iterator.h

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/******************************************************************************
The MIT License(MIT)
 
Embedded Template Library.
https://github.com/ETLCPP/etl
https://www.etlcpp.com
 
Copyright(c) 2017 John Wellbelove
 
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#ifndef ETL_ITERATOR_INCLUDED
#define ETL_ITERATOR_INCLUDED
 
#include "platform.h"
#include "invoke.h"
#include "type_traits.h"
#include "utility.h"
#include "private/addressof.h"
 
#if ETL_USING_STL || defined(ETL_IN_UNIT_TEST)
  #include <iterator>
#endif

 
namespace etl
{
  //***************************************************************************
  // iterator tags
  struct input_iterator_tag
  {
  };
  struct output_iterator_tag
  {
  };
  struct forward_iterator_tag : public input_iterator_tag
  {
  };
  struct bidirectional_iterator_tag : public forward_iterator_tag
  {
  };
  struct random_access_iterator_tag : public bidirectional_iterator_tag
  {
  };
  // struct contiguous_iterator_tag : public random_access_iterator_tag {};
 
  //***************************************************************************
  // iterator_traits
 
#if ETL_USING_CPP11
 
  // Primary template: falls through to std::iterator_traits when STL is available (C++20+),
  // otherwise empty (SFINAE-safe fallback for iterators without nested typedefs).
  template <typename TIterator, typename = void>
  struct iterator_traits
  #if ETL_USING_STL && ETL_USING_CPP20
    : std::iterator_traits<TIterator>
  #endif
  {
  };
 
  // Specialization for iterators that define the standard nested typedefs.
  template <typename TIterator>
  struct iterator_traits<TIterator, etl::void_t< typename TIterator::iterator_category, typename TIterator::value_type,
                                                 typename TIterator::difference_type, typename TIterator::pointer, typename TIterator::reference >>
  {
    typedef typename TIterator::iterator_category iterator_category;
    typedef typename TIterator::value_type        value_type;
    typedef typename TIterator::difference_type   difference_type;
    typedef typename TIterator::pointer           pointer;
    typedef typename TIterator::reference         reference;
  };
 
  #if ETL_USING_STL && ETL_USING_CPP20
  // Specialization for std::common_iterator (C++20).
  template <typename I, typename S>
  struct iterator_traits<std::common_iterator<I, S>, void> : std::iterator_traits<std::common_iterator<I, S>>
  {
  };
  #endif
 
  // For pointers.
  template <typename T>
  struct iterator_traits<T*, void>
  {
    typedef ETL_OR_STD::random_access_iterator_tag iterator_category;
    typedef T                                      value_type;
    typedef ptrdiff_t                              difference_type;
    typedef typename etl::remove_cv<T>::type*      pointer;
    typedef T&                                     reference;
  };
 
  // For const pointers.
  template <typename T>
  struct iterator_traits<const T*, void>
  {
    typedef ETL_OR_STD::random_access_iterator_tag  iterator_category;
    typedef T                                       value_type;
    typedef ptrdiff_t                               difference_type;
    typedef const typename etl::remove_cv<T>::type* pointer;
    typedef const T&                                reference;
  };
 
#else // C++03
 
  // Primary template: unconditionally extracts nested typedefs.
  template <typename TIterator>
  struct iterator_traits
  {
    typedef typename TIterator::iterator_category iterator_category;
    typedef typename TIterator::value_type        value_type;
    typedef typename TIterator::difference_type   difference_type;
    typedef typename TIterator::pointer           pointer;
    typedef typename TIterator::reference         reference;
  };
 
  // For pointers.
  template <typename T>
  struct iterator_traits<T*>
  {
    typedef ETL_OR_STD::random_access_iterator_tag iterator_category;
    typedef T                                      value_type;
    typedef ptrdiff_t                              difference_type;
    typedef typename etl::remove_cv<T>::type*      pointer;
    typedef T&                                     reference;
  };
 
  // For const pointers.
  template <typename T>
  struct iterator_traits<const T*>
  {
    typedef ETL_OR_STD::random_access_iterator_tag  iterator_category;
    typedef T                                       value_type;
    typedef ptrdiff_t                               difference_type;
    typedef const typename etl::remove_cv<T>::type* pointer;
    typedef const T&                                reference;
  };
 
#endif
 
  //***************************************************************************
  // advance
  template <typename TIterator, typename TDistance>
  ETL_CONSTEXPR14 void advance_helper(TIterator& itr, TDistance n, ETL_OR_STD::input_iterator_tag)
  {
    while (n-- > 0)
    {
      ++itr;
    }
  }
 
  template <typename TIterator, typename TDistance>
  ETL_CONSTEXPR14 void advance_helper(TIterator& itr, TDistance n, ETL_OR_STD::output_iterator_tag)
  {
    while (n-- > 0)
    {
      ++itr;
    }
  }
 
  template <typename TIterator, typename TDistance>
  ETL_CONSTEXPR14 void advance_helper(TIterator& itr, TDistance n, ETL_OR_STD::forward_iterator_tag)
  {
    while (n-- > 0)
    {
      ++itr;
    }
  }
 
  template <typename TIterator, typename TDistance>
  ETL_CONSTEXPR14 void advance_helper(TIterator& itr, TDistance n, ETL_OR_STD::bidirectional_iterator_tag)
  {
    if (n > 0)
    {
      while (n--)
      {
        ++itr;
      }
    }
    else
    {
      while (n++)
      {
        --itr;
      }
    }
  }
 
  template <typename TIterator, typename TDistance>
  ETL_CONSTEXPR14 void advance_helper(TIterator& itr, TDistance n, ETL_OR_STD::random_access_iterator_tag)
  {
    typedef typename etl::iterator_traits<TIterator>::difference_type diff_t;
    itr += static_cast<diff_t>(n);
  }
 
  template <typename TIterator, typename TDistance>
  ETL_CONSTEXPR14 void advance(TIterator& itr, TDistance n)
  {
    typedef typename etl::iterator_traits<TIterator>::iterator_category tag;
 
    advance_helper(itr, n, tag());
  }
 
  //***************************************************************************
  // distance
  template <typename TIterator>
  ETL_CONSTEXPR14 typename etl::iterator_traits<TIterator>::difference_type distance_helper(TIterator first, TIterator last, ETL_OR_STD::input_iterator_tag)
  {
    typename etl::iterator_traits<TIterator>::difference_type d = 0;
 
    while (first != last)
    {
      ++d;
      ++first;
    }
 
    return d;
  }
 
  template <typename TIterator>
  ETL_CONSTEXPR14 typename etl::iterator_traits<TIterator>::difference_type distance_helper(TIterator first, TIterator last,
                                                                                      ETL_OR_STD::forward_iterator_tag)
  {
    typename etl::iterator_traits<TIterator>::difference_type d = 0;
 
    while (first != last)
    {
      ++d;
      ++first;
    }
 
    return d;
  }
 
  template <typename TIterator>
  ETL_CONSTEXPR14 typename etl::iterator_traits<TIterator>::difference_type distance_helper(TIterator first, TIterator last,
                                                                                      ETL_OR_STD::bidirectional_iterator_tag)
  {
    typename etl::iterator_traits<TIterator>::difference_type d = 0;
 
    while (first != last)
    {
      ++d;
      ++first;
    }
 
    return d;
  }
 
  template <typename TIterator>
  ETL_CONSTEXPR14 typename etl::iterator_traits<TIterator>::difference_type distance_helper(TIterator first, TIterator last,
                                                                                      ETL_OR_STD::random_access_iterator_tag)
  {
    return last - first;
  }
 
  template <typename TIterator>
  ETL_CONSTEXPR14 typename etl::iterator_traits<TIterator>::difference_type distance(TIterator first, TIterator last)
  {
    typedef typename etl::iterator_traits<TIterator>::iterator_category tag;
 
