libstdc++-v3/include/debug/forward_list

   1 // <forward_list> -*- C++ -*-
   2
   3 // Copyright (C) 2010-2024 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 debug/forward_list
  26  *  This file is a GNU debug extension to the Standard C++ Library.
  27  */
  28
  29 #ifndef _GLIBCXX_DEBUG_FORWARD_LIST
  30 #define _GLIBCXX_DEBUG_FORWARD_LIST 1
  31
  32 #pragma GCC system_header
  33
  34 #include <bits/c++config.h>
  35 namespace std _GLIBCXX_VISIBILITY(default) { namespace __debug {
  36   template<typename _Tp, typename _Allocator> class forward_list;
  37 } } // namespace std::__debug
  38
  39 #include <forward_list>
  40 #include <debug/safe_sequence.h>
  41 #include <debug/safe_container.h>
  42 #include <debug/safe_iterator.h>
  43
  44 // Special validity check for forward_list ranges.
  45 #define __glibcxx_check_valid_fl_range(_First,_Last,_Dist)              \
  46 _GLIBCXX_DEBUG_VERIFY(_First._M_valid_range(_Last, _Dist, false),       \
  47                       _M_message(__gnu_debug::__msg_valid_range)        \
  48                       ._M_iterator(_First, #_First)                     \
  49                       ._M_iterator(_Last, #_Last))
  50
  51 namespace __gnu_debug
  52 {
  53   /// Special iterators swap and invalidation for forward_list because of the
  54   /// before_begin iterator.
  55   template<typename _SafeSequence>
  56     class _Safe_forward_list
  57     : public _Safe_sequence<_SafeSequence>
  58     {
  59       _SafeSequence&
  60       _M_this() noexcept
  61       { return *static_cast<_SafeSequence*>(this); }
  62
  63       static void
  64       _M_swap_aux(_Safe_sequence_base& __lhs,
  65                   _Safe_iterator_base*& __lhs_iterators,
  66                   _Safe_sequence_base& __rhs,
  67                   _Safe_iterator_base*& __rhs_iterators);
  68
  69       void _M_swap_single(_Safe_sequence_base&) noexcept;
  70
  71     protected:
  72       void
  73       _M_invalidate_all()
  74       {
  75         using _Base_const_iterator = __decltype(_M_this()._M_base().cend());
  76         this->_M_invalidate_if([this](_Base_const_iterator __it)
  77         {
  78           return __it != _M_this()._M_base().cbefore_begin()
  79             && __it != _M_this()._M_base().cend(); });
  80       }
  81
  82       void _M_swap(_Safe_sequence_base&) noexcept;
  83     };
  84
  85    template<typename _SafeSequence>
  86     void
  87     _Safe_forward_list<_SafeSequence>::
  88     _M_swap_aux(_Safe_sequence_base& __lhs,
  89                 _Safe_iterator_base*& __lhs_iterators,
  90                 _Safe_sequence_base& __rhs,
  91                 _Safe_iterator_base*& __rhs_iterators)
  92     {
  93       using const_iterator = typename _SafeSequence::const_iterator;
  94       _Safe_iterator_base* __bbegin_its = 0;
  95       _Safe_iterator_base* __last_bbegin = 0;
  96       _SafeSequence& __rseq = static_cast<_SafeSequence&>(__rhs);
  97
  98       for (_Safe_iterator_base* __iter = __lhs_iterators; __iter;)
  99         {
 100           // Even iterator is cast to const_iterator, not a problem.
