heap object or the contained object itself.
83 union _Storage
84 {
85 constexpr _Storage() : _M_ptr{nullptr} {}
86
87 // Prevent trivial copies of this type, buffer might hold a non-POD.
88 _Storage(const _Storage&) = delete;
89 _Storage& operator=(const _Storage&) = delete;
90
91 void* _M_ptr;
92 aligned_storage<sizeof(_M_ptr), alignof(void*)>::type _M_buffer;
93 };
94
95 template<typename _Tp, typename _Safe = is_nothrow_move_constructible<_Tp>,
96 bool _Fits = (sizeof(_Tp) <= sizeof(_Storage))
97 && (alignof(_Tp) <= alignof(_Storage))>
98 using _Internal = std::integral_constant<bool, _Safe::value && _Fits>;
99
100 template<typename _Tp>
101 struct _Manager_internal; // uses small-object optimization
102
103 template<typename _Tp>
104 struct _Manager_external; // creates contained object on the heap
105
106 template<typename _Tp>
107 using _Manager = __conditional_t<_Internal<_Tp>::value,
108 _Manager_internal<_Tp>,
109 _Manager_external<_Tp>>;
110
111 template<typename _Tp, typename _VTp = decay_t<_Tp>>
112 using _Decay_if_not_any = enable_if_t<!is_same_v<_VTp, any>, _VTp>;
113
114 /// Emplace with an object created from @p __args as the contained object.
115 template <typename _Tp, typename... _Args,
116 typename _Mgr = _Manager<_Tp>>
117 void __do_emplace(_Args&&... __args)
118 {
119 reset();
120 _Mgr::_S_create(_M_storage, std::forward<_Args>(__args)...);
121 _M_manager = &_Mgr::_S_manage;
122 }
123
124 /// Emplace with an object created from @p __il and @p __args as
125 /// the contained object.
126 template <typename _Tp, typename _Up, typename... _Args,
127 typename _Mgr = _Manager<_Tp>>
128 void __do_emplace(initializer_list<_Up> __il, _Args&&... __args)
129 {
130 reset();
131 _Mgr::_S_create(_M_storage, __il, std::forward<_Args>(__args)...);
132 _M_manager = &_Mgr::_S_manage;
133 }
134
135 template <typename _Res, typename _Tp, typename... _Args>
136 using __any_constructible
137 = enable_if<__and_<is_copy_constructible<_Tp>,
138 is_constructible<_Tp, _Args...>>::value,
139 _Res>;
140
141 template <typename _Tp, typename... _Args>
142 using __any_constructible_t
143 = typename __any_constructible<bool, _Tp, _Args...>::type;
144
145 template<typename _VTp, typename... _Args>
146 using __emplace_t
147 = typename __any_constructible<_VTp&, _VTp, _Args...>::type;
148
149 public:
150 // construct/destruct
151
152 /// Default constructor, creates an empty object.
153 constexpr any() noexcept : _M_manager(nullptr) { }
154
155 /// Copy constructor, copies the state of @p __other
156 any(const any& __other)
157 {
158 if (!__other.has_value())
159 _M_manager = nullptr;
160 else
161 {
162 _Arg __arg;
163 __arg._M_any = this;
164 __other._M_manager(_Op_clone, &__other, &__arg);
165 }
166 }
167
168 /**
169 * @brief Move constructor, transfer the state from @p __other
170 *
171 * @post @c !__other.has_value() (this postcondition is a GNU extension)
172 */
173 any(any&& __other) noexcept
174 {
175 if (!__other.has_value())
176 _M_manager = nullptr;
177 else
178 {
179 _Arg __arg;
180 __arg._M_any = this;
181 __other._M_manager(_Op_xfer, &__other, &__arg);
182 }
183 }
184
185 /// Construct with a copy of @p __value as the contained object.
186 template <typename _Tp, typename _VTp = _Decay_if_not_any<_Tp>,
187 typename _Mgr = _Manager<_VTp>,
188 enable_if_t<is_copy_constructible_v<_VTp>
189 && !__is_in_place_type_v<_VTp>, bool> = true>
190 any(_Tp&& __value)
191 : _M_manager(&_Mgr::_S_manage)
192 {
193 _Mgr::_S_create(_M_storage, std::forward<_Tp>(__value));
194 }
195
196 /// Construct with an object created from @p __args as the contained object.
