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Edit File: stl_iterator.h

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

// Copyright (C) 2001-2018 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 bits/stl_iterator.h
 *  This is an internal header file, included by other library headers.
 *  Do not attempt to use it directly. @headername{iterator}
 *
 *  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>
#include <bits/ptr_traits.h>

#if __cplusplus > 201402L
# define __cpp_lib_array_constexpr 201603
#endif

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

/**
   * @addtogroup iterators
   * @{
   */

// 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
   *
   *  <em>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.</em> [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;

typedef iterator_traits<_Iterator>		__traits_type;

public:
      typedef _Iterator					iterator_type;
      typedef typename __traits_type::difference_type	difference_type;
      typedef typename __traits_type::pointer		pointer;
      typedef typename __traits_type::reference		reference;

/**
       *  The default constructor value-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
      // 1012. reverse_iterator default ctor should value initialize
      _GLIBCXX17_CONSTEXPR
      reverse_iterator() : current() { }

/**
       *  This %iterator will move in the opposite direction that @p x does.
      */
      explicit _GLIBCXX17_CONSTEXPR
      reverse_iterator(iterator_type __x) : current(__x) { }

/**
       *  The copy constructor is normal.
      */
      _GLIBCXX17_CONSTEXPR
      reverse_iterator(const reverse_iterator& __x)
      : current(__x.current) { }

/**
       *  A %reverse_iterator across other types can be copied if the
       *  underlying %iterator can be converted to the type of @c current.
      */
      template<typename _Iter>
	_GLIBCXX17_CONSTEXPR
        reverse_iterator(const reverse_iterator<_Iter>& __x)
	: current(__x.base()) { }

/**
       *  @return  @c current, the %iterator used for underlying work.
      */
      _GLIBCXX17_CONSTEXPR iterator_type
      base() const
      { return current; }

/**
       *  @return  A reference to the value at @c --current
       *
       *  This requires that @c --current is dereferenceable.
       *
       *  @warning This implementation requires that for an iterator of the
       *           underlying iterator type, @c x, a reference obtained by
       *           @c *x remains valid after @c x has been modified or
       *           destroyed. This is a bug: http://gcc.gnu.org/PR51823
      */
      _GLIBCXX17_CONSTEXPR reference
      operator*() const
      {
	_Iterator __tmp = current;
	return *--__tmp;
      }

/**
       *  @return  A pointer to the value at @c --current
       *
       *  This requires that @c --current is dereferenceable.
      */
      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 2188. Reverse iterator does not fully support targets that overload &
      _GLIBCXX17_CONSTEXPR pointer
      operator->() const
      { return std::__addressof(operator*()); }

/**
       *  @return  @c *this
       *
       *  Decrements the underlying iterator.
      */
      _GLIBCXX17_CONSTEXPR reverse_iterator&
      operator++()
      {
	--current;
	return *this;
      }

/**
       *  @return  The original value of @c *this
       *
       *  Decrements the underlying iterator.
      */
      _GLIBCXX17_CONSTEXPR reverse_iterator
      operator++(int)
      {
	reverse_iterator __tmp = *this;
	--current;
	return __tmp;
      }

/**
       *  @return  @c *this
       *
       *  Increments the underlying iterator.
      */
      _GLIBCXX17_CONSTEXPR reverse_iterator&
      operator--()
      {
	++current;
	return *this;
      }

/**
       *  @return  A reverse_iterator with the previous value of @c *this
       *
       *  Increments the underlying iterator.
      */
      _GLIBCXX17_CONSTEXPR reverse_iterator
      operator--(int)
      {
	reverse_iterator __tmp = *this;
	++current;
	return __tmp;
      }

/**
       *  @return  A reverse_iterator that refers to @c current - @a __n
       *
       *  The underlying iterator must be a Random Access Iterator.
      */
      _GLIBCXX17_CONSTEXPR reverse_iterator
      operator+(difference_type __n) const
      { return reverse_iterator(current - __n); }

