Andrei Alexandrescu <andrei <at> metalanguage.com> writes:
A design that has a bidirectional iterator walking freely up and down between two limits would be difficult to port to ranges. (If the iterator is random-access, things are trivial.) Ranges can only shrink, they never grow unless assigned from the outside.
I don't see a problem with this case. The limits are a range, and the internal bidirectional iterator is a subrange of that range. There's no reason why a subrange couldn't be allowed to grow since we know its enclosing range.
Another example of an iterator-based design that's not easy to replicate with ranges is Boost Multi-Index.
Right. Suffix arrays are a similar case (indeed, suffix arrays can be represented straightforwardly with Boost.MultiIndex). However, I suspect that the overwhelming majority of uses of Boost.MultiIndex are better thought of as permutations rather than a containers-of-iterators. If there was an abstract notion of permutation that was just as high-level as ranges, most of these problems may go away. I say "most". I've used a containter-of-iterators to represent inverted indexes, and they are definitely not permutations. Andrew Bromage