If I understand Giovanni's implementation correctly, it only needs to expand one layer at a time.
Let's expand it: iterator begin() const{ return iterator(begin(m_range), end(m_range), m_f); } --> return iterator( iterator( begin(subrange), end(subrange), m_f ), iterator( end(subrange), end(subrange), m_f ), m_f); --> ... The expansion will terminate when begin/end(sub...subrange) is the base iterator. Then the call is made to the filter_iterator ctor, which calls the associated_range<filter_iterator> ctor, which condenses everything back down. Arno -- Dr. Arno Schoedl · aschoedl@think-cell.com Technical Director think-cell Software GmbH · Invalidenstr. 34 · 10115 Berlin, Germany http://www.think-cell.com · phone +49-30-666473-10 · toll-free (US) +1-800-891-8091 Directors: Dr. Markus Hannebauer, Dr. Arno Schoedl · Amtsgericht Charlottenburg, HRB 85229