text: // List implementation -*- C++ -*-
  
  // Copyright (C) 2001, 2002, 2003, 2004 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 2, 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.
  
  // You should have received a copy of the GNU General Public License along
  // with this library; see the file COPYING.  If not, write to the Free
  // Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307,
  // USA.
  
  // As a special exception, you may use this file as part of a free software
  // library without restriction.  Specifically, if other files instantiate
  // templates or use macros or inline functions from this file, or you compile
  // this file and link it with other files to produce an executable, this
  // file does not by itself cause the resulting executable to be covered by
  // the GNU General Public License.  This exception does not however
  // invalidate any other reasons why the executable file might be covered by
  // the GNU General Public License.
  
  /*
   *
   * Copyright (c) 1994
   * Hewlett-Packard Company
   *
   * Permission to use, copy, modify, distribute and sell this software
   * and its documentation for any purpose is hereby granted without fee,
   * provided that the above copyright notice appear in all copies and
   * that both that copyright notice and this permission notice appear
   * in supporting documentation.  Hewlett-Packard Company makes no
   * representations about the suitability of this software for any
   * purpose.  It is provided "as is" without express or implied warranty.
   *
   *
   * Copyright (c) 1996,1997
   * Silicon Graphics Computer Systems, Inc.
   *
   * Permission to use, copy, modify, distribute and sell this software
   * and its documentation for any purpose is hereby granted without fee,
   * provided that the above copyright notice appear in all copies and
   * that both that copyright notice and this permission notice appear
   * in supporting documentation.  Silicon Graphics makes no
   * representations about the suitability of this software for any
   * purpose.  It is provided "as is" without express or implied warranty.
   */
  
  /** @file stl_list.h
   *  This is an internal header file, included by other library headers.
   *  You should not attempt to use it directly.
   */
  
  #ifndef _LIST_H
  #define _LIST_H 1
  
  #include <bits/concept_check.h>
  
  namespace _GLIBCXX_STD
  {
    // Supporting structures are split into common and templated types; the
    // latter publicly inherits from the former in an effort to reduce code
    // duplication.  This results in some "needless" static_cast'ing later on,
    // but it's all safe downcasting.
  
    /// @if maint Common part of a node in the %list.  @endif
    struct _List_node_base
    {
      _List_node_base* _M_next;   ///< Self-explanatory
      _List_node_base* _M_prev;   ///< Self-explanatory
  
      static void
      swap(_List_node_base& __x, _List_node_base& __y);
  
      void
      transfer(_List_node_base * const __first,
  	     _List_node_base * const __last);
  
      void
      reverse();
  
      void
      hook(_List_node_base * const __position);
  
      void
      unhook();
    };
  
    /// @if maint An actual node in the %list.  @endif
    template<typename _Tp>
      struct _List_node : public _List_node_base
      {
        _Tp _M_data;                ///< User's data.
      };
  
    /**
     *  @brief A list::iterator.
     *
     *  @if maint
     *  All the functions are op overloads.
     *  @endif
    */
    template<typename _Tp>
      struct _List_iterator
      {
        typedef _List_iterator<_Tp>           _Self;
        typedef _List_node<_Tp>               _Node;
  
        typedef ptrdiff_t                     difference_type;
        typedef bidirectional_iterator_tag    iterator_category;
        typedef _Tp                           value_type;
        typedef _Tp*                          pointer;
        typedef _Tp&                          reference;
  
        _List_iterator() { }
  
        _List_iterator(_List_node_base* __x)
        : _M_node(__x) { }
  
        // Must downcast from List_node_base to _List_node to get to _M_data.
        reference
        operator*() const
        { return static_cast<_Node*>(_M_node)->_M_data; }
  
        pointer
        operator->() const
        { return &static_cast<_Node*>(_M_node)->_M_data; }
  
        _Self&
        operator++()
        {
  	_M_node = _M_node->_M_next;
  	return *this;
        }
  
        _Self
        operator++(int)
        {
  	_Self __tmp = *this;
  	_M_node = _M_node->_M_next;
  	return __tmp;
        }
  
        _Self&
        operator--()
        {
  	_M_node = _M_node->_M_prev;
  	return *this;
        }
  
        _Self
        operator--(int)
        {
  	_Self __tmp = *this;
  	_M_node = _M_node->_M_prev;
  	return __tmp;
        }
  
        bool
        operator==(const _Self& __x) const
        { return _M_node == __x._M_node; }
  
        bool
        operator!=(const _Self& __x) const
        { return _M_node != __x._M_node; }
  
        // The only member points to the %list element.
        _List_node_base* _M_node;
      };
  