197 template <typename _Tp, typename... _Args, typename _VTp = decay_t<_Tp>,
198 typename _Mgr = _Manager<_VTp>,
199 __any_constructible_t<_VTp, _Args&&...> = false>
200 explicit
201 any(in_place_type_t<_Tp>, _Args&&... __args)
202 : _M_manager(&_Mgr::_S_manage)
203 {
204 _Mgr::_S_create(_M_storage, std::forward<_Args>(__args)...);
205 }
206
207 /// Construct with an object created from @p __il and @p __args as
208 /// the contained object.
209 template <typename _Tp, typename _Up, typename... _Args,
210 typename _VTp = decay_t<_Tp>, typename _Mgr = _Manager<_VTp>,
211 __any_constructible_t<_VTp, initializer_list<_Up>&,
212 _Args&&...> = false>
213 explicit
214 any(in_place_type_t<_Tp>, initializer_list<_Up> __il, _Args&&... __args)
215 : _M_manager(&_Mgr::_S_manage)
216 {
217 _Mgr::_S_create(_M_storage, __il, std::forward<_Args>(__args)...);
218 }
219
220 /// Destructor, calls @c reset()
221 ~any() { reset(); }
222
223 // assignments
224
225 /// Copy the state of another object.
226 any&
227 operator=(const any& __rhs)
228 {
229 *this = any(__rhs);
230 return *this;
231 }
232
233 /**
234 * @brief Move assignment operator
235 *
236 * @post @c !__rhs.has_value() (not guaranteed for other implementations)
237 */
238 any&
239 operator=(any&& __rhs) noexcept
240 {
241 if (!__rhs.has_value())
242 reset();
243 else if (this != &__rhs)
244 {
245 reset();
246 _Arg __arg;
247 __arg._M_any = this;
248 __rhs._M_manager(_Op_xfer, &__rhs, &__arg);
249 }
250 return *this;
251 }
252
253 /// Store a copy of @p __rhs as the contained object.
254 template<typename _Tp>
255 enable_if_t<is_copy_constructible<_Decay_if_not_any<_Tp>>::value, any&>
256 operator=(_Tp&& __rhs)
257 {
258 *this = any(std::forward<_Tp>(__rhs));
259 return *this;
260 }
261
262 /// Emplace with an object created from @p __args as the contained object.
263 template <typename _Tp, typename... _Args>
264 __emplace_t<decay_t<_Tp>, _Args...>
265 emplace(_Args&&... __args)
266 {
267 using _VTp = decay_t<_Tp>;
268 __do_emplace<_VTp>(std::forward<_Args>(__args)...);
269 return *any::_Manager<_VTp>::_S_access(_M_storage);
270 }
271
272 /// Emplace with an object created from @p __il and @p __args as
273 /// the contained object.
274 template <typename _Tp, typename _Up, typename... _Args>
275 __emplace_t<decay_t<_Tp>, initializer_list<_Up>&, _Args&&...>
276 emplace(initializer_list<_Up> __il, _Args&&... __args)
277 {
278 using _VTp = decay_t<_Tp>;
279 __do_emplace<_VTp, _Up>(__il, std::forward<_Args>(__args)...);
280 return *any::_Manager<_VTp>::_S_access(_M_storage);
281 }
282
283 // modifiers
284
285 /// If not empty, destroy the contained object.
286 void reset() noexcept
287 {
288 if (has_value())
289 {
290 _M_manager(_Op_destroy, this, nullptr);
291 _M_manager = nullptr;
292 }
293 }
294
295 /// Exchange state with another object.