/**
       *  @return  *this
       *
       *  Moves the underlying iterator backwards @a __n steps.
       *  The underlying iterator must be a Random Access Iterator.
      */
      _GLIBCXX17_CONSTEXPR reverse_iterator&
      operator+=(difference_type __n)
      {
	current -= __n;
	return *this;
      }

/**
       *  @return  A reverse_iterator that refers to @c current - @a __n
       *
       *  The underlying iterator must be a Random Access Iterator.
      */
      _GLIBCXX17_CONSTEXPR reverse_iterator
      operator-(difference_type __n) const
      { return reverse_iterator(current + __n); }

/**
       *  @return  *this
       *
       *  Moves the underlying iterator forwards @a __n steps.
       *  The underlying iterator must be a Random Access Iterator.
      */
      _GLIBCXX17_CONSTEXPR reverse_iterator&
      operator-=(difference_type __n)
      {
	current += __n;
	return *this;
      }

/**
       *  @return  The value at @c current - @a __n - 1
       *
       *  The underlying iterator must be a Random Access Iterator.
      */
      _GLIBCXX17_CONSTEXPR 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 _GLIBCXX17_CONSTEXPR bool
    operator==(const reverse_iterator<_Iterator>& __x,
	       const reverse_iterator<_Iterator>& __y)
    { return __x.base() == __y.base(); }

template<typename _Iterator>
    inline _GLIBCXX17_CONSTEXPR bool
    operator<(const reverse_iterator<_Iterator>& __x,
	      const reverse_iterator<_Iterator>& __y)
    { return __y.base() < __x.base(); }

template<typename _Iterator>
    inline _GLIBCXX17_CONSTEXPR bool
    operator!=(const reverse_iterator<_Iterator>& __x,
	       const reverse_iterator<_Iterator>& __y)
    { return !(__x == __y); }

template<typename _Iterator>
    inline _GLIBCXX17_CONSTEXPR bool
    operator>(const reverse_iterator<_Iterator>& __x,
	      const reverse_iterator<_Iterator>& __y)
    { return __y < __x; }

template<typename _Iterator>
    inline _GLIBCXX17_CONSTEXPR bool
    operator<=(const reverse_iterator<_Iterator>& __x,
	       const reverse_iterator<_Iterator>& __y)
    { return !(__y < __x); }

template<typename _Iterator>
    inline _GLIBCXX17_CONSTEXPR bool
    operator>=(const reverse_iterator<_Iterator>& __x,
	       const reverse_iterator<_Iterator>& __y)
    { return !(__x < __y); }

// _GLIBCXX_RESOLVE_LIB_DEFECTS
  // DR 280. Comparison of reverse_iterator to const reverse_iterator.
  template<typename _IteratorL, typename _IteratorR>
    inline _GLIBCXX17_CONSTEXPR bool
    operator==(const reverse_iterator<_IteratorL>& __x,
	       const reverse_iterator<_IteratorR>& __y)
    { return __x.base() == __y.base(); }

template<typename _IteratorL, typename _IteratorR>
    inline _GLIBCXX17_CONSTEXPR bool
    operator<(const reverse_iterator<_IteratorL>& __x,
	      const reverse_iterator<_IteratorR>& __y)
    { return __y.base() < __x.base(); }

template<typename _IteratorL, typename _IteratorR>
    inline _GLIBCXX17_CONSTEXPR bool
    operator!=(const reverse_iterator<_IteratorL>& __x,
	       const reverse_iterator<_IteratorR>& __y)
    { return !(__x == __y); }

template<typename _IteratorL, typename _IteratorR>
    inline _GLIBCXX17_CONSTEXPR bool
    operator>(const reverse_iterator<_IteratorL>& __x,
	      const reverse_iterator<_IteratorR>& __y)
    { return __y < __x; }

template<typename _IteratorL, typename _IteratorR>
    inline _GLIBCXX17_CONSTEXPR bool
    operator<=(const reverse_iterator<_IteratorL>& __x,
	       const reverse_iterator<_IteratorR>& __y)
    { return !(__y < __x); }

template<typename _IteratorL, typename _IteratorR>
    inline _GLIBCXX17_CONSTEXPR bool
    operator>=(const reverse_iterator<_IteratorL>& __x,
	       const reverse_iterator<_IteratorR>& __y)
    { return !(__x < __y); }
  //@}