 101           _Safe_iterator_base* __victim_base = __iter;
 102           const_iterator* __victim =
 103             static_cast<const_iterator*>(__victim_base);
 104           __iter = __iter->_M_next;
 105           if (__victim->base() == __rseq._M_base().cbefore_begin())
 106             {
 107               __victim->_M_unlink();
 108               if (__lhs_iterators == __victim_base)
 109                 __lhs_iterators = __victim_base->_M_next;
 110               if (__bbegin_its)
 111                 {
 112                   __victim_base->_M_next = __bbegin_its;
 113                   __bbegin_its->_M_prior = __victim_base;
 114                 }
 115               else
 116                 __last_bbegin = __victim_base;
 117               __bbegin_its = __victim_base;
 118             }
 119           else
 120             __victim_base->_M_sequence = std::__addressof(__lhs);
 121         }
 122
 123       if (__bbegin_its)
 124         {
 125           if (__rhs_iterators)
 126             {
 127               __rhs_iterators->_M_prior = __last_bbegin;
 128               __last_bbegin->_M_next = __rhs_iterators;
 129             }
 130           __rhs_iterators = __bbegin_its;
 131         }
 132     }
 133
 134    template<typename _SafeSequence>
 135     void
 136     _Safe_forward_list<_SafeSequence>::
 137     _M_swap_single(_Safe_sequence_base& __other) noexcept
 138     {
 139       std::swap(_M_this()._M_iterators, __other._M_iterators);
 140       std::swap(_M_this()._M_const_iterators, __other._M_const_iterators);
 141       // Useless, always 1 on forward_list
 142       //std::swap(_M_this()_M_version, __other._M_version);
 143       _Safe_iterator_base* __this_its = _M_this()._M_iterators;
 144       _M_swap_aux(__other, __other._M_iterators,
 145                   _M_this(), _M_this()._M_iterators);
 146       _Safe_iterator_base* __this_const_its = _M_this()._M_const_iterators;
 147       _M_swap_aux(__other, __other._M_const_iterators,
 148                   _M_this(), _M_this()._M_const_iterators);
 149       _M_swap_aux(_M_this(), __this_its,
 150                   __other, __other._M_iterators);
 151       _M_swap_aux(_M_this(), __this_const_its,
 152                   __other, __other._M_const_iterators);
 153     }
 154
 155   /* Special forward_list _M_swap version that does not swap the
 156    * before-begin ownership.*/
 157    template<typename _SafeSequence>
 158     void
 159     _Safe_forward_list<_SafeSequence>::
 160     _M_swap(_Safe_sequence_base& __other) noexcept
 161     {
 162       // We need to lock both sequences to swap
 163       using namespace __gnu_cxx;
 164       __mutex *__this_mutex = &_M_this()._M_get_mutex();
 165       __mutex *__other_mutex =
 166         &static_cast<_SafeSequence&>(__other)._M_get_mutex();
 167       if (__this_mutex == __other_mutex)
 168         {
 169           __scoped_lock __lock(*__this_mutex);
 170           _M_swap_single(__other);
 171         }
 172       else
 173         {
 174           __scoped_lock __l1(__this_mutex < __other_mutex
 175                              ? *__this_mutex : *__other_mutex);
 176           __scoped_lock __l2(__this_mutex < __other_mutex
 177                              ? *__other_mutex : *__this_mutex);
 178           _M_swap_single(__other);
 179         }
 180     }
 181 }
 182
 183 namespace std _GLIBCXX_VISIBILITY(default)
 184 {
 185 namespace __debug
 186 {
 187   /// Class std::forward_list with safety/checking/debug instrumentation.
 188   template<typename _Tp, typename _Alloc = std::allocator<_Tp> >
 189     class forward_list
 190     : public __gnu_debug::_Safe_container<
 191         forward_list<_Tp, _Alloc>, _Alloc, __gnu_debug::_Safe_forward_list>,
 192       public _GLIBCXX_STD_C::forward_list<_Tp, _Alloc>
 193     {
 194       typedef _GLIBCXX_STD_C::forward_list<_Tp, _Alloc>         _Base;
 195       typedef __gnu_debug::_Safe_container<
 196         forward_list, _Alloc, __gnu_debug::_Safe_forward_list>  _Safe;
 197
 198       typedef typename _Base::iterator          _Base_iterator;
 199       typedef typename _Base::const_iterator    _Base_const_iterator;
 200
 201       template<typename _ItT, typename _SeqT, typename _CatT>
 202         friend class ::__gnu_debug::_Safe_iterator;
 203
 204       // Reference wrapper for base class. See PR libstdc++/90102.
