1// Implementation of std::function -*- C++ -*-
2
3// Copyright (C) 2004-2017 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/bits/function.h
26 * This is an internal header file, included by other library headers.
27 * Do not attempt to use it directly. @headername{functional}
28 */
29
30#ifndef _GLIBCXX_STD_FUNCTION_H
31#define _GLIBCXX_STD_FUNCTION_H 1
32
33#pragma GCC system_header
34
35#if __cplusplus < 201103L
36# include <bits/c++0x_warning.h>
37#else
38
39#if __cpp_rtti
40# include <typeinfo>
41#endif
42#include <bits/stl_function.h>
43#include <bits/invoke.h>
44#include <bits/refwrap.h>
45#include <bits/functexcept.h>
46
47namespace std _GLIBCXX_VISIBILITY(default)
48{
49_GLIBCXX_BEGIN_NAMESPACE_VERSION
50
51 /**
52 * Derives from @c unary_function or @c binary_function, or perhaps
53 * nothing, depending on the number of arguments provided. The
54 * primary template is the basis case, which derives nothing.
55 */
56 template<typename _Res, typename... _ArgTypes>
57 struct _Maybe_unary_or_binary_function { };
58
59 /// Derives from @c unary_function, as appropriate.
60 template<typename _Res, typename _T1>
61 struct _Maybe_unary_or_binary_function<_Res, _T1>
62 : std::unary_function<_T1, _Res> { };
63
64 /// Derives from @c binary_function, as appropriate.
65 template<typename _Res, typename _T1, typename _T2>
66 struct _Maybe_unary_or_binary_function<_Res, _T1, _T2>
67 : std::binary_function<_T1, _T2, _Res> { };
68
69
70 /**
71 * @brief Exception class thrown when class template function's
72 * operator() is called with an empty target.
73 * @ingroup exceptions
74 */
75 class bad_function_call : public std::exception
76 {
77 public:
78 virtual ~bad_function_call() noexcept;
79
80 const char* what() const noexcept;
81 };
82
83 /**
84 * Trait identifying "location-invariant" types, meaning that the
85 * address of the object (or any of its members) will not escape.
86 * Trivially copyable types are location-invariant and users can
87 * specialize this trait for other types.
88 */
89 template<typename _Tp>
90 struct __is_location_invariant
91 : is_trivially_copyable<_Tp>::type
92 { };
93
94 class _Undefined_class;
95
96 union _Nocopy_types
97 {
98 void* _M_object;
99 const void* _M_const_object;
100 void (*_M_function_pointer)();
101 void (_Undefined_class::*_M_member_pointer)();
102 };
103
104 union [[gnu::may_alias]] _Any_data
105 {
106 void* _M_access() { return &_M_pod_data[0]; }
107 const void* _M_access() const { return &_M_pod_data[0]; }
108
109 template<typename _Tp>
110 _Tp&
111 _M_access()
112 { return *static_cast<_Tp*>(_M_access()); }
113
114 template<typename _Tp>
115 const _Tp&
116 _M_access() const
117 { return *static_cast<const _Tp*>(_M_access()); }
118
119 _Nocopy_types _M_unused;
120 char _M_pod_data[sizeof(_Nocopy_types)];
121 };
122
123 enum _Manager_operation
124 {
125 __get_type_info,
126 __get_functor_ptr,
127 __clone_functor,
128 __destroy_functor
129 };
130
131 // Simple type wrapper that helps avoid annoying const problems
132 // when casting between void pointers and pointers-to-pointers.
133 template<typename _Tp>
134 struct _Simple_type_wrapper
135 {
136 _Simple_type_wrapper(_Tp __value) : __value(__value) { }
137
138 _Tp __value;
139 };
140
141 template<typename _Tp>
142 struct __is_location_invariant<_Simple_type_wrapper<_Tp> >
143 : __is_location_invariant<_Tp>
144 { };
145
146 template<typename _Signature>
147 class function;
148
149 /// Base class of all polymorphic function object wrappers.