    /**
     *  @brief A list::const_iterator.
     *
     *  @if maint
     *  All the functions are op overloads.
     *  @endif
    */
    template<typename _Tp>
      struct _List_const_iterator
      {
        typedef _List_const_iterator<_Tp>     _Self;
        typedef const _List_node<_Tp>         _Node;
        typedef _List_iterator<_Tp>           iterator;
  
        typedef ptrdiff_t                     difference_type;
        typedef bidirectional_iterator_tag    iterator_category;
        typedef _Tp                           value_type;
        typedef const _Tp*                    pointer;
        typedef const _Tp&                    reference;
  
        _List_const_iterator() { }
  
        _List_const_iterator(const _List_node_base* __x)
        : _M_node(__x) { }
  
        _List_const_iterator(const iterator& __x)
        : _M_node(__x._M_node) { }
  
        // Must downcast from List_node_base to _List_node to get to
        // _M_data.
        reference
        operator*() const
        { return static_cast<_Node*>(_M_node)->_M_data; }
  
        pointer
        operator->() const
        { return &static_cast<_Node*>(_M_node)->_M_data; }
  
        _Self&
        operator++()
        {
  	_M_node = _M_node->_M_next;
  	return *this;
        }
  
        _Self
        operator++(int)
        {
  	_Self __tmp = *this;
  	_M_node = _M_node->_M_next;
  	return __tmp;
        }
  
        _Self&
        operator--()
        {
  	_M_node = _M_node->_M_prev;
  	return *this;
        }
  
        _Self
        operator--(int)
        {
  	_Self __tmp = *this;
  	_M_node = _M_node->_M_prev;
  	return __tmp;
        }
  
        bool
        operator==(const _Self& __x) const
        { return _M_node == __x._M_node; }
  
        bool
        operator!=(const _Self& __x) const
        { return _M_node != __x._M_node; }
  
        // The only member points to the %list element.
        const _List_node_base* _M_node;
      };
  
    template<typename _Val>
      inline bool
      operator==(const _List_iterator<_Val>& __x,
  	       const _List_const_iterator<_Val>& __y)
      { return __x._M_node == __y._M_node; }
  
    template<typename _Val>
      inline bool
      operator!=(const _List_iterator<_Val>& __x,
                 const _List_const_iterator<_Val>& __y)
      { return __x._M_node != __y._M_node; }
  
  
    /**
     *  @if maint
     *  See bits/stl_deque.h's _Deque_base for an explanation.
     *  @endif
    */
    template<typename _Tp, typename _Alloc>
      class _List_base
      {
      protected:
        // NOTA BENE
        // The stored instance is not actually of "allocator_type"'s
        // type.  Instead we rebind the type to
        // Allocator<List_node<Tp>>, which according to [20.1.5]/4
        // should probably be the same.  List_node<Tp> is not the same
        // size as Tp (it's two pointers larger), and specializations on
        // Tp may go unused because List_node<Tp> is being bound
        // instead.
        //
        // We put this to the test in the constructors and in
        // get_allocator, where we use conversions between
        // allocator_type and _Node_Alloc_type. The conversion is
        // required by table 32 in [20.1.5].
        typedef typename _Alloc::template rebind<_List_node<_Tp> >::other
  
        _Node_Alloc_type;
  
        struct _List_impl 
  	: public _Node_Alloc_type {
  	_List_node_base _M_node;
  	_List_impl (const _Node_Alloc_type& __a)
  	  : _Node_Alloc_type(__a)
  	{ }
        };
  
        _List_impl _M_impl;
  
        _List_node<_Tp>*
        _M_get_node()
        { return _M_impl._Node_Alloc_type::allocate(1); }
        
        void
        _M_put_node(_List_node<_Tp>* __p)
        { _M_impl._Node_Alloc_type::deallocate(__p, 1); }
        
    public:
        typedef _Alloc allocator_type;
  
        allocator_type
        get_allocator() const
        { return allocator_type(*static_cast<const _Node_Alloc_type*>(&this->_M_impl)); }
  
        _List_base(const allocator_type& __a)
  	: _M_impl(__a)
        { _M_init(); }
  
        // This is what actually destroys the list.
        ~_List_base()
        { _M_clear(); }
  
        void
        _M_clear();
  
        void
        _M_init()
        {
          this->_M_impl._M_node._M_next = &this->_M_impl._M_node;
          this->_M_impl._M_node._M_prev = &this->_M_impl._M_node;
        }
      };
  
