iterator_range.h

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// ------------------------------------------------------------------------
//
// SPDX-License-Identifier: LGPL-2.1-or-later
// Copyright (C) 2014 - 2025 by the deal.II authors
//
// This file is part of the deal.II library.
//
// Part of the source code is dual licensed under Apache-2.0 WITH
// LLVM-exception OR LGPL-2.1-or-later. Detailed license information
// governing the source code and code contributions can be found in
// LICENSE.md and CONTRIBUTING.md at the top level directory of deal.II.
//
// ------------------------------------------------------------------------
 
#ifndef dealii_iterator_range_h
#define dealii_iterator_range_h
 
 
#include <deal.II/base/config.h>
 
#include <deal.II/base/std_cxx20/type_traits.h>
#include <deal.II/base/template_constraints.h>
 
#include <iterator>
 
DEAL_II_NAMESPACE_OPEN
 
 
// Forward declaration
#ifndef DOXYGEN
template <typename Iterator>
class IteratorOverIterators;
#endif
 

template <typename Iterator>
class IteratorRange
{
public:
  using IteratorOverIterators = ::IteratorOverIterators<Iterator>;
 

  using iterator = Iterator;

  IteratorRange();

  IteratorRange(const iterator begin, const iterator end);

  IteratorOverIterators
  begin();

  IteratorOverIterators
  begin() const;

  IteratorOverIterators
  end() const;

  IteratorOverIterators
  end();
 
private:
  const IteratorOverIterators it_begin;
  const IteratorOverIterators it_end;
};
 
 

template <typename Iterator>
class IteratorOverIterators
{
public:
  using BaseIterator = Iterator;

  explicit IteratorOverIterators(const BaseIterator &iterator);

  const BaseIterator &
  operator*() const;

  const BaseIterator *
  operator->() const;

  IteratorOverIterators &
  operator++();

  IteratorOverIterators
  operator++(int);

  bool
  operator!=(const IteratorOverIterators &i_o_i) const;

  operator const BaseIterator &() const;

  using iterator_category = std::forward_iterator_tag;
  using value_type        = Iterator;
  using difference_type   = typename Iterator::difference_type;
  using pointer           = Iterator *;
  using reference         = Iterator &;
 
private:
  BaseIterator element_of_iterator_collection;
};
 
 

template <typename BaseIterator>
IteratorRange<BaseIterator>
make_iterator_range(const BaseIterator                             &begin,
                    const std_cxx20::type_identity_t<BaseIterator> &end)
{
  IteratorRange<BaseIterator> ir(begin, end);
  return ir;
}
 
 
// ------------------- template member functions
 
 
template <typename Iterator>
inline IteratorOverIterators<Iterator>::IteratorOverIterators(
  const BaseIterator &iterator)
  : element_of_iterator_collection(iterator)
{}
 
 
 
template <typename Iterator>
inline const typename IteratorOverIterators<Iterator>::BaseIterator &
IteratorOverIterators<Iterator>::operator*() const
{
  return element_of_iterator_collection;
}
 
 
 
template <typename Iterator>
inline const typename IteratorOverIterators<Iterator>::BaseIterator *
IteratorOverIterators<Iterator>::operator->() const
{
  return &element_of_iterator_collection;
}
 
 
 
template <typename Iterator>
inline IteratorOverIterators<Iterator> &
IteratorOverIterators<Iterator>::operator++()
{
  ++element_of_iterator_collection;
  return *this;
}
 
 
 
template <typename Iterator>
inline IteratorOverIterators<Iterator>
IteratorOverIterators<Iterator>::operator++(int)
{
  const IteratorOverIterators old_value = *this;
  ++element_of_iterator_collection;
  return *old_value;
}
 
 
 
template <typename Iterator>
inline bool
IteratorOverIterators<Iterator>::operator!=(
  const IteratorOverIterators &i_o_i) const
{
  return element_of_iterator_collection != i_o_i.element_of_iterator_collection;
}
 
 
 
template <typename Iterator>
inline IteratorOverIterators<Iterator>::operator const BaseIterator &() const
{
  return element_of_iterator_collection;
}
 
 
 
template <typename Iterator>
inline IteratorRange<Iterator>::IteratorRange()
  : it_begin()
  , it_end()
{}
 
 
 
template <typename Iterator>
inline IteratorRange<Iterator>::IteratorRange(const iterator b,
                                              const iterator e)
  : it_begin(b)
  , it_end(e)
{}
 
 
template <typename Iterator>
inline typename IteratorRange<Iterator>::IteratorOverIterators
IteratorRange<Iterator>::begin()
{
  return it_begin;
}
 
 
template <typename Iterator>
inline typename IteratorRange<Iterator>::IteratorOverIterators
IteratorRange<Iterator>::begin() const
{
  return it_begin;
}
 
 
template <typename Iterator>
inline typename IteratorRange<Iterator>::IteratorOverIterators
IteratorRange<Iterator>::end()
{
  return it_end;
}
 
 
template <typename Iterator>
inline typename IteratorRange<Iterator>::IteratorOverIterators
IteratorRange<Iterator>::end() const
{
  return it_end;
}
 
 
DEAL_II_NAMESPACE_CLOSE
 
#endif