stl_iterator_base_types.h

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// Types used in iterator implementation -*- C++ -*-

// Copyright (C) 2001-2026 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
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// any later version.

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/*
 *
 * 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

#ifdef _GLIBCXX_SYSHDR
#pragma GCC system_header
#endif

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

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

#if __cplusplus > 201703L && __cpp_concepts >= 201907L
# include <bits/iterator_concepts.h>
#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 { };

#if __cplusplus > 201703L
  /// Contiguous iterators point to objects stored contiguously in memory.
  struct contiguous_iterator_tag : public random_access_iterator_tag { };
#endif
  ///@}

  /**
   *  @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 _GLIBCXX17_DEPRECATED 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.
  */
  template<typename _Iterator>
    struct iterator_traits;

#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 { };

#if ! __cpp_lib_concepts

  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;
    };
#endif // ! concepts

  template<typename _Iterator>
    struct iterator_traits
    : public __iterator_traits<_Iterator> { };

#else // ! C++11
  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 // C++11

#if __cplusplus > 201703L
  /// Partial specialization for object pointer types.
  template<typename _Tp>
#if __cpp_concepts >= 201907L
    requires is_object_v<_Tp>
#endif
    struct iterator_traits<_Tp*>
    {
      using iterator_concept  = contiguous_iterator_tag;
      using iterator_category = random_access_iterator_tag;
      using value_type        = remove_cv_t<_Tp>;
      using difference_type   = ptrdiff_t;
      using pointer           = _Tp*;
      using reference         = _Tp&;
    };
#else
  /// 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;
    };
#endif

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

  ///@}

#if __cplusplus >= 201103L
  template<typename _Iter>
    using __iter_category_t
      = typename iterator_traits<_Iter>::iterator_category;

  template<typename _InIter>
    using _RequireInputIter =
      __enable_if_t<is_convertible<__iter_category_t<_InIter>,
                                   input_iterator_tag>::value>;

#if __cpp_concepts
  template<typename _InIter>
    concept __has_input_iter_cat
      = is_convertible_v<__iter_category_t<_InIter>, input_iterator_tag>;

#ifdef __cpp_lib_concepts
  // Is a Cpp17InputIterator or satisfies std::input_iterator.
  template<typename _InIterator>
    concept __any_input_iterator
      = input_iterator<_InIterator> || __has_input_iter_cat<_InIterator>;
#endif
#endif

  template<typename _It,
           typename _Cat = __iter_category_t<_It>>
    struct __is_random_access_iter
      : is_base_of<random_access_iterator_tag, _Cat>
    {
      typedef is_base_of<random_access_iterator_tag, _Cat> _Base;
      enum { __value = _Base::value };
    };
#else
  template<typename _It, typename _Traits = iterator_traits<_It>,
           typename _Cat = typename _Traits::iterator_category>
    struct __is_random_access_iter
    { enum { __value = __is_base_of(random_access_iterator_tag, _Cat) }; };
#endif

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace

#if __glibcxx_algorithm_default_value_type // C++ >= 26
# define _GLIBCXX26_DEF_VAL_T(T) = T
# define _GLIBCXX26_ALGO_DEF_VAL_T(_Iterator) \
     = typename iterator_traits<_Iterator>::value_type
#else
# define _GLIBCXX26_DEF_VAL_T(T)
# define _GLIBCXX26_ALGO_DEF_VAL_T(_Iterator)
#endif

#endif /* _STL_ITERATOR_BASE_TYPES_H */