How is the separation of common_data and unique_data different from a separation of ranges and iterators? If iterators of ranges can rely on their range to exist, this is where common data like functors, end iterators etc. can be stored.
Naturally the point is to store the common data once when you need to store more than one iterator to the same sequence -- in a range, for example.
If you're asking why I bother reconstituting the whole iterator out of its parts, instead of simply referring to the common_data stored in the range: an adapted iterator is a useful concept regardless of whether anyone is using a range abstraction.
You could provide an adapted_iterator and also an adapted_range. If we subscribe to the rule that ranges must stay valid for their iterators to be valid, the adapted_range::iterator can use the common data stored in the range, while the adapted_iterator stores the common data itself. Both could even be derived from the same source code. Do you then still need a factored iterator? Or do you want to avoid people having to use the range abstraction? If you pass iterator pairs to algorithms instead of ranges, at least this parameter passing would have to pass the common data redundantly, even if inside the algorithm, say when many iterators have to be stored, the common data is stripped and stored separately. -- 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