You need to be able to take two adapted iterators and turn them into a range. Do you want that range to contain redundant data? I don't.
Hei, maybe this is all that we need! Let's have a metafunction that given an iterator type returns its preferred range type (the associated range). The default might be boost.range or even std::pair. The developer of an iterator adaptor, can specialize the metafunction so that the associate range is the optimum representation for an iterator pair.
Do you think this would be enough? It seems too simple to me, so probably I'm missing something...
I wouldn't know what to do when my iterator_adaptor needs three iterators to the same range. I could store two efficiently as a range and retrieve them when needed by querying range::begin()/end(), but what do I do with the third? Dave's factored iterators go further in the same direction, basically dropping the requirement that the common data must be a range, it can be anything. Both proposals have the disadvantage that I need to wrap/unwrap the [common data (Dave)/range (Giovanni)] whenever I change one of the wrapped iterators. I'd rather store the common data explicitly, and have indirections inside the iterators that point to it. Correct me if I misunderstand one of the two proposals. 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