 205       struct _Base_ref
 206       {
 207         _Base_ref(const _Base& __r) : _M_ref(__r) { }
 208
 209         const _Base& _M_ref;
 210       };
 211
 212     public:
 213       typedef typename _Base::reference         reference;
 214       typedef typename _Base::const_reference   const_reference;
 215
 216       typedef __gnu_debug::_Safe_iterator<
 217         _Base_iterator, forward_list>           iterator;
 218       typedef __gnu_debug::_Safe_iterator<
 219         _Base_const_iterator, forward_list>     const_iterator;
 220
 221       typedef typename _Base::size_type         size_type;
 222       typedef typename _Base::difference_type   difference_type;
 223
 224       typedef _Tp                               value_type;
 225       typedef typename _Base::allocator_type    allocator_type;
 226       typedef typename _Base::pointer           pointer;
 227       typedef typename _Base::const_pointer     const_pointer;
 228
 229       // 23.2.3.1 construct/copy/destroy:
 230
 231       forward_list() = default;
 232
 233       explicit
 234       forward_list(const allocator_type& __al) noexcept
 235       : _Base(__al) { }
 236
 237       forward_list(const forward_list& __list, const allocator_type& __al)
 238       : _Base(__list, __al)
 239       { }
 240
 241       forward_list(forward_list&& __list, const allocator_type& __al)
 242         noexcept(
 243           std::is_nothrow_constructible<_Base,
 244             _Base, const allocator_type&>::value )
 245       : _Safe(std::move(__list), __al),
 246         _Base(std::move(__list), __al)
 247       { }
 248
 249       explicit
 250       forward_list(size_type __n, const allocator_type& __al = allocator_type())
 251       : _Base(__n, __al)
 252       { }
 253
 254       forward_list(size_type __n, const __type_identity_t<_Tp>& __value,
 255                    const allocator_type& __al = allocator_type())
 256       : _Base(__n, __value, __al)
 257       { }
 258
 259       template<typename _InputIterator,
 260                typename = std::_RequireInputIter<_InputIterator>>
 261         forward_list(_InputIterator __first, _InputIterator __last,
 262                      const allocator_type& __al = allocator_type())
 263         : _Base(__gnu_debug::__base(
 264                   __glibcxx_check_valid_constructor_range(__first, __last)),
 265                 __gnu_debug::__base(__last), __al)
 266         { }
 267
 268       forward_list(const forward_list&) = default;
 269
 270       forward_list(forward_list&&) = default;
 271
 272       forward_list(std::initializer_list<_Tp> __il,
 273                    const allocator_type& __al = allocator_type())
 274       : _Base(__il, __al)
 275       { }
 276
 277       ~forward_list() = default;
 278
 279       forward_list(_Base_ref __x) : _Base(__x._M_ref) { }
 280
 281       forward_list&
 282       operator=(const forward_list&) = default;
 283
 284       forward_list&
 285       operator=(forward_list&&) = default;
 286
 287       forward_list&
 288       operator=(std::initializer_list<_Tp> __il)
 289       {
 290         _Base::operator=(__il);
 291         this->_M_invalidate_all();
 292         return *this;
 293       }
 294
 295       template<typename _InputIterator,
 296                typename = std::_RequireInputIter<_InputIterator>>
 297         void
 298         assign(_InputIterator __first, _InputIterator __last)
 299         {
 300           typename __gnu_debug::_Distance_traits<_InputIterator>::__type __dist;
 301           __glibcxx_check_valid_range2(__first, __last, __dist);
 302
 303           if (__dist.second >= __gnu_debug::__dp_sign)
 304             _Base::assign(__gnu_debug::__unsafe(__first),
 305                           __gnu_debug::__unsafe(__last));
 306           else
 307             _Base::assign(__first, __last);
 308
 309           this->_M_invalidate_all();
 310         }
 311
 312       void
 313       assign(size_type __n, const _Tp& __val)
 314       {
 315         _Base::assign(__n, __val);
 316         this->_M_invalidate_all();
 317       }
 318
 319       void
 320       assign(std::initializer_list<_Tp> __il)
 321       {
 322         _Base::assign(__il);
 323         this->_M_invalidate_all();
 324       }
 325
 326       using _Base::get_allocator;
 327
 328       // iterators:
 329
 330       [[__nodiscard__]]
 331       iterator
 332       before_begin() noexcept
 333       { return { _Base::before_begin(), this }; }
 334
 335       [[__nodiscard__]]
 336       const_iterator
 337       before_begin() const noexcept
 338       { return { _Base::before_begin(), this }; }
 339
 340       [[__nodiscard__]]
 341       iterator
 342       begin() noexcept
 343       { return { _Base::begin(), this }; }
 344
 345       [[__nodiscard__]]
 346       const_iterator
 347       begin() const noexcept
 348       { return { _Base::begin(), this }; }
 349
 350       [[__nodiscard__]]
 351       iterator
 352       end() noexcept
 353       { return { _Base::end(), this }; }
 354
 355       [[__nodiscard__]]
 356       const_iterator
 357       end() const noexcept
 358       { return { _Base::end(), this }; }
 359
 360       [[__nodiscard__]]
 361       const_iterator
 362       cbegin() const noexcept
 363       { return { _Base::cbegin(), this }; }
 364
 365       [[__nodiscard__]]
 366       const_iterator
 367       cbefore_begin() const noexcept
 368       { return { _Base::cbefore_begin(), this }; }
 369
 370       [[__nodiscard__]]
 371       const_iterator