    /**
     *  @brief A standard container with linear time access to elements,
     *  and fixed time insertion/deletion at any point in the sequence.
     *
     *  @ingroup Containers
     *  @ingroup Sequences
     *
     *  Meets the requirements of a <a href="tables.html#65">container</a>, a
     *  <a href="tables.html#66">reversible container</a>, and a
     *  <a href="tables.html#67">sequence</a>, including the
     *  <a href="tables.html#68">optional sequence requirements</a> with the
     *  %exception of @c at and @c operator[].
     *
     *  This is a @e doubly @e linked %list.  Traversal up and down the
     *  %list requires linear time, but adding and removing elements (or
     *  @e nodes) is done in constant time, regardless of where the
     *  change takes place.  Unlike std::vector and std::deque,
     *  random-access iterators are not provided, so subscripting ( @c
     *  [] ) access is not allowed.  For algorithms which only need
     *  sequential access, this lack makes no difference.
     *
     *  Also unlike the other standard containers, std::list provides
     *  specialized algorithms %unique to linked lists, such as
     *  splicing, sorting, and in-place reversal.
     *
     *  @if maint
     *  A couple points on memory allocation for list<Tp>:
     *
     *  First, we never actually allocate a Tp, we allocate
     *  List_node<Tp>'s and trust [20.1.5]/4 to DTRT.  This is to ensure
     *  that after elements from %list<X,Alloc1> are spliced into
     *  %list<X,Alloc2>, destroying the memory of the second %list is a
     *  valid operation, i.e., Alloc1 giveth and Alloc2 taketh away.
     *
     *  Second, a %list conceptually represented as
     *  @code
     *    A <---> B <---> C <---> D
     *  @endcode
     *  is actually circular; a link exists between A and D.  The %list
     *  class holds (as its only data member) a private list::iterator
     *  pointing to @e D, not to @e A!  To get to the head of the %list,
     *  we start at the tail and move forward by one.  When this member
     *  iterator's next/previous pointers refer to itself, the %list is
     *  %empty.  @endif
    */
    template<typename _Tp, typename _Alloc = allocator<_Tp> >
      class list : protected _List_base<_Tp, _Alloc>
      {
        // concept requirements
        __glibcxx_class_requires(_Tp, _SGIAssignableConcept)
  
        typedef _List_base<_Tp, _Alloc>                   _Base;
  
      public:
        typedef _Tp                                        value_type;
        typedef typename _Alloc::pointer                   pointer;
        typedef typename _Alloc::const_pointer             const_pointer;
        typedef typename _Alloc::reference                 reference;
        typedef typename _Alloc::const_reference           const_reference;
        typedef _List_iterator<_Tp>                        iterator;
        typedef _List_const_iterator<_Tp>                  const_iterator;
        typedef std::reverse_iterator<const_iterator>      const_reverse_iterator;
        typedef std::reverse_iterator<iterator>            reverse_iterator;
        typedef size_t                                     size_type;
        typedef ptrdiff_t                                  difference_type;
        typedef typename _Base::allocator_type             allocator_type;
  
      protected:
        // Note that pointers-to-_Node's can be ctor-converted to
        // iterator types.
        typedef _List_node<_Tp>				_Node;
  
        /** @if maint
         *  One data member plus two memory-handling functions.  If the
         *  _Alloc type requires separate instances, then one of those
         *  will also be included, accumulated from the topmost parent.
         *  @endif
         */
        using _Base::_M_impl;
        using _Base::_M_put_node;
        using _Base::_M_get_node;
  
        /**
         *  @if maint
         *  @param  x  An instance of user data.
         *
         *  Allocates space for a new node and constructs a copy of @a x in it.
         *  @endif
         */
        _Node*
        _M_create_node(const value_type& __x)
        {
  	_Node* __p = this->_M_get_node();
  	try
  	  {
  	    std::_Construct(&__p->_M_data, __x);
  	  }
  	catch(...)
  	  {
  	    _M_put_node(__p);
  	    __throw_exception_again;
  	  }
  	return __p;
        }
  
        /**
         *  @if maint
         *  Allocates space for a new node and default-constructs a new
         *  instance of @c value_type in it.
         *  @endif
         */
        _Node*
        _M_create_node()
        {
  	_Node* __p = this->_M_get_node();
  	try
  	  {
  	    std::_Construct(&__p->_M_data);
  	  }
  	catch(...)
  	  {
  	    _M_put_node(__p);
  	    __throw_exception_again;
  	  }
  	return __p;
        }
  
      public:
        // [23.2.2.1] construct/copy/destroy
        // (assign() and get_allocator() are also listed in this section)
        /**
         *  @brief  Default constructor creates no elements.
         */
        explicit
        list(const allocator_type& __a = allocator_type())
        : _Base(__a) { }
  
        /**
         *  @brief  Create a %list with copies of an exemplar element.
         *  @param  n  The number of elements to initially create.
         *  @param  value  An element to copy.
         *
         *  This constructor fills the %list with @a n copies of @a value.
         */
        list(size_type __n, const value_type& __value,
  	   const allocator_type& __a = allocator_type())
        : _Base(__a)
        { this->insert(begin(), __n, __value); }
  
