debug/list

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// Debugging list implementation -*- C++ -*-

// Copyright (C) 2003-2026 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.

/** @file debug/list
 *  This file is a GNU debug extension to the Standard C++ Library.
 */

#ifndef _GLIBCXX_DEBUG_LIST
#define _GLIBCXX_DEBUG_LIST 1

#ifdef _GLIBCXX_SYSHDR
#pragma GCC system_header
#endif

#include <bits/c++config.h>
namespace std _GLIBCXX_VISIBILITY(default) { namespace __debug {
  template<typename _Tp, typename _Allocator> class list;
} } // namespace std::__debug

#include <list>
#include <debug/safe_sequence.h>
#include <debug/safe_container.h>
#include <debug/safe_iterator.h>

namespace std _GLIBCXX_VISIBILITY(default)
{
namespace __debug
{
  /// Class std::list with safety/checking/debug instrumentation.
  template<typename _Tp, typename _Allocator = std::allocator<_Tp> >
    class list
    : public __gnu_debug::_Safe_container<
        list<_Tp, _Allocator>, _Allocator,
        __gnu_debug::_Safe_node_sequence>,
      public _GLIBCXX_STD_C::list<_Tp, _Allocator>
    {
      typedef _GLIBCXX_STD_C::list<_Tp, _Allocator>             _Base;
      typedef __gnu_debug::_Safe_container<
        list, _Allocator, __gnu_debug::_Safe_node_sequence>     _Safe;

      typedef typename _Base::iterator          _Base_iterator;
      typedef typename _Base::const_iterator    _Base_const_iterator;
      typedef __gnu_debug::_Equal_to<_Base_const_iterator>      _Equal;
      typedef __gnu_debug::_Not_equal_to<_Base_const_iterator>  _Not_equal;

      template<typename _ItT, typename _SeqT, typename _CatT>
        friend class ::__gnu_debug::_Safe_iterator;

      // Reference wrapper for base class. Disambiguates list(const _Base&)
      // from copy constructor by requiring a user-defined conversion.
      // See PR libstdc++/90102.
      struct _Base_ref
      {
        _Base_ref(const _Base& __r) : _M_ref(__r) { }

        const _Base& _M_ref;
      };

    public:
      typedef typename _Base::reference                 reference;
      typedef typename _Base::const_reference           const_reference;

      typedef __gnu_debug::_Safe_iterator<_Base_iterator, list>
                                                        iterator;
      typedef __gnu_debug::_Safe_iterator<_Base_const_iterator, list>
                                                        const_iterator;

      typedef typename _Base::size_type                 size_type;
      typedef typename _Base::difference_type           difference_type;

      typedef _Tp                                       value_type;
      typedef _Allocator                                allocator_type;
      typedef typename _Base::pointer                   pointer;
      typedef typename _Base::const_pointer             const_pointer;
      typedef std::reverse_iterator<iterator>           reverse_iterator;
      typedef std::reverse_iterator<const_iterator>     const_reverse_iterator;

      // 23.2.2.1 construct/copy/destroy:

#if __cplusplus < 201103L
      list()
      : _Base() { }

      list(const list& __x)
      : _Base(__x) { }

      ~list() { }
#else
      list() = default;
      list(const list&) = default;
      list(list&&) = default;

      list(initializer_list<value_type> __l,
           const allocator_type& __a = allocator_type())
      : _Base(__l, __a) { }

      ~list() = default;

      list(const list& __x, const __type_identity_t<allocator_type>& __a)
      : _Base(__x, __a) { }

      list(list&& __x, const __type_identity_t<allocator_type>& __a)
        noexcept(
          std::is_nothrow_constructible<_Base,
            _Base, const allocator_type&>::value )
      : _Safe(std::move(__x), __a),
        _Base(std::move(__x), __a) { }
#endif

      explicit
      list(const _Allocator& __a) _GLIBCXX_NOEXCEPT
      : _Base(__a) { }

#if __cplusplus >= 201103L
      explicit
      list(size_type __n, const allocator_type& __a = allocator_type())
      : _Base(__n, __a) { }

      list(size_type __n, const __type_identity_t<_Tp>& __value,
           const _Allocator& __a = _Allocator())
      : _Base(__n, __value, __a) { }
#else
      explicit
      list(size_type __n, const _Tp& __value = _Tp(),
           const _Allocator& __a = _Allocator())
      : _Base(__n, __value, __a) { }
#endif

