1 // Implementation of std::function -*- C++ -*- 2 3 // Copyright (C) 2004-2019 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 include/bits/std_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 47 namespace std _GLIBCXX_VISIBILITY(default) 48 { 49 _GLIBCXX_BEGIN_NAMESPACE_VERSION 50 51 /** 52 * @brief Exception class thrown when class template function's 53 * operator() is called with an empty target. 54 * @ingroup exceptions 55 */ 56 class bad_function_call : public std::exception 57 { 58 public: 59 virtual ~bad_function_call() noexcept; 60 61 const char* what() const noexcept; 62 }; 63 64 /** 65 * Trait identifying "location-invariant" types, meaning that the 66 * address of the object (or any of its members) will not escape. 67 * Trivially copyable types are location-invariant and users can 68 * specialize this trait for other types. 69 */ 70 template<typename _Tp> 71 struct __is_location_invariant 72 : is_trivially_copyable<_Tp>::type 73 { }; 74 75 class _Undefined_class; 76 77 union _Nocopy_types 78 { 79 void* _M_object; 80 const void* _M_const_object; 81 void (*_M_function_pointer)(); 82 void (_Undefined_class::*_M_member_pointer)(); 83 }; 84 85 union [[gnu::may_alias]] _Any_data 86 { 87 void* _M_access() { return &_M_pod_data[0]; } 88 const void* _M_access() const { return &_M_pod_data[0]; } 89 90 template<typename _Tp> 91 _Tp& 92 _M_access() 93 { return *static_cast<_Tp*>(_M_access()); } 94 95 template<typename _Tp> 96 const _Tp& 97 _M_access() const 98 { return *static_cast<const _Tp*>(_M_access()); } 99 100 _Nocopy_types _M_unused; 101 char _M_pod_data[sizeof(_Nocopy_types)]; 102 }; 103 104 enum _Manager_operation 105 { 106 __get_type_info, 107 __get_functor_ptr, 108 __clone_functor, 109 __destroy_functor 110 }; 111 112 // Simple type wrapper that helps avoid annoying const problems 113 // when casting between void pointers and pointers-to-pointers. 114 template<typename _Tp> 115 struct _Simple_type_wrapper 116 { 117 _Simple_type_wrapper(_Tp __value) : __value(__value) { } 118 119 _Tp __value; 120 }; 121 122 template<typename _Tp> 123 struct __is_location_invariant<_Simple_type_wrapper<_Tp> > 124 : __is_location_invariant<_Tp> 125 { }; 126 127 template<typename _Signature> 128 class function; 129 130 /// Base class of all polymorphic function object wrappers. 131 class _Function_base 132 { 133 public: 134 static const size_t _M_max_size = sizeof(_Nocopy_types); 135 static const size_t _M_max_align = __alignof__(_Nocopy_types); 136 137 template<typename _Functor> 138 class _Base_manager 139 { 140 protected: 141 static const bool __stored_locally = 142 (__is_location_invariant<_Functor>::value 143 && sizeof(_Functor) <= _M_max_size 144 && __alignof__(_Functor) <= _M_max_align 145 && (_M_max_align % __alignof__(_Functor) == 0)); 146 147 typedef integral_constant<bool, __stored_locally> _Local_storage; 148 149 // Retrieve a pointer to the function object 150 static _Functor* 151 _M_get_pointer(const _Any_data& __source) 152 { 153 if _GLIBCXX17_CONSTEXPR (__stored_locally) 154 { 155 const _Functor& __f = __source._M_access<_Functor>(); 156 return const_cast<_Functor*>(std::__addressof(__f)); 157 } 158 else // have stored a pointer 159 return __source._M_access<_Functor*>(); 160 } 161 162 // Clone a location-invariant function object that fits within 163 // an _Any_data structure. 164 static void 165 _M_clone(_Any_data& __dest, const _Any_data& __source, true_type) 166 { 167 ::new (__dest._M_access()) _Functor(__source._M_access<_Functor>()); 168 } 169 170 // Clone a function object that is not location-invariant or 171 // that cannot fit into an _Any_data structure. 