    return distance_helper(first, last, tag());
  }
 
  //***************************************************************************
  // Previous
  template <typename TIterator>
  ETL_CONSTEXPR14 TIterator prev(TIterator itr, typename etl::iterator_traits<TIterator>::difference_type n = 1)
  {
    etl::advance(itr, -n);
 
    return itr;
  }
 
  //***************************************************************************
  // Next
  template <typename TIterator>
  ETL_CONSTEXPR14 TIterator next(TIterator itr, typename etl::iterator_traits<TIterator>::difference_type n = 1)
  {
    etl::advance(itr, n);
 
    return itr;
  }
 
  //***************************************************************************
  // reverse_iterator
  template <typename TIterator>
  class reverse_iterator
  {
  public:
 
    typedef typename iterator_traits<TIterator>::iterator_category iterator_category;
    typedef typename iterator_traits<TIterator>::value_type        value_type;
    typedef typename iterator_traits<TIterator>::difference_type   difference_type;
    typedef typename iterator_traits<TIterator>::pointer           pointer;
    typedef typename iterator_traits<TIterator>::reference         reference;
 
    typedef TIterator iterator_type;
 
    ETL_CONSTEXPR14 reverse_iterator()
      : current()
    {
    }
 
    ETL_CONSTEXPR14 explicit reverse_iterator(TIterator itr)
      : current(itr)
    {
    }
 
    template <typename TOther>
    ETL_CONSTEXPR14 reverse_iterator(const reverse_iterator<TOther>& other)
      : current(other.base())
    {
    }
 
    template <class TOther>
    ETL_CONSTEXPR14 reverse_iterator& operator=(const reverse_iterator<TOther>& other)
    {
      current = other.base();
 
      return (*this);
    }
 
    ETL_CONSTEXPR14 TIterator base() const
    {
      return current;
    }
 
    ETL_NODISCARD ETL_CONSTEXPR14 reference operator*() const
    {
      TIterator temp = current;
 
      return *(--temp);
    }
 
    ETL_NODISCARD ETL_CONSTEXPR14 pointer operator->() const
    {
      TIterator temp = current;
 
      return &(*--temp);
    }
 
    ETL_CONSTEXPR14 reverse_iterator& operator++()
    {
      --current;
 
      return *this;
    }
 
    ETL_CONSTEXPR14 reverse_iterator operator++(int)
    {
      reverse_iterator temp = *this;
      --current;
 
      return temp;
    }
 
    ETL_CONSTEXPR14 reverse_iterator& operator--()
    {
      ++current;
 
      return (*this);
    }
 
    ETL_CONSTEXPR14 reverse_iterator operator--(int)
    {
      reverse_iterator temp = *this;
      ++current;
 
      return temp;
    }
 
    ETL_CONSTEXPR14 reverse_iterator& operator+=(const difference_type offset)
    {
      current -= offset;
 
      return (*this);
    }
 
    ETL_CONSTEXPR14 reverse_iterator& operator-=(const difference_type offset)
    {
      current += offset;
 
      return (*this);
    }
 
    ETL_NODISCARD ETL_CONSTEXPR14 reverse_iterator operator+(const difference_type offset) const
    {
      return reverse_iterator(current - offset);
    }
 
    ETL_NODISCARD ETL_CONSTEXPR14 reverse_iterator operator-(const difference_type offset) const
    {
      return (reverse_iterator(current + offset));
    }
 
    ETL_NODISCARD ETL_CONSTEXPR14 reference operator[](const difference_type offset) const
    {
      return (*(*this + offset));
    }
 
  protected:
 
    TIterator current;
  };
 
  template <typename TIterator>
  ETL_CONSTEXPR14 bool operator==(const reverse_iterator<TIterator>& lhs, const reverse_iterator<TIterator>& rhs)
  {
    return lhs.base() == rhs.base();
  }
 
  template <typename TIterator>
  ETL_CONSTEXPR14 bool operator!=(const reverse_iterator<TIterator>& lhs, const reverse_iterator<TIterator>& rhs)
  {
    return !(lhs == rhs);
  }
 
  template <typename TIterator>
  ETL_CONSTEXPR14 bool operator<(const reverse_iterator<TIterator>& lhs, const reverse_iterator<TIterator>& rhs)
  {
    return rhs.base() < lhs.base();
  }
 
  template <typename TIterator>
  ETL_CONSTEXPR14 bool operator>(const reverse_iterator<TIterator>& lhs, const reverse_iterator<TIterator>& rhs)
  {
    return rhs < lhs;
  }
 
  template <typename TIterator>
  ETL_CONSTEXPR14 bool operator<=(const reverse_iterator<TIterator>& lhs, const reverse_iterator<TIterator>& rhs)
  {
    return !(rhs < lhs);
  }
 
  template <typename TIterator>
  ETL_CONSTEXPR14 bool operator>=(const reverse_iterator<TIterator>& lhs, const reverse_iterator<TIterator>& rhs)
  {
    return !(lhs < rhs);
  }
 
  template <typename TIterator>
  ETL_CONSTEXPR14 typename reverse_iterator<TIterator>::difference_type operator-(const reverse_iterator<TIterator>& lhs,
                                                                            const reverse_iterator<TIterator>& rhs)
  {
    return rhs.base() - lhs.base();
  }
 
  template <typename TIterator, class TDifference>
  ETL_CONSTEXPR14 reverse_iterator<TIterator> operator+(TDifference n, const reverse_iterator<TIterator>& itr)
  {
    return itr.operator+(n);
  }
 
  //***************************************************************************
  //***************************************************************************
  template <typename TCategory, typename T, typename TDistance = ptrdiff_t, typename TPointer = T*, typename TReference = T& >
  struct iterator
  {
    typedef T          value_type;
    typedef TDistance  difference_type;
    typedef TPointer   pointer;
    typedef TReference reference;
    typedef TCategory  iterator_category;
  };
 
#if ETL_USING_CPP11
  //***************************************************************************
  // move_iterator
  template <typename TIterator>
  class move_iterator
  {
  public:
 
    typedef typename iterator_traits<TIterator>::iterator_category iterator_category;
    typedef typename iterator_traits<TIterator>::value_type        value_type;
    typedef typename iterator_traits<TIterator>::difference_type   difference_type;
    typedef TIterator                                              iterator_type;
    typedef TIterator                                              pointer;
    typedef value_type&&                                           reference;
 
    ETL_CONSTEXPR move_iterator()
      : current()
    {
    }
 
    ETL_CONSTEXPR explicit move_iterator(TIterator itr)
      : current(itr)
    {
    }
 
    template <typename U>
    ETL_CONSTEXPR move_iterator(const move_iterator<U>& itr)
      : current(itr.base())
    {
    }
 
    template <typename U>
    ETL_CONSTEXPR14 move_iterator& operator=(const move_iterator<U>& itr)
    {
      current = itr.current;
      return *this;
    }
 
    ETL_CONSTEXPR iterator_type base() const
    {
      return current;
    }
 
    ETL_CONSTEXPR pointer operator->() const
    {
      return current;
    }
 
    ETL_CONSTEXPR reference operator*() const
    {
      return etl::move(*current);
    }
 
    ETL_CONSTEXPR14 move_iterator& operator++()
    {
      ++current;
      return *this;
    }
 
    ETL_CONSTEXPR14 move_iterator& operator--()
    {
      --current;
      return *this;
    }
 
    ETL_CONSTEXPR14 move_iterator operator++(int)
    {
      move_iterator temp = *this;
      ++current;
      return temp;
    }
 
    ETL_CONSTEXPR14 move_iterator operator--(int)
    {
      move_iterator temp = *this;
      --current;
      return temp;
    }
 