#if __cplusplus >= 201103L
      template<class _InputIterator,
               typename = std::_RequireInputIter<_InputIterator>>
#else
      template<class _InputIterator>
#endif
        list(_InputIterator __first, _InputIterator __last,
             const _Allocator& __a = _Allocator())
        : _Base(__gnu_debug::__base(
                  __glibcxx_check_valid_constructor_range(__first, __last)),
                __gnu_debug::__base(__last), __a)
        { }

#if __glibcxx_containers_ranges // C++ >= 23
      template<__detail::__container_compatible_range<_Tp> _Rg>
        list(from_range_t, _Rg&& __rg, const _Allocator& __a = _Allocator())
        : _Base(std::from_range, std::forward<_Rg>(__rg), __a)
        { }
#endif

      list(_Base_ref __x)
      : _Base(__x._M_ref) { }

#if __cplusplus >= 201103L
      list&
      operator=(const list&) = default;

      list&
      operator=(list&&) = default;

      list&
      operator=(initializer_list<value_type> __l)
      {
        this->_M_invalidate_all();
        _Base::operator=(__l);
        return *this;
      }

      void
      assign(initializer_list<value_type> __l)
      {
        _Base::assign(__l);
        this->_M_invalidate_all();
      }
#endif

#if __cplusplus >= 201103L
      template<class _InputIterator,
               typename = std::_RequireInputIter<_InputIterator>>
#else
      template<class _InputIterator>
#endif
        void
        assign(_InputIterator __first, _InputIterator __last)
        {
          typename __gnu_debug::_Distance_traits<_InputIterator>::__type __dist;
          __glibcxx_check_valid_range2(__first, __last, __dist);

          if (__dist.second >= __gnu_debug::__dp_sign)
            _Base::assign(__gnu_debug::__unsafe(__first),
                          __gnu_debug::__unsafe(__last));
          else
            _Base::assign(__first, __last);

          this->_M_invalidate_all();
        }

#if __glibcxx_containers_ranges // C++ >= 23
      template<__detail::__container_compatible_range<_Tp> _Rg>
        void
        assign_range(_Rg&& __rg)
        {
          // Have to reimplement this function, so that we use the debug
          // version of erase, which invalidates the correct iterators.

          static_assert(assignable_from<_Tp&, ranges::range_reference_t<_Rg>>);

          auto __first1 = _Base::begin();
          const auto __last1 = _Base::end();
          auto __first2 = ranges::begin(__rg);
          const auto __last2 = ranges::end(__rg);
          for (; __first1 != __last1 && __first2 != __last2;
               ++__first1, (void)++__first2)
            *__first1 = *__first2;
          if (__first2 == __last2)
            erase(const_iterator(__first1, this),
                  const_iterator(__last1, this));
          else
            _Base::insert_range(__last1,
                                ranges::subrange(std::move(__first2), __last2));
        }
#endif

      void
      assign(size_type __n, const _Tp& __t)
      {
        _Base::assign(__n, __t);
        this->_M_invalidate_all();
      }

      using _Base::get_allocator;

      // iterators:
      _GLIBCXX_NODISCARD
      iterator
      begin() _GLIBCXX_NOEXCEPT
      { return iterator(_Base::begin(), this); }

      _GLIBCXX_NODISCARD
      const_iterator
      begin() const _GLIBCXX_NOEXCEPT
      { return const_iterator(_Base::begin(), this); }

      _GLIBCXX_NODISCARD
      iterator
      end() _GLIBCXX_NOEXCEPT
      { return iterator(_Base::end(), this); }

      _GLIBCXX_NODISCARD
      const_iterator
      end() const _GLIBCXX_NOEXCEPT
      { return const_iterator(_Base::end(), this); }

      _GLIBCXX_NODISCARD
      reverse_iterator
      rbegin() _GLIBCXX_NOEXCEPT
      { return reverse_iterator(end()); }

      _GLIBCXX_NODISCARD
      const_reverse_iterator
      rbegin() const _GLIBCXX_NOEXCEPT
      { return const_reverse_iterator(end()); }

      _GLIBCXX_NODISCARD
      reverse_iterator
      rend() _GLIBCXX_NOEXCEPT
      { return reverse_iterator(begin()); }