150 class _Function_base
151 {
152 public:
153 static const std::size_t _M_max_size = sizeof(_Nocopy_types);
154 static const std::size_t _M_max_align = __alignof__(_Nocopy_types);
155
156 template<typename _Functor>
157 class _Base_manager
158 {
159 protected:
160 static const bool __stored_locally =
161 (__is_location_invariant<_Functor>::value
162 && sizeof(_Functor) <= _M_max_size
163 && __alignof__(_Functor) <= _M_max_align
164 && (_M_max_align % __alignof__(_Functor) == 0));
165
166 typedef integral_constant<bool, __stored_locally> _Local_storage;
167
168 // Retrieve a pointer to the function object
169 static _Functor*
170 _M_get_pointer(const _Any_data& __source)
171 {
172 const _Functor* __ptr =
173 __stored_locally? std::__addressof(__source._M_access<_Functor>())
174 /* have stored a pointer */ : __source._M_access<_Functor*>();
175 return const_cast<_Functor*>(__ptr);
176 }
177
178 // Clone a location-invariant function object that fits within
179 // an _Any_data structure.
180 static void
181 _M_clone(_Any_data& __dest, const _Any_data& __source, true_type)
182 {
183 ::new (__dest._M_access()) _Functor(__source._M_access<_Functor>());
184 }
185
186 // Clone a function object that is not location-invariant or
187 // that cannot fit into an _Any_data structure.
188 static void
189 _M_clone(_Any_data& __dest, const _Any_data& __source, false_type)
190 {
191 __dest._M_access<_Functor*>() =
192 new _Functor(*__source._M_access<_Functor*>());
193 }
194
195 // Destroying a location-invariant object may still require
196 // destruction.
197 static void
198 _M_destroy(_Any_data& __victim, true_type)
199 {
200 __victim._M_access<_Functor>().~_Functor();
201 }
202
203 // Destroying an object located on the heap.
204 static void
205 _M_destroy(_Any_data& __victim, false_type)
206 {
207 delete __victim._M_access<_Functor*>();
208 }
209
210 public:
211 static bool
212 _M_manager(_Any_data& __dest, const _Any_data& __source,
213 _Manager_operation __op)
214 {
215 switch (__op)
216 {
217#if __cpp_rtti
218 case __get_type_info:
219 __dest._M_access<const type_info*>() = &typeid(_Functor);
220 break;
221#endif
222 case __get_functor_ptr:
223 __dest._M_access<_Functor*>() = _M_get_pointer(__source);
224 break;
225
226 case __clone_functor:
227 _M_clone(__dest, __source, _Local_storage());
228 break;
229
230 case __destroy_functor:
231 _M_destroy(__dest, _Local_storage());
232 break;
233 }
234 return false;
235 }
236
237 static void
238 _M_init_functor(_Any_data& __functor, _Functor&& __f)
239 { _M_init_functor(__functor, std::move(__f), _Local_storage()); }
240
241 template<typename _Signature>
242 static bool
243 _M_not_empty_function(const function<_Signature>& __f)
244 { return static_cast<bool>(__f); }
245
246 template<typename _Tp>
247 static bool
248 _M_not_empty_function(_Tp* __fp)
249 { return __fp != nullptr; }
250
251 template<typename _Class, typename _Tp>
252 static bool
253 _M_not_empty_function(_Tp _Class::* __mp)
254 { return __mp != nullptr; }
255
256 template<typename _Tp>
257 static bool
258 _M_not_empty_function(const _Tp&)
259 { return true; }
260
261 private:
262 static void
263 _M_init_functor(_Any_data& __functor, _Functor&& __f, true_type)
264 { ::new (__functor._M_access()) _Functor(std::move(__f)); }
265
266 static void
267 _M_init_functor(_Any_data& __functor, _Functor&& __f, false_type)
268 { __functor._M_access<_Functor*>() = new _Functor(std::move(__f)); }
269 };
270
271 _Function_base() : _M_manager(nullptr) { }
272
273 ~_Function_base()
274 {
275 if (_M_manager)
276 _M_manager(_M_functor, _M_functor, __destroy_functor);
277 }
278
279 bool _M_empty() const { return !_M_manager; }
280
281 typedef bool (*_Manager_type)(_Any_data&, const _Any_data&,
282 _Manager_operation);
283
284 _Any_data _M_functor;
285 _Manager_type _M_manager;
286 };
287
288 template<typename _Signature, typename _Functor>