        /**
         *  @brief  Create a %list with default elements.
         *  @param  n  The number of elements to initially create.
         *
         *  This constructor fills the %list with @a n copies of a
         *  default-constructed element.
         */
        explicit
        list(size_type __n)
        : _Base(allocator_type())
        { this->insert(begin(), __n, value_type()); }
  
        /**
         *  @brief  %List copy constructor.
         *  @param  x  A %list of identical element and allocator types.
         *
         *  The newly-created %list uses a copy of the allocation object used
         *  by @a x.
         */
        list(const list& __x)
        : _Base(__x.get_allocator())
        { this->insert(begin(), __x.begin(), __x.end()); }
  
        /**
         *  @brief  Builds a %list from a range.
         *  @param  first  An input iterator.
         *  @param  last  An input iterator.
         *
         *  Create a %list consisting of copies of the elements from
         *  [@a first,@a last).  This is linear in N (where N is
         *  distance(@a first,@a last)).
         *
         *  @if maint
         *  We don't need any dispatching tricks here, because insert does all of
         *  that anyway.
         *  @endif
         */
        template<typename _InputIterator>
          list(_InputIterator __first, _InputIterator __last,
  	     const allocator_type& __a = allocator_type())
          : _Base(__a)
          { this->insert(begin(), __first, __last); }
  
        /**
         *  No explicit dtor needed as the _Base dtor takes care of
         *  things.  The _Base dtor only erases the elements, and note
         *  that if the elements themselves are pointers, the pointed-to
         *  memory is not touched in any way.  Managing the pointer is
         *  the user's responsibilty.
         */
  
        /**
         *  @brief  %List assignment operator.
         *  @param  x  A %list of identical element and allocator types.
         *
         *  All the elements of @a x are copied, but unlike the copy
         *  constructor, the allocator object is not copied.
         */
        list&
        operator=(const list& __x);
  
        /**
         *  @brief  Assigns a given value to a %list.
         *  @param  n  Number of elements to be assigned.
         *  @param  val  Value to be assigned.
         *
         *  This function fills a %list with @a n copies of the given
         *  value.  Note that the assignment completely changes the %list
         *  and that the resulting %list's size is the same as the number
         *  of elements assigned.  Old data may be lost.
         */
        void
        assign(size_type __n, const value_type& __val)
        { _M_fill_assign(__n, __val); }
  
        /**
         *  @brief  Assigns a range to a %list.
         *  @param  first  An input iterator.
         *  @param  last   An input iterator.
         *
         *  This function fills a %list with copies of the elements in the
         *  range [@a first,@a last).
         *
         *  Note that the assignment completely changes the %list and
         *  that the resulting %list's size is the same as the number of
         *  elements assigned.  Old data may be lost.
         */
        template<typename _InputIterator>
          void
          assign(_InputIterator __first, _InputIterator __last)
          {
  	  // Check whether it's an integral type.  If so, it's not an iterator.
  	  typedef typename _Is_integer<_InputIterator>::_Integral _Integral;
  	  _M_assign_dispatch(__first, __last, _Integral());
  	}
  
        /// Get a copy of the memory allocation object.
        allocator_type
        get_allocator() const
        { return _Base::get_allocator(); }
  
        // iterators
        /**
         *  Returns a read/write iterator that points to the first element in the
         *  %list.  Iteration is done in ordinary element order.
         */
        iterator
        begin()
        { return this->_M_impl._M_node._M_next; }
  
        /**
         *  Returns a read-only (constant) iterator that points to the
         *  first element in the %list.  Iteration is done in ordinary
         *  element order.
         */
        const_iterator
        begin() const
        { return this->_M_impl._M_node._M_next; }
  
        /**
         *  Returns a read/write iterator that points one past the last
         *  element in the %list.  Iteration is done in ordinary element
         *  order.
         */
        iterator
        end() { return &this->_M_impl._M_node; }
  
        /**
         *  Returns a read-only (constant) iterator that points one past
         *  the last element in the %list.  Iteration is done in ordinary
         *  element order.
         */
        const_iterator
        end() const
        { return &this->_M_impl._M_node; }
  
        /**
         *  Returns a read/write reverse iterator that points to the last
         *  element in the %list.  Iteration is done in reverse element
         *  order.
         */
        reverse_iterator
        rbegin()
        { return reverse_iterator(end()); }
  
        /**
         *  Returns a read-only (constant) reverse iterator that points to
         *  the last element in the %list.  Iteration is done in reverse
         *  element order.
         */
        const_reverse_iterator
        rbegin() const
        { return const_reverse_iterator(end()); }
  
