I'm trying to find out what the specific example applications are. I have a suspicion that range adapters or single-level iterator adaptors may not be the best way to address these applications and may even sacrifice significant performance, but I can't tell until I know what the applications are. Just so, single-level iterators (or ordinary range adapters, which don't add anything conceptually to iterators) are not the best way to address iteration over hierarchical data structures, which is why we have segmented iterators.
This is a typical one, copied straight from our code: grdlns->InsertGridlines( vecgvepsSource, make_first_range(vecpairanchorsrcgrdln), GridlineInsertionPositions( make_transform_range( make_transform_range( make_first_range( vecpairanchorsrcgrdln ), boost::mem_fn(&_vector< Ref<CGridlineAnchor> >::begin) ), boost::mem_fn( &CGridlineAnchor::Binding ) ), vecgrdlnSnapped), vecgrdlnSnapped ); This is a case in point: I did not write this code, and in the absence of specific guidelines against, the programmer decided to stack transform_range. In this case, performance-wise, this is no better or worse than using a single transform_range with boost::bind. Likewise, people may innocently write rng | filtered( funcA ) | filtered( funcB ) | filtered( funcC ) | filtered( funcD ) | filtered( funcE ) blissfully unaware of any performance penalty.
However, it seems to me that you already have a general answer in mind, and it might be better to back up and look at the real problems you want to solve before moving on to the answer.
Would it be my turn now to ask for some credit ;-) ? 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