289 class _Function_handler;
290
291 template<typename _Res, typename _Functor, typename... _ArgTypes>
292 class _Function_handler<_Res(_ArgTypes...), _Functor>
293 : public _Function_base::_Base_manager<_Functor>
294 {
295 typedef _Function_base::_Base_manager<_Functor> _Base;
296
297 public:
298 static _Res
299 _M_invoke(const _Any_data& __functor, _ArgTypes&&... __args)
300 {
301 return (*_Base::_M_get_pointer(__functor))(
302 std::forward<_ArgTypes>(__args)...);
303 }
304 };
305
306 template<typename _Functor, typename... _ArgTypes>
307 class _Function_handler<void(_ArgTypes...), _Functor>
308 : public _Function_base::_Base_manager<_Functor>
309 {
310 typedef _Function_base::_Base_manager<_Functor> _Base;
311
312 public:
313 static void
314 _M_invoke(const _Any_data& __functor, _ArgTypes&&... __args)
315 {
316 (*_Base::_M_get_pointer(__functor))(
317 std::forward<_ArgTypes>(__args)...);
318 }
319 };
320
321 template<typename _Class, typename _Member, typename _Res,
322 typename... _ArgTypes>
323 class _Function_handler<_Res(_ArgTypes...), _Member _Class::*>
324 : public _Function_handler<void(_ArgTypes...), _Member _Class::*>
325 {
326 typedef _Function_handler<void(_ArgTypes...), _Member _Class::*>
327 _Base;
328
329 public:
330 static _Res
331 _M_invoke(const _Any_data& __functor, _ArgTypes&&... __args)
332 {
333 return std::__invoke(_Base::_M_get_pointer(__functor)->__value,
334 std::forward<_ArgTypes>(__args)...);
335 }
336 };
337
338 template<typename _Class, typename _Member, typename... _ArgTypes>
339 class _Function_handler<void(_ArgTypes...), _Member _Class::*>
340 : public _Function_base::_Base_manager<
341 _Simple_type_wrapper< _Member _Class::* > >
342 {
343 typedef _Member _Class::* _Functor;
344 typedef _Simple_type_wrapper<_Functor> _Wrapper;
345 typedef _Function_base::_Base_manager<_Wrapper> _Base;
346
347 public:
348 static bool
349 _M_manager(_Any_data& __dest, const _Any_data& __source,
350 _Manager_operation __op)
351 {
352 switch (__op)
353 {
354#if __cpp_rtti
355 case __get_type_info:
356 __dest._M_access<const type_info*>() = &typeid(_Functor);
357 break;
358#endif
359 case __get_functor_ptr:
360 __dest._M_access<_Functor*>() =
361 &_Base::_M_get_pointer(__source)->__value;
362 break;
363
364 default:
365 _Base::_M_manager(__dest, __source, __op);
366 }
367 return false;
368 }
369
370 static void
371 _M_invoke(const _Any_data& __functor, _ArgTypes&&... __args)
372 {
373 std::__invoke(_Base::_M_get_pointer(__functor)->__value,
374 std::forward<_ArgTypes>(__args)...);
375 }
376 };
377
378 template<typename _From, typename _To>
379 using __check_func_return_type
380 = __or_<is_void<_To>, is_same<_From, _To>, is_convertible<_From, _To>>;
381
382 /**
383 * @brief Primary class template for std::function.
384 * @ingroup functors
385 *
386 * Polymorphic function wrapper.
387 */
388 template<typename _Res, typename... _ArgTypes>
389 class function<_Res(_ArgTypes...)>
390 : public _Maybe_unary_or_binary_function<_Res, _ArgTypes...>,
391 private _Function_base
392 {
393 template<typename _Func,
394 typename _Res2 = typename result_of<_Func&(_ArgTypes...)>::type>
395 struct _Callable : __check_func_return_type<_Res2, _Res> { };
396
397 // Used so the return type convertibility checks aren't done when
398 // performing overload resolution for copy construction/assignment.
399 template<typename _Tp>
400 struct _Callable<function, _Tp> : false_type { };
401
402 template<typename _Cond, typename _Tp>
403 using _Requires = typename enable_if<_Cond::value, _Tp>::type;
404
405 public:
406 typedef _Res result_type;
407
408 // [3.7.2.1] construct/copy/destroy
409
410 /**
411 * @brief Default construct creates an empty function call wrapper.
412 * @post @c !(bool)*this
413 */
414 function() noexcept
415 : _Function_base() { }
416
417 /**
418 * @brief Creates an empty function call wrapper.