172 static void 173 _M_clone(_Any_data& __dest, const _Any_data& __source, false_type) 174 { 175 __dest._M_access<_Functor*>() = 176 new _Functor(*__source._M_access<const _Functor*>()); 177 } 178 179 // Destroying a location-invariant object may still require 180 // destruction. 181 static void 182 _M_destroy(_Any_data& __victim, true_type) 183 { 184 __victim._M_access<_Functor>().~_Functor(); 185 } 186 187 // Destroying an object located on the heap. 188 static void 189 _M_destroy(_Any_data& __victim, false_type) 190 { 191 delete __victim._M_access<_Functor*>(); 192 } 193 194 public: 195 static bool 196 _M_manager(_Any_data& __dest, const _Any_data& __source, 197 _Manager_operation __op) 198 { 199 switch (__op) 200 { 201 #if __cpp_rtti 202 case __get_type_info: 203 __dest._M_access<const type_info*>() = &typeid(_Functor); 204 break; 205 #endif 206 case __get_functor_ptr: 207 __dest._M_access<_Functor*>() = _M_get_pointer(__source); 208 break; 209 210 case __clone_functor: 211 _M_clone(__dest, __source, _Local_storage()); 212 break; 213 214 case __destroy_functor: 215 _M_destroy(__dest, _Local_storage()); 216 break; 217 } 218 return false; 219 } 220 221 static void 222 _M_init_functor(_Any_data& __functor, _Functor&& __f) 223 { _M_init_functor(__functor, std::move(__f), _Local_storage()); } 224 225 template<typename _Signature> 226 static bool 227 _M_not_empty_function(const function<_Signature>& __f) 228 { return static_cast<bool>(__f); } 229 230 template<typename _Tp> 231 static bool 232 _M_not_empty_function(_Tp* __fp) 233 { return __fp != nullptr; } 234 235 template<typename _Class, typename _Tp> 236 static bool 237 _M_not_empty_function(_Tp _Class::* __mp) 238 { return __mp != nullptr; } 239 240 template<typename _Tp> 241 static bool 242 _M_not_empty_function(const _Tp&) 243 { return true; } 244 245 private: 246 static void 247 _M_init_functor(_Any_data& __functor, _Functor&& __f, true_type) 248 { ::new (__functor._M_access()) _Functor(std::move(__f)); } 249 250 static void 251 _M_init_functor(_Any_data& __functor, _Functor&& __f, false_type) 252 { __functor._M_access<_Functor*>() = new _Functor(std::move(__f)); } 253 }; 254 255 _Function_base() : _M_manager(nullptr) { } 256 257 ~_Function_base() 258 { 259 if (_M_manager) 260 _M_manager(_M_functor, _M_functor, __destroy_functor); 261 } 262 263 bool _M_empty() const { return !_M_manager; } 264 265 typedef bool (*_Manager_type)(_Any_data&, const _Any_data&, 266 _Manager_operation); 267 268 _Any_data _M_functor; 269 _Manager_type _M_manager; 270 }; 271 272 template<typename _Signature, typename _Functor> 273 class _Function_handler; 274 275 template<typename _Res, typename _Functor, typename... _ArgTypes> 276 class _Function_handler<_Res(_ArgTypes...), _Functor> 277 : public _Function_base::_Base_manager<_Functor> 278 { 279 typedef _Function_base::_Base_manager<_Functor> _Base; 280 281 public: 282 static _Res 283 _M_invoke(const _Any_data& __functor, _ArgTypes&&... __args) 284 { 285 return (*_Base::_M_get_pointer(__functor))( 286 std::forward<_ArgTypes>(__args)...); 287 } 288 }; 289 290 template<typename _Functor, typename... _ArgTypes> 291 class _Function_handler<void(_ArgTypes...), _Functor> 292 : public _Function_base::_Base_manager<_Functor> 293 { 294 typedef _Function_base::_Base_manager<_Functor> _Base; 295 296 public: 297 static void 298 _M_invoke(const _Any_data& __functor, _ArgTypes&&... __args) 299 { 300 (*_Base::_M_get_pointer(__functor))( 301 std::forward<_ArgTypes>(__args)...); 302 } 303 }; 304 305 template<typename _Class, typename _Member, typename _Res, 306 typename... _ArgTypes> 307 class _Function_handler<_Res(_ArgTypes...), _Member _Class::*> 308 : public _Function_handler<void(_ArgTypes...), _Member _Class::*> 309 { 310 typedef _Function_handler<void(_ArgTypes...), _Member _Class::*> 311 _Base; 312 313 public: 314 static _Res 315 _M_invoke(const _Any_data& __functor, _ArgTypes&&... __args) 316 { 317 return std::__invoke(_Base::_M_get_pointer(__functor)->__value, 318 std::forward<_ArgTypes>(__args)...); 319 } 320 }; 321 322 template<typename _Class, typename _Member, typename... _ArgTypes> 323 class _Function_handler<void(_ArgTypes...), _Member _Class::*> 324 : public _Function_base::_Base_manager< 325 _Simple_type_wrapper< _Member _Class::* > > 326 { 327 typedef _Member _Class::* _Functor; 328 typedef _Simple_type_wrapper<_Functor> _Wrapper; 329 typedef _Function_base::_Base_manager<_Wrapper> _Base; 330 331 public: 332 static bool 333 _M_manager(_Any_data& __dest, const _Any_data& __source, 334 _Manager_operation __op) 335 { 336 switch (__op) 337 { 338 #if __cpp_rtti 339 case __get_type_info: 340 __dest._M_access<const type_info*>() = &typeid(_Functor); 341 break; 342 #endif 343 case __get_functor_ptr: 344 __dest._M_access<_Functor*>() = 345 &_Base::_M_get_pointer(__source)->__value; 346 break; 347 348 default: 349 _Base::_M_manager(__dest, __source, __op); 350 } 351 return false; 352 } 353 354 static void 355 _M_invoke(const _Any_data& __functor, _ArgTypes&&... __args) 356 { 357 std::__invoke(_Base::_M_get_pointer(__functor)->__value, 358 std::forward<_ArgTypes>(__args)...); 359 } 360 }; 361 362 /** 363 * @brief Primary class template for std::function. 364 * @ingroup functors 365 * 366 * Polymorphic function wrapper. 367 */ 368 template<typename _Res, typename... _ArgTypes> 369 class function<_Res(_ArgTypes...)> 370 : public _Maybe_unary_or_binary_function<_Res, _ArgTypes...>, 371 private _Function_base 372 { 373 template<typename _Func, 374 typename _Res2 = __invoke_result<_Func&, _ArgTypes...>> 375 struct _Callable 376 : __is_invocable_impl<_Res2, _Res>::type 377 { }; 378 379 // Used so the return type convertibility checks aren't done when 380 // performing overload resolution for copy construction/assignment. 381 template<typename _Tp> 382 struct _Callable<function, _Tp> : false_type { }; 383 384 template<typename _Cond, typename _Tp> 385 using _Requires = typename enable_if<_Cond::value, _Tp>::type; 386 387 public: 388 typedef _Res result_type; 389 390 // [3.7.2.1] construct/copy/destroy 391 392 /** 393 * @brief Default construct creates an empty function call wrapper. 394 * @post @c !(bool)*this 395 */ 396 function() noexcept 397 : _Function_base() { } 398 399 /** 400 * @brief Creates an empty function call wrapper. 401 * @post @c !(bool)*this 402 */ 403 function(nullptr_t) noexcept 404 : _Function_base() { } 405 406 /** 407 * @brief %Function copy constructor. 408 * @param __x A %function object with identical call signature. 409 * @post @c bool(*this) == bool(__x) 410 * 411 * The newly-created %function contains a copy of the target of @a 412 * __x (if it has one). 413 */ 414 function(const function& __x); 415 416 /** 417 * @brief %Function move constructor. 418 * @param __x A %function object rvalue with identical call signature. 419 * 420 * The newly-created %function contains the target of @a __x 421 * (if it has one). 422 */ 423 function(function&& __x) noexcept : _Function_base() 424 { 425 __x.swap(*this); 426 } 427 428 /** 429 * @brief Builds a %function that targets a copy of the incoming 430 * function object. 