 372       cend() const noexcept
 373       { return { _Base::cend(), this }; }
 374
 375       using _Base::empty;
 376       using _Base::max_size;
 377
 378       // element access:
 379
 380       [[__nodiscard__]]
 381       reference
 382       front()
 383       {
 384         __glibcxx_check_nonempty();
 385         return _Base::front();
 386       }
 387
 388       [[__nodiscard__]]
 389       const_reference
 390       front() const
 391       {
 392         __glibcxx_check_nonempty();
 393         return _Base::front();
 394       }
 395
 396       // modifiers:
 397
 398       using _Base::emplace_front;
 399       using _Base::push_front;
 400
 401       void
 402       pop_front()
 403       {
 404         __glibcxx_check_nonempty();
 405         this->_M_invalidate_if([this](_Base_const_iterator __it)
 406           { return __it == this->_M_base().cbegin(); });
 407         _Base::pop_front();
 408       }
 409
 410       template<typename... _Args>
 411         iterator
 412         emplace_after(const_iterator __pos, _Args&&... __args)
 413         {
 414           __glibcxx_check_insert_after(__pos);
 415           return { _Base::emplace_after(__pos.base(),
 416                                         std::forward<_Args>(__args)...),
 417                    this };
 418         }
 419
 420       iterator
 421       insert_after(const_iterator __pos, const _Tp& __val)
 422       {
 423         __glibcxx_check_insert_after(__pos);
 424         return { _Base::insert_after(__pos.base(), __val), this };
 425       }
 426
 427       iterator
 428       insert_after(const_iterator __pos, _Tp&& __val)
 429       {
 430         __glibcxx_check_insert_after(__pos);
 431         return { _Base::insert_after(__pos.base(), std::move(__val)), this };
 432       }
 433
 434       iterator
 435       insert_after(const_iterator __pos, size_type __n, const _Tp& __val)
 436       {
 437         __glibcxx_check_insert_after(__pos);
 438         return { _Base::insert_after(__pos.base(), __n, __val), this };
 439       }
 440
 441       template<typename _InputIterator,
 442                typename = std::_RequireInputIter<_InputIterator>>
 443         iterator
 444         insert_after(const_iterator __pos,
 445                      _InputIterator __first, _InputIterator __last)
 446         {
 447           typename __gnu_debug::_Distance_traits<_InputIterator>::__type __dist;
 448           __glibcxx_check_insert_range_after(__pos, __first, __last, __dist);
 449
 450           if (__dist.second >= __gnu_debug::__dp_sign)
 451             return
 452               {
 453                 _Base::insert_after(__pos.base(),
 454                                     __gnu_debug::__unsafe(__first),
 455                                     __gnu_debug::__unsafe(__last)),
 456                 this
 457               };
 458           else
 459             return { _Base::insert_after(__pos.base(), __first, __last), this };
 460         }
 461
 462       iterator
 463       insert_after(const_iterator __pos, std::initializer_list<_Tp> __il)
 464       {
 465         __glibcxx_check_insert_after(__pos);
 466         return { _Base::insert_after(__pos.base(), __il), this };
 467       }
 468
 469       iterator
 470       erase_after(const_iterator __pos)
 471       {
 472         __glibcxx_check_erase_after(__pos);
 473
 474         _Base_const_iterator __next = std::next(__pos.base());
 475         this->_M_invalidate_if([__next](_Base_const_iterator __it)
 476                                { return __it == __next; });
 477         return { _Base::erase_after(__pos.base()), this };
 478       }
 479
 480       iterator
 481       erase_after(const_iterator __pos, const_iterator __last)
 482       {
 483         __glibcxx_check_erase_range_after(__pos, __last);
 484         for (_Base_const_iterator __victim = std::next(__pos.base());
 485             __victim != __last.base(); ++__victim)
 486           {
 487             _GLIBCXX_DEBUG_VERIFY(__victim != _Base::cend(),
 488                                   _M_message(__gnu_debug::__msg_valid_range2)
 489                                   ._M_sequence(*this, "this")
 490                                   ._M_iterator(__pos, "pos")
 491                                   ._M_iterator(__last, "last"));
 492             this->_M_invalidate_if([__victim](_Base_const_iterator __it)
 493               { return __it == __victim; });
 494           }
 495
 496         return { _Base::erase_after(__pos.base(), __last.base()), this };
 497       }
 498
 499       void
 500       swap(forward_list& __list)
 501         noexcept( noexcept(declval<_Base&>().swap(__list)) )
 502       {
 503         _Safe::_M_swap(__list);
 504         _Base::swap(__list);
 505       }
 506
 507       void
 508       resize(size_type __sz)
 509       {
 510         this->_M_detach_singular();
 511
 512         // if __sz < size(), invalidate all iterators in [begin+__sz, end()
 513         _Base_iterator __victim = _Base::begin();
 514         _Base_iterator __end = _Base::end();
 515         for (size_type __i = __sz; __victim != __end && __i > 0; --__i)
 516           ++__victim;
 517
 518         for (; __victim != __end; ++__victim)
 519           {
 520             this->_M_invalidate_if([__victim](_Base_const_iterator __it)
 521               { return __it == __victim; });
 522           }
 523
 524         __try
 525           {
 526             _Base::resize(__sz);
 527           }
 528         __catch(...)