419 * @post @c !(bool)*this
420 */
421 function(nullptr_t) noexcept
422 : _Function_base() { }
423
424 /**
425 * @brief %Function copy constructor.
426 * @param __x A %function object with identical call signature.
427 * @post @c bool(*this) == bool(__x)
428 *
429 * The newly-created %function contains a copy of the target of @a
430 * __x (if it has one).
431 */
432 function(const function& __x);
433
434 /**
435 * @brief %Function move constructor.
436 * @param __x A %function object rvalue with identical call signature.
437 *
438 * The newly-created %function contains the target of @a __x
439 * (if it has one).
440 */
441 function(function&& __x) noexcept : _Function_base()
442 {
443 __x.swap(*this);
444 }
445
446 /**
447 * @brief Builds a %function that targets a copy of the incoming
448 * function object.
449 * @param __f A %function object that is callable with parameters of
450 * type @c T1, @c T2, ..., @c TN and returns a value convertible
451 * to @c Res.
452 *
453 * The newly-created %function object will target a copy of
454 * @a __f. If @a __f is @c reference_wrapper<F>, then this function
455 * object will contain a reference to the function object @c
456 * __f.get(). If @a __f is a NULL function pointer or NULL
457 * pointer-to-member, the newly-created object will be empty.
458 *
459 * If @a __f is a non-NULL function pointer or an object of type @c
460 * reference_wrapper<F>, this function will not throw.
461 */
462 template<typename _Functor,
463 typename = _Requires<__not_<is_same<_Functor, function>>, void>,
464 typename = _Requires<_Callable<_Functor>, void>>
465 function(_Functor);
466
467 /**
468 * @brief %Function assignment operator.
469 * @param __x A %function with identical call signature.
470 * @post @c (bool)*this == (bool)x
471 * @returns @c *this
472 *
473 * The target of @a __x is copied to @c *this. If @a __x has no
474 * target, then @c *this will be empty.
475 *
476 * If @a __x targets a function pointer or a reference to a function
477 * object, then this operation will not throw an %exception.
478 */
479 function&
480 operator=(const function& __x)
481 {
482 function(__x).swap(*this);
483 return *this;
484 }
485
486 /**
487 * @brief %Function move-assignment operator.
488 * @param __x A %function rvalue with identical call signature.
489 * @returns @c *this
490 *
491 * The target of @a __x is moved to @c *this. If @a __x has no
492 * target, then @c *this will be empty.
493 *
494 * If @a __x targets a function pointer or a reference to a function
495 * object, then this operation will not throw an %exception.
496 */
497 function&
498 operator=(function&& __x) noexcept
499 {
500 function(std::move(__x)).swap(*this);
501 return *this;
502 }
503
504 /**
505 * @brief %Function assignment to zero.
506 * @post @c !(bool)*this
507 * @returns @c *this
508 *
509 * The target of @c *this is deallocated, leaving it empty.
510 */
511 function&
512 operator=(nullptr_t) noexcept
513 {
514 if (_M_manager)
515 {
516 _M_manager(_M_functor, _M_functor, __destroy_functor);
517 _M_manager = nullptr;
518 _M_invoker = nullptr;
519 }
520 return *this;
521 }
522
523 /**
524 * @brief %Function assignment to a new target.
525 * @param __f A %function object that is callable with parameters of
526 * type @c T1, @c T2, ..., @c TN and returns a value convertible
527 * to @c Res.
528 * @return @c *this
529 *
530 * This %function object wrapper will target a copy of @a
531 * __f. If @a __f is @c reference_wrapper<F>, then this function
532 * object will contain a reference to the function object @c
533 * __f.get(). If @a __f is a NULL function pointer or NULL
534 * pointer-to-member, @c this object will be empty.
535 *
536 * If @a __f is a non-NULL function pointer or an object of type @c
537 * reference_wrapper<F>, this function will not throw.
538 */
539 template<typename _Functor>
540 _Requires<_Callable<typename decay<_Functor>::type>, function&>
541 operator=(_Functor&& __f)
542 {
543 function(std::forward<_Functor>(__f)).swap(*this);
544 return *this;
545 }
546
547 /// @overload
548 template<typename _Functor>
549 function&
550 operator=(reference_wrapper<_Functor> __f) noexcept
551 {
552 function(__f).swap(*this);
553 return *this;
554 }
555
556 // [3.7.2.2] function modifiers
557
558 /**
559 * @brief Swap the targets of two %function objects.