    ETL_CONSTEXPR move_iterator operator+(difference_type n) const
    {
      return move_iterator(current + n);
    }
 
    ETL_CONSTEXPR move_iterator operator-(difference_type n) const
    {
      return move_iterator(current - n);
    }
 
    ETL_CONSTEXPR14 move_iterator& operator+=(difference_type n)
    {
      current += n;
      return *this;
    }
 
    ETL_CONSTEXPR14 move_iterator& operator-=(difference_type n)
    {
      current -= n;
      return *this;
    }
 
    ETL_CONSTEXPR reference operator[](difference_type n) const
    {
      return etl::move(current[n]);
    }
 
  private:
 
    TIterator current;
  };
 
  template <typename TIterator>
  ETL_CONSTEXPR bool operator==(const etl::move_iterator<TIterator>& lhs, const etl::move_iterator<TIterator>& rhs)
  {
    return lhs.base() == rhs.base();
  }
 
  template <typename TIterator>
  ETL_CONSTEXPR bool operator!=(const etl::move_iterator<TIterator>& lhs, const etl::move_iterator<TIterator>& rhs)
  {
    return !(lhs == rhs);
  }
 
  template <typename TIterator>
  ETL_CONSTEXPR bool operator<(const etl::move_iterator<TIterator>& lhs, const etl::move_iterator<TIterator>& rhs)
  {
    return lhs.base() < rhs.base();
  }
 
  template <typename TIterator>
  ETL_CONSTEXPR bool operator<=(const etl::move_iterator<TIterator>& lhs, const etl::move_iterator<TIterator>& rhs)
  {
    return !(rhs < lhs);
  }
 
  template <typename TIterator>
  ETL_CONSTEXPR bool operator>(const etl::move_iterator<TIterator>& lhs, const etl::move_iterator<TIterator>& rhs)
  {
    return (rhs < lhs);
  }
 
  template <typename TIterator>
  ETL_CONSTEXPR bool operator>=(const etl::move_iterator<TIterator>& lhs, const etl::move_iterator<TIterator>& rhs)
  {
    return !(lhs < rhs);
  }
 
  template <typename TIterator>
  ETL_CONSTEXPR move_iterator<TIterator> operator+(typename move_iterator<TIterator>::difference_type n, const move_iterator<TIterator>& rhs)
  {
    return rhs + n;
  }
 
  template <typename TIterator1, typename TIterator2 >
  ETL_CONSTEXPR auto operator-(const move_iterator<TIterator1>& lhs, const move_iterator<TIterator2>& rhs) -> decltype(lhs.base() - rhs.base())
  {
    return lhs.base() - rhs.base();
  }
 
  template <typename TIterator>
  ETL_CONSTEXPR etl::move_iterator<TIterator> make_move_iterator(TIterator itr)
  {
    return etl::move_iterator<TIterator>(itr);
  }
 
#endif // ETL_USING_CPP11
 
  //***************************************************************************
  // back_insert_iterator
  //***************************************************************************
 
  //***************************************************************************
  //***************************************************************************
  template <typename TContainer>
  class back_insert_iterator : public etl::iterator<ETL_OR_STD::output_iterator_tag, void, void, void, void>
  {
  public:
 
    typedef TContainer container_type;
 
    //***************************************************************************
    //***************************************************************************
    explicit ETL_CONSTEXPR14 back_insert_iterator(TContainer& c)
      : container(etl::addressof(c))
    {
    }
 
    //***************************************************************************
    //***************************************************************************
    ETL_CONSTEXPR14 back_insert_iterator& operator=(const typename TContainer::value_type& value)
    {
      container->push_back(value);
 
      return (*this);
    }
 
#if ETL_USING_CPP11
    //***************************************************************************
    //***************************************************************************
    ETL_CONSTEXPR14 back_insert_iterator& operator=(typename TContainer::value_type&& value)
    {
      container->push_back(etl::move(value));
 
      return (*this);
    }
#endif // ETL_USING_CPP11
 
    //***************************************************************************
    //***************************************************************************
    ETL_NODISCARD ETL_CONSTEXPR14 back_insert_iterator& operator*()
    {
      return (*this);
    }
 
    //***************************************************************************
    //***************************************************************************
    ETL_CONSTEXPR14 back_insert_iterator& operator++()
    {
      return (*this);
    }
 
    //***************************************************************************
    //***************************************************************************
    ETL_CONSTEXPR14 back_insert_iterator operator++(int)
    {
      return (*this);
    }
 
  protected:
 
    TContainer* container;
  };
 
  //***************************************************************************
  //***************************************************************************
  template <typename TContainer>
  ETL_NODISCARD ETL_CONSTEXPR14 etl::back_insert_iterator<TContainer> back_inserter(TContainer& container)
  {
    return etl::back_insert_iterator<TContainer>(container);
  }
 
  //***************************************************************************
  // front_insert_iterator
  //***************************************************************************
 
  //***************************************************************************
  //***************************************************************************
  template <typename TContainer>
  class front_insert_iterator : public etl::iterator<ETL_OR_STD::output_iterator_tag, void, void, void, void>
  {
  public:
 
    typedef TContainer container_type;
 
    //***************************************************************************
    //***************************************************************************
    explicit ETL_CONSTEXPR14 front_insert_iterator(TContainer& c)
      : container(etl::addressof(c))
    {
    }
 
    //***************************************************************************
    //***************************************************************************
    ETL_CONSTEXPR14 front_insert_iterator& operator=(const typename TContainer::value_type& value)
    {
      container->push_front(value);
      return (*this);
    }
 
#if ETL_USING_CPP11
    //***************************************************************************
    //***************************************************************************
    ETL_CONSTEXPR14 front_insert_iterator& operator=(typename TContainer::value_type&& value)
    {
      container->push_front(etl::move(value));
      return (*this);
    }
#endif // ETL_USING_CPP11
 
    //***************************************************************************
    //***************************************************************************
    ETL_NODISCARD ETL_CONSTEXPR14 front_insert_iterator& operator*()
    {
      return (*this);
    }
 
    //***************************************************************************
    //***************************************************************************
    ETL_CONSTEXPR14 front_insert_iterator& operator++()
    {
      return (*this);
    }
 
    //***************************************************************************
    //***************************************************************************
    ETL_CONSTEXPR14 front_insert_iterator operator++(int)
    {
      return (*this);
    }
 
  protected:
 
    TContainer* container;
  };
 
  //***************************************************************************
  //***************************************************************************
  template <typename TContainer>
  ETL_NODISCARD ETL_CONSTEXPR14 etl::front_insert_iterator<TContainer> front_inserter(TContainer& container)
  {
    return etl::front_insert_iterator<TContainer>(container);
  }
 
  //***************************************************************************
  // push_insert_iterator
  //***************************************************************************
 
  //***************************************************************************
  //***************************************************************************
  template <typename TContainer>
  class push_insert_iterator : public etl::iterator<ETL_OR_STD::output_iterator_tag, void, void, void, void>
  {
  public:
 
    typedef TContainer container_type;
 
    //***************************************************************************
    //***************************************************************************
    explicit ETL_CONSTEXPR14 push_insert_iterator(TContainer& c)
      : container(etl::addressof(c))
    {
    }
 
    //***************************************************************************
    //***************************************************************************
    ETL_CONSTEXPR14 push_insert_iterator& operator=(const typename TContainer::value_type& value)
    {
      container->push(value);
 
      return (*this);
    }
 
#if ETL_USING_CPP11
    //***************************************************************************
    //***************************************************************************
    ETL_CONSTEXPR14 push_insert_iterator& operator=(typename TContainer::value_type&& value)
    {
      container->push(etl::move(value));
 
      return (*this);
    }
#endif // ETL_USING_CPP11
 
    //***************************************************************************
    //***************************************************************************
    ETL_NODISCARD ETL_CONSTEXPR14 push_insert_iterator& operator*()
    {
      return (*this);
    }
 
