stl_iterator.h

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// Iterators -*- C++ -*-

// Copyright (C) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009
// 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/>.

/*
 *
 * 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) 1996-1998
 * 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_iterator.h
 *  This is an internal header file, included by other library headers.
 *  You should not attempt to use it directly.
 *
 *  This file implements reverse_iterator, back_insert_iterator,
 *  front_insert_iterator, insert_iterator, __normal_iterator, and their
 *  supporting functions and overloaded operators.
 */

#ifndef _STL_ITERATOR_H
#define _STL_ITERATOR_H 1

#include <bits/cpp_type_traits.h>
#include <ext/type_traits.h>
#include <bits/move.h>

_GLIBCXX_BEGIN_NAMESPACE(std)

  // 24.4.1 Reverse iterators
  /**
   *  "Bidirectional and random access iterators have corresponding reverse
   *  %iterator adaptors that iterate through the data structure in the
   *  opposite direction.  They have the same signatures as the corresponding
   *  iterators.  The fundamental relation between a reverse %iterator and its
   *  corresponding %iterator @c i is established by the identity:
   *  @code
   *      &*(reverse_iterator(i)) == &*(i - 1)
   *  @endcode
   *
   *  This mapping is dictated by the fact that while there is always a
   *  pointer past the end of an array, there might not be a valid pointer
   *  before the beginning of an array." [24.4.1]/1,2
   *
   *  Reverse iterators can be tricky and surprising at first.  Their
   *  semantics make sense, however, and the trickiness is a side effect of
   *  the requirement that the iterators must be safe.
  */
  template<typename _Iterator>
    class reverse_iterator
    : public iterator<typename iterator_traits<_Iterator>::iterator_category,
              typename iterator_traits<_Iterator>::value_type,
              typename iterator_traits<_Iterator>::difference_type,
              typename iterator_traits<_Iterator>::pointer,
                      typename iterator_traits<_Iterator>::reference>
    {
    protected:
      _Iterator current;

    public:
      typedef _Iterator                        iterator_type;
      typedef typename iterator_traits<_Iterator>::difference_type
                                   difference_type;
      typedef typename iterator_traits<_Iterator>::reference   reference;
      typedef typename iterator_traits<_Iterator>::pointer     pointer;

    public:
      /**
       *  The default constructor default-initializes member @p current.
       *  If it is a pointer, that means it is zero-initialized.
      */
      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 235 No specification of default ctor for reverse_iterator
      reverse_iterator() : current() { }

      /**
       *  This %iterator will move in the opposite direction that @p x does.
      */
      explicit
      reverse_iterator(iterator_type __x) : current(__x) { }

      /**
       *  The copy constructor is normal.
      */
      reverse_iterator(const reverse_iterator& __x)
      : current(__x.current) { }

      /**
       *  A reverse_iterator across other types can be copied in the normal
       *  fashion.
      */
      template<typename _Iter>
        reverse_iterator(const reverse_iterator<_Iter>& __x)
    : current(__x.base()) { }

      /**
       *  @return  @c current, the %iterator used for underlying work.
      */
      iterator_type
      base() const
      { return current; }

      /**
       *  @return  TODO
       *
       *  @doctodo
      */
      reference
      operator*() const
      {
    _Iterator __tmp = current;
    return *--__tmp;
      }

      /**
       *  @return  TODO
       *
       *  @doctodo
      */
      pointer
      operator->() const
      { return &(operator*()); }

      /**
       *  @return  TODO
       *
       *  @doctodo
      */
      reverse_iterator&
      operator++()
      {
    --current;
    return *this;
      }

      /**
       *  @return  TODO
       *
       *  @doctodo
      */
      reverse_iterator
      operator++(int)
      {
    reverse_iterator __tmp = *this;
    --current;
    return __tmp;
      }

      /**
       *  @return  TODO
       *
       *  @doctodo
      */
      reverse_iterator&
      operator--()
      {
    ++current;
    return *this;
      }

      /**
       *  @return  TODO
       *
       *  @doctodo
      */
      reverse_iterator
      operator--(int)
      {
    reverse_iterator __tmp = *this;
    ++current;
    return __tmp;
      }

      /**
       *  @return  TODO
       *
       *  @doctodo
      */
      reverse_iterator
      operator+(difference_type __n) const
      { return reverse_iterator(current - __n); }

