increment() { for( difference_type i=0; i<N && !base.empty(); ++i ) { base.increment(); // the adapted_range::increment which increments begin, base is a range } }
I don't think you're fully appreciating what a huge impact such a complex implementation of increment() would have on performance.
Sorry, I meant this as the implementation for forward range. You don't want to use increment for random_access ranges, obviously. Thinking about it some more, I believe the associated_range abstraction is not quite the right one yet. It works for forward_ranges, which is why I did not notice earlier, but not for bidirectional and random_access_ranges. The correct abstration is bounded_iterator, which is an iterator + the knowledge of whatever bounds it needs. The extra functionality offered over iterators is to test overrun of begin/end in increment/decrement/advance. begin/end may have a bool return value whether increment/decrement succeeded or not, and advance may return the difference_type that actually got executed until begin/end was reached. The bounded_forward_iterator is a bit similar to a range. Its base iterator implementation must store the current iterator + the end. This is essentially what Giovanni introduced as associated_range. The bounded_bidrectional_iterator and bounded_random_access_iterator base implementation must store begin, current and end base iterators. All iterators needing the underlying iterator bounds can then run on top of bounded_iterators, and are implement the bounded_iterator interface themselves. I think this eliminates all space overhead of any adaptors we have been mentioning so far. In particular this applies to strided_iterators of all categories. The corresponding adaptor ranges would return bounded iterators from their begin()/end() functions. They store their base range internally instead of two iterator adaptors, to avoid any space overhead in ranges. 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