      _GLIBCXX_NODISCARD
      const_reverse_iterator
      rend() const _GLIBCXX_NOEXCEPT
      { return const_reverse_iterator(begin()); }

#if __cplusplus >= 201103L
      [[__nodiscard__]]
      const_iterator
      cbegin() const noexcept
      { return const_iterator(_Base::begin(), this); }

      [[__nodiscard__]]
      const_iterator
      cend() const noexcept
      { return const_iterator(_Base::end(), this); }

      [[__nodiscard__]]
      const_reverse_iterator
      crbegin() const noexcept
      { return const_reverse_iterator(end()); }

      [[__nodiscard__]]
      const_reverse_iterator
      crend() const noexcept
      { return const_reverse_iterator(begin()); }
#endif

      // 23.2.2.2 capacity:
      using _Base::empty;
      using _Base::size;
      using _Base::max_size;

#if __cplusplus >= 201103L
      void
      resize(size_type __sz)
      {
        const list* __this = this;
        __this->_M_detach_singular();

        // if __sz < size(), invalidate all iterators in [begin + __sz, end())
        _Base_iterator __victim = _Base::begin();
        _Base_iterator __end = _Base::end();
        for (size_type __i = __sz; __victim != __end && __i > 0; --__i)
          ++__victim;

        for (; __victim != __end; ++__victim)
          this->_M_invalidate_if(_Equal(__victim));

        __try
          {
            _Base::resize(__sz);
          }
        __catch(...)
          {
            __this->_M_revalidate_singular();
            __throw_exception_again;
          }
      }

      void
      resize(size_type __sz, const _Tp& __c)
      {
        const list* __this = this;
        __this->_M_detach_singular();

        // if __sz < size(), invalidate all iterators in [begin + __sz, end())
        _Base_iterator __victim = _Base::begin();
        _Base_iterator __end = _Base::end();
        for (size_type __i = __sz; __victim != __end && __i > 0; --__i)
          ++__victim;

        for (; __victim != __end; ++__victim)
          this->_M_invalidate_if(_Equal(__victim));

        __try
          {
            _Base::resize(__sz, __c);
          }
        __catch(...)
          {
            __this->_M_revalidate_singular();
            __throw_exception_again;
          }
      }
#else
      void
      resize(size_type __sz, _Tp __c = _Tp())
      {
        const list* __this = this;
        __this->_M_detach_singular();

        // if __sz < size(), invalidate all iterators in [begin + __sz, end())
        _Base_iterator __victim = _Base::begin();
        _Base_iterator __end = _Base::end();
        for (size_type __i = __sz; __victim != __end && __i > 0; --__i)
          ++__victim;

        for (; __victim != __end; ++__victim)
          this->_M_invalidate_if(_Equal(__victim));

        __try
          {
            _Base::resize(__sz, __c);
          }
        __catch(...)
          {
            __this->_M_revalidate_singular();
            __throw_exception_again;
          }
      }
#endif

      // element access:
      _GLIBCXX_NODISCARD
      reference
      front() _GLIBCXX_NOEXCEPT
      {
        __glibcxx_check_nonempty();
        return _Base::front();
      }

      _GLIBCXX_NODISCARD
      const_reference
      front() const _GLIBCXX_NOEXCEPT
      {
        __glibcxx_check_nonempty();
        return _Base::front();
      }

      _GLIBCXX_NODISCARD
      reference
      back() _GLIBCXX_NOEXCEPT
      {
        __glibcxx_check_nonempty();
        return _Base::back();
      }

      _GLIBCXX_NODISCARD
      const_reference
      back() const _GLIBCXX_NOEXCEPT
      {
        __glibcxx_check_nonempty();
        return _Base::back();
      }

      // 23.2.2.3 modifiers:
      using _Base::push_front;

#if __cplusplus >= 201103L
      using _Base::emplace_front;
#endif

#if __glibcxx_containers_ranges // C++ >= 23
      using _Base::prepend_range;
      using _Base::append_range;
#endif

      void
      pop_front() _GLIBCXX_NOEXCEPT
      {
        __glibcxx_check_nonempty();
        this->_M_invalidate_if(_Equal(_Base::begin()));
        _Base::pop_front();
      }

      using _Base::push_back;