      /**
       *  @return  TODO
       *
       *  @doctodo
      */
      reverse_iterator&
      operator+=(difference_type __n)
      {
    current -= __n;
    return *this;
      }

      /**
       *  @return  TODO
       *
       *  @doctodo
      */
      reverse_iterator
      operator-(difference_type __n) const
      { return reverse_iterator(current + __n); }

      /**
       *  @return  TODO
       *
       *  @doctodo
      */
      reverse_iterator&
      operator-=(difference_type __n)
      {
    current += __n;
    return *this;
      }

      /**
       *  @return  TODO
       *
       *  @doctodo
      */
      reference
      operator[](difference_type __n) const
      { return *(*this + __n); }
    };

  //@{
  /**
   *  @param  x  A %reverse_iterator.
   *  @param  y  A %reverse_iterator.
   *  @return  A simple bool.
   *
   *  Reverse iterators forward many operations to their underlying base()
   *  iterators.  Others are implemented in terms of one another.
   *
  */
  template<typename _Iterator>
    inline bool
    operator==(const reverse_iterator<_Iterator>& __x,
           const reverse_iterator<_Iterator>& __y)
    { return __x.base() == __y.base(); }

  template<typename _Iterator>
    inline bool
    operator<(const reverse_iterator<_Iterator>& __x,
          const reverse_iterator<_Iterator>& __y)
    { return __y.base() < __x.base(); }

  template<typename _Iterator>
    inline bool
    operator!=(const reverse_iterator<_Iterator>& __x,
           const reverse_iterator<_Iterator>& __y)
    { return !(__x == __y); }

  template<typename _Iterator>
    inline bool
    operator>(const reverse_iterator<_Iterator>& __x,
          const reverse_iterator<_Iterator>& __y)
    { return __y < __x; }

  template<typename _Iterator>
    inline bool
    operator<=(const reverse_iterator<_Iterator>& __x,
           const reverse_iterator<_Iterator>& __y)
    { return !(__y < __x); }

  template<typename _Iterator>
    inline bool
    operator>=(const reverse_iterator<_Iterator>& __x,
           const reverse_iterator<_Iterator>& __y)
    { return !(__x < __y); }

  template<typename _Iterator>
    inline typename reverse_iterator<_Iterator>::difference_type
    operator-(const reverse_iterator<_Iterator>& __x,
          const reverse_iterator<_Iterator>& __y)
    { return __y.base() - __x.base(); }

  template<typename _Iterator>
    inline reverse_iterator<_Iterator>
    operator+(typename reverse_iterator<_Iterator>::difference_type __n,
          const reverse_iterator<_Iterator>& __x)
    { return reverse_iterator<_Iterator>(__x.base() - __n); }

  // _GLIBCXX_RESOLVE_LIB_DEFECTS
  // DR 280. Comparison of reverse_iterator to const reverse_iterator.
  template<typename _IteratorL, typename _IteratorR>
    inline bool
    operator==(const reverse_iterator<_IteratorL>& __x,
           const reverse_iterator<_IteratorR>& __y)
    { return __x.base() == __y.base(); }

  template<typename _IteratorL, typename _IteratorR>
    inline bool
    operator<(const reverse_iterator<_IteratorL>& __x,
          const reverse_iterator<_IteratorR>& __y)
    { return __y.base() < __x.base(); }

  template<typename _IteratorL, typename _IteratorR>
    inline bool
    operator!=(const reverse_iterator<_IteratorL>& __x,
           const reverse_iterator<_IteratorR>& __y)
    { return !(__x == __y); }

  template<typename _IteratorL, typename _IteratorR>
    inline bool
    operator>(const reverse_iterator<_IteratorL>& __x,
          const reverse_iterator<_IteratorR>& __y)
    { return __y < __x; }

  template<typename _IteratorL, typename _IteratorR>
    inline bool
    operator<=(const reverse_iterator<_IteratorL>& __x,
           const reverse_iterator<_IteratorR>& __y)
    { return !(__y < __x); }

  template<typename _IteratorL, typename _IteratorR>
    inline bool
    operator>=(const reverse_iterator<_IteratorL>& __x,
           const reverse_iterator<_IteratorR>& __y)
    { return !(__x < __y); }

  template<typename _IteratorL, typename _IteratorR>
#ifdef __GXX_EXPERIMENTAL_CXX0X__
    // DR 685.
    inline auto
    operator-(const reverse_iterator<_IteratorL>& __x,
          const reverse_iterator<_IteratorR>& __y)
    -> decltype(__y.base() - __x.base())
#else
    inline typename reverse_iterator<_IteratorL>::difference_type
    operator-(const reverse_iterator<_IteratorL>& __x,
          const reverse_iterator<_IteratorR>& __y)
#endif
    { return __y.base() - __x.base(); }
  //@}