        /**
         *  Returns a read/write reverse iterator that points to one
         *  before the first element in the %list.  Iteration is done in
         *  reverse element order.
         */
        reverse_iterator
        rend()
        { return reverse_iterator(begin()); }
  
        /**
         *  Returns a read-only (constant) reverse iterator that points to one
         *  before the first element in the %list.  Iteration is done in reverse
         *  element order.
         */
        const_reverse_iterator
        rend() const
        { return const_reverse_iterator(begin()); }
  
        // [23.2.2.2] capacity
        /**
         *  Returns true if the %list is empty.  (Thus begin() would equal
         *  end().)
         */
        bool
        empty() const
        { return this->_M_impl._M_node._M_next == &this->_M_impl._M_node; }
  
        /**  Returns the number of elements in the %list.  */
        size_type
        size() const
        { return std::distance(begin(), end()); }
  
        /**  Returns the size() of the largest possible %list.  */
        size_type
        max_size() const
        { return size_type(-1); }
  
        /**
         *  @brief Resizes the %list to the specified number of elements.
         *  @param new_size Number of elements the %list should contain.
         *  @param x Data with which new elements should be populated.
         *
         *  This function will %resize the %list to the specified number
         *  of elements.  If the number is smaller than the %list's
         *  current size the %list is truncated, otherwise the %list is
         *  extended and new elements are populated with given data.
         */
        void
        resize(size_type __new_size, const value_type& __x);
  
        /**
         *  @brief  Resizes the %list to the specified number of elements.
         *  @param  new_size  Number of elements the %list should contain.
         *
         *  This function will resize the %list to the specified number of
         *  elements.  If the number is smaller than the %list's current
         *  size the %list is truncated, otherwise the %list is extended
         *  and new elements are default-constructed.
         */
        void
        resize(size_type __new_size)
        { this->resize(__new_size, value_type()); }
  
        // element access
        /**
         *  Returns a read/write reference to the data at the first
         *  element of the %list.
         */
        reference
        front()
        { return *begin(); }
  
        /**
         *  Returns a read-only (constant) reference to the data at the first
         *  element of the %list.
         */
        const_reference
        front() const
        { return *begin(); }
  
        /**
         *  Returns a read/write reference to the data at the last element
         *  of the %list.
         */
        reference
        back()
        { return *(--end()); }
  
        /**
         *  Returns a read-only (constant) reference to the data at the last
         *  element of the %list.
         */
        const_reference
        back() const
        { return *(--end()); }
  
        // [23.2.2.3] modifiers
        /**
         *  @brief  Add data to the front of the %list.
         *  @param  x  Data to be added.
         *
         *  This is a typical stack operation.  The function creates an
         *  element at the front of the %list and assigns the given data
         *  to it.  Due to the nature of a %list this operation can be
         *  done in constant time, and does not invalidate iterators and
         *  references.
         */
        void
        push_front(const value_type& __x)
        { this->_M_insert(begin(), __x); }
  
        /**
         *  @brief  Removes first element.
         *
         *  This is a typical stack operation.  It shrinks the %list by
         *  one.  Due to the nature of a %list this operation can be done
         *  in constant time, and only invalidates iterators/references to
         *  the element being removed.
         *
         *  Note that no data is returned, and if the first element's data
         *  is needed, it should be retrieved before pop_front() is
         *  called.
         */
        void
        pop_front()
        { this->_M_erase(begin()); }
  
        /**
         *  @brief  Add data to the end of the %list.
         *  @param  x  Data to be added.
         *
         *  This is a typical stack operation.  The function creates an
         *  element at the end of the %list and assigns the given data to
         *  it.  Due to the nature of a %list this operation can be done
         *  in constant time, and does not invalidate iterators and
         *  references.
         */
        void
        push_back(const value_type& __x)
        { this->_M_insert(end(), __x); }
  
        /**
         *  @brief  Removes last element.
         *
         *  This is a typical stack operation.  It shrinks the %list by
         *  one.  Due to the nature of a %list this operation can be done
         *  in constant time, and only invalidates iterators/references to
         *  the element being removed.
         *
         *  Note that no data is returned, and if the last element's data
         *  is needed, it should be retrieved before pop_back() is called.
         */
        void
        pop_back()
        { this->_M_erase(this->_M_impl._M_node._M_prev); }
  
        /**
         *  @brief  Inserts given value into %list before specified iterator.
         *  @param  position  An iterator into the %list.
         *  @param  x  Data to be inserted.
         *  @return  An iterator that points to the inserted data.
         *
         *  This function will insert a copy of the given value before
         *  the specified location.  Due to the nature of a %list this
         *  operation can be done in constant time, and does not
         *  invalidate iterators and references.
         */
        iterator
        insert(iterator __position, const value_type& __x);
  