#if __cplusplus < 201103L
  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 _IteratorL, typename _IteratorR>
    inline typename reverse_iterator<_IteratorL>::difference_type
    operator-(const reverse_iterator<_IteratorL>& __x,
	      const reverse_iterator<_IteratorR>& __y)
    { return __y.base() - __x.base(); }
#else
  // _GLIBCXX_RESOLVE_LIB_DEFECTS
  // DR 685. reverse_iterator/move_iterator difference has invalid signatures
  template<typename _IteratorL, typename _IteratorR>
    inline _GLIBCXX17_CONSTEXPR auto
    operator-(const reverse_iterator<_IteratorL>& __x,
	      const reverse_iterator<_IteratorR>& __y)
    -> decltype(__y.base() - __x.base())
    { return __y.base() - __x.base(); }
#endif

template<typename _Iterator>
    inline _GLIBCXX17_CONSTEXPR reverse_iterator<_Iterator>
    operator+(typename reverse_iterator<_Iterator>::difference_type __n,
	      const reverse_iterator<_Iterator>& __x)
    { return reverse_iterator<_Iterator>(__x.base() - __n); }

#if __cplusplus >= 201103L
  // Same as C++14 make_reverse_iterator but used in C++03 mode too.
  template<typename _Iterator>
    inline _GLIBCXX17_CONSTEXPR reverse_iterator<_Iterator>
    __make_reverse_iterator(_Iterator __i)
    { return reverse_iterator<_Iterator>(__i); }

# if __cplusplus > 201103L
#  define __cpp_lib_make_reverse_iterator 201402

// _GLIBCXX_RESOLVE_LIB_DEFECTS
  // DR 2285. make_reverse_iterator
  /// Generator function for reverse_iterator.
  template<typename _Iterator>
    inline _GLIBCXX17_CONSTEXPR reverse_iterator<_Iterator>
    make_reverse_iterator(_Iterator __i)
    { return reverse_iterator<_Iterator>(__i); }
# endif
#endif

#if __cplusplus >= 201103L
  template<typename _Iterator>
    auto
    __niter_base(reverse_iterator<_Iterator> __it)
    -> decltype(__make_reverse_iterator(__niter_base(__it.base())))
    { return __make_reverse_iterator(__niter_base(__it.base())); }

template<typename _Iterator>
    struct __is_move_iterator<reverse_iterator<_Iterator> >
      : __is_move_iterator<_Iterator>
    { };

template<typename _Iterator>
    auto
    __miter_base(reverse_iterator<_Iterator> __it)
    -> decltype(__make_reverse_iterator(__miter_base(__it.base())))
    { return __make_reverse_iterator(__miter_base(__it.base())); }
#endif

// 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(std::__addressof(__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 @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.
      */
#if __cplusplus < 201103L
      back_insert_iterator&
      operator=(typename _Container::const_reference __value)
      {
	container->push_back(__value);
	return *this;
      }
#else
      back_insert_iterator&
      operator=(const typename _Container::value_type& __value)
      {
	container->push_back(__value);
	return *this;
      }

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 @a move.)
      back_insert_iterator&
      operator++()
      { return *this; }

/// Simply returns *this.  (This %iterator does not @a 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(std::__addressof(__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 @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.
      */
#if __cplusplus < 201103L
      front_insert_iterator&
      operator=(typename _Container::const_reference __value)
      {
	container->push_front(__value);
	return *this;
      }
#else
      front_insert_iterator&
      operator=(const typename _Container::value_type& __value)
      {
	container->push_front(__value);
	return *this;
      }

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 @a move.)
      front_insert_iterator&
      operator++()
      { return *this; }