  // 24.4.2.2.1 back_insert_iterator
  /**
   *  @brief  Turns assignment into insertion.
   *
   *  These are output iterators, constructed from a container-of-T.
   *  Assigning a T to the iterator appends it to the container using
   *  push_back.
   *
   *  Tip:  Using the back_inserter function to create these iterators can
   *  save typing.
  */
  template<typename _Container>
    class back_insert_iterator
    : public iterator<output_iterator_tag, void, void, void, void>
    {
    protected:
      _Container* container;

    public:
      /// A nested typedef for the type of whatever container you used.
      typedef _Container          container_type;

      /// The only way to create this %iterator is with a container.
      explicit
      back_insert_iterator(_Container& __x) : container(&__x) { }

      /**
       *  @param  value  An instance of whatever type
       *                 container_type::const_reference is; presumably a
       *                 reference-to-const T for container<T>.
       *  @return  This %iterator, for chained operations.
       *
       *  This kind of %iterator doesn't really have a "position" in the
       *  container (you can think of the position as being permanently at
       *  the end, if you like).  Assigning a value to the %iterator will
       *  always append the value to the end of the container.
      */
      back_insert_iterator&
      operator=(typename _Container::const_reference __value)
      {
    container->push_back(__value);
    return *this;
      }

#ifdef __GXX_EXPERIMENTAL_CXX0X__
      back_insert_iterator&
      operator=(typename _Container::value_type&& __value)
      {
    container->push_back(std::move(__value));
    return *this;
      }
#endif

      /// Simply returns *this.
      back_insert_iterator&
      operator*()
      { return *this; }

      /// Simply returns *this.  (This %iterator does not "move".)
      back_insert_iterator&
      operator++()
      { return *this; }

      /// Simply returns *this.  (This %iterator does not "move".)
      back_insert_iterator
      operator++(int)
      { return *this; }
    };

  /**
   *  @param  x  A container of arbitrary type.
   *  @return  An instance of back_insert_iterator working on @p x.
   *
   *  This wrapper function helps in creating back_insert_iterator instances.
   *  Typing the name of the %iterator requires knowing the precise full
   *  type of the container, which can be tedious and impedes generic
   *  programming.  Using this function lets you take advantage of automatic
   *  template parameter deduction, making the compiler match the correct
   *  types for you.
  */
  template<typename _Container>
    inline back_insert_iterator<_Container>
    back_inserter(_Container& __x)
    { return back_insert_iterator<_Container>(__x); }

  /**
   *  @brief  Turns assignment into insertion.
   *
   *  These are output iterators, constructed from a container-of-T.
   *  Assigning a T to the iterator prepends it to the container using
   *  push_front.
   *
   *  Tip:  Using the front_inserter function to create these iterators can
   *  save typing.
  */
  template<typename _Container>
    class front_insert_iterator
    : public iterator<output_iterator_tag, void, void, void, void>
    {
    protected:
      _Container* container;

    public:
      /// A nested typedef for the type of whatever container you used.
      typedef _Container          container_type;

      /// The only way to create this %iterator is with a container.
      explicit front_insert_iterator(_Container& __x) : container(&__x) { }

      /**
       *  @param  value  An instance of whatever type
       *                 container_type::const_reference is; presumably a
       *                 reference-to-const T for container<T>.
       *  @return  This %iterator, for chained operations.
       *
       *  This kind of %iterator doesn't really have a "position" in the
       *  container (you can think of the position as being permanently at
       *  the front, if you like).  Assigning a value to the %iterator will
       *  always prepend the value to the front of the container.
      */
      front_insert_iterator&
      operator=(typename _Container::const_reference __value)
      {
    container->push_front(__value);
    return *this;
      }