        /**
         *  @brief  Inserts a number of copies of given data into the %list.
         *  @param  position  An iterator into the %list.
         *  @param  n  Number of elements to be inserted.
         *  @param  x  Data to be inserted.
         *
         *  This function will insert a specified number of copies of the
         *  given data before the location specified by @a position.
         *
         *  Due to the nature of a %list this operation can be done in
         *  constant time, and does not invalidate iterators and
         *  references.
         */
        void
        insert(iterator __position, size_type __n, const value_type& __x)
        { _M_fill_insert(__position, __n, __x); }
  
        /**
         *  @brief  Inserts a range into the %list.
         *  @param  position  An iterator into the %list.
         *  @param  first  An input iterator.
         *  @param  last   An input iterator.
         *
         *  This function will insert copies of the data in the range [@a
         *  first,@a last) into the %list before the location specified by
         *  @a position.
         *
         *  Due to the nature of a %list this operation can be done in
         *  constant time, and does not invalidate iterators and
         *  references.
         */
        template<typename _InputIterator>
          void
          insert(iterator __position, _InputIterator __first,
  	       _InputIterator __last)
          {
  	  // Check whether it's an integral type.  If so, it's not an iterator.
  	  typedef typename _Is_integer<_InputIterator>::_Integral _Integral;
  	  _M_insert_dispatch(__position, __first, __last, _Integral());
  	}
  
        /**
         *  @brief  Remove element at given position.
         *  @param  position  Iterator pointing to element to be erased.
         *  @return  An iterator pointing to the next element (or end()).
         *
         *  This function will erase the element at the given position and thus
         *  shorten the %list by one.
         *
         *  Due to the nature of a %list this operation can be done in
         *  constant time, and only invalidates iterators/references to
         *  the element being removed.  The user is also cautioned that
         *  this function only erases the element, and that if the element
         *  is itself a pointer, the pointed-to memory is not touched in
         *  any way.  Managing the pointer is the user's responsibilty.
         */
        iterator
        erase(iterator __position);
  
        /**
         *  @brief  Remove a range of elements.
         *  @param  first  Iterator pointing to the first element to be erased.
         *  @param  last  Iterator pointing to one past the last element to be
         *                erased.
         *  @return  An iterator pointing to the element pointed to by @a last
         *           prior to erasing (or end()).
         *
         *  This function will erase the elements in the range @a
         *  [first,last) and shorten the %list accordingly.
         *
         *  Due to the nature of a %list this operation can be done in
         *  constant time, and only invalidates iterators/references to
         *  the element being removed.  The user is also cautioned that
         *  this function only erases the elements, and that if the
         *  elements themselves are pointers, the pointed-to memory is not
         *  touched in any way.  Managing the pointer is the user's
         *  responsibilty.
         */
        iterator
        erase(iterator __first, iterator __last)
        {
  	while (__first != __last)
  	  __first = erase(__first);
  	return __last;
        }
  
        /**
         *  @brief  Swaps data with another %list.
         *  @param  x  A %list of the same element and allocator types.
         *
         *  This exchanges the elements between two lists in constant
         *  time.  Note that the global std::swap() function is
         *  specialized such that std::swap(l1,l2) will feed to this
         *  function.
         */
        void
        swap(list& __x)
        { _List_node_base::swap(this->_M_impl._M_node,__x._M_impl._M_node); }
  
        /**
         *  Erases all the elements.  Note that this function only erases
         *  the elements, and that if the elements themselves are
         *  pointers, the pointed-to memory is not touched in any way.
         *  Managing the pointer is the user's responsibilty.
         */
        void
        clear()
        {
          _Base::_M_clear();
          _Base::_M_init();
        }
  
        // [23.2.2.4] list operations
        /**
         *  @brief  Insert contents of another %list.
         *  @param  position  Iterator referencing the element to insert before.
         *  @param  x  Source list.
         *
         *  The elements of @a x are inserted in constant time in front of
         *  the element referenced by @a position.  @a x becomes an empty
         *  list.
         */
        void
        splice(iterator __position, list& __x)
        {
  	if (!__x.empty())
  	  this->_M_transfer(__position, __x.begin(), __x.end());
        }
  
        /**
         *  @brief  Insert element from another %list.
         *  @param  position  Iterator referencing the element to insert before.
         *  @param  x  Source list.
         *  @param  i  Iterator referencing the element to move.
         *
         *  Removes the element in list @a x referenced by @a i and
         *  inserts it into the current list before @a position.
         */
        void
        splice(iterator __position, list&, iterator __i)
        {
  	iterator __j = __i;
  	++__j;
  	if (__position == __i || __position == __j)
  	  return;
  	this->_M_transfer(__position, __i, __j);
        }
  