296 void swap(any& __rhs) noexcept
297 {
298 if (!has_value() && !__rhs.has_value())
299 return;
300
301 if (has_value() && __rhs.has_value())
302 {
303 if (this == &__rhs)
304 return;
305
306 any __tmp;
307 _Arg __arg;
308 __arg._M_any = &__tmp;
309 __rhs._M_manager(_Op_xfer, &__rhs, &__arg);
310 __arg._M_any = &__rhs;
311 _M_manager(_Op_xfer, this, &__arg);
312 __arg._M_any = this;
313 __tmp._M_manager(_Op_xfer, &__tmp, &__arg);
314 }
315 else
316 {
317 any* __empty = !has_value() ? this : &__rhs;
318 any* __full = !has_value() ? &__rhs : this;
319 _Arg __arg;
320 __arg._M_any = __empty;
321 __full->_M_manager(_Op_xfer, __full, &__arg);
322 }
323 }
324
325 // observers
326
327 /// Reports whether there is a contained object or not.
328 bool has_value() const noexcept { return _M_manager != nullptr; }
329
330#if __cpp_rtti
331 /// The @c typeid of the contained object, or @c typeid(void) if empty.
332 const type_info& type() const noexcept
333 {
334 if (!has_value())
335 return typeid(void);
336 _Arg __arg;
337 _M_manager(_Op_get_type_info, this, &__arg);
338 return *__arg._M_typeinfo;
339 }
340#endif
341
342 /// @cond undocumented
343 template<typename _Tp>
344 static constexpr bool __is_valid_cast()
345 { return __or_<is_reference<_Tp>, is_copy_constructible<_Tp>>::value; }
346 /// @endcond
347
348 private:
349 enum _Op {
350 _Op_access, _Op_get_type_info, _Op_clone, _Op_destroy, _Op_xfer
351 };
352
353 union _Arg
354 {
355 void* _M_obj;
356 const std::type_info* _M_typeinfo;
357 any* _M_any;
358 };
359
360 void (*_M_manager)(_Op, const any*, _Arg*);
361 _Storage _M_storage;
362
363 /// @cond undocumented
364 template<typename _Tp>
365 friend void* __any_caster(const any* __any);
366 /// @endcond
367
368 // Manage in-place contained object.
369 template<typename _Tp>
370 struct _Manager_internal
371 {
372 static void
373 _S_manage(_Op __which, const any* __anyp, _Arg* __arg);
374
375 template<typename _Up>
376 static void
377 _S_create(_Storage& __storage, _Up&& __value)
378 {
379 void* __addr = &__storage._M_buffer;
380 ::new (__addr) _Tp(std::forward<_Up>(__value));
381 }
382
383 template<typename... _Args>
384 static void
385 _S_create(_Storage& __storage, _Args&&... __args)
386 {
387 void* __addr = &__storage._M_buffer;
388 ::new (__addr) _Tp(std::forward<_Args>(__args)...);
389 }
390
391 static _Tp*
392 _S_access(const _Storage& __storage)
393 {
394 // The contained object is in __storage._M_buffer
395 const void* __addr = &__storage._M_buffer;
396 return static_cast<_Tp*>(const_cast<void*>(__addr));
397 }
398 };
399
400 // Manage external contained object.
401 template<typename _Tp>
402 struct _Manager_external
403 {
404 static void
405 _S_manage(_Op __which, const any* __anyp, _Arg* __arg);
406
407 template<typename _Up>
408 static void
409 _S_create(_Storage& __storage, _Up&& __value)
410 {
411 __storage._M_ptr = new _Tp(std::forward<_Up>(__value));
412 }
413 template<typename... _Args>
414 static void
415 _S_create(_Storage& __storage, _Args&&... __args)
416 {
417 __storage._M_ptr = new _Tp(std::forward<_Args>(__args)...);
418 }
419 static _Tp*
420 _S_access(const _Storage& __storage)
421 {
422 // The contained object is in *__storage._M_ptr
423 return static_cast<_Tp*>(__storage._M_ptr);
424 }
425 };
426 };
427
428 /// Exchange the states of two @c any objects.
429 inline void swap(any& __x, any& __y) noexcept { __x.swap(__y); }
430
431 /// Create an `any` holding a `_Tp` constructed from `__args...`.