/// Simply returns *this.  (This %iterator does not @a 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(std::__addressof(__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
      */
#if __cplusplus < 201103L
      insert_iterator&
      operator=(typename _Container::const_reference __value)
      {
	iter = container->insert(iter, __value);
	++iter;
	return *this;
      }
#else
      insert_iterator&
      operator=(const typename _Container::value_type& __value)
      {
	iter = container->insert(iter, __value);
	++iter;
	return *this;
      }

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 @a move.)
      insert_iterator&
      operator++()
      { return *this; }

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

/**
   *  @param __x  A container of arbitrary type.
   *  @param __i  An iterator into the container.
   *  @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));
    }

// @} group iterators

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace

namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

// This iterator adapter is @a 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;

typedef iterator_traits<_Iterator>		__traits_type;

public:
      typedef _Iterator					iterator_type;
      typedef typename __traits_type::iterator_category iterator_category;
      typedef typename __traits_type::value_type  	value_type;
      typedef typename __traits_type::difference_type 	difference_type;
      typedef typename __traits_type::reference 	reference;
      typedef typename __traits_type::pointer   	pointer;

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

explicit
      __normal_iterator(const _Iterator& __i) _GLIBCXX_NOEXCEPT
      : _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) _GLIBCXX_NOEXCEPT
        : _M_current(__i.base()) { }

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

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

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

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

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

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

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

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

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

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

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

const _Iterator&
      base() const _GLIBCXX_NOEXCEPT
      { 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)
    _GLIBCXX_NOEXCEPT
    { 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)
    _GLIBCXX_NOEXCEPT
    { 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)
    _GLIBCXX_NOEXCEPT
    { 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)
    _GLIBCXX_NOEXCEPT
    { 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)
    _GLIBCXX_NOEXCEPT
    { 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)
    _GLIBCXX_NOEXCEPT
    { 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)
    _GLIBCXX_NOEXCEPT
    { 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)
    _GLIBCXX_NOEXCEPT
    { 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)
    _GLIBCXX_NOEXCEPT
    { 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)
    _GLIBCXX_NOEXCEPT
    { 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)
    _GLIBCXX_NOEXCEPT
    { 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)
    _GLIBCXX_NOEXCEPT
    { 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>
#if __cplusplus >= 201103L
    // DR 685.
    inline auto
    operator-(const __normal_iterator<_IteratorL, _Container>& __lhs,
	      const __normal_iterator<_IteratorR, _Container>& __rhs) noexcept
    -> 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)
    _GLIBCXX_NOEXCEPT
    { 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)
    _GLIBCXX_NOEXCEPT
    { return __normal_iterator<_Iterator, _Container>(__i.base() + __n); }

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

template<typename _Iterator, typename _Container>
    _Iterator
    __niter_base(__gnu_cxx::__normal_iterator<_Iterator, _Container> __it)
    { return __it.base(); }

#if __cplusplus >= 201103L

/**
   * @addtogroup iterators
   * @{
   */

// 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;

typedef iterator_traits<_Iterator>		__traits_type;
      typedef typename __traits_type::reference		__base_ref;

public:
      typedef _Iterator					iterator_type;
      typedef typename __traits_type::iterator_category iterator_category;
      typedef typename __traits_type::value_type  	value_type;
      typedef typename __traits_type::difference_type	difference_type;
      // NB: DR 680.
      typedef _Iterator					pointer;
      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 2106. move_iterator wrapping iterators returning prvalues
      typedef typename conditional<is_reference<__base_ref>::value,
			 typename remove_reference<__base_ref>::type&&,
			 __base_ref>::type		reference;

_GLIBCXX17_CONSTEXPR
      move_iterator()
      : _M_current() { }

explicit _GLIBCXX17_CONSTEXPR
      move_iterator(iterator_type __i)
      : _M_current(__i) { }

template<typename _Iter>
	_GLIBCXX17_CONSTEXPR
	move_iterator(const move_iterator<_Iter>& __i)
	: _M_current(__i.base()) { }

_GLIBCXX17_CONSTEXPR iterator_type
      base() const
      { return _M_current; }