        /**
         *  @brief  Insert range from another %list.
         *  @param  position  Iterator referencing the element to insert before.
         *  @param  x  Source list.
         *  @param  first  Iterator referencing the start of range in x.
         *  @param  last  Iterator referencing the end of range in x.
         *
         *  Removes elements in the range [first,last) and inserts them
         *  before @a position in constant time.
         *
         *  Undefined if @a position is in [first,last).
         */
        void
        splice(iterator __position, list&, iterator __first, iterator __last)
        {
  	if (__first != __last)
  	  this->_M_transfer(__position, __first, __last);
        }
  
        /**
         *  @brief  Remove all elements equal to value.
         *  @param  value  The value to remove.
         *
         *  Removes every element in the list equal to @a value.
         *  Remaining elements stay in list order.  Note that this
         *  function only erases the elements, and that if the elements
         *  themselves are pointers, the pointed-to memory is not
         *  touched in any way.  Managing the pointer is the user's
         *  responsibilty.
         */
        void
        remove(const _Tp& __value);
  
        /**
         *  @brief  Remove all elements satisfying a predicate.
         *  @param  Predicate  Unary predicate function or object.
         *
         *  Removes every element in the list for which the predicate
         *  returns true.  Remaining elements stay in list order.  Note
         *  that this function only erases the elements, and that if the
         *  elements themselves are pointers, the pointed-to memory is
         *  not touched in any way.  Managing the pointer is the user's
         *  responsibilty.
         */
        template<typename _Predicate>
        void
        remove_if(_Predicate);
  
        /**
         *  @brief  Remove consecutive duplicate elements.
         *
         *  For each consecutive set of elements with the same value,
         *  remove all but the first one.  Remaining elements stay in
         *  list order.  Note that this function only erases the
         *  elements, and that if the elements themselves are pointers,
         *  the pointed-to memory is not touched in any way.  Managing
         *  the pointer is the user's responsibilty.
         */
        void
        unique();
  
        /**
         *  @brief  Remove consecutive elements satisfying a predicate.
         *  @param  BinaryPredicate  Binary predicate function or object.
         *
         *  For each consecutive set of elements [first,last) that
         *  satisfy predicate(first,i) where i is an iterator in
         *  [first,last), remove all but the first one.  Remaining
         *  elements stay in list order.  Note that this function only
         *  erases the elements, and that if the elements themselves are
         *  pointers, the pointed-to memory is not touched in any way.
         *  Managing the pointer is the user's responsibilty.
         */
        template<typename _BinaryPredicate>
          void
          unique(_BinaryPredicate);
  
        /**
         *  @brief  Merge sorted lists.
         *  @param  x  Sorted list to merge.
         *
         *  Assumes that both @a x and this list are sorted according to
         *  operator<().  Merges elements of @a x into this list in
         *  sorted order, leaving @a x empty when complete.  Elements in
         *  this list precede elements in @a x that are equal.
         */
        void
        merge(list& __x);
  
        /**
         *  @brief  Merge sorted lists according to comparison function.
         *  @param  x  Sorted list to merge.
         *  @param StrictWeakOrdering Comparison function definining
         *  sort order.
         *
         *  Assumes that both @a x and this list are sorted according to
         *  StrictWeakOrdering.  Merges elements of @a x into this list
         *  in sorted order, leaving @a x empty when complete.  Elements
         *  in this list precede elements in @a x that are equivalent
         *  according to StrictWeakOrdering().
         */
        template<typename _StrictWeakOrdering>
          void
          merge(list&, _StrictWeakOrdering);
  
        /**
         *  @brief  Reverse the elements in list.
         *
         *  Reverse the order of elements in the list in linear time.
         */
        void
        reverse()
        { this->_M_impl._M_node.reverse(); }
  
        /**
         *  @brief  Sort the elements.
         *
         *  Sorts the elements of this list in NlogN time.  Equivalent
         *  elements remain in list order.
         */
        void
        sort();
  
        /**
         *  @brief  Sort the elements according to comparison function.
         *
         *  Sorts the elements of this list in NlogN time.  Equivalent
         *  elements remain in list order.
         */
        template<typename _StrictWeakOrdering>
          void
          sort(_StrictWeakOrdering);
  
      protected:
        // Internal assign functions follow.
  
        // Called by the range assign to implement [23.1.1]/9
        template<typename _Integer>
          void
          _M_assign_dispatch(_Integer __n, _Integer __val, __true_type)
          {
  	  _M_fill_assign(static_cast<size_type>(__n),
  			 static_cast<value_type>(__val));
  	}
  
        // Called by the range assign to implement [23.1.1]/9
        template<typename _InputIterator>
          void
          _M_assign_dispatch(_InputIterator __first, _InputIterator __last,
  			   __false_type);
  
        // Called by assign(n,t), and the range assign when it turns out
        // to be the same thing.
        void
        _M_fill_assign(size_type __n, const value_type& __val);
  
  
        // Internal insert functions follow.
  