 529           {
 530             this->_M_revalidate_singular();
 531             __throw_exception_again;
 532           }
 533       }
 534
 535       void
 536       resize(size_type __sz, const value_type& __val)
 537       {
 538         this->_M_detach_singular();
 539
 540         // if __sz < size(), invalidate all iterators in [begin+__sz, end())
 541         _Base_iterator __victim = _Base::begin();
 542         _Base_iterator __end = _Base::end();
 543         for (size_type __i = __sz; __victim != __end && __i > 0; --__i)
 544           ++__victim;
 545
 546         for (; __victim != __end; ++__victim)
 547           {
 548             this->_M_invalidate_if([__victim](_Base_const_iterator __it)
 549               { return __it == __victim; });
 550           }
 551
 552         __try
 553           {
 554             _Base::resize(__sz, __val);
 555           }
 556         __catch(...)
 557           {
 558             this->_M_revalidate_singular();
 559             __throw_exception_again;
 560           }
 561       }
 562
 563       void
 564       clear() noexcept
 565       {
 566         _Base::clear();
 567         this->_M_invalidate_all();
 568       }
 569
 570       // 23.2.3.5 forward_list operations:
 571       void
 572       splice_after(const_iterator __pos, forward_list&& __list)
 573       {
 574         __glibcxx_check_insert_after(__pos);
 575         _GLIBCXX_DEBUG_VERIFY(std::__addressof(__list) != this,
 576                               _M_message(__gnu_debug::__msg_self_splice)
 577                               ._M_sequence(*this, "this"));
 578         _GLIBCXX_DEBUG_VERIFY(__list.get_allocator() == this->get_allocator(),
 579                               _M_message(__gnu_debug::__msg_splice_alloc)
 580                               ._M_sequence(*this)
 581                               ._M_sequence(__list, "__list"));
 582         this->_M_transfer_from_if(__list, [&__list](_Base_const_iterator __it)
 583           {
 584             return __it != __list._M_base().cbefore_begin()
 585                    && __it != __list._M_base().end();
 586           });
 587         _Base::splice_after(__pos.base(), std::move(__list));
 588       }
 589
 590       void
 591       splice_after(const_iterator __pos, forward_list& __list)
 592       { splice_after(__pos, std::move(__list)); }
 593
 594       void
 595       splice_after(const_iterator __pos, forward_list&& __list,
 596                    const_iterator __i)
 597       {
 598         __glibcxx_check_insert_after(__pos);
 599         _GLIBCXX_DEBUG_VERIFY(__i._M_before_dereferenceable(),
 600                               _M_message(__gnu_debug::__msg_splice_bad)
 601                               ._M_iterator(__i, "__i"));
 602         _GLIBCXX_DEBUG_VERIFY(__i._M_attached_to(std::__addressof(__list)),
 603                               _M_message(__gnu_debug::__msg_splice_other)
 604                               ._M_iterator(__i, "__i")
 605                               ._M_sequence(__list, "__list"));
 606         _GLIBCXX_DEBUG_VERIFY(__list.get_allocator() == this->get_allocator(),
 607                               _M_message(__gnu_debug::__msg_splice_alloc)
 608                               ._M_sequence(*this)
 609                               ._M_sequence(__list, "__list"));
 610
 611         // _GLIBCXX_RESOLVE_LIB_DEFECTS
 612         // 250. splicing invalidates iterators
 613         _Base_const_iterator __next = std::next(__i.base());
 614         this->_M_transfer_from_if(__list, [__next](_Base_const_iterator __it)
 615           { return __it == __next; });
 616         _Base::splice_after(__pos.base(), std::move(__list), __i.base());
 617       }
 618
 619       void
 620       splice_after(const_iterator __pos, forward_list& __list,
 621                    const_iterator __i)
 622       { splice_after(__pos, std::move(__list), __i); }
 623
 624       void
 625       splice_after(const_iterator __pos, forward_list&& __list,
 626                    const_iterator __before, const_iterator __last)
 627       {
 628         typename __gnu_debug::_Distance_traits<const_iterator>::__type __dist;
 629         auto __listptr = std::__addressof(__list);
 630         __glibcxx_check_insert_after(__pos);
 631         __glibcxx_check_valid_fl_range(__before, __last, __dist);
 632         _GLIBCXX_DEBUG_VERIFY(__before._M_attached_to(__listptr),
 633                               _M_message(__gnu_debug::__msg_splice_other)
