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
// 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
 
#ifdef _GLIBCXX_SYSHDR
#pragma GCC system_header
#endif
 
#include <bits/c++config.h>
 
#if __cplusplus >= 201103L
# include <type_traits>  // For __void_t, is_convertible, __enable_if_t
#else
# include <ext/type_traits.h> // For __gnu_cxx::__enable_if
#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 `operator++` and the like.  (How could there be?)
   *
   *  @deprecated Deprecated since C++17. The recommended alternative is to
   *  simply define the typedefs directly in your iterator class.
  */
  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 declares aliases for the nested typedefs from the Iterator
   *  argument.  Partial specializations for pointers define the typedefs
   *  appropriately for the semantics of pointers.
  */
  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
 
  /// @cond undocumented
  /**
   *  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
 
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wc++14-extensions" // variable templates
  template<typename _Iter, typename = void>
    const bool __enable_for_each_segment = false;
 
  template<typename _Iter>
    const bool __enable_for_each_segment<_Iter,
#if __cplusplus >= 201103L
      __enable_if_t<_Iter::_S_enable_for_each_segment>
#else
      typename __gnu_cxx::__enable_if<_Iter::_S_enable_for_each_segment, void>::__type
#endif
      > = true;
#pragma GCC diagnostic pop
 
#if __cpp_lib_concepts
  template<typename _Iter>
    concept __segmented_iterator = __enable_for_each_segment<_Iter>;
#endif
 
  /// @endcond
  /// @}
 
_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 */