image_pair_iterator

typedef std::pair<cv::Mat&,cv::Mat&> image_pair;

class image_pair_iterator
    : public boost::iterator_facade<image_pair_iterator,
				    image_pair,
				    boost::forward_traversal_tag>
{
public:
    image_pair_iterator() : m_index(-1) {}
    explicit image_pair_iterator(const std::string& mask0,
				 const std::string& mask1,
				 int index_begin=0,
				 int index_end=-1) 
	: m_mask0(mask0),
	  m_mask1(mask1),
	  m_index(index_begin-1),
	  m_index_end(index_end),
	  m_do_alloc(true)
	{
	    this->increment();
	}
    
private:
    friend class boost::iterator_core_access;
    void increment() { 
	std::cout << "image_pair_iterator created" << std::endl;
	m_index++;
	m_do_alloc = true;
	std::string file_name0 = str(boost::format(m_mask0) % m_index),
	            file_name1 = str(boost::format(m_mask1) % m_index);
	if (!boost::filesystem::exists(file_name0) ||
	    !boost::filesystem::exists(file_name1)) {
	    m_index = -1;
	} else {
	    m_image0 = std::shared_ptr<cv::Mat>(new cv::Mat(imread(file_name0, IMREAD_GRAYSCALE)));
	    m_image1 = std::shared_ptr<cv::Mat>(new cv::Mat(imread(file_name1, IMREAD_GRAYSCALE)));
	    m_pair   = std::shared_ptr<image_pair>(new image_pair(*m_image0, *m_image1));
	}
    }
    bool equal(image_pair_iterator const &other) const {
	std::cout << "image_pair_iterator equal()" << std::endl;
	return m_index == -1 || other.m_index == -1 ? m_index == other.m_index :
	    m_index == other.m_index &&
	    m_mask0 == other.m_mask0 &&
	    m_mask1 == other.m_mask1;
    }
    image_pair& dereference() const {
	std::cout << "image_pair_iterator dereference()" << std::endl;
	assert(m_index >= 0);
	return *m_pair;
    }
    int                         m_index, m_index_end;
    bool                        m_do_alloc;
    std::string                 m_mask0, m_mask1;
    std::shared_ptr<cv::Mat>    m_image0, m_image1;
    std::shared_ptr<image_pair> m_pair;
};