#if __cplusplus >= 201103L
      using _Base::emplace_back;
#endif

      void
      pop_back() _GLIBCXX_NOEXCEPT
      {
        __glibcxx_check_nonempty();
        this->_M_invalidate_if(_Equal(--_Base::end()));
        _Base::pop_back();
      }

#if __cplusplus >= 201103L
      template<typename... _Args>
        iterator
        emplace(const_iterator __position, _Args&&... __args)
        {
          __glibcxx_check_insert(__position);
          return  { _Base::emplace(__position.base(),
                                   std::forward<_Args>(__args)...), this };
        }
#endif

     iterator
#if __cplusplus >= 201103L
     insert(const_iterator __position, const _Tp& __x)
#else
     insert(iterator __position, const _Tp& __x)
#endif
     {
       __glibcxx_check_insert(__position);
       return iterator(_Base::insert(__position.base(), __x), this);
     }

#if __cplusplus >= 201103L
      iterator
      insert(const_iterator __position, _Tp&& __x)
      { return emplace(__position, std::move(__x)); }

      iterator
      insert(const_iterator __p, initializer_list<value_type> __l)
      {
        __glibcxx_check_insert(__p);
        return { _Base::insert(__p.base(), __l), this };
      }
#endif

#if __cplusplus >= 201103L
      iterator
      insert(const_iterator __position, size_type __n, const _Tp& __x)
      {
        __glibcxx_check_insert(__position);
        return { _Base::insert(__position.base(), __n, __x), this };
      }
#else
      void
      insert(iterator __position, size_type __n, const _Tp& __x)
      {
        __glibcxx_check_insert(__position);
        _Base::insert(__position.base(), __n, __x);
      }
#endif

#if __cplusplus >= 201103L
      template<class _InputIterator,
               typename = std::_RequireInputIter<_InputIterator>>
        iterator
        insert(const_iterator __position, _InputIterator __first,
               _InputIterator __last)
        {
          typename __gnu_debug::_Distance_traits<_InputIterator>::__type __dist;
          __glibcxx_check_insert_range(__position, __first, __last, __dist);
          if (__dist.second >= __gnu_debug::__dp_sign)
            return
              {
                _Base::insert(__position.base(),
                              __gnu_debug::__unsafe(__first),
                              __gnu_debug::__unsafe(__last)),
                this
              };
          else
            return { _Base::insert(__position.base(), __first, __last), this };
        }
#else
      template<class _InputIterator>
        void
        insert(iterator __position, _InputIterator __first,
               _InputIterator __last)
        {
          typename __gnu_debug::_Distance_traits<_InputIterator>::__type __dist;
          __glibcxx_check_insert_range(__position, __first, __last, __dist);

          if (__dist.second >= __gnu_debug::__dp_sign)
            _Base::insert(__position.base(), __gnu_debug::__unsafe(__first),
                                             __gnu_debug::__unsafe(__last));
          else
            _Base::insert(__position.base(), __first, __last);
        }
#endif

#if __glibcxx_containers_ranges // C++ >= 23
      template<__detail::__container_compatible_range<_Tp> _Rg>
        iterator
        insert_range(const_iterator __position, _Rg&& __rg)
        {
          auto __ret = _Base::insert_range(__position.base(),
                                           std::forward<_Rg>(__rg));
          return { __ret, this };
        }
#endif

    private:
      _Base_iterator
#if __cplusplus >= 201103L
      _M_erase(_Base_const_iterator __position) noexcept
#else
      _M_erase(_Base_iterator __position)
#endif
      {
        this->_M_invalidate_if(_Equal(__position));
        return _Base::erase(__position);
      }

    public:
      iterator
#if __cplusplus >= 201103L
      erase(const_iterator __position) noexcept
#else
      erase(iterator __position)
#endif
      {
        __glibcxx_check_erase(__position);
        return iterator(_M_erase(__position.base()), this);
      }

      iterator
#if __cplusplus >= 201103L
      erase(const_iterator __first, const_iterator __last) noexcept
#else
      erase(iterator __first, iterator __last)
#endif
      {
        // _GLIBCXX_RESOLVE_LIB_DEFECTS
        // 151. can't currently clear() empty container
        __glibcxx_check_erase_range(__first, __last);
        for (_Base_const_iterator __victim = __first.base();
             __victim != __last.base(); ++__victim)
          {
            _GLIBCXX_DEBUG_VERIFY(__victim != _Base::end(),
                                  _M_message(__gnu_debug::__msg_valid_range)
                                  ._M_iterator(__first, "position")
                                  ._M_iterator(__last, "last"));
            this->_M_invalidate_if(_Equal(__victim));
          }