 634                               ._M_sequence(__list, "list")
 635                               ._M_iterator(__before, "before"));
 636         _GLIBCXX_DEBUG_VERIFY(__before._M_dereferenceable()
 637                               || __before._M_is_before_begin(),
 638                               _M_message(__gnu_debug::__msg_valid_range2)
 639                               ._M_sequence(__list, "list")
 640                               ._M_iterator(__before, "before")
 641                               ._M_iterator(__last, "last"));
 642         _GLIBCXX_DEBUG_VERIFY(__before != __last,
 643                               _M_message(__gnu_debug::__msg_valid_range2)
 644                               ._M_sequence(__list, "list")
 645                               ._M_iterator(__before, "before")
 646                               ._M_iterator(__last, "last"));
 647         _GLIBCXX_DEBUG_VERIFY(__list.get_allocator() == this->get_allocator(),
 648                               _M_message(__gnu_debug::__msg_splice_alloc)
 649                               ._M_sequence(*this)
 650                               ._M_sequence(__list, "__list"));
 651
 652         for (_Base_const_iterator __tmp = std::next(__before.base());
 653              __tmp != __last.base(); ++__tmp)
 654           {
 655             _GLIBCXX_DEBUG_VERIFY(__tmp != __list._M_base().end(),
 656                                   _M_message(__gnu_debug::__msg_valid_range2)
 657                                   ._M_sequence(__list, "list")
 658                                   ._M_iterator(__before, "before")
 659                                   ._M_iterator(__last, "last"));
 660             _GLIBCXX_DEBUG_VERIFY(__listptr != this || __tmp != __pos.base(),
 661                                   _M_message(__gnu_debug::__msg_splice_overlap)
 662                                   ._M_iterator(__tmp, "position")
 663                                   ._M_iterator(__before, "before")
 664                                   ._M_iterator(__last, "last"));
 665             // _GLIBCXX_RESOLVE_LIB_DEFECTS
 666             // 250. splicing invalidates iterators
 667             this->_M_transfer_from_if(__list, [__tmp](_Base_const_iterator __it)
 668               { return __it == __tmp; });
 669           }
 670
 671         _Base::splice_after(__pos.base(), std::move(__list),
 672                             __before.base(), __last.base());
 673       }
 674
 675       void
 676       splice_after(const_iterator __pos, forward_list& __list,
 677                    const_iterator __before, const_iterator __last)
 678       { splice_after(__pos, std::move(__list), __before, __last); }
 679
 680     private:
 681 #if __cplusplus > 201703L
 682       using __remove_return_type = size_type;
 683 # define _GLIBCXX_FWDLIST_REMOVE_RETURN_TYPE_TAG \
 684       __attribute__((__abi_tag__("__cxx20")))
 685 # define _GLIBCXX20_ONLY(__expr) __expr
 686 #else
 687       using __remove_return_type = void;
 688 # define _GLIBCXX_FWDLIST_REMOVE_RETURN_TYPE_TAG
 689 # define _GLIBCXX20_ONLY(__expr)
 690 #endif
 691
 692     public:
 693       _GLIBCXX_FWDLIST_REMOVE_RETURN_TYPE_TAG
 694       __remove_return_type
 695       remove(const _Tp& __val)
 696       {
 697         if (!this->_M_iterators && !this->_M_const_iterators)
 698           return _Base::remove(__val);
 699
 700         size_type __removed __attribute__((__unused__)) = 0;
 701         _Base __to_destroy(get_allocator());
 702         _Base_const_iterator __x = _Base::cbefore_begin();
 703         _Base_const_iterator __old = __x++;
 704         while (__x != _Base::cend())
 705           {
 706             if (*__x == __val)
 707               {
 708                 _Base_const_iterator __next = std::next(__old);
 709                 this->_M_invalidate_if([__next](_Base_const_iterator __it)
 710                                        { return __it == __next; });
 711                 __to_destroy.splice_after(__to_destroy.cbefore_begin(),
 712                                           *this, __old);
 713                 __x = __old;
 714                 _GLIBCXX20_ONLY( __removed++ );
 715               }
 716
 717             __old = __x++;
 718           }
 719
 720         return _GLIBCXX20_ONLY( __removed );
 721       }
 722
 723       template<typename _Pred>
 724         __remove_return_type
 725         remove_if(_Pred __pred)
 726         {