        // Called by the range insert to implement [23.1.1]/9
        template<typename _Integer>
          void
          _M_insert_dispatch(iterator __pos, _Integer __n, _Integer __x,
  			   __true_type)
          {
  	  _M_fill_insert(__pos, static_cast<size_type>(__n),
  			 static_cast<value_type>(__x));
  	}
  
        // Called by the range insert to implement [23.1.1]/9
        template<typename _InputIterator>
          void
          _M_insert_dispatch(iterator __pos,
  			   _InputIterator __first, _InputIterator __last,
  			   __false_type)
          {
  	  for ( ; __first != __last; ++__first)
  	    _M_insert(__pos, *__first);
  	}
  
        // Called by insert(p,n,x), and the range insert when it turns out
        // to be the same thing.
        void
        _M_fill_insert(iterator __pos, size_type __n, const value_type& __x)
        {
  	for ( ; __n > 0; --__n)
  	  _M_insert(__pos, __x);
        }
  
  
        // Moves the elements from [first,last) before position.
        void
        _M_transfer(iterator __position, iterator __first, iterator __last)
        { __position._M_node->transfer(__first._M_node,__last._M_node); }
  
        // Inserts new element at position given and with value given.
        void
        _M_insert(iterator __position, const value_type& __x)
        {
          _Node* __tmp = _M_create_node(__x);
          __tmp->hook(__position._M_node);
        }
  
        // Erases element at position given.
        void
        _M_erase(iterator __position)
        {
          __position._M_node->unhook();
          _Node* __n = static_cast<_Node*>(__position._M_node);
          std::_Destroy(&__n->_M_data);
          _M_put_node(__n);
        }
      };
  
    /**
     *  @brief  List equality comparison.
     *  @param  x  A %list.
     *  @param  y  A %list of the same type as @a x.
     *  @return  True iff the size and elements of the lists are equal.
     *
     *  This is an equivalence relation.  It is linear in the size of
     *  the lists.  Lists are considered equivalent if their sizes are
     *  equal, and if corresponding elements compare equal.
    */
    template<typename _Tp, typename _Alloc>
      inline bool
      operator==(const list<_Tp,_Alloc>& __x, const list<_Tp,_Alloc>& __y)
      {
        typedef typename list<_Tp,_Alloc>::const_iterator const_iterator;
        const_iterator __end1 = __x.end();
        const_iterator __end2 = __y.end();
  
        const_iterator __i1 = __x.begin();
        const_iterator __i2 = __y.begin();
        while (__i1 != __end1 && __i2 != __end2 && *__i1 == *__i2)
  	{
  	  ++__i1;
  	  ++__i2;
  	}
        return __i1 == __end1 && __i2 == __end2;
      }
  
    /**
     *  @brief  List ordering relation.
     *  @param  x  A %list.
     *  @param  y  A %list of the same type as @a x.
     *  @return  True iff @a x is lexicographically less than @a y.
     *
     *  This is a total ordering relation.  It is linear in the size of the
     *  lists.  The elements must be comparable with @c <.
     *
     *  See std::lexicographical_compare() for how the determination is made.
    */
    template<typename _Tp, typename _Alloc>
      inline bool
      operator<(const list<_Tp,_Alloc>& __x, const list<_Tp,_Alloc>& __y)
      { return std::lexicographical_compare(__x.begin(), __x.end(),
  					  __y.begin(), __y.end()); }
  
    /// Based on operator==
    template<typename _Tp, typename _Alloc>
      inline bool
      operator!=(const list<_Tp,_Alloc>& __x, const list<_Tp,_Alloc>& __y)
      { return !(__x == __y); }
  
    /// Based on operator<
    template<typename _Tp, typename _Alloc>
      inline bool
      operator>(const list<_Tp,_Alloc>& __x, const list<_Tp,_Alloc>& __y)
      { return __y < __x; }
  
    /// Based on operator<
    template<typename _Tp, typename _Alloc>
      inline bool
      operator<=(const list<_Tp,_Alloc>& __x, const list<_Tp,_Alloc>& __y)
      { return !(__y < __x); }
  
    /// Based on operator<
    template<typename _Tp, typename _Alloc>
      inline bool
      operator>=(const list<_Tp,_Alloc>& __x, const list<_Tp,_Alloc>& __y)
      { return !(__x < __y); }
  
    /// See std::list::swap().
    template<typename _Tp, typename _Alloc>
      inline void
      swap(list<_Tp, _Alloc>& __x, list<_Tp, _Alloc>& __y)
      { __x.swap(__y); }
  } // namespace std
  
  #endif /* _LIST_H */
  
  