560 * @param __x A %function with identical call signature.
561 *
562 * Swap the targets of @c this function object and @a __f. This
563 * function will not throw an %exception.
564 */
565 void swap(function& __x) noexcept
566 {
567 std::swap(_M_functor, __x._M_functor);
568 std::swap(_M_manager, __x._M_manager);
569 std::swap(_M_invoker, __x._M_invoker);
570 }
571
572 // [3.7.2.3] function capacity
573
574 /**
575 * @brief Determine if the %function wrapper has a target.
576 *
577 * @return @c true when this %function object contains a target,
578 * or @c false when it is empty.
579 *
580 * This function will not throw an %exception.
581 */
582 explicit operator bool() const noexcept
583 { return !_M_empty(); }
584
585 // [3.7.2.4] function invocation
586
587 /**
588 * @brief Invokes the function targeted by @c *this.
589 * @returns the result of the target.
590 * @throws bad_function_call when @c !(bool)*this
591 *
592 * The function call operator invokes the target function object
593 * stored by @c this.
594 */
595 _Res operator()(_ArgTypes... __args) const;
596
597#if __cpp_rtti
598 // [3.7.2.5] function target access
599 /**
600 * @brief Determine the type of the target of this function object
601 * wrapper.
602 *
603 * @returns the type identifier of the target function object, or
604 * @c typeid(void) if @c !(bool)*this.
605 *
606 * This function will not throw an %exception.
607 */
608 const type_info& target_type() const noexcept;
609
610 /**
611 * @brief Access the stored target function object.
612 *
613 * @return Returns a pointer to the stored target function object,
614 * if @c typeid(_Functor).equals(target_type()); otherwise, a NULL
615 * pointer.
616 *
617 * This function does not throw exceptions.
618 *
619 * @{
620 */
621 template<typename _Functor> _Functor* target() noexcept;
622
623 template<typename _Functor> const _Functor* target() const noexcept;
624 // @}
625#endif
626
627 private:
628 using _Invoker_type = _Res (*)(const _Any_data&, _ArgTypes&&...);
629 _Invoker_type _M_invoker;
630 };
631
632#if __cpp_deduction_guides >= 201606
633 template<typename>
634 struct __function_guide_helper
635 { };
636
637 template<typename _Res, typename _Tp, bool _Nx, typename... _Args>
638 struct __function_guide_helper<
639 _Res (_Tp::*) (_Args...) noexcept(_Nx)
640 >
641 { using type = _Res(_Args...); };
642
643 template<typename _Res, typename _Tp, bool _Nx, typename... _Args>
644 struct __function_guide_helper<
645 _Res (_Tp::*) (_Args...) & noexcept(_Nx)
646 >
647 { using type = _Res(_Args...); };
648
649 template<typename _Res, typename _Tp, bool _Nx, typename... _Args>
650 struct __function_guide_helper<
651 _Res (_Tp::*) (_Args...) const noexcept(_Nx)
652 >
653 { using type = _Res(_Args...); };
654
655 template<typename _Res, typename _Tp, bool _Nx, typename... _Args>
656 struct __function_guide_helper<
657 _Res (_Tp::*) (_Args...) const & noexcept(_Nx)
658 >
659 { using type = _Res(_Args...); };
660
661 template<typename _Res, typename... _ArgTypes>
662 function(_Res(*)(_ArgTypes...)) -> function<_Res(_ArgTypes...)>;
663
664 template<typename _Functor, typename _Signature = typename
665 __function_guide_helper<decltype(&_Functor::operator())>::type>
666 function(_Functor) -> function<_Signature>;
667#endif
668
669 // Out-of-line member definitions.