431 * @param __f A %function object that is callable with parameters of 432 * type @c T1, @c T2, ..., @c TN and returns a value convertible 433 * to @c Res. 434 * 435 * The newly-created %function object will target a copy of 436 * @a __f. If @a __f is @c reference_wrapper<F>, then this function 437 * object will contain a reference to the function object @c 438 * __f.get(). If @a __f is a NULL function pointer or NULL 439 * pointer-to-member, the newly-created object will be empty. 440 * 441 * If @a __f is a non-NULL function pointer or an object of type @c 442 * reference_wrapper<F>, this function will not throw. 443 */ 444 template<typename _Functor, 445 typename = _Requires<__not_<is_same<_Functor, function>>, void>, 446 typename = _Requires<_Callable<_Functor>, void>> 447 function(_Functor); 448 449 /** 450 * @brief %Function assignment operator. 451 * @param __x A %function with identical call signature. 452 * @post @c (bool)*this == (bool)x 453 * @returns @c *this 454 * 455 * The target of @a __x is copied to @c *this. If @a __x has no 456 * target, then @c *this will be empty. 457 * 458 * If @a __x targets a function pointer or a reference to a function 459 * object, then this operation will not throw an %exception. 460 */ 461 function& 462 operator=(const function& __x) 463 { 464 function(__x).swap(*this); 465 return *this; 466 } 467 468 /** 469 * @brief %Function move-assignment operator. 470 * @param __x A %function rvalue with identical call signature. 471 * @returns @c *this 472 * 473 * The target of @a __x is moved 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=(function&& __x) noexcept 481 { 482 function(std::move(__x)).swap(*this); 483 return *this; 484 } 485 486 /** 487 * @brief %Function assignment to zero. 488 * @post @c !(bool)*this 489 * @returns @c *this 490 * 491 * The target of @c *this is deallocated, leaving it empty. 492 */ 493 function& 494 operator=(nullptr_t) noexcept 495 { 496 if (_M_manager) 497 { 498 _M_manager(_M_functor, _M_functor, __destroy_functor); 499 _M_manager = nullptr; 500 _M_invoker = nullptr; 501 } 502 return *this; 503 } 504 505 /** 506 * @brief %Function assignment to a new target. 507 * @param __f A %function object that is callable with parameters of 508 * type @c T1, @c T2, ..., @c TN and returns a value convertible 509 * to @c Res. 510 * @return @c *this 511 * 512 * This %function object wrapper will target a copy of @a 513 * __f. If @a __f is @c reference_wrapper<F>, then this function 514 * object will contain a reference to the function object @c 515 * __f.get(). If @a __f is a NULL function pointer or NULL 516 * pointer-to-member, @c this object will be empty. 517 * 518 * If @a __f is a non-NULL function pointer or an object of type @c 519 * reference_wrapper<F>, this function will not throw. 520 */ 521 template<typename _Functor> 522 _Requires<_Callable<typename decay<_Functor>::type>, function&> 523 operator=(_Functor&& __f) 524 { 525 function(std::forward<_Functor>(__f)).swap(*this); 526 return *this; 527 } 528 529 /// @overload 530 template<typename _Functor> 531 function& 532 operator=(reference_wrapper<_Functor> __f) noexcept 533 { 534 function(__f).swap(*this); 535 return *this; 536 } 537 538 // [3.7.2.2] function modifiers 539 540 /** 541 * @brief Swap the targets of two %function objects. 542 * @param __x A %function with identical call signature. 543 * 544 * Swap the targets of @c this function object and @a __f. This 545 * function will not throw an %exception. 