    //***************************************************************************
    //***************************************************************************
    ETL_CONSTEXPR14 push_insert_iterator& operator++()
    {
      return (*this);
    }
 
    //***************************************************************************
    //***************************************************************************
    ETL_CONSTEXPR14 push_insert_iterator operator++(int)
    {
      return (*this);
    }
 
  protected:
 
    TContainer* container;
  };
 
  //***************************************************************************
  //***************************************************************************
  template <typename TContainer>
  ETL_NODISCARD ETL_CONSTEXPR14 etl::push_insert_iterator<TContainer> push_inserter(TContainer& container)
  {
    return etl::push_insert_iterator<TContainer>(container);
  }
 
  //***************************************************************************
  // Helper templates.
  //***************************************************************************
  template <typename T>
  struct is_input_iterator
  {
    static ETL_CONSTANT bool value = etl::is_same<typename etl::iterator_traits<T>::iterator_category, ETL_OR_STD::input_iterator_tag>::value;
  };
 
  template <typename T>
  ETL_CONSTANT bool is_input_iterator<T>::value;
 
  template <typename T>
  struct is_output_iterator
  {
    static ETL_CONSTANT bool value = etl::is_same<typename etl::iterator_traits<T>::iterator_category, ETL_OR_STD::output_iterator_tag>::value;
  };
 
  template <typename T>
  ETL_CONSTANT bool is_output_iterator<T>::value;
 
  template <typename T>
  struct is_forward_iterator
  {
    static ETL_CONSTANT bool value = etl::is_same<typename etl::iterator_traits<T>::iterator_category, ETL_OR_STD::forward_iterator_tag>::value;
  };
 
  template <typename T>
  ETL_CONSTANT bool is_forward_iterator<T>::value;
 
  template <typename T>
  struct is_bidirectional_iterator
  {
    static ETL_CONSTANT bool value = etl::is_same<typename etl::iterator_traits<T>::iterator_category, ETL_OR_STD::bidirectional_iterator_tag>::value;
  };
 
  template <typename T>
  ETL_CONSTANT bool is_bidirectional_iterator<T>::value;
 
  // Deprecated
  template <typename T>
  struct is_random_iterator
  {
    static ETL_CONSTANT bool value = etl::is_same<typename etl::iterator_traits<T>::iterator_category, ETL_OR_STD::random_access_iterator_tag>::value;
  };
 
  template <typename T>
  ETL_CONSTANT bool is_random_iterator<T>::value;
 
  template <typename T>
  struct is_random_access_iterator
  {
    static ETL_CONSTANT bool value = etl::is_same<typename etl::iterator_traits<T>::iterator_category, ETL_OR_STD::random_access_iterator_tag>::value;
  };
 
  template <typename T>
  ETL_CONSTANT bool is_random_access_iterator<T>::value;
 
  template <typename T>
  struct is_input_iterator_concept
  {
    static
      ETL_CONSTANT bool value = etl::is_input_iterator<T>::value || etl::is_forward_iterator<T>::value || etl::is_bidirectional_iterator<T>::value
                             || etl::is_random_iterator<T>::value;
  };
 
  template <typename T>
  ETL_CONSTANT bool is_input_iterator_concept<T>::value;
 
  template <typename T>
  struct is_output_iterator_concept
  {
    static
      ETL_CONSTANT bool value = etl::is_output_iterator<T>::value || etl::is_forward_iterator<T>::value || etl::is_bidirectional_iterator<T>::value
                             || etl::is_random_iterator<T>::value;
  };
 
  template <typename T>
  ETL_CONSTANT bool is_output_iterator_concept<T>::value;
 
  template <typename T>
  struct is_forward_iterator_concept
  {
    static
      ETL_CONSTANT bool value = etl::is_forward_iterator<T>::value || etl::is_bidirectional_iterator<T>::value || etl::is_random_iterator<T>::value;
  };
 
  template <typename T>
  ETL_CONSTANT bool is_forward_iterator_concept<T>::value;
 
  template <typename T>
  struct is_bidirectional_iterator_concept
  {
    static ETL_CONSTANT bool value = etl::is_bidirectional_iterator<T>::value || etl::is_random_iterator<T>::value;
  };
 
  template <typename T>
  ETL_CONSTANT bool is_bidirectional_iterator_concept<T>::value;
 
  // Deprecated
  template <typename T>
  struct is_random_iterator_concept
  {
    static ETL_CONSTANT bool value = etl::is_random_iterator<T>::value;
  };
 
  // Deprecated
  template <typename T>
  ETL_CONSTANT bool is_random_iterator_concept<T>::value;
 
  // Deprecated
  template <typename T>
  struct is_random_access_iterator_concept
  {
    static ETL_CONSTANT bool value = etl::is_random_access_iterator<T>::value;
  };
 
  // Deprecated
  template <typename T>
  ETL_CONSTANT bool is_random_access_iterator_concept<T>::value;
 
#if ETL_USING_CPP11
  //***************************************************************************
  //***************************************************************************
  namespace private_iterator
  {
    // Check if T has iterator_category (i.e., is an iterator)
    template <typename T, typename = void>
    struct has_iterator_category : etl::false_type
    {
    };
 
    template <typename T>
    struct has_iterator_category<T, etl::void_t<typename T::iterator_category>> : etl::true_type
    {
    };
 
    // is_container: has iterator/const_iterator/begin/end but does NOT have iterator_category
    template <typename T, typename = void>
    struct is_container : etl::false_type
    {
    };
 
    template <typename T>
    struct is_container<
      T, etl::void_t< typename T::iterator, typename T::const_iterator, decltype(etl::declval<T&>().begin()), decltype(etl::declval<T&>().end()) >>
      : etl::bool_constant<!has_iterator_category<T>::value>
    {
    };
  } // namespace private_iterator
#endif
 
#if ETL_NOT_USING_STL || ETL_CPP11_NOT_SUPPORTED
  #if ETL_USING_CPP11
 
  //*****************************************************************************
  //*****************************************************************************
  template <typename TContainer, typename = etl::void_t<decltype(etl::declval<TContainer&>().begin())> >
  ETL_CONSTEXPR typename etl::enable_if<private_iterator::is_container<TContainer>::value, typename TContainer::iterator>::type
    begin(TContainer& container)
  {
    return container.begin();
  }
 
  //*****************************************************************************
  //*****************************************************************************
  template <typename TContainer, typename = etl::void_t<decltype(etl::declval<const TContainer&>().begin())> >
  ETL_CONSTEXPR typename etl::enable_if<private_iterator::is_container<TContainer>::value, typename TContainer::const_iterator>::type
    begin(const TContainer& container)
  {
    return container.begin();
  }
 
  //*****************************************************************************
  //*****************************************************************************
  template <typename TContainer, typename = etl::void_t<decltype(etl::declval<const TContainer&>().cbegin())> >
  ETL_CONSTEXPR typename etl::enable_if<private_iterator::is_container<TContainer>::value, typename TContainer::const_iterator>::type
    cbegin(const TContainer& container)
  {
    return container.cbegin();
  }
 
  //*****************************************************************************
  //*****************************************************************************
  template <typename TContainer, typename = etl::void_t<decltype(etl::declval<TContainer&>().end())> >
  ETL_CONSTEXPR typename etl::enable_if<private_iterator::is_container<TContainer>::value, typename TContainer::iterator>::type end(TContainer& container)
  {
    return container.end();
  }
 
  //*****************************************************************************
  //*****************************************************************************
  template <typename TContainer, typename = etl::void_t<decltype(etl::declval<const TContainer&>().end())> >
  ETL_CONSTEXPR typename etl::enable_if<private_iterator::is_container<TContainer>::value, typename TContainer::const_iterator>::type
    end(const TContainer& container)
  {
    return container.end();
  }
 