432 template <typename _Tp, typename... _Args>
433 inline
434 enable_if_t<is_constructible_v<any, in_place_type_t<_Tp>, _Args...>, any>
435 make_any(_Args&&... __args)
436 {
437 return any(in_place_type<_Tp>, std::forward<_Args>(__args)...);
438 }
439
440 /// Create an `any` holding a `_Tp` constructed from `__il` and `__args...`.
441 template <typename _Tp, typename _Up, typename... _Args>
442 inline
443 enable_if_t<is_constructible_v<any, in_place_type_t<_Tp>,
444 initializer_list<_Up>&, _Args...>, any>
445 make_any(initializer_list<_Up> __il, _Args&&... __args)
446 {
447 return any(in_place_type<_Tp>, __il, std::forward<_Args>(__args)...);
448 }
449
450 /**
451 * @brief Access the contained object.
452 *
453 * @tparam _ValueType A const-reference or CopyConstructible type.
454 * @param __any The object to access.
455 * @return The contained object.
456 * @throw bad_any_cast If <code>
457 * __any.type() != typeid(remove_reference_t<_ValueType>)
458 * </code>
459 */
460 template<typename _ValueType>
461 inline _ValueType any_cast(const any& __any)
462 {
463 using _Up = __remove_cvref_t<_ValueType>;
464 static_assert(any::__is_valid_cast<_ValueType>(),
465 "Template argument must be a reference or CopyConstructible type");
466 static_assert(is_constructible_v<_ValueType, const _Up&>,
467 "Template argument must be constructible from a const value.");
468 auto __p = any_cast<_Up>(&__any);
469 if (__p)
470 return static_cast<_ValueType>(*__p);
471 __throw_bad_any_cast();
472 }
473
474 /**
475 * @brief Access the contained object.
476 *
477 * @tparam _ValueType A reference or CopyConstructible type.
478 * @param __any The object to access.
479 * @return The contained object.
480 * @throw bad_any_cast If <code>
481 * __any.type() != typeid(remove_reference_t<_ValueType>)
482 * </code>
483 *
484 * @{
485 */
486 template<typename _ValueType>
487 inline _ValueType any_cast(any& __any)
488 {
489 using _Up = __remove_cvref_t<_ValueType>;
490 static_assert(any::__is_valid_cast<_ValueType>(),
491 "Template argument must be a reference or CopyConstructible type");
492 static_assert(is_constructible_v<_ValueType, _Up&>,
493 "Template argument must be constructible from an lvalue.");
494 auto __p = any_cast<_Up>(&__any);
495 if (__p)
496 return static_cast<_ValueType>(*__p);
497 __throw_bad_any_cast();
498 }
499
500 template<typename _ValueType>
501 inline _ValueType any_cast(any&& __any)
502 {
503 using _Up = __remove_cvref_t<_ValueType>;
504 static_assert(any::__is_valid_cast<_ValueType>(),
505 "Template argument must be a reference or CopyConstructible type");
506 static_assert(is_constructible_v<_ValueType, _Up>,
507 "Template argument must be constructible from an rvalue.");
508 auto __p = any_cast<_Up>(&__any);
509 if (__p)
510 return static_cast<_ValueType>(std::move(*__p));
511 __throw_bad_any_cast();
512 }
513 /// @}
514
515 /// @cond undocumented
516 template<typename _Tp>
517 void* __any_caster(const any* __any)
518 {
519 // any_cast<T> returns non-null if __any->type() == typeid(T) and
520 // typeid(T) ignores cv-qualifiers so remove them:
521 using _Up = remove_cv_t<_Tp>;
522 // The contained value has a decayed type, so if decay_t<U> is not U,
523 // then it's not possible to have a contained value of type U:
524 if constexpr (!is_same_v<decay_t<_Up>, _Up>)
525 return nullptr;
526 // Only copy constructible types can be used for contained values:
527 else if constexpr (!is_copy_constructible_v<_Up>)
528 return nullptr;
529 // First try comparing function addresses, which works without RTTI
530 else if (__any->_M_manager == &any::_Manager<_Up>::_S_manage
531#if __cpp_rtti
532 || __any->type() == typeid(_Tp)
533#endif
534 )
535 {
536 return any::_Manager<_Up>::_S_access(__any->_M_storage);
537 }
538 return nullptr;
539 }
540 /// @endcond
541
542 /**
543 * @brief Access the contained object.
