Custom iterator implementation returning OpenCV Mat

I have written an adapter class that allows iteration over the rows of a Mat object from OpenCV. For those interested, here is the Mat documentation, but the salient points are as follows:

• Mat is a reference-counted header to a shared data buffer.

• Mat::row() returns another Mat, which provides a view of a single row of the larger Mat.

• Mat_ is a templated version of Mat offering the same interface but better type safety. Mat_ and Mat can be converted to one another.

This is my first attempt at writing custom iterators, so I am interested in feedback on correctness and general points to improve. It seems like my use of mutable is suspect, but I don't know if I can avoid it.

Here are the class definitions:

RowRange.hpp

```
#ifndef CV_ADAPTERS_ROWRANGE_HPP
#define CV_ADAPTERS_ROWRANGE_HPP

#include
#include

namespace cv
{

template
class RowRangeConstIterator : public std::iterator
{
public:
RowRangeConstIterator()
: data()
, row()
, position()
{}

RowRangeConstIterator(const cv::Mat_& m, int index)
: data(m)
, row()
, position(index)
{
CV_DbgAssert(position >= 0 && position & operator*() const
{
setRow();
return row;
}

const cv::Mat_* operator->() const
{
setRow();
return &row;
}

// Logical comparison
bool operator==(const RowRangeConstIterator& that) const
{
return this->position == that.position;
}

bool operator!=(const RowRangeConstIterator& that) const
{
return !(*this == that);
}

bool operatorposition (const RowRangeConstIterator& that) const
{
return this->position > that.position;
}

bool operator that);
}

bool operator>=(const RowRangeConstIterator& that) const
{
return !(*this

Disclaimer: I am not a CV expert.

Overall, LGTM.

-
Relational operators (==, !=, etc) should not be members but friends. If such operators do not treat their operands symmetrically, expect problems with implicit conversion.

-
It is recommended to define operator> in terms of operator

-
I don't see why row should be a member.

-
I understand that position is declared int just because cv::Mat_::rows is int (which is a shame). It'd be nice to have a type of position inferred.

-
Last, but not least. This iterator can serve a much wider spectrum of classes than just cv::Mat. Its only dependency on the underlying class is in rows and row` methods.

StackExchange Code Review Q#57351, answer score: 2