  //*****************************************************************************
  //*****************************************************************************
  template <typename TContainer, typename = etl::void_t<decltype(etl::declval<const TContainer&>().cend())> >
  ETL_CONSTEXPR typename etl::enable_if<private_iterator::is_container<TContainer>::value, typename TContainer::const_iterator>::type
    cend(const TContainer& container)
  {
    return container.cend();
  }
  #else
  // C++03 fallback:
  //  - no SFINAE guards needed since std::ranges does not exist
  //  - no constraint needed as C++26 ADL issue doesn't apply
  //*****************************************************************************
  //*****************************************************************************
  template <typename TContainer>
  typename TContainer::iterator begin(TContainer& container)
  {
    return container.begin();
  }
 
  //*****************************************************************************
  //*****************************************************************************
  template <typename TContainer>
  typename TContainer::const_iterator begin(const TContainer& container)
  {
    return container.begin();
  }
 
  //*****************************************************************************
  //*****************************************************************************
  template <typename TContainer>
  typename TContainer::const_iterator cbegin(const TContainer& container)
  {
    return container.cbegin();
  }
 
  //*****************************************************************************
  //*****************************************************************************
  template <typename TContainer>
  typename TContainer::iterator end(TContainer& container)
  {
    return container.end();
  }
 
  //*****************************************************************************
  //*****************************************************************************
  template <typename TContainer>
  typename TContainer::const_iterator end(const TContainer& container)
  {
    return container.end();
  }
 
  //*****************************************************************************
  //*****************************************************************************
  template <typename TContainer>
  typename TContainer::const_iterator cend(const TContainer& container)
  {
    return container.cend();
  }
  #endif
 
  //*****************************************************************************
  //*****************************************************************************
  template <typename TValue, size_t Array_Size>
  ETL_CONSTEXPR TValue* begin(TValue (&data)[Array_Size])
  {
    return &data[0];
  }
 
  //*****************************************************************************
  //*****************************************************************************
  template <typename TValue, size_t Array_Size>
  ETL_CONSTEXPR const TValue* begin(const TValue (&data)[Array_Size])
  {
    return &data[0];
  }
 
  //*****************************************************************************
  //*****************************************************************************
  template <typename TValue, size_t Array_Size>
  ETL_CONSTEXPR const TValue* cbegin(const TValue (&data)[Array_Size])
  {
    return &data[0];
  }
 
  //*****************************************************************************
  //*****************************************************************************
  template <typename TValue, size_t Array_Size>
  ETL_CONSTEXPR TValue* end(TValue (&data)[Array_Size])
  {
    return &data[Array_Size];
  }
 
  //*****************************************************************************
  //*****************************************************************************
  template <typename TValue, size_t Array_Size>
  ETL_CONSTEXPR const TValue* end(const TValue (&data)[Array_Size])
  {
    return &data[Array_Size];
  }
 
  //*****************************************************************************
  //*****************************************************************************
  template <typename TValue, size_t Array_Size>
  ETL_CONSTEXPR const TValue* cend(const TValue (&data)[Array_Size])
  {
    return &data[Array_Size];
  }
#endif
 
#if ETL_NOT_USING_STL || ETL_CPP14_NOT_SUPPORTED
  #if ETL_USING_CPP11
  //*****************************************************************************
  //*****************************************************************************
  template <typename TContainer, typename = etl::void_t<decltype(etl::declval<TContainer&>().rbegin())> >
  ETL_CONSTEXPR typename etl::enable_if<private_iterator::is_container<TContainer>::value, typename TContainer::reverse_iterator>::type
    rbegin(TContainer& container)
  {
    return container.rbegin();
  }
 
  //*****************************************************************************
  //*****************************************************************************
  template <typename TContainer, typename = etl::void_t<decltype(etl::declval<const TContainer&>().rbegin())> >
  ETL_CONSTEXPR typename etl::enable_if<private_iterator::is_container<TContainer>::value, typename TContainer::const_reverse_iterator>::type
    rbegin(const TContainer& container)
  {
    return container.rbegin();
  }
 
  //*****************************************************************************
  //*****************************************************************************
  template <typename TContainer, typename = etl::void_t<decltype(etl::declval<const TContainer&>().crbegin())> >
  ETL_CONSTEXPR typename etl::enable_if<private_iterator::is_container<TContainer>::value, typename TContainer::const_reverse_iterator>::type
    crbegin(const TContainer& container)
  {
    return container.crbegin();
  }
 
  //*****************************************************************************
  //*****************************************************************************
  template <typename TContainer, typename = etl::void_t<decltype(etl::declval<TContainer&>().rend())> >
  ETL_CONSTEXPR typename etl::enable_if<private_iterator::is_container<TContainer>::value, typename TContainer::reverse_iterator>::type
    rend(TContainer& container)
  {
    return container.rend();
  }
 
  //*****************************************************************************
  //*****************************************************************************
  template <typename TContainer, typename = etl::void_t<decltype(etl::declval<const TContainer&>().rend())> >
  ETL_CONSTEXPR typename etl::enable_if<private_iterator::is_container<TContainer>::value, typename TContainer::const_reverse_iterator>::type
    rend(const TContainer& container)
  {
    return container.rend();
  }
 
  //*****************************************************************************
  //*****************************************************************************
  template <typename TContainer, typename = etl::void_t<decltype(etl::declval<const TContainer&>().crend())> >
  ETL_CONSTEXPR typename etl::enable_if<private_iterator::is_container<TContainer>::value, typename TContainer::const_reverse_iterator>::type
    crend(const TContainer& container)
  {
    return container.crend();
  }
  #else
  // C++03 fallback:
  //  - no SFINAE guards needed since std::ranges does not exist.
  //  - no constraint needed as C++26 ADL issue doesn't apply
  //*****************************************************************************
  //*****************************************************************************
  template <typename TContainer>
  typename TContainer::reverse_iterator rbegin(TContainer& container)
  {
    return container.rbegin();
  }
 
  //*****************************************************************************
  //*****************************************************************************
  template <typename TContainer>
  typename TContainer::const_reverse_iterator rbegin(const TContainer& container)
  {
    return container.rbegin();
  }
 
  //*****************************************************************************
  //*****************************************************************************
  template <typename TContainer>
  typename TContainer::const_reverse_iterator crbegin(const TContainer& container)
  {
    return container.crbegin();
  }
 
  //*****************************************************************************
  //*****************************************************************************
  template <typename TContainer>
  typename TContainer::reverse_iterator rend(TContainer& container)
  {
    return container.rend();
  }
 
  //*****************************************************************************
  //*****************************************************************************
  template <typename TContainer>
  typename TContainer::const_reverse_iterator rend(const TContainer& container)
  {
    return container.rend();
  }
 
  //*****************************************************************************
  //*****************************************************************************
  template <typename TContainer>
  typename TContainer::const_reverse_iterator crend(const TContainer& container)
  {
    return container.crend();
  }
  #endif
 
  //*****************************************************************************
  //*****************************************************************************
  template <typename TValue, size_t Array_Size>
  ETL_OR_STD::reverse_iterator<TValue*> rbegin(TValue (&data)[Array_Size])
  {
    return ETL_OR_STD::reverse_iterator<TValue*>(&data[Array_Size]);
  }
 
  //*****************************************************************************
  //*****************************************************************************
  template <typename TValue, size_t Array_Size>
  ETL_CONSTEXPR ETL_OR_STD::reverse_iterator<const TValue*> crbegin(const TValue (&data)[Array_Size])
  {
    return ETL_OR_STD::reverse_iterator<const TValue*>(&data[Array_Size]);
  }
 
