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stl_iterator_base_types.h

// Types used in iterator implementation -*- 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_base_types.h
 *  This is an internal header file, included by other library headers.
 *  Do not attempt to use it directly. @headername{iterator}
 *
 *  This file contains all of the general iterator-related utility types,
 *  such as iterator_traits and struct iterator.
 */

#ifndef _STL_ITERATOR_BASE_TYPES_H
#define _STL_ITERATOR_BASE_TYPES_H 1

#pragma GCC system_header

#include <bits/c++config.h>

#if __cplusplus >= 201103L
# include <type_traits>  // For __void_t, is_convertible
#endif

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

/**
   *  @defgroup iterators Iterators
   *  Abstractions for uniform iterating through various underlying types.
  */
  //@{

/**
   *  @defgroup iterator_tags Iterator Tags
   *  These are empty types, used to distinguish different iterators.  The
   *  distinction is not made by what they contain, but simply by what they
   *  are.  Different underlying algorithms can then be used based on the
   *  different operations supported by different iterator types.
  */
  //@{ 
  ///  Marking input iterators.
  struct input_iterator_tag { };

///  Marking output iterators.
  struct output_iterator_tag { };

/// Forward iterators support a superset of input iterator operations.
  struct forward_iterator_tag : public input_iterator_tag { };

/// Bidirectional iterators support a superset of forward iterator
  /// operations.
  struct bidirectional_iterator_tag : public forward_iterator_tag { };

/// Random-access iterators support a superset of bidirectional
  /// iterator operations.
  struct random_access_iterator_tag : public bidirectional_iterator_tag { };
  //@}

/**
   *  @brief  Common %iterator class.
   *
   *  This class does nothing but define nested typedefs.  %Iterator classes
   *  can inherit from this class to save some work.  The typedefs are then
   *  used in specializations and overloading.
   *
   *  In particular, there are no default implementations of requirements
   *  such as @c operator++ and the like.  (How could there be?)
  */
  template<typename _Category, typename _Tp, typename _Distance = ptrdiff_t,
           typename _Pointer = _Tp*, typename _Reference = _Tp&>
    struct iterator
    {
      /// One of the @link iterator_tags tag types@endlink.
      typedef _Category  iterator_category;
      /// The type "pointed to" by the iterator.
      typedef _Tp        value_type;
      /// Distance between iterators is represented as this type.
      typedef _Distance  difference_type;
      /// This type represents a pointer-to-value_type.
      typedef _Pointer   pointer;
      /// This type represents a reference-to-value_type.
      typedef _Reference reference;
    };

/**
   *  @brief  Traits class for iterators.
   *
   *  This class does nothing but define nested typedefs.  The general
   *  version simply @a forwards the nested typedefs from the Iterator
   *  argument.  Specialized versions for pointers and pointers-to-const
   *  provide tighter, more correct semantics.
  */
#if __cplusplus >= 201103L
  // _GLIBCXX_RESOLVE_LIB_DEFECTS
  // 2408. SFINAE-friendly common_type/iterator_traits is missing in C++14
  template<typename _Iterator, typename = __void_t<>>
    struct __iterator_traits { };

template<typename _Iterator>
    struct __iterator_traits<_Iterator,
			     __void_t<typename _Iterator::iterator_category,
				      typename _Iterator::value_type,
				      typename _Iterator::difference_type,
				      typename _Iterator::pointer,
				      typename _Iterator::reference>>
    {
      typedef typename _Iterator::iterator_category iterator_category;
      typedef typename _Iterator::value_type        value_type;
      typedef typename _Iterator::difference_type   difference_type;
      typedef typename _Iterator::pointer           pointer;
      typedef typename _Iterator::reference         reference;
    };

template<typename _Iterator>
    struct iterator_traits
    : public __iterator_traits<_Iterator> { };
#else
  template<typename _Iterator>
    struct iterator_traits
    {
      typedef typename _Iterator::iterator_category iterator_category;
      typedef typename _Iterator::value_type        value_type;
      typedef typename _Iterator::difference_type   difference_type;
      typedef typename _Iterator::pointer           pointer;
      typedef typename _Iterator::reference         reference;
    };
#endif

/// Partial specialization for pointer types.
  template<typename _Tp>
    struct iterator_traits<_Tp*>
    {
      typedef random_access_iterator_tag iterator_category;
      typedef _Tp                         value_type;
      typedef ptrdiff_t                   difference_type;
      typedef _Tp*                        pointer;
      typedef _Tp&                        reference;
    };

/// Partial specialization for const pointer types.
  template<typename _Tp>
    struct iterator_traits<const _Tp*>
    {
      typedef random_access_iterator_tag iterator_category;
      typedef _Tp                         value_type;
      typedef ptrdiff_t                   difference_type;
      typedef const _Tp*                  pointer;
      typedef const _Tp&                  reference;
    };

/**
   *  This function is not a part of the C++ standard but is syntactic
   *  sugar for internal library use only.
  */
  template<typename _Iter>
    inline _GLIBCXX_CONSTEXPR
    typename iterator_traits<_Iter>::iterator_category
    __iterator_category(const _Iter&)
    { return typename iterator_traits<_Iter>::iterator_category(); }

//@}

#if __cplusplus < 201103L
  // If _Iterator has a base returns it otherwise _Iterator is returned
  // untouched
  template<typename _Iterator, bool _HasBase>
    struct _Iter_base
    {
      typedef _Iterator iterator_type;
      static iterator_type _S_base(_Iterator __it)
      { return __it; }
    };

template<typename _Iterator>
    struct _Iter_base<_Iterator, true>
    {
      typedef typename _Iterator::iterator_type iterator_type;
      static iterator_type _S_base(_Iterator __it)
      { return __it.base(); }
    };
#endif

#if __cplusplus >= 201103L
  template<typename _InIter>
    using _RequireInputIter = typename
      enable_if<is_convertible<typename
		iterator_traits<_InIter>::iterator_category,
			       input_iterator_tag>::value>::type;
#endif

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace

#endif /* _STL_ITERATOR_BASE_TYPES_H */

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