#ifdef __GXX_EXPERIMENTAL_CXX0X__
      front_insert_iterator&
      operator=(typename _Container::value_type&& __value)
      {
    container->push_front(std::move(__value));
    return *this;
      }
#endif

      /// Simply returns *this.
      front_insert_iterator&
      operator*()
      { return *this; }

      /// Simply returns *this.  (This %iterator does not "move".)
      front_insert_iterator&
      operator++()
      { return *this; }

      /// Simply returns *this.  (This %iterator does not "move".)
      front_insert_iterator
      operator++(int)
      { return *this; }
    };

  /**
   *  @param  x  A container of arbitrary type.
   *  @return  An instance of front_insert_iterator working on @p x.
   *
   *  This wrapper function helps in creating front_insert_iterator instances.
   *  Typing the name of the %iterator requires knowing the precise full
   *  type of the container, which can be tedious and impedes generic
   *  programming.  Using this function lets you take advantage of automatic
   *  template parameter deduction, making the compiler match the correct
   *  types for you.
  */
  template<typename _Container>
    inline front_insert_iterator<_Container>
    front_inserter(_Container& __x)
    { return front_insert_iterator<_Container>(__x); }

  /**
   *  @brief  Turns assignment into insertion.
   *
   *  These are output iterators, constructed from a container-of-T.
   *  Assigning a T to the iterator inserts it in the container at the
   *  %iterator's position, rather than overwriting the value at that
   *  position.
   *
   *  (Sequences will actually insert a @e copy of the value before the
   *  %iterator's position.)
   *
   *  Tip:  Using the inserter function to create these iterators can
   *  save typing.
  */
  template<typename _Container>
    class insert_iterator
    : public iterator<output_iterator_tag, void, void, void, void>
    {
    protected:
      _Container* container;
      typename _Container::iterator iter;

    public:
      /// A nested typedef for the type of whatever container you used.
      typedef _Container          container_type;

      /**
       *  The only way to create this %iterator is with a container and an
       *  initial position (a normal %iterator into the container).
      */
      insert_iterator(_Container& __x, typename _Container::iterator __i)
      : container(&__x), iter(__i) {}

      /**
       *  @param  value  An instance of whatever type
       *                 container_type::const_reference is; presumably a
       *                 reference-to-const T for container<T>.
       *  @return  This %iterator, for chained operations.
       *
       *  This kind of %iterator maintains its own position in the
       *  container.  Assigning a value to the %iterator will insert the
       *  value into the container at the place before the %iterator.
       *
       *  The position is maintained such that subsequent assignments will
       *  insert values immediately after one another.  For example,
       *  @code
       *     // vector v contains A and Z
       *
       *     insert_iterator i (v, ++v.begin());
       *     i = 1;
       *     i = 2;
       *     i = 3;
       *
       *     // vector v contains A, 1, 2, 3, and Z
       *  @endcode
      */
      insert_iterator&
      operator=(typename _Container::const_reference __value)
      {
    iter = container->insert(iter, __value);
    ++iter;
    return *this;
      }

#ifdef __GXX_EXPERIMENTAL_CXX0X__
      insert_iterator&
      operator=(typename _Container::value_type&& __value)
      {
    iter = container->insert(iter, std::move(__value));
    ++iter;
    return *this;
      }
#endif

      /// Simply returns *this.
      insert_iterator&
      operator*()
      { return *this; }

      /// Simply returns *this.  (This %iterator does not "move".)
      insert_iterator&
      operator++()
      { return *this; }

      /// Simply returns *this.  (This %iterator does not "move".)
      insert_iterator&
      operator++(int)
      { return *this; }
    };

  /**
   *  @param  x  A container of arbitrary type.
   *  @return  An instance of insert_iterator working on @p x.
   *
   *  This wrapper function helps in creating insert_iterator instances.
   *  Typing the name of the %iterator requires knowing the precise full
   *  type of the container, which can be tedious and impedes generic
   *  programming.  Using this function lets you take advantage of automatic
   *  template parameter deduction, making the compiler match the correct
   *  types for you.
  */
  template<typename _Container, typename _Iterator>
    inline insert_iterator<_Container>
    inserter(_Container& __x, _Iterator __i)
    {
      return insert_iterator<_Container>(__x,
                     typename _Container::iterator(__i));
    }