  //*****************************************************************************
  //*****************************************************************************
  template <typename TValue, size_t Array_Size>
  ETL_CONSTEXPR ETL_OR_STD::reverse_iterator<TValue*> rend(TValue (&data)[Array_Size])
  {
    return ETL_OR_STD::reverse_iterator<TValue*>(&data[0]);
  }
 
  //*****************************************************************************
  //*****************************************************************************
  template <typename TValue, size_t Array_Size>
  ETL_CONSTEXPR ETL_OR_STD::reverse_iterator<const TValue*> crend(const TValue (&data)[Array_Size])
  {
    return ETL_OR_STD::reverse_iterator<const TValue*>(&data[0]);
  }
#endif
 
#if ETL_NOT_USING_STL || ETL_CPP17_NOT_SUPPORTED
  //**************************************************************************
  //**************************************************************************
  template <typename TContainer>
  ETL_CONSTEXPR typename TContainer::size_type size(const TContainer& container)
  {
    return container.size();
  }

  template <typename TValue, size_t Array_Size>
  ETL_CONSTEXPR size_t size(TValue (&)[Array_Size])
  {
    return Array_Size;
  }
#endif
 
  //**************************************************************************
  //**************************************************************************
  template <typename T, size_t Array_Size>
  char (&array_size(T (&array)[Array_Size]))[Array_Size];
 
#define ETL_ARRAY_SIZE(a) sizeof(etl::array_size(a))
 
#if ETL_NOT_USING_STL || ETL_CPP17_NOT_SUPPORTED
  //**************************************************************************
  //**************************************************************************
  template <typename TContainer>
  ETL_CONSTEXPR typename TContainer::pointer data(TContainer& container)
  {
    return container.data();
  }
 
  //**************************************************************************
  //**************************************************************************
  template <typename TContainer>
  ETL_CONSTEXPR typename TContainer::const_pointer data(const TContainer& container)
  {
    return container.data();
  }

  template <typename TValue, size_t Array_Size>
  ETL_CONSTEXPR TValue* data(TValue (&a)[Array_Size])
  {
    return a;
  }

  template <typename TValue, size_t Array_Size>
  ETL_CONSTEXPR const TValue* data(const TValue (&a)[Array_Size])
  {
    return a;
  }
#endif
 
#if ETL_USING_CPP17
  template <class T>
  using iter_value_t = typename etl::iterator_traits<etl::remove_cvref_t<T>>::value_type;
 
  template <class T>
  using iter_reference_t = decltype(*etl::declval<T&>());
 
  #if ETL_USING_CPP20
  template <class T>
  using iter_const_reference_t = typename etl::common_reference_t<const etl::iter_value_t<T>&&, etl::iter_reference_t<T>>;
  #endif
 
  template <class T>
  using iter_difference_t = typename etl::iterator_traits<etl::remove_cvref_t<T>>::difference_type;
 
  template <class I, class Proj>
  using projected_value_t = etl::remove_cvref_t<etl::invoke_result_t<Proj&, etl::iter_reference_t<I>>>;
 
  namespace ranges
  {
    namespace private_ranges
    {
      struct begin
      {
        template <class T>
        constexpr auto operator()(T& t) const
        {
          return ETL_OR_STD::begin(t);
        }
      };
 
      struct end
      {
        template <class T>
        constexpr auto operator()(T& t) const
        {
          return ETL_OR_STD::end(t);
        }
      };
 
      struct cbegin
      {
        template <class T>
        constexpr auto operator()(T& t) const
        {
          return ETL_OR_STD::cbegin(t);
        }
      };
 
      struct cend
      {
        template <class T>
        constexpr auto operator()(T& t) const
        {
          return ETL_OR_STD::cend(t);
        }
      };
 
      struct rbegin
      {
        template <class T>
        constexpr auto operator()(T& t) const
        {
          return ETL_OR_STD::rbegin(t);
        }
      };
 
      struct rend
      {
        template <class T>
        constexpr auto operator()(T& t) const
        {
          return ETL_OR_STD::rend(t);
        }
      };
 
      struct crbegin
      {
        template <class T>
        constexpr auto operator()(T& t) const
        {
          return ETL_OR_STD::crbegin(t);
        }
      };
 
      struct crend
      {
        template <class T>
        constexpr auto operator()(T& t) const
        {
          return ETL_OR_STD::crend(t);
        }
      };
 
      template <class T, class = void>
      struct has_size_member : etl::false_type
      {
      };
 
      template <class T>
      struct has_size_member< T, etl::void_t<decltype(etl::declval<const T&>().size())>> : etl::true_type
      {
      };
 
      template <class T, class = void>
      struct has_empty_member : etl::false_type
      {
      };
 
      template <class T>
      struct has_empty_member< T, etl::void_t<decltype(etl::declval<const T&>().empty())>> : etl::true_type
      {
      };
 
      struct distance
      {
        // Overload for common ranges (iterator == sentinel type)
        template <typename I, typename = etl::enable_if_t< etl::is_input_iterator_concept<I>::value || etl::is_output_iterator_concept<I>::value>>
        constexpr etl::iter_difference_t<I> operator()(I first, I last) const
        {
          if constexpr (etl::is_random_access_iterator_concept<I>::value)
          {
            return last - first;
          }
          else
          {
            etl::iter_difference_t<I> n = 0;
            while (!(first == last))
            {
              ++first;
              ++n;
            }
            return n;
          }
        }
 
        // Overload for non-common ranges (iterator != sentinel type)
        template <typename I, typename S,
                  typename = etl::enable_if_t< (etl::is_input_iterator_concept<I>::value || etl::is_output_iterator_concept<I>::value)
                                               && !etl::is_same<I, S>::value>>
        constexpr etl::iter_difference_t<I> operator()(I first, S last) const
        {
          etl::iter_difference_t<I> n = 0;
          while (!(first == last))
          {
            ++first;
            ++n;
          }
          return n;
        }
      };
 
      struct size
      {
        template <class T>
        constexpr size_t operator()(T&& t) const
        {
          using U = etl::remove_cvref_t<T>;
 
          if constexpr (has_size_member<U>::value)
          {
            return static_cast<size_t>(t.size());
          }
          else
          {
            using iter_type = decltype(ETL_OR_STD::begin(t));
            static_assert(etl::is_forward_iterator_concept<iter_type>::value, "ranges::size requires a sized range or at least a forward range; "
                                                                              "single-pass input ranges are not supported");
            return static_cast<size_t>(distance{}(ETL_OR_STD::begin(t), ETL_OR_STD::end(t)));
          }
        }
      };
 
      struct ssize
      {
        template <class T>
        constexpr auto operator()(T&& t) const
        {
          using U = etl::remove_cvref_t<T>;
 
          if constexpr (has_size_member<U>::value)
          {
            return static_cast<ptrdiff_t>(t.size());
          }
          else
          {
            using iter_type = decltype(ETL_OR_STD::begin(t));
            static_assert(etl::is_forward_iterator_concept<iter_type>::value, "ranges::ssize requires a sized range or at least a forward range; "
                                                                              "single-pass input ranges are not supported");
            return static_cast<ptrdiff_t>(distance{}(ETL_OR_STD::begin(t), ETL_OR_STD::end(t)));
          }
        }
      };
 
      struct empty
      {
        template <class T>
        constexpr auto operator()(T&& t) const
        {
          using U = etl::remove_cvref_t<T>;
 
          if constexpr (has_empty_member<U>::value)
          {
            return t.empty();
          }
          else
          {
            return ETL_OR_STD::cbegin(t) == ETL_OR_STD::cend(t);
          }
        }
      };
 
      struct data
      {
        template <class T>
        constexpr auto operator()(T& t) const
        {
          return ETL_OR_STD::data(t);
        }
      };
 
      struct cdata
      {
        template <class T>
        constexpr etl::add_pointer_t< etl::add_const_t<etl::remove_pointer_t< decltype(ETL_OR_STD::data(etl::declval<T&>()))>>> operator()(T& t) const
        {
          return ETL_OR_STD::data(t);
        }
      };
    } // namespace private_ranges
 
    inline constexpr private_ranges::begin    begin;
    inline constexpr private_ranges::end      end;
    inline constexpr private_ranges::cbegin   cbegin;
    inline constexpr private_ranges::cend     cend;
    inline constexpr private_ranges::rbegin   rbegin;
    inline constexpr private_ranges::rend     rend;
    inline constexpr private_ranges::crbegin  crbegin;
    inline constexpr private_ranges::crend    crend;
    inline constexpr private_ranges::size     size;
    inline constexpr private_ranges::ssize    ssize;
    inline constexpr private_ranges::empty    empty;
    inline constexpr private_ranges::data     data;
    inline constexpr private_ranges::cdata    cdata;
    inline constexpr private_ranges::distance distance;
 