        return iterator(_Base::erase(__first.base(), __last.base()), this);
      }

      void
      swap(list& __x)
      _GLIBCXX_NOEXCEPT_IF( noexcept(declval<_Base&>().swap(__x)) )
      {
        _Safe::_M_swap(__x);
        _Base::swap(__x);
      }

      void
      clear() _GLIBCXX_NOEXCEPT
      {
        _Base::clear();
        this->_M_invalidate_all();
      }

      // 23.2.2.4 list operations:
      void
#if __cplusplus >= 201103L
      splice(const_iterator __position, list&& __x) noexcept
#else
      splice(iterator __position, list& __x)
#endif
      {
        _GLIBCXX_DEBUG_VERIFY(std::__addressof(__x) != this,
                              _M_message(__gnu_debug::__msg_self_splice)
                              ._M_sequence(*this, "this"));
        this->_M_transfer_from_if(__x, _Not_equal(__x._M_base().end()));
        _Base::splice(__position.base(), _GLIBCXX_MOVE(__x));
      }

#if __cplusplus >= 201103L
      void
      splice(const_iterator __position, list& __x) noexcept
      { splice(__position, std::move(__x)); }
#endif

      void
#if __cplusplus >= 201103L
      splice(const_iterator __position, list&& __x, const_iterator __i) noexcept
#else
      splice(iterator __position, list& __x, iterator __i)
#endif
      {
        __glibcxx_check_insert(__position);

        // We used to perform the splice_alloc check:  not anymore, redundant
        // after implementing the relevant bits of N1599.

        _GLIBCXX_DEBUG_VERIFY(__i._M_dereferenceable(),
                              _M_message(__gnu_debug::__msg_splice_bad)
                              ._M_iterator(__i, "__i"));
        _GLIBCXX_DEBUG_VERIFY(__i._M_attached_to(std::__addressof(__x)),
                              _M_message(__gnu_debug::__msg_splice_other)
                              ._M_iterator(__i, "__i")._M_sequence(__x, "__x"));

        // _GLIBCXX_RESOLVE_LIB_DEFECTS
        // 250. splicing invalidates iterators
        this->_M_transfer_from_if(__x, _Equal(__i.base()));
        _Base::splice(__position.base(), _GLIBCXX_MOVE(__x),
                      __i.base());
      }

#if __cplusplus >= 201103L
      void
      splice(const_iterator __position, list& __x, const_iterator __i) noexcept
      { splice(__position, std::move(__x), __i); }
#endif

      void
#if __cplusplus >= 201103L
      splice(const_iterator __position, list&& __x, const_iterator __first,
             const_iterator __last) noexcept
#else
      splice(iterator __position, list& __x, iterator __first,
             iterator __last)
#endif
      {
        __glibcxx_check_insert(__position);
        __glibcxx_check_valid_range(__first, __last);
        _GLIBCXX_DEBUG_VERIFY(__first._M_attached_to(std::__addressof(__x)),
                              _M_message(__gnu_debug::__msg_splice_other)
                              ._M_sequence(__x, "x")
                              ._M_iterator(__first, "first"));

        // We used to perform the splice_alloc check:  not anymore, redundant
        // after implementing the relevant bits of N1599.

        for (_Base_const_iterator __tmp = __first.base();
             __tmp != __last.base(); ++__tmp)
          {
            _GLIBCXX_DEBUG_VERIFY(__tmp != _Base::end(),
                                  _M_message(__gnu_debug::__msg_valid_range)
                                  ._M_iterator(__first, "first")
                                  ._M_iterator(__last, "last"));
            _GLIBCXX_DEBUG_VERIFY(std::__addressof(__x) != this
                                  || __tmp != __position.base(),
                                _M_message(__gnu_debug::__msg_splice_overlap)
                                  ._M_iterator(__tmp, "position")
                                  ._M_iterator(__first, "first")
                                  ._M_iterator(__last, "last"));

            // _GLIBCXX_RESOLVE_LIB_DEFECTS
            // 250. splicing invalidates iterators
            this->_M_transfer_from_if(__x, _Equal(__tmp));
          }