_GLIBCXX17_CONSTEXPR reference
      operator*() const
      { return static_cast<reference>(*_M_current); }

_GLIBCXX17_CONSTEXPR pointer
      operator->() const
      { return _M_current; }

_GLIBCXX17_CONSTEXPR move_iterator&
      operator++()
      {
	++_M_current;
	return *this;
      }

_GLIBCXX17_CONSTEXPR move_iterator
      operator++(int)
      {
	move_iterator __tmp = *this;
	++_M_current;
	return __tmp;
      }

_GLIBCXX17_CONSTEXPR move_iterator&
      operator--()
      {
	--_M_current;
	return *this;
      }

_GLIBCXX17_CONSTEXPR move_iterator
      operator--(int)
      {
	move_iterator __tmp = *this;
	--_M_current;
	return __tmp;
      }

_GLIBCXX17_CONSTEXPR move_iterator
      operator+(difference_type __n) const
      { return move_iterator(_M_current + __n); }

_GLIBCXX17_CONSTEXPR move_iterator&
      operator+=(difference_type __n)
      {
	_M_current += __n;
	return *this;
      }

_GLIBCXX17_CONSTEXPR move_iterator
      operator-(difference_type __n) const
      { return move_iterator(_M_current - __n); }
    
      _GLIBCXX17_CONSTEXPR move_iterator&
      operator-=(difference_type __n)
      { 
	_M_current -= __n;
	return *this;
      }

_GLIBCXX17_CONSTEXPR reference
      operator[](difference_type __n) const
      { return std::move(_M_current[__n]); }
    };

// Note: See __normal_iterator operators note from Gaby to understand
  // why there are always 2 versions for most of the move_iterator
  // operators.
  template<typename _IteratorL, typename _IteratorR>
    inline _GLIBCXX17_CONSTEXPR bool
    operator==(const move_iterator<_IteratorL>& __x,
	       const move_iterator<_IteratorR>& __y)
    { return __x.base() == __y.base(); }

template<typename _Iterator>
    inline _GLIBCXX17_CONSTEXPR bool
    operator==(const move_iterator<_Iterator>& __x,
	       const move_iterator<_Iterator>& __y)
    { return __x.base() == __y.base(); }

template<typename _IteratorL, typename _IteratorR>
    inline _GLIBCXX17_CONSTEXPR bool
    operator!=(const move_iterator<_IteratorL>& __x,
	       const move_iterator<_IteratorR>& __y)
    { return !(__x == __y); }

template<typename _Iterator>
    inline _GLIBCXX17_CONSTEXPR bool
    operator!=(const move_iterator<_Iterator>& __x,
	       const move_iterator<_Iterator>& __y)
    { return !(__x == __y); }

template<typename _IteratorL, typename _IteratorR>
    inline _GLIBCXX17_CONSTEXPR bool
    operator<(const move_iterator<_IteratorL>& __x,
	      const move_iterator<_IteratorR>& __y)
    { return __x.base() < __y.base(); }

template<typename _Iterator>
    inline _GLIBCXX17_CONSTEXPR bool
    operator<(const move_iterator<_Iterator>& __x,
	      const move_iterator<_Iterator>& __y)
    { return __x.base() < __y.base(); }

template<typename _IteratorL, typename _IteratorR>
    inline _GLIBCXX17_CONSTEXPR bool
    operator<=(const move_iterator<_IteratorL>& __x,
	       const move_iterator<_IteratorR>& __y)
    { return !(__y < __x); }

template<typename _Iterator>
    inline _GLIBCXX17_CONSTEXPR bool
    operator<=(const move_iterator<_Iterator>& __x,
	       const move_iterator<_Iterator>& __y)
    { return !(__y < __x); }

template<typename _IteratorL, typename _IteratorR>
    inline _GLIBCXX17_CONSTEXPR bool
    operator>(const move_iterator<_IteratorL>& __x,
	      const move_iterator<_IteratorR>& __y)
    { return __y < __x; }