    //*************************************************************************
    //*************************************************************************
 
    template <class T>
    using iterator_t = decltype(etl::ranges::begin(etl::declval<T&>()));
 
    template <class T>
    using const_iterator_t = decltype(etl::ranges::cbegin(etl::declval<T&>()));
 
    template <class T>
    using sentinel_t = decltype(etl::ranges::end(etl::declval<T&>()));
 
    template <class T>
    using const_sentinel_t = decltype(etl::ranges::cend(etl::declval<T&>()));
 
    template <class T>
    using range_size_t = decltype(etl::ranges::size(etl::declval<T&>()));
 
    template <class T>
    using range_difference_t = etl::iter_difference_t<etl::ranges::iterator_t<T>>;
 
    template <class T>
    using range_value_t = etl::iter_value_t<etl::ranges::iterator_t<T>>;
 
    template <class T>
    using range_reference_t = etl::iter_reference_t<ranges::iterator_t<T>>;
 
    struct advance_fn
    {
      template <typename I, typename = etl::enable_if_t< (etl::is_input_iterator_concept<I>::value || etl::is_output_iterator_concept<I>::value)
                                                         && etl::is_integral<etl::iter_difference_t<I>>::value>>
      constexpr void operator()(I& i, etl::iter_difference_t<I> n) const
      {
        if constexpr (etl::is_random_access_iterator_concept<I>::value)
        {
          i += n;
        }
        else
        {
          while (n > 0)
          {
            --n;
            ++i;
          }
 
          if constexpr (etl::is_bidirectional_iterator_concept<I>::value)
          {
            while (n < 0)
            {
              ++n;
              --i;
            }
          }
        }
      }
 
      template <typename I, typename S,
                typename = etl::enable_if_t< (etl::is_input_iterator_concept<I>::value || etl::is_output_iterator_concept<I>::value)
                                             && !etl::is_integral<S>::value>>
      constexpr void operator()(I& i, S bound) const
      {
        if constexpr (etl::is_assignable_v<I&, S>)
        {
          i = etl::move(bound);
        }
        else if constexpr (etl::is_same_v<S, I> && etl::is_random_access_iterator_concept<I>::value)
        {
          (*this)(i, bound - i);
        }
        else
        {
          while (!(i == bound))
          {
            ++i;
          }
        }
      }
 
      template <typename I, typename S,
                typename = etl::enable_if_t< etl::is_input_iterator_concept<I>::value || etl::is_output_iterator_concept<I>::value>>
      constexpr etl::iter_difference_t<I> operator()(I& i, etl::iter_difference_t<I> n, S bound) const
      {
        if constexpr (etl::is_same_v<S, I> && etl::is_random_access_iterator_concept<I>::value)
        {
          const auto dist = bound - i;
 
          if ((n >= 0 && dist >= 0 && n >= dist) || (n <= 0 && dist <= 0 && n <= dist))
          {
            (*this)(i, bound);
            return n - dist;
          }
 
          (*this)(i, n);
          return 0;
        }
        else
        {
          while (n > 0 && !(i == bound))
          {
            --n;
            ++i;
          }
 
          if constexpr (etl::is_bidirectional_iterator_concept<I>::value)
          {
            while (n < 0 && !(i == bound))
            {
              ++n;
              --i;
            }
          }
 
          return n;
        }
      }
    };
 
    inline constexpr auto advance = advance_fn();
 
    struct prev_fn
    {
      template <typename I, typename = etl::enable_if_t< etl::is_bidirectional_iterator_concept<I>::value>>
      constexpr I operator()(I i) const
      {
        --i;
        return i;
      }
 
      template <typename I, typename = etl::enable_if_t< etl::is_bidirectional_iterator_concept<I>::value>>
      constexpr I operator()(I i, etl::iter_difference_t<I> n) const
      {
        ranges::advance(i, -n);
        return i;
      }
 
      template <typename I, typename = etl::enable_if_t< etl::is_bidirectional_iterator_concept<I>::value>>
      constexpr I operator()(I i, etl::iter_difference_t<I> n, I bound) const
      {
        ranges::advance(i, -n, bound);
        return i;
      }
    };
 
    inline constexpr auto prev = prev_fn();
 
    struct next_fn
    {
      template <typename I, typename = etl::enable_if_t< etl::is_input_iterator_concept<I>::value || etl::is_output_iterator_concept<I>::value>>
      constexpr I operator()(I i) const
      {
        ++i;
        return i;
      }
 
      template <typename I, typename = etl::enable_if_t< (etl::is_input_iterator_concept<I>::value || etl::is_output_iterator_concept<I>::value)
                                                         && etl::is_integral<etl::iter_difference_t<I>>::value>>
      constexpr I operator()(I i, etl::iter_difference_t<I> n) const
      {
        ranges::advance(i, n);
        return i;
      }
 
      template <typename I, typename S,
                typename = etl::enable_if_t< (etl::is_input_iterator_concept<I>::value || etl::is_output_iterator_concept<I>::value)
                                             && !etl::is_integral<S>::value>>
      constexpr I operator()(I i, S bound) const
      {
        ranges::advance(i, bound);
        return i;
      }
 
      template <typename I, typename S,
                typename = etl::enable_if_t< (etl::is_input_iterator_concept<I>::value || etl::is_output_iterator_concept<I>::value)
                                             && !etl::is_integral<S>::value>>
      constexpr I operator()(I i, etl::iter_difference_t<I> n, S bound) const
      {
        ranges::advance(i, n, bound);
        return i;
      }
    };
 
    inline constexpr auto next = next_fn();
  } // namespace ranges
 
  struct unreachable_sentinel_t
  {
  };
 
  inline constexpr unreachable_sentinel_t unreachable_sentinel{};
 
  template <typename I>
  constexpr bool operator==(unreachable_sentinel_t, const I&) noexcept
  {
    return false;
  }
 
  template <typename I>
  constexpr bool operator==(const I&, unreachable_sentinel_t) noexcept
  {
    return false;
  }
 
  template <typename I>
  constexpr bool operator!=(unreachable_sentinel_t, const I& i) noexcept
  {
    return !(unreachable_sentinel_t{} == i);
  }
 
  template <typename I>
  constexpr bool operator!=(const I& i, unreachable_sentinel_t) noexcept
  {
    return !(i == unreachable_sentinel_t{});
  }
 
  struct default_sentinel_t
  {
  };
 
  inline constexpr default_sentinel_t default_sentinel{};
 
  namespace private_iterator
  {
    template <typename T, typename = void>
    struct has_arrow_operator : etl::false_type
    {
    };
 
    template <typename T>
    struct has_arrow_operator< T, etl::void_t<decltype(etl::declval<const T&>().operator->())>> : etl::true_type
    {
    };
 