546 */ 547 void swap(function& __x) noexcept 548 { 549 std::swap(_M_functor, __x._M_functor); 550 std::swap(_M_manager, __x._M_manager); 551 std::swap(_M_invoker, __x._M_invoker); 552 } 553 554 // [3.7.2.3] function capacity 555 556 /** 557 * @brief Determine if the %function wrapper has a target. 558 * 559 * @return @c true when this %function object contains a target, 560 * or @c false when it is empty. 561 * 562 * This function will not throw an %exception. 563 */ 564 explicit operator bool() const noexcept 565 { return !_M_empty(); } 566 567 // [3.7.2.4] function invocation 568 569 /** 570 * @brief Invokes the function targeted by @c *this. 571 * @returns the result of the target. 572 * @throws bad_function_call when @c !(bool)*this 573 * 574 * The function call operator invokes the target function object 575 * stored by @c this. 576 */ 577 _Res operator()(_ArgTypes... __args) const; 578 579 #if __cpp_rtti 580 // [3.7.2.5] function target access 581 /** 582 * @brief Determine the type of the target of this function object 583 * wrapper. 584 * 585 * @returns the type identifier of the target function object, or 586 * @c typeid(void) if @c !(bool)*this. 587 * 588 * This function will not throw an %exception. 589 */ 590 const type_info& target_type() const noexcept; 591 592 /** 593 * @brief Access the stored target function object. 594 * 595 * @return Returns a pointer to the stored target function object, 596 * if @c typeid(_Functor).equals(target_type()); otherwise, a NULL 597 * pointer. 598 * 599 * This function does not throw exceptions. 600 * 601 * @{ 602 */ 603 template<typename _Functor> _Functor* target() noexcept; 604 605 template<typename _Functor> const _Functor* target() const noexcept; 606 // @} 607 #endif 608 609 private: 610 using _Invoker_type = _Res (*)(const _Any_data&, _ArgTypes&&...); 611 _Invoker_type _M_invoker; 612 }; 613 614 #if __cpp_deduction_guides >= 201606 615 template<typename> 616 struct __function_guide_helper 617 { }; 618 619 template<typename _Res, typename _Tp, bool _Nx, typename... _Args> 620 struct __function_guide_helper< 621 _Res (_Tp::*) (_Args...) noexcept(_Nx) 622 > 623 { using type = _Res(_Args...); }; 624 625 template<typename _Res, typename _Tp, bool _Nx, typename... _Args> 626 struct __function_guide_helper< 627 _Res (_Tp::*) (_Args...) & noexcept(_Nx) 628 > 629 { using type = _Res(_Args...); }; 630 631 template<typename _Res, typename _Tp, bool _Nx, typename... _Args> 632 struct __function_guide_helper< 633 _Res (_Tp::*) (_Args...) const noexcept(_Nx) 634 > 635 { using type = _Res(_Args...); }; 636 637 template<typename _Res, typename _Tp, bool _Nx, typename... _Args> 638 struct __function_guide_helper< 639 _Res (_Tp::*) (_Args...) const & noexcept(_Nx) 640 > 641 { using type = _Res(_Args...); }; 642 643 template<typename _Res, typename... _ArgTypes> 644 function(_Res(*)(_ArgTypes...)) -> function<_Res(_ArgTypes...)>; 645 646 template<typename _Functor, typename _Signature = typename 647 __function_guide_helper<decltype(&_Functor::operator())>::type> 648 function(_Functor) -> function<_Signature>; 649 #endif 650 651 // Out-of-line member definitions. 652 template<typename _Res, typename... _ArgTypes> 653 function<_Res(_ArgTypes...)>:: 654 function(const function& __x) 655 : _Function_base() 656 { 657 if (static_cast<bool>(__x)) 658 { 659 __x._M_manager(_M_functor, __x._M_functor, __clone_functor); 660 _M_invoker = __x._M_invoker; 661 _M_manager = __x._M_manager; 662 } 663 } 664 665 template<typename _Res, typename... _ArgTypes> 666 template<typename _Functor, typename, typename> 667 function<_Res(_ArgTypes...)