544 *
545 * @tparam _ValueType The type of the contained object.
546 * @param __any A pointer to the object to access.
547 * @return The address of the contained object if <code>
548 * __any != nullptr && __any.type() == typeid(_ValueType)
549 * </code>, otherwise a null pointer.
550 *
551 * @{
552 */
553 template<typename _ValueType>
554 inline const _ValueType* any_cast(const any* __any) noexcept
555 {
556 if constexpr (is_object_v<_ValueType>)
557 if (__any)
558 return static_cast<_ValueType*>(__any_caster<_ValueType>(__any));
559 return nullptr;
560 }
561
562 template<typename _ValueType>
563 inline _ValueType* any_cast(any* __any) noexcept
564 {
565 if constexpr (is_object_v<_ValueType>)
566 if (__any)
567 return static_cast<_ValueType*>(__any_caster<_ValueType>(__any));
568 return nullptr;
569 }
570 /// @}
571
572 template<typename _Tp>
573 void
574 any::_Manager_internal<_Tp>::
575 _S_manage(_Op __which, const any* __any, _Arg* __arg)
576 {
577 // The contained object is in _M_storage._M_buffer
578 auto __ptr = reinterpret_cast<const _Tp*>(&__any->_M_storage._M_buffer);
579 switch (__which)
580 {
581 case _Op_access:
582 __arg->_M_obj = const_cast<_Tp*>(__ptr);
583 break;
584 case _Op_get_type_info:
585#if __cpp_rtti
586 __arg->_M_typeinfo = &typeid(_Tp);
587#endif
588 break;
589 case _Op_clone:
590 ::new(&__arg->_M_any->_M_storage._M_buffer) _Tp(*__ptr);
591 __arg->_M_any->_M_manager = __any->_M_manager;
592 break;
593 case _Op_destroy:
594 __ptr->~_Tp();
595 break;
596 case _Op_xfer:
597 ::new(&__arg->_M_any->_M_storage._M_buffer) _Tp
598 (std::move(*const_cast<_Tp*>(__ptr)));
599 __ptr->~_Tp();
600 __arg->_M_any->_M_manager = __any->_M_manager;
601 const_cast<any*>(__any)->_M_manager = nullptr;
602 break;
603 }
604 }
605
606 template<typename _Tp>
607 void
608 any::_Manager_external<_Tp>::
609 _S_manage(_Op __which, const any* __any, _Arg* __arg)
610 {
611 // The contained object is *_M_storage._M_ptr
612 auto __ptr = static_cast<const _Tp*>(__any->_M_storage._M_ptr);
613 switch (__which)
614 {
615 case _Op_access:
616 __arg->_M_obj = const_cast<_Tp*>(__ptr);
617 break;
618 case _Op_get_type_info:
619#if __cpp_rtti
620 __arg->_M_typeinfo = &typeid(_Tp);
621#endif
622 break;
623 case _Op_clone:
624 __arg->_M_any->_M_storage._M_ptr = new _Tp(*__ptr);
625 __arg->_M_any->_M_manager = __any->_M_manager;
626 break;
627 case _Op_destroy:
628 delete __ptr;
629 break;
630 case _Op_xfer:
631 __arg->_M_any->_M_storage._M_ptr = __any->_M_storage._M_ptr;
632 __arg->_M_any->_M_manager = __any->_M_manager;
633 const_cast<any*>(__any)->_M_manager = nullptr;
634 break;
635 }
636 }
637
638 /// @}
639
640 namespace __detail::__variant
641 {
642 template<typename> struct _Never_valueless_alt; // see <variant>
643
644 // Provide the strong exception-safety guarantee when emplacing an
645 // any into a variant.
646 template<>
647 struct _Never_valueless_alt<std::any>
648 : std::true_type
649 { };
650 } // namespace __detail::__variant
651
652_GLIBCXX_END_NAMESPACE_VERSION
653} // namespace std
654
655#endif // C++17
656#endif // _GLIBCXX_ANY