Hi Neil, Neil Groves wrote:
I will submit a fix to boost-trunk today. After a couple of days of passes on boost-trunk I shall merge to boost-release.
The ticket (#5014) just has been closed, but the test case in the ticket still prints out wrong results. This is because, when constructing strided_range, the end iterator of an input range should advance forward rather than backward. Advancing the end iterator forward might cause overflow, so implementing strided_iterator needs some care to handle "overflowed" end iterators. I can think of the following implementation: // Partial specialization (for Random Access Range) template <typename BaseIterator> class strided_iterator<BaseIterator, boost::random_access_traversal_tag> : public iterator_facade</* ... */> { public: // ... private: // iterator_facade core operations reference dereference() const { return *(m_begin + m_stride * m_offset); } bool equal(strided_iterator const& other) const { return m_begin == other.m_begin && m_offset == other.m_offset; } void increment() { ++m_offset; } void decrement() { --m_offset; } void advance(difference_type n) { m_offset += n; } difference_type distance_to(strided_iterator const& other) const { other.m_offset - m_offset; } // data BaseIterator m_begin; // the begin iterator of an input range difference_type m_offset; // the number of strides taken by this iterator difference_type m_stride; }; For Single Pass Range (including Forward and Bidirectional Ranges), I think it's better to use a different implementation to avoid using size() function. To achieve this, strided_iterator stores the end iterator of the input range: (When constructing strided_range, the end iterator of an input range does not need to be advanced anymore in this implementation.) // Primary template (for Single Pass, Forward and Bidirectional Ranges) template <typename BaseIterator, typename TraversalCategory> class strided_iterator : public iterator_adaptor</* ... */> { public: // ... private: // adapted core operations void increment() { difference_type i = 0; do { ++this->base_reference(); ++i; } while (this->base_reference() != m_end && i < m_stride); } // data difference_type m_stride; BaseIterator m_end; }; I don't know whether we should implement decrement() function for Bidirectional Range. Regards, Michel