>:: 668 function(_Functor __f) 669 : _Function_base() 670 { 671 typedef _Function_handler<_Res(_ArgTypes...), _Functor> _My_handler; 672 673 if (_My_handler::_M_not_empty_function(__f)) 674 { 675 _My_handler::_M_init_functor(_M_functor, std::move(__f)); 676 _M_invoker = &_My_handler::_M_invoke; 677 _M_manager = &_My_handler::_M_manager; 678 } 679 } 680 681 template<typename _Res, typename... _ArgTypes> 682 _Res 683 function<_Res(_ArgTypes...)>:: 684 operator()(_ArgTypes... __args) const 685 { 686 if (_M_empty()) 687 __throw_bad_function_call(); 688 return _M_invoker(_M_functor, std::forward<_ArgTypes>(__args)...); 689 } 690 691 #if __cpp_rtti 692 template<typename _Res, typename... _ArgTypes> 693 const type_info& 694 function<_Res(_ArgTypes...)>:: 695 target_type() const noexcept 696 { 697 if (_M_manager) 698 { 699 _Any_data __typeinfo_result; 700 _M_manager(__typeinfo_result, _M_functor, __get_type_info); 701 return *__typeinfo_result._M_access<const type_info*>(); 702 } 703 else 704 return typeid(void); 705 } 706 707 template<typename _Res, typename... _ArgTypes> 708 template<typename _Functor> 709 _Functor* 710 function<_Res(_ArgTypes...)>:: 711 target() noexcept 712 { 713 const function* __const_this = this; 714 const _Functor* __func = __const_this->template target<_Functor>(); 715 return const_cast<_Functor*>(__func); 716 } 717 718 template<typename _Res, typename... _ArgTypes> 719 template<typename _Functor> 720 const _Functor* 721 function<_Res(_ArgTypes...)>:: 722 target() const noexcept 723 { 724 if (typeid(_Functor) == target_type() && _M_manager) 725 { 726 _Any_data __ptr; 727 _M_manager(__ptr, _M_functor, __get_functor_ptr); 728 return __ptr._M_access<const _Functor*>(); 729 } 730 else 731 return nullptr; 732 } 733 #endif 734 735 // [20.7.15.2.6] null pointer comparisons 736 737 /** 738 * @brief Compares a polymorphic function object wrapper against 0 739 * (the NULL pointer). 740 * @returns @c true if the wrapper has no target, @c false otherwise 741 * 742 * This function will not throw an %exception. 743 */ 744 template<typename _Res, typename... _Args> 745 inline bool 746 operator==(const function<_Res(_Args...)>& __f, nullptr_t) noexcept 747 { return !static_cast<bool>(__f); } 748 749 /// @overload 750 template<typename _Res, typename... _Args> 751 inline bool 752 operator==(nullptr_t, const function<_Res(_Args...)>& __f) noexcept 753 { return !static_cast<bool>(__f); } 754 755 /** 756 * @brief Compares a polymorphic function object wrapper against 0 757 * (the NULL pointer). 758 * @returns @c false if the wrapper has no target, @c true 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 // [20.7.15.2.7] specialized algorithms 775 776 /** 777 * @brief Swap the targets of two polymorphic function object wrappers. 778 * 779 * This function will not throw an %exception. 780 */ 781 // _GLIBCXX_RESOLVE_LIB_DEFECTS 782 // 2062. Effect contradictions w/o no-throw guarantee of std::function swaps 783 template<typename _Res, typename... _Args> 784 inline void 785 swap(function<_Res(_Args...)>& __x, function<_Res(_Args...)>& __y) noexcept 786 { __x.swap(__y); } 787 788 #if __cplusplus >= 201703L 789 namespace __detail::__variant 790 { 791 template<typename> struct _Never_valueless_alt; // see <variant> 792 793 // Provide the strong exception-safety guarantee when emplacing a 794 // function into a variant. 795 template<typename _Signature> 796 struct _Never_valueless_alt<std::function<_Signature>> 797 : std::true_type 798 { }; 799 } // namespace __detail::__variant 800 #endif // C++17 801 802 _GLIBCXX_END_NAMESPACE_VERSION 803 } // namespace std 804 805 #endif // C++11 806 #endif // _GLIBCXX_STD_FUNCTION_H 807