    //***********************************
    //***********************************
    template <typename TValue>
    struct arrow_proxy
    {
      TValue stored;
 
      constexpr arrow_proxy(TValue value)
        : stored(etl::move(value))
      {
      }
      constexpr const TValue* operator->() const noexcept
      {
        return etl::addressof(stored);
      }
    };
  } // namespace private_iterator
 
  template <class I>
  class counted_iterator
  {
    template <class>
    friend class counted_iterator;
 
  public:
 
    using iterator_type     = I;
    using value_type        = etl::iter_value_t<I>;
    using difference_type   = etl::iter_difference_t<I>;
    using iterator_category = typename etl::iterator_traits<iterator_type>::iterator_category;
    using pointer           = typename etl::iterator_traits<iterator_type>::pointer;
    using reference         = typename etl::iterator_traits<iterator_type>::reference;
 
    constexpr counted_iterator() = default;
 
    constexpr counted_iterator(I x, etl::iter_difference_t<I> n)
      : current(etl::move(x))
      , length(n)
    {
    }
 
    template <class I2>
    constexpr counted_iterator(const counted_iterator<I2>& other)
      : current(other.current)
      , length(other.length)
    {
    }
 
    template <class I2>
    constexpr counted_iterator& operator=(const counted_iterator<I2>& other)
    {
      current = other.current;
      length  = other.length;
      return *this;
    }
 
    constexpr const I& base() const& noexcept
    {
      return current;
    }
 
    constexpr I base() &&
    {
      return etl::move(current);
    }
 
    constexpr etl::iter_difference_t<I> count() const noexcept
    {
      return length;
    }
 
    constexpr decltype(auto) operator*() const
    {
      return *current;
    }
 
    // operator-> for iterator types that provide a member operator->
    template < typename J = I, etl::enable_if_t<(etl::is_input_iterator_concept<J>::value || etl::is_output_iterator_concept<J>::value)
                                                  && private_iterator::has_arrow_operator<J>::value,
                                                int> = 0>
    constexpr auto operator->() const noexcept
    {
      return current.operator->();
    }
 
    // operator-> fallback for raw-pointer iterators (addressof is always safe)
    template < typename J = I, etl::enable_if_t<(etl::is_input_iterator_concept<J>::value || etl::is_output_iterator_concept<J>::value)
                                                  && !private_iterator::has_arrow_operator<J>::value && etl::is_pointer<J>::value,
                                                int> = 0>
    constexpr auto operator->() const noexcept
    {
      return current;
    }
 
    // operator-> fallback for class-type iterators without member operator->
    // When *current yields an lvalue reference, just take its address.
    template < typename J = I, etl::enable_if_t< (etl::is_input_iterator_concept<J>::value || etl::is_output_iterator_concept<J>::value)
                                                   && !private_iterator::has_arrow_operator<J>::value && !etl::is_pointer<J>::value
                                                   && etl::is_lvalue_reference< decltype(*etl::declval<const J&>())>::value,
                                                 int> = 0>
    constexpr auto operator->() const noexcept
    {
      return etl::addressof(*current);
    }
 
    // operator-> fallback for class-type iterators without member operator->
    // When *current yields a prvalue / proxy, use an owning proxy so the
    // address remains valid.
    template < typename J = I, etl::enable_if_t< (etl::is_input_iterator_concept<J>::value || etl::is_output_iterator_concept<J>::value)
                                                   && !private_iterator::has_arrow_operator<J>::value && !etl::is_pointer<J>::value
                                                   && !etl::is_lvalue_reference< decltype(*etl::declval<const J&>())>::value,
                                                 int> = 0>
    constexpr auto operator->() const
    {
      return private_iterator::arrow_proxy<value_type>{*current};
    }
 
    template < typename J = I, etl::enable_if_t<etl::is_random_access_iterator<J>::value, int> = 0>
    constexpr decltype(auto) operator[](etl::iter_difference_t<I> n) const
    {
      return current[n];
    }
 
    constexpr counted_iterator& operator++()
    {
      ++current;
      --length;
      return *this;
    }
 
    constexpr counted_iterator operator++(int)
    {
      counted_iterator tmp = *this;
      current++;
      length--;
      return tmp;
    }
 
    template < typename J = I, etl::enable_if_t<etl::is_random_access_iterator<J>::value, int> = 0>
    constexpr counted_iterator& operator+=(etl::iter_difference_t<I> n)
    {
      current += n;
      length -= n;
      return *this;
    }
 
    template < typename J = I, etl::enable_if_t<etl::is_random_access_iterator<J>::value, int> = 0>
    constexpr counted_iterator operator+(etl::iter_difference_t<I> n) const
    {
      counted_iterator result{*this};
      result += n;
      return result;
    }
 
    constexpr counted_iterator& operator--()
    {
      --current;
      ++length;
      return *this;
    }
 
    constexpr counted_iterator operator--(int)
    {
      counted_iterator tmp = *this;
      current--;
      length++;
      return tmp;
    }
 
    template < typename J = I, etl::enable_if_t<etl::is_random_access_iterator<J>::value, int> = 0>
    constexpr counted_iterator& operator-=(etl::iter_difference_t<I> n)
    {
      current -= n;
      length += n;
      return *this;
    }
 
    template < typename J = I, etl::enable_if_t<etl::is_random_access_iterator<J>::value, int> = 0>
    constexpr counted_iterator operator-(etl::iter_difference_t<I> n) const
    {
      counted_iterator result{*this};
      result -= n;
      return result;
    }
 
    friend constexpr bool operator==(const counted_iterator& x, const counted_iterator& y)
    {
      return x.length == y.length;
    }
 
    friend constexpr bool operator==(const counted_iterator& x, etl::default_sentinel_t)
    {
      return x.count() == 0;
    }
 
    friend constexpr bool operator==(etl::default_sentinel_t, const counted_iterator& x)
    {
      return x.count() == 0;
    }
 
    friend constexpr bool operator!=(const counted_iterator& x, etl::default_sentinel_t)
    {
      return x.count() != 0;
    }
 
    friend constexpr bool operator!=(etl::default_sentinel_t, const counted_iterator& y)
    {
      return y.count() != 0;
    }
 
    template < typename J = I, etl::enable_if_t<etl::is_random_access_iterator<J>::value, int> = 0>
    friend constexpr counted_iterator operator+(etl::iter_difference_t<I> n, const counted_iterator& x)
    {
      return counted_iterator(x.current + n, x.length - n);
    }
 
    friend constexpr etl::iter_difference_t<I> operator-(const counted_iterator& x, const counted_iterator& y)
    {
      return y.length - x.length;
    }
 
    friend constexpr etl::iter_difference_t<I> operator-(const counted_iterator& x, etl::default_sentinel_t)
    {
      return -x.length;
    }
 
    friend constexpr etl::iter_difference_t<I> operator-(etl::default_sentinel_t, const counted_iterator& y)
    {
      return y.length;
    }
 
  private:
 
    I               current{};
    difference_type length{};
  };
 
  template <typename TIterator,
            typename = etl::enable_if_t<etl::is_base_of< etl::counted_iterator<typename TIterator::iterator_type>, TIterator>::value>>
  constexpr typename etl::iterator_traits<TIterator>::difference_type distance(TIterator first, etl::default_sentinel_t)
  {
    return first.count();
  }
#endif
 
#if ETL_USING_CPP14
  template <class T, typename = void>
  struct is_range : etl::false_type
  {
  };
 
  template <class T>
  struct is_range< T, etl::void_t<decltype(ETL_OR_STD::begin(etl::declval<T&>())), decltype(ETL_OR_STD::end(etl::declval<T&>()))>> : etl::true_type
  {
  };
 
  #if ETL_USING_CPP17
  template <typename T>
  inline constexpr bool is_range_v = is_range<T>::value;
  #endif
#endif
} // namespace etl
 
#endif