template<typename _Iterator>
    inline _GLIBCXX17_CONSTEXPR bool
    operator>(const move_iterator<_Iterator>& __x,
	      const move_iterator<_Iterator>& __y)
    { return __y < __x; }

template<typename _IteratorL, typename _IteratorR>
    inline _GLIBCXX17_CONSTEXPR bool
    operator>=(const move_iterator<_IteratorL>& __x,
	       const move_iterator<_IteratorR>& __y)
    { return !(__x < __y); }

template<typename _Iterator>
    inline _GLIBCXX17_CONSTEXPR bool
    operator>=(const move_iterator<_Iterator>& __x,
	       const move_iterator<_Iterator>& __y)
    { return !(__x < __y); }

// DR 685.
  template<typename _IteratorL, typename _IteratorR>
    inline _GLIBCXX17_CONSTEXPR 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 _GLIBCXX17_CONSTEXPR move_iterator<_Iterator>
    operator+(typename move_iterator<_Iterator>::difference_type __n,
	      const move_iterator<_Iterator>& __x)
    { return __x + __n; }

template<typename _Iterator>
    inline _GLIBCXX17_CONSTEXPR move_iterator<_Iterator>
    make_move_iterator(_Iterator __i)
    { return move_iterator<_Iterator>(__i); }

template<typename _Iterator, typename _ReturnType
    = typename conditional<__move_if_noexcept_cond
      <typename iterator_traits<_Iterator>::value_type>::value,
                _Iterator, move_iterator<_Iterator>>::type>
    inline _GLIBCXX17_CONSTEXPR _ReturnType
    __make_move_if_noexcept_iterator(_Iterator __i)
    { return _ReturnType(__i); }

// Overload for pointers that matches std::move_if_noexcept more closely,
  // returning a constant iterator when we don't want to move.
  template<typename _Tp, typename _ReturnType
    = typename conditional<__move_if_noexcept_cond<_Tp>::value,
			   const _Tp*, move_iterator<_Tp*>>::type>
    inline _GLIBCXX17_CONSTEXPR _ReturnType
    __make_move_if_noexcept_iterator(_Tp* __i)
    { return _ReturnType(__i); }

// @} group iterators

template<typename _Iterator>
    auto
    __niter_base(move_iterator<_Iterator> __it)
    -> decltype(make_move_iterator(__niter_base(__it.base())))
    { return make_move_iterator(__niter_base(__it.base())); }

template<typename _Iterator>
    struct __is_move_iterator<move_iterator<_Iterator> >
    {
      enum { __value = 1 };
      typedef __true_type __type;
    };

template<typename _Iterator>
    auto
    __miter_base(move_iterator<_Iterator> __it)
    -> decltype(__miter_base(__it.base()))
    { return __miter_base(__it.base()); }

#define _GLIBCXX_MAKE_MOVE_ITERATOR(_Iter) std::make_move_iterator(_Iter)
#define _GLIBCXX_MAKE_MOVE_IF_NOEXCEPT_ITERATOR(_Iter) \
  std::__make_move_if_noexcept_iterator(_Iter)
#else
#define _GLIBCXX_MAKE_MOVE_ITERATOR(_Iter) (_Iter)
#define _GLIBCXX_MAKE_MOVE_IF_NOEXCEPT_ITERATOR(_Iter) (_Iter)
#endif // C++11

#if __cpp_deduction_guides >= 201606
  // These helper traits are used for deduction guides
  // of associative containers.
  template<typename _InputIterator>
    using __iter_key_t = remove_const_t<
    typename iterator_traits<_InputIterator>::value_type::first_type>;

template<typename _InputIterator>
    using __iter_val_t =
    typename iterator_traits<_InputIterator>::value_type::second_type;

template<typename _T1, typename _T2>
    struct pair;

template<typename _InputIterator>
    using __iter_to_alloc_t =
    pair<add_const_t<__iter_key_t<_InputIterator>>,
	 __iter_val_t<_InputIterator>>;

#endif

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace

#ifdef _GLIBCXX_DEBUG
# include <debug/stl_iterator.h>
#endif

#endif