_GLIBCXX_END_NAMESPACE

_GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx)

  // This iterator adapter is 'normal' in the sense that it does not
  // change the semantics of any of the operators of its iterator
  // parameter.  Its primary purpose is to convert an iterator that is
  // not a class, e.g. a pointer, into an iterator that is a class.
  // The _Container parameter exists solely so that different containers
  // using this template can instantiate different types, even if the
  // _Iterator parameter is the same.
  using std::iterator_traits;
  using std::iterator;
  template<typename _Iterator, typename _Container>
    class __normal_iterator
    {
    protected:
      _Iterator _M_current;

    public:
      typedef _Iterator                      iterator_type;
      typedef typename iterator_traits<_Iterator>::iterator_category
                                                             iterator_category;
      typedef typename iterator_traits<_Iterator>::value_type  value_type;
      typedef typename iterator_traits<_Iterator>::difference_type
                                                             difference_type;
      typedef typename iterator_traits<_Iterator>::reference reference;
      typedef typename iterator_traits<_Iterator>::pointer   pointer;

      __normal_iterator() : _M_current(_Iterator()) { }

      explicit
      __normal_iterator(const _Iterator& __i) : _M_current(__i) { }

      // Allow iterator to const_iterator conversion
      template<typename _Iter>
        __normal_iterator(const __normal_iterator<_Iter,
              typename __enable_if<
               (std::__are_same<_Iter, typename _Container::pointer>::__value),
              _Container>::__type>& __i)
        : _M_current(__i.base()) { }

      // Forward iterator requirements
      reference
      operator*() const
      { return *_M_current; }

      pointer
      operator->() const
      { return _M_current; }

      __normal_iterator&
      operator++()
      {
    ++_M_current;
    return *this;
      }

      __normal_iterator
      operator++(int)
      { return __normal_iterator(_M_current++); }

      // Bidirectional iterator requirements
      __normal_iterator&
      operator--()
      {
    --_M_current;
    return *this;
      }

      __normal_iterator
      operator--(int)
      { return __normal_iterator(_M_current--); }

      // Random access iterator requirements
      reference
      operator[](const difference_type& __n) const
      { return _M_current[__n]; }

      __normal_iterator&
      operator+=(const difference_type& __n)
      { _M_current += __n; return *this; }

      __normal_iterator
      operator+(const difference_type& __n) const
      { return __normal_iterator(_M_current + __n); }

      __normal_iterator&
      operator-=(const difference_type& __n)
      { _M_current -= __n; return *this; }

      __normal_iterator
      operator-(const difference_type& __n) const
      { return __normal_iterator(_M_current - __n); }

      const _Iterator&
      base() const
      { return _M_current; }
    };

  // Note: In what follows, the left- and right-hand-side iterators are
  // allowed to vary in types (conceptually in cv-qualification) so that
  // comparison between cv-qualified and non-cv-qualified iterators be
  // valid.  However, the greedy and unfriendly operators in std::rel_ops
  // will make overload resolution ambiguous (when in scope) if we don't
  // provide overloads whose operands are of the same type.  Can someone
  // remind me what generic programming is about? -- Gaby

  // Forward iterator requirements
  template<typename _IteratorL, typename _IteratorR, typename _Container>
    inline bool
    operator==(const __normal_iterator<_IteratorL, _Container>& __lhs,
           const __normal_iterator<_IteratorR, _Container>& __rhs)
    { return __lhs.base() == __rhs.base(); }

  template<typename _Iterator, typename _Container>
    inline bool
    operator==(const __normal_iterator<_Iterator, _Container>& __lhs,
           const __normal_iterator<_Iterator, _Container>& __rhs)
    { return __lhs.base() == __rhs.base(); }

  template<typename _IteratorL, typename _IteratorR, typename _Container>
    inline bool
    operator!=(const __normal_iterator<_IteratorL, _Container>& __lhs,
           const __normal_iterator<_IteratorR, _Container>& __rhs)
    { return __lhs.base() != __rhs.base(); }

  template<typename _Iterator, typename _Container>
    inline bool
    operator!=(const __normal_iterator<_Iterator, _Container>& __lhs,
           const __normal_iterator<_Iterator, _Container>& __rhs)
    { return __lhs.base() != __rhs.base(); }