        _Base::splice(__position.base(), _GLIBCXX_MOVE(__x),
                      __first.base(), __last.base());
      }

#if __cplusplus >= 201103L
      void
      splice(const_iterator __position, list& __x,
             const_iterator __first, const_iterator __last) noexcept
      { splice(__position, std::move(__x), __first, __last); }
#endif

    private:
#if __cplusplus > 201703L
      typedef size_type __remove_return_type;
# define _GLIBCXX_LIST_REMOVE_RETURN_TYPE_TAG \
      __attribute__((__abi_tag__("__cxx20")))
# define _GLIBCXX20_ONLY(__expr) __expr
#else
      typedef void __remove_return_type;
# define _GLIBCXX_LIST_REMOVE_RETURN_TYPE_TAG
# define _GLIBCXX20_ONLY(__expr)
#endif

    public:
      _GLIBCXX_LIST_REMOVE_RETURN_TYPE_TAG
      __remove_return_type
      remove(const _Tp& __value)
      {
        if (!this->_M_iterators && !this->_M_const_iterators)
          return _Base::remove(__value);

#if !_GLIBCXX_USE_CXX11_ABI
        size_type __removed __attribute__((__unused__)) = 0;
#endif
        _Base __to_destroy(get_allocator());
        _Base_iterator __first = _Base::begin();
        _Base_iterator __last = _Base::end();
        while (__first != __last)
          {
            _Base_iterator __next = __first;
            ++__next;
            if (*__first == __value)
              {
                // _GLIBCXX_RESOLVE_LIB_DEFECTS
                // 526. Is it undefined if a function in the standard changes
                // in parameters?
                this->_M_invalidate_if(_Equal(__first));
                __to_destroy.splice(__to_destroy.begin(), *this, __first);
#if !_GLIBCXX_USE_CXX11_ABI
                _GLIBCXX20_ONLY( __removed++ );
#endif
              }

            __first = __next;
          }

#if !_GLIBCXX_USE_CXX11_ABI
        return _GLIBCXX20_ONLY( __removed );
#else
        return _GLIBCXX20_ONLY( __to_destroy.size() );
#endif
      }

      template<class _Predicate>
        __remove_return_type
        remove_if(_Predicate __pred)
        {
          if (!this->_M_iterators && !this->_M_const_iterators)
            return _Base::remove_if(__pred);

#if !_GLIBCXX_USE_CXX11_ABI
          size_type __removed __attribute__((__unused__)) = 0;
#endif
          _Base __to_destroy(get_allocator());
          for (_Base_iterator __x = _Base::begin(); __x != _Base::end(); )
          {
            _Base_iterator __next = __x;
            ++__next;
            if (__pred(*__x))
              {
                this->_M_invalidate_if(_Equal(__x));
                __to_destroy.splice(__to_destroy.begin(), *this, __x);
#if !_GLIBCXX_USE_CXX11_ABI
                _GLIBCXX20_ONLY( __removed++ );
#endif
              }

            __x = __next;
          }

#if !_GLIBCXX_USE_CXX11_ABI
          return _GLIBCXX20_ONLY( __removed );
#else
          return _GLIBCXX20_ONLY( __to_destroy.size() );
#endif
        }

      _GLIBCXX_LIST_REMOVE_RETURN_TYPE_TAG
      __remove_return_type
      unique()
      {
        if (!this->_M_iterators && !this->_M_const_iterators)
          return _Base::unique();

        if (empty())
          return _GLIBCXX20_ONLY(0);

#if !_GLIBCXX_USE_CXX11_ABI
        size_type __removed __attribute__((__unused__)) = 0;
#endif
        _Base __to_destroy(get_allocator());
        _Base_iterator __first = _Base::begin();
        _Base_iterator __last = _Base::end();
        _Base_iterator __next = __first;
        while (++__next != __last)
          if (*__first == *__next)
            {
              this->_M_invalidate_if(_Equal(__next));
              __to_destroy.splice(__to_destroy.begin(), *this, __next);
              __next = __first;
#if !_GLIBCXX_USE_CXX11_ABI
              _GLIBCXX20_ONLY( __removed++ );
#endif
            }
          else
            __first = __next;