 727           if (!this->_M_iterators && !this->_M_const_iterators)
 728             return _Base::remove_if(__pred);
 729
 730           size_type __removed __attribute__((__unused__)) = 0;
 731           _Base __to_destroy(get_allocator());
 732           _Base_iterator __x = _Base::before_begin();
 733           _Base_iterator __old = __x++;
 734           while (__x != _Base::end())
 735             {
 736               if (__pred(*__x))
 737                 {
 738                   this->_M_invalidate_if([__x](_Base_const_iterator __it)
 739                                          { return __it == __x; });
 740                   __to_destroy.splice_after(__to_destroy.cbefore_begin(),
 741                                             *this, __old);
 742                   __x = __old;
 743                   _GLIBCXX20_ONLY( __removed++ );
 744                 }
 745
 746               __old = __x++;
 747             }
 748
 749           return _GLIBCXX20_ONLY( __removed );
 750         }
 751
 752       _GLIBCXX_FWDLIST_REMOVE_RETURN_TYPE_TAG
 753       __remove_return_type
 754       unique()
 755       { return unique(std::equal_to<_Tp>()); }
 756
 757       template<typename _BinPred>
 758         __remove_return_type
 759         unique(_BinPred __binary_pred)
 760         {
 761           if (!this->_M_iterators && !this->_M_const_iterators)
 762             return _Base::unique(__binary_pred);
 763
 764           _Base_const_iterator __first = _Base::cbegin();
 765           _Base_const_iterator __last = _Base::cend();
 766           if (__first == __last)
 767             return _GLIBCXX20_ONLY(0);
 768
 769           size_type __removed __attribute__((__unused__)) = 0;
 770           _Base __to_destroy(get_allocator());
 771           _Base_const_iterator __next = std::next(__first);
 772           while (__next != __last)
 773             {
 774               if (__binary_pred(*__first, *__next))
 775                 {
 776                   this->_M_invalidate_if([__next](_Base_const_iterator __it)
 777                                          { return __it == __next; });
 778                   __to_destroy.splice_after(__to_destroy.cbefore_begin(),
 779                                             *this, __first);
 780                   __next = __first;
 781                   _GLIBCXX20_ONLY( __removed++ );
 782                 }
 783
 784               __first = __next++;
 785             }
 786
 787           return _GLIBCXX20_ONLY( __removed );
 788         }
 789
 790 #undef _GLIBCXX_FWDLIST_REMOVE_RETURN_TYPE_TAG
 791 #undef _GLIBCXX20_ONLY
 792
 793       void
 794       merge(forward_list&& __list)
 795       {
 796         if (this != std::__addressof(__list))
 797         {
 798           __glibcxx_check_sorted(_Base::begin(), _Base::end());
 799           __glibcxx_check_sorted(__list._M_base().begin(),
 800                                  __list._M_base().end());
 801           this->_M_transfer_from_if(__list, [&__list](_Base_const_iterator __it)
 802             {
 803               return __it != __list._M_base().cbefore_begin()
 804                      && __it != __list._M_base().cend();
 805             });
 806           _Base::merge(std::move(__list));
 807         }
 808       }
 809
 810       void
 811       merge(forward_list& __list)
 812       { merge(std::move(__list)); }
 813
 814       template<typename _Comp>
 815         void
 816         merge(forward_list&& __list, _Comp __comp)
 817         {
 818           if (this != std::__addressof(__list))
 819           {
 820             __glibcxx_check_sorted_pred(_Base::begin(), _Base::end(), __comp);
 821             __glibcxx_check_sorted_pred(__list._M_base().begin(),
 822                                         __list._M_base().end(), __comp);
 823             this->_M_transfer_from_if(__list,
 824                                       [&__list](_Base_const_iterator __it)
 825               {
 826                 return __it != __list._M_base().cbefore_begin()
 827                        && __it != __list._M_base().cend();
 828               });
 829             _Base::merge(std::move(__list), __comp);
 830           }
 831         }
 832
 833       template<typename _Comp>
 834         void
 835         merge(forward_list& __list, _Comp __comp)
 836         { merge(std::move(__list), __comp); }
 837
 838       using _Base::sort;
 839       using _Base::reverse;
 840
 841       _Base&
 842       _M_base() noexcept { return *this; }