  // Random access iterator requirements
  template<typename _IteratorL, typename _IteratorR, typename _Container>
    inline bool
    operator<(const __normal_iterator<_IteratorL, _Container>& __lhs,
          const __normal_iterator<_IteratorR, _Container>& __rhs)
    { return __lhs.base() < __rhs.base(); }

  template<typename _Iterator, typename _Container>
    inline bool
    operator<(const __normal_iterator<_Iterator, _Container>& __lhs,
          const __normal_iterator<_Iterator, _Container>& __rhs)
    { return __lhs.base() < __rhs.base(); }

  template<typename _IteratorL, typename _IteratorR, typename _Container>
    inline bool
    operator>(const __normal_iterator<_IteratorL, _Container>& __lhs,
          const __normal_iterator<_IteratorR, _Container>& __rhs)
    { return __lhs.base() > __rhs.base(); }

  template<typename _Iterator, typename _Container>
    inline bool
    operator>(const __normal_iterator<_Iterator, _Container>& __lhs,
          const __normal_iterator<_Iterator, _Container>& __rhs)
    { return __lhs.base() > __rhs.base(); }

  template<typename _IteratorL, typename _IteratorR, typename _Container>
    inline bool
    operator<=(const __normal_iterator<_IteratorL, _Container>& __lhs,
           const __normal_iterator<_IteratorR, _Container>& __rhs)
    { return __lhs.base() <= __rhs.base(); }

  template<typename _Iterator, typename _Container>
    inline bool
    operator<=(const __normal_iterator<_Iterator, _Container>& __lhs,
           const __normal_iterator<_Iterator, _Container>& __rhs)
    { return __lhs.base() <= __rhs.base(); }

  template<typename _IteratorL, typename _IteratorR, typename _Container>
    inline bool
    operator>=(const __normal_iterator<_IteratorL, _Container>& __lhs,
           const __normal_iterator<_IteratorR, _Container>& __rhs)
    { return __lhs.base() >= __rhs.base(); }

  template<typename _Iterator, typename _Container>
    inline bool
    operator>=(const __normal_iterator<_Iterator, _Container>& __lhs,
           const __normal_iterator<_Iterator, _Container>& __rhs)
    { return __lhs.base() >= __rhs.base(); }

  // _GLIBCXX_RESOLVE_LIB_DEFECTS
  // According to the resolution of DR179 not only the various comparison
  // operators but also operator- must accept mixed iterator/const_iterator
  // parameters.
  template<typename _IteratorL, typename _IteratorR, typename _Container>
#ifdef __GXX_EXPERIMENTAL_CXX0X__
    // DR 685.
    inline auto
    operator-(const __normal_iterator<_IteratorL, _Container>& __lhs,
          const __normal_iterator<_IteratorR, _Container>& __rhs)
    -> decltype(__lhs.base() - __rhs.base())
#else
    inline typename __normal_iterator<_IteratorL, _Container>::difference_type
    operator-(const __normal_iterator<_IteratorL, _Container>& __lhs,
          const __normal_iterator<_IteratorR, _Container>& __rhs)
#endif
    { return __lhs.base() - __rhs.base(); }

  template<typename _Iterator, typename _Container>
    inline typename __normal_iterator<_Iterator, _Container>::difference_type
    operator-(const __normal_iterator<_Iterator, _Container>& __lhs,
          const __normal_iterator<_Iterator, _Container>& __rhs)
    { return __lhs.base() - __rhs.base(); }

  template<typename _Iterator, typename _Container>
    inline __normal_iterator<_Iterator, _Container>
    operator+(typename __normal_iterator<_Iterator, _Container>::difference_type
          __n, const __normal_iterator<_Iterator, _Container>& __i)
    { return __normal_iterator<_Iterator, _Container>(__i.base() + __n); }

_GLIBCXX_END_NAMESPACE

#ifdef __GXX_EXPERIMENTAL_CXX0X__

_GLIBCXX_BEGIN_NAMESPACE(std)