#if !_GLIBCXX_USE_CXX11_ABI
        return _GLIBCXX20_ONLY( __removed );
#else
        return _GLIBCXX20_ONLY( __to_destroy.size() );
#endif
      }

      template<class _BinaryPredicate>
        __remove_return_type
        unique(_BinaryPredicate __binary_pred)
        {
          if (!this->_M_iterators && !this->_M_const_iterators)
            return _Base::unique(__binary_pred);

          if (empty())
            return _GLIBCXX20_ONLY(0);


#if !_GLIBCXX_USE_CXX11_ABI
          size_type __removed __attribute__((__unused__)) = 0;
#endif
          _Base __to_destroy(get_allocator());
          _Base_iterator __first = _Base::begin();
          _Base_iterator __last = _Base::end();
          _Base_iterator __next = __first;
          while (++__next != __last)
            if (__binary_pred(*__first, *__next))
              {
                this->_M_invalidate_if(_Equal(__next));
                __to_destroy.splice(__to_destroy.begin(), *this, __next);
                __next = __first;
#if !_GLIBCXX_USE_CXX11_ABI
                _GLIBCXX20_ONLY( __removed++ );
#endif
              }
            else
              __first = __next;

#if !_GLIBCXX_USE_CXX11_ABI
        return _GLIBCXX20_ONLY( __removed );
#else
        return _GLIBCXX20_ONLY( __to_destroy.size() );
#endif
        }

#undef _GLIBCXX_LIST_REMOVE_RETURN_TYPE_TAG
#undef _GLIBCXX20_ONLY

      void
#if __cplusplus >= 201103L
      merge(list&& __x)
#else
      merge(list& __x)
#endif
      {
        // _GLIBCXX_RESOLVE_LIB_DEFECTS
        // 300. list::merge() specification incomplete
        if (this != std::__addressof(__x))
          {
            __glibcxx_check_sorted(_Base::begin(), _Base::end());
            __glibcxx_check_sorted(__x.begin().base(), __x.end().base());
            this->_M_transfer_from_if(__x, _Not_equal(__x._M_base().end()));
            _Base::merge(_GLIBCXX_MOVE(__x));
          }
      }

#if __cplusplus >= 201103L
      void
      merge(list& __x)
      { merge(std::move(__x)); }
#endif

      template<class _Compare>
        void
#if __cplusplus >= 201103L
        merge(list&& __x, _Compare __comp)
#else
        merge(list& __x, _Compare __comp)
#endif
        {
          // _GLIBCXX_RESOLVE_LIB_DEFECTS
          // 300. list::merge() specification incomplete
          if (this != std::__addressof(__x))
            {
              __glibcxx_check_sorted_pred(_Base::begin(), _Base::end(),
                                          __comp);
              __glibcxx_check_sorted_pred(__x.begin().base(), __x.end().base(),
                                          __comp);
              this->_M_transfer_from_if(__x, _Not_equal(__x._M_base().end()));
              _Base::merge(_GLIBCXX_MOVE(__x), __comp);
            }
        }

#if __cplusplus >= 201103L
      template<typename _Compare>
        void
        merge(list& __x, _Compare __comp)
        { merge(std::move(__x), __comp); }
#endif

      void
      sort() { _Base::sort(); }

      template<typename _StrictWeakOrdering>
        void
        sort(_StrictWeakOrdering __pred) { _Base::sort(__pred); }

      using _Base::reverse;

      _Base&
      _M_base() _GLIBCXX_NOEXCEPT       { return *this; }

      const _Base&
      _M_base() const _GLIBCXX_NOEXCEPT { return *this; }
    };

#if __cpp_deduction_guides >= 201606
  template<typename _InputIterator, typename _ValT
             = typename iterator_traits<_InputIterator>::value_type,
           typename _Allocator = allocator<_ValT>,
           typename = _RequireInputIter<_InputIterator>,
           typename = _RequireAllocator<_Allocator>>
    list(_InputIterator, _InputIterator, _Allocator = _Allocator())
      -> list<_ValT, _Allocator>;

  template<typename _Tp, typename _Allocator = allocator<_Tp>,
           typename = _RequireAllocator<_Allocator>>
    list(size_t, _Tp, _Allocator = _Allocator())
      -> list<_Tp, _Allocator>;