670 template<typename _Res, typename... _ArgTypes>
671 function<_Res(_ArgTypes...)>::
672 function(const function& __x)
673 : _Function_base()
674 {
675 if (static_cast<bool>(__x))
676 {
677 __x._M_manager(_M_functor, __x._M_functor, __clone_functor);
678 _M_invoker = __x._M_invoker;
679 _M_manager = __x._M_manager;
680 }
681 }
682
683 template<typename _Res, typename... _ArgTypes>
684 template<typename _Functor, typename, typename>
685 function<_Res(_ArgTypes...)>::
686 function(_Functor __f)
687 : _Function_base()
688 {
689 typedef _Function_handler<_Res(_ArgTypes...), _Functor> _My_handler;
690
691 if (_My_handler::_M_not_empty_function(__f))
692 {
693 _My_handler::_M_init_functor(_M_functor, std::move(__f));
694 _M_invoker = &_My_handler::_M_invoke;
695 _M_manager = &_My_handler::_M_manager;
696 }
697 }
698
699 template<typename _Res, typename... _ArgTypes>
700 _Res
701 function<_Res(_ArgTypes...)>::
702 operator()(_ArgTypes... __args) const
703 {
704 if (_M_empty())
705 __throw_bad_function_call();
706 return _M_invoker(_M_functor, std::forward<_ArgTypes>(__args)...);
707 }
708
709#if __cpp_rtti
710 template<typename _Res, typename... _ArgTypes>
711 const type_info&
712 function<_Res(_ArgTypes...)>::
713 target_type() const noexcept
714 {
715 if (_M_manager)
716 {
717 _Any_data __typeinfo_result;
718 _M_manager(__typeinfo_result, _M_functor, __get_type_info);
719 return *__typeinfo_result._M_access<const type_info*>();
720 }
721 else
722 return typeid(void);
723 }
724
725 template<typename _Res, typename... _ArgTypes>
726 template<typename _Functor>
727 _Functor*
728 function<_Res(_ArgTypes...)>::
729 target() noexcept
730 {
731 const function* __const_this = this;
732 const _Functor* __func = __const_this->template target<_Functor>();
733 return const_cast<_Functor*>(__func);
734 }
735
736 template<typename _Res, typename... _ArgTypes>
737 template<typename _Functor>
738 const _Functor*
739 function<_Res(_ArgTypes...)>::
740 target() const noexcept
741 {
742 if (typeid(_Functor) == target_type() && _M_manager)
743 {
744 _Any_data __ptr;
745 _M_manager(__ptr, _M_functor, __get_functor_ptr);
746 return __ptr._M_access<const _Functor*>();
747 }
748 else
749 return nullptr;
750 }
751#endif
752
753 // [20.7.15.2.6] null pointer comparisons
754
755 /**
756 * @brief Compares a polymorphic function object wrapper against 0
757 * (the NULL pointer).
758 * @returns @c true if the wrapper has no target, @c false otherwise
759 *
760 * This function will not throw an %exception.
761 */
762 template<typename _Res, typename... _Args>
763 inline bool
764 operator==(const function<_Res(_Args...)>& __f, nullptr_t) noexcept
765 { return !static_cast<bool>(__f); }
766
767 /// @overload
768 template<typename _Res, typename... _Args>
769 inline bool
770 operator==(nullptr_t, const function<_Res(_Args...)>& __f) noexcept
771 { return !static_cast<bool>(__f); }
772
773 /**
774 * @brief Compares a polymorphic function object wrapper against 0
775 * (the NULL pointer).
776 * @returns @c false if the wrapper has no target, @c true otherwise
777 *
778 * This function will not throw an %exception.
779 */
780 template<typename _Res, typename... _Args>
781 inline bool
782 operator!=(const function<_Res(_Args...)>& __f, nullptr_t) noexcept
783 { return static_cast<bool>(__f); }
784
785 /// @overload
786 template<typename _Res, typename... _Args>
787 inline bool
788 operator!=(nullptr_t, const function<_Res(_Args...)>& __f) noexcept
789 { return static_cast<bool>(__f); }
790
791
792 // [20.7.15.2.7] specialized algorithms
793
794 /**
795 * @brief Swap the targets of two polymorphic function object wrappers.
796 *
797 * This function will not throw an %exception.
798 */
799 // _GLIBCXX_RESOLVE_LIB_DEFECTS
800 // 2062. Effect contradictions w/o no-throw guarantee of std::function swaps
801 template<typename _Res, typename... _Args>
802 inline void
803 swap(function<_Res(_Args...)>& __x, function<_Res(_Args...)>& __y) noexcept
804 { __x.swap(__y); }
805
806_GLIBCXX_END_NAMESPACE_VERSION
807} // namespace std
808
809#endif // C++11
810
811#endif // _GLIBCXX_STD_FUNCTION_H
812