  // 24.4.3  Move iterators
  /**
   *  Class template move_iterator is an iterator adapter with the same
   *  behavior as the underlying iterator except that its dereference
   *  operator implicitly converts the value returned by the underlying
   *  iterator's dereference operator to an rvalue reference.  Some
   *  generic algorithms can be called with move iterators to replace
   *  copying with moving.
   */
  template<typename _Iterator>
    class move_iterator
    {
    protected:
      _Iterator _M_current;

    public:
      typedef _Iterator                                        iterator_type;
      typedef typename iterator_traits<_Iterator>::difference_type
                                                               difference_type;
      // NB: DR 680.
      typedef _Iterator                                        pointer;
      typedef typename iterator_traits<_Iterator>::value_type  value_type;
      typedef typename iterator_traits<_Iterator>::iterator_category
                                                               iterator_category;
      typedef value_type&&                                     reference;

    public:
      move_iterator()
      : _M_current() { }

      explicit
      move_iterator(iterator_type __i)
      : _M_current(__i) { }

      template<typename _Iter>
    move_iterator(const move_iterator<_Iter>& __i)
    : _M_current(__i.base()) { }

      iterator_type
      base() const
      { return _M_current; }

      reference
      operator*() const
      { return *_M_current; }

      pointer
      operator->() const
      { return _M_current; }

      move_iterator&
      operator++()
      {
    ++_M_current;
    return *this;
      }

      move_iterator
      operator++(int)
      {
    move_iterator __tmp = *this;
    ++_M_current;
    return __tmp;
      }

      move_iterator&
      operator--()
      {
    --_M_current;
    return *this;
      }

      move_iterator
      operator--(int)
      {
    move_iterator __tmp = *this;
    --_M_current;
    return __tmp;
      }

      move_iterator
      operator+(difference_type __n) const
      { return move_iterator(_M_current + __n); }

      move_iterator&
      operator+=(difference_type __n)
      {
    _M_current += __n;
    return *this;
      }

      move_iterator
      operator-(difference_type __n) const
      { return move_iterator(_M_current - __n); }
    
      move_iterator&
      operator-=(difference_type __n)
      { 
    _M_current -= __n;
    return *this;
      }

      reference
      operator[](difference_type __n) const
      { return _M_current[__n]; }
    };

  template<typename _IteratorL, typename _IteratorR>
    inline bool
    operator==(const move_iterator<_IteratorL>& __x,
           const move_iterator<_IteratorR>& __y)
    { return __x.base() == __y.base(); }

  template<typename _IteratorL, typename _IteratorR>
    inline bool
    operator!=(const move_iterator<_IteratorL>& __x,
           const move_iterator<_IteratorR>& __y)
    { return !(__x == __y); }

  template<typename _IteratorL, typename _IteratorR>
    inline bool
    operator<(const move_iterator<_IteratorL>& __x,
          const move_iterator<_IteratorR>& __y)
    { return __x.base() < __y.base(); }

  template<typename _IteratorL, typename _IteratorR>
    inline bool
    operator<=(const move_iterator<_IteratorL>& __x,
           const move_iterator<_IteratorR>& __y)
    { return !(__y < __x); }

  template<typename _IteratorL, typename _IteratorR>
    inline bool
    operator>(const move_iterator<_IteratorL>& __x,
          const move_iterator<_IteratorR>& __y)
    { return __y < __x; }

  template<typename _IteratorL, typename _IteratorR>
    inline bool
    operator>=(const move_iterator<_IteratorL>& __x,
           const move_iterator<_IteratorR>& __y)
    { return !(__x < __y); }

  // DR 685.
  template<typename _IteratorL, typename _IteratorR>
    inline auto
    operator-(const move_iterator<_IteratorL>& __x,
          const move_iterator<_IteratorR>& __y)
    -> decltype(__x.base() - __y.base())
    { return __x.base() - __y.base(); }

  template<typename _Iterator>
    inline move_iterator<_Iterator>
    operator+(typename move_iterator<_Iterator>::difference_type __n,
          const move_iterator<_Iterator>& __x)
    { return __x + __n; }

  template<typename _Iterator>
    inline move_iterator<_Iterator>
    make_move_iterator(const _Iterator& __i)
    { return move_iterator<_Iterator>(__i); }

_GLIBCXX_END_NAMESPACE

#define _GLIBCXX_MAKE_MOVE_ITERATOR(_Iter) std::make_move_iterator(_Iter)
#else
#define _GLIBCXX_MAKE_MOVE_ITERATOR(_Iter) (_Iter)
#endif // __GXX_EXPERIMENTAL_CXX0X__

#endif