boost::gil::RandomAccessNDLocatorConcept

template<typename Loc>
struct RandomAccessNDLocatorConcept;

concept RandomAccessNDLocatorConcept<Regular Loc>
{
    typename value_type;        // value over which the locator navigates
    typename reference;         // result of dereferencing
    typename difference_type; where PointNDConcept<difference_type>; // return value of operator-.
    typename const_t;           // same as Loc, but operating over immutable values
    typename cached_location_t; // type to store relative location (for efficient repeated access)
    typename point_t  = difference_type;

    static const size_t num_dimensions; // dimensionality of the locator
    where num_dimensions = point_t::num_dimensions;

    // The difference_type and iterator type along each dimension. The iterators may only differ in
    // difference_type. Their value_type must be the same as Loc::value_type
    template <size_t D>
    struct axis
    {
        typename coord_t = point_t::axis<D>::coord_t;
        typename iterator; where RandomAccessTraversalConcept<iterator>; // iterator along D-th axis.
        where iterator::value_type == value_type;
    };

    // Defines the type of a locator similar to this type, except it invokes Deref upon dereferencing
    template <PixelDereferenceAdaptorConcept Deref>
    struct add_deref
    {
        typename type;
            where RandomAccessNDLocatorConcept<type>;
        static type make(const Loc& loc, const Deref& deref);
    };

    Loc& operator+=(Loc&, const difference_type&);
    Loc& operator-=(Loc&, const difference_type&);
    Loc operator+(const Loc&, const difference_type&);
    Loc operator-(const Loc&, const difference_type&);

    reference operator*(const Loc&);
    reference operator[](const Loc&, const difference_type&);

    // Storing relative location for faster repeated access and accessing it
    cached_location_t Loc::cache_location(const difference_type&) const;
    reference operator[](const Loc&,const cached_location_t&);

    // Accessing iterators along a given dimension at the current location or at a given offset
    template <size_t D> axis<D>::iterator&       Loc::axis_iterator();
    template <size_t D> axis<D>::iterator const& Loc::axis_iterator() const;
    template <size_t D> axis<D>::iterator        Loc::axis_iterator(const difference_type&) const;
};