#if __glibcxx_containers_ranges // C++ >= 23
  template<ranges::input_range _Rg,
           typename _Allocator = allocator<ranges::range_value_t<_Rg>>>
    list(from_range_t, _Rg&&, _Allocator = _Allocator())
      -> list<ranges::range_value_t<_Rg>, _Allocator>;
#endif
#endif

  template<typename _Tp, typename _Alloc>
    inline bool
    operator==(const list<_Tp, _Alloc>& __lhs,
               const list<_Tp, _Alloc>& __rhs)
    { return __lhs._M_base() == __rhs._M_base(); }

#if __cpp_lib_three_way_comparison
  template<typename _Tp, typename _Alloc>
    constexpr __detail::__synth3way_t<_Tp>
    operator<=>(const list<_Tp, _Alloc>& __x, const list<_Tp, _Alloc>& __y)
    { return __x._M_base() <=> __y._M_base(); }
#else
  template<typename _Tp, typename _Alloc>
    inline bool
    operator!=(const list<_Tp, _Alloc>& __lhs,
               const list<_Tp, _Alloc>& __rhs)
    { return __lhs._M_base() != __rhs._M_base(); }

  template<typename _Tp, typename _Alloc>
    inline bool
    operator<(const list<_Tp, _Alloc>& __lhs,
              const list<_Tp, _Alloc>& __rhs)
    { return __lhs._M_base() < __rhs._M_base(); }

  template<typename _Tp, typename _Alloc>
    inline bool
    operator<=(const list<_Tp, _Alloc>& __lhs,
               const list<_Tp, _Alloc>& __rhs)
    { return __lhs._M_base() <= __rhs._M_base(); }

  template<typename _Tp, typename _Alloc>
    inline bool
    operator>=(const list<_Tp, _Alloc>& __lhs,
               const list<_Tp, _Alloc>& __rhs)
    { return __lhs._M_base() >= __rhs._M_base(); }

  template<typename _Tp, typename _Alloc>
    inline bool
    operator>(const list<_Tp, _Alloc>& __lhs,
              const list<_Tp, _Alloc>& __rhs)
    { return __lhs._M_base() > __rhs._M_base(); }
#endif // three-way comparison

  template<typename _Tp, typename _Alloc>
    inline void
    swap(list<_Tp, _Alloc>& __lhs, list<_Tp, _Alloc>& __rhs)
    _GLIBCXX_NOEXCEPT_IF(noexcept(__lhs.swap(__rhs)))
    { __lhs.swap(__rhs); }

} // namespace __debug

#ifdef __glibcxx_erase_if // C++ >= 20 && HOSTED
_GLIBCXX_BEGIN_NAMESPACE_VERSION
  template<typename _Tp, typename _Alloc, typename _Predicate>
    inline typename __debug::list<_Tp, _Alloc>::size_type
    erase_if(__debug::list<_Tp, _Alloc>& __cont, _Predicate __pred)
    { return __cont.remove_if(__pred); }

  template<typename _Tp, typename _Alloc,
           typename _Up _GLIBCXX26_DEF_VAL_T(_Tp)>
    inline typename __debug::list<_Tp, _Alloc>::size_type
    erase(__debug::list<_Tp, _Alloc>& __cont, const _Up& __value)
    {
      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 4135. helper lambda of std::erase for list should specify return type
      return std::erase_if(__cont, [&](const auto& __elem) -> bool {
          return __elem == __value;
      });
    }
_GLIBCXX_END_NAMESPACE_VERSION
#endif // __glibcxx_erase_if
} // namespace std

namespace __gnu_debug
{
#ifndef _GLIBCXX_USE_CXX11_ABI
  // If not using C++11 list::size() is not in O(1) so we do not use it.
  template<typename _Tp, typename _Alloc>
    struct _Sequence_traits<std::__debug::list<_Tp, _Alloc> >
    {
      typedef typename std::__debug::list<_Tp, _Alloc>::iterator _It;

      static typename _Distance_traits<_It>::__type
      _S_size(const std::__debug::list<_Tp, _Alloc>& __seq)
      {
        return __seq.empty()
          ? std::make_pair(0, __dp_exact) : std::make_pair(1, __dp_sign);
      }
    };
#endif

#ifndef _GLIBCXX_DEBUG_PEDANTIC
  template<class _Tp, class _Alloc>
    struct _Insert_range_from_self_is_safe<std::__debug::list<_Tp, _Alloc> >
    { enum { __value = 1 }; };
#endif
}

#endif