 843
 844       const _Base&
 845       _M_base() const noexcept { return *this; }
 846     };
 847
 848 #if __cpp_deduction_guides >= 201606
 849   template<typename _InputIterator, typename _ValT
 850              = typename iterator_traits<_InputIterator>::value_type,
 851            typename _Allocator = allocator<_ValT>,
 852            typename = _RequireInputIter<_InputIterator>,
 853            typename = _RequireAllocator<_Allocator>>
 854     forward_list(_InputIterator, _InputIterator, _Allocator = _Allocator())
 855       -> forward_list<_ValT, _Allocator>;
 856
 857   template<typename _Tp, typename _Allocator = allocator<_Tp>,
 858            typename = _RequireAllocator<_Allocator>>
 859     forward_list(size_t, _Tp, _Allocator = _Allocator())
 860       -> forward_list<_Tp, _Allocator>;
 861 #endif
 862
 863   template<typename _Tp, typename _Alloc>
 864     bool
 865     operator==(const forward_list<_Tp, _Alloc>& __lx,
 866                const forward_list<_Tp, _Alloc>& __ly)
 867     { return __lx._M_base() == __ly._M_base(); }
 868
 869 #if __cpp_lib_three_way_comparison
 870   template<typename _Tp, typename _Alloc>
 871     constexpr __detail::__synth3way_t<_Tp>
 872     operator<=>(const forward_list<_Tp, _Alloc>& __x,
 873                 const forward_list<_Tp, _Alloc>& __y)
 874     { return __x._M_base() <=> __y._M_base(); }
 875 #else
 876   template<typename _Tp, typename _Alloc>
 877     inline bool
 878     operator<(const forward_list<_Tp, _Alloc>& __lx,
 879               const forward_list<_Tp, _Alloc>& __ly)
 880     { return __lx._M_base() < __ly._M_base(); }
 881
 882   template<typename _Tp, typename _Alloc>
 883     inline bool
 884     operator!=(const forward_list<_Tp, _Alloc>& __lx,
 885                const forward_list<_Tp, _Alloc>& __ly)
 886     { return !(__lx == __ly); }
 887
 888   /// Based on operator<
 889   template<typename _Tp, typename _Alloc>
 890     inline bool
 891     operator>(const forward_list<_Tp, _Alloc>& __lx,
 892               const forward_list<_Tp, _Alloc>& __ly)
 893     { return (__ly < __lx); }
 894
 895   /// Based on operator<
 896   template<typename _Tp, typename _Alloc>
 897     inline bool
 898     operator>=(const forward_list<_Tp, _Alloc>& __lx,
 899                const forward_list<_Tp, _Alloc>& __ly)
 900     { return !(__lx < __ly); }
 901
 902   /// Based on operator<
 903   template<typename _Tp, typename _Alloc>
 904     inline bool
 905     operator<=(const forward_list<_Tp, _Alloc>& __lx,
 906                const forward_list<_Tp, _Alloc>& __ly)
 907     { return !(__ly < __lx); }
 908 #endif // three-way comparison
 909
 910   /// See std::forward_list::swap().
 911   template<typename _Tp, typename _Alloc>
 912     inline void
 913     swap(forward_list<_Tp, _Alloc>& __lx, forward_list<_Tp, _Alloc>& __ly)
 914     noexcept(noexcept(__lx.swap(__ly)))
 915     { __lx.swap(__ly); }
 916
 917 } // namespace __debug
 918 } // namespace std
 919
 920 namespace __gnu_debug
 921 {
 922   template<typename _Tp, typename _Alloc>
 923     struct _BeforeBeginHelper<std::__debug::forward_list<_Tp, _Alloc> >
 924     {
 925       typedef std::__debug::forward_list<_Tp, _Alloc> _Sequence;
 926
 927       template<typename _Iterator>
 928         static bool
 929         _S_Is(const _Safe_iterator<_Iterator, _Sequence>& __it)
 930         {
 931           return
 932             __it.base() == __it._M_get_sequence()->_M_base().before_begin();
 933         }
 934
 935       template<typename _Iterator>
 936         static bool
 937         _S_Is_Beginnest(const _Safe_iterator<_Iterator, _Sequence>& __it)
 938         { return _S_Is(__it); }
 939     };
 940
 941   template<typename _Tp, typename _Alloc>
 942     struct _Sequence_traits<std::__debug::forward_list<_Tp, _Alloc> >
 943     {
 944       typedef typename std::__debug::forward_list<_Tp, _Alloc>::iterator _It;
 945
 946       static typename _Distance_traits<_It>::__type
 947       _S_size(const std::__debug::forward_list<_Tp, _Alloc>& __seq)
 948       {
 949         return __seq.empty()
 950           ? std::make_pair(0, __dp_exact) : std::make_pair(1, __dp_sign);
 951       }
 952     };
 953
 954 #ifndef _GLIBCXX_DEBUG_PEDANTIC
 955   template<class _Tp, class _Alloc>
 956     struct _Insert_range_from_self_is_safe<
 957       std::__debug::forward_list<_Tp, _Alloc> >
 958     { enum { __value = 1 }; };
 959 #endif
 960 }
 961
 962 #endif