Christian Engström <christian.engstrom@glindra.org> writes:
The reason why they are derived, in turn, is that we want the proxy iterators and the underlying "normal" iterators to be implicitly convertable to each other in both directions. If both conversions were user defined, as they would have to be if the proxy iterators could not utilize the implicit derived-to-base conversion, this would lead to a host of ambiguity problems, since the compiler has no reason to prefer one conversion over the other.
The classic example is the expression a == b, which becomes ambiguous because the compiler is just as happy to carry out the comparison as either b_type(a) == b or a == a_type(b) if both conversions are available as implicit user defined conversions, and there is no == operator defined for the mixed types case.
A classic example of a problem that can bve solved more elegantly by the iterator adaptors library, *without* the problematic two-way implicit conversion -- and it *is* problematic, even if one direction is derived-to-base. You asked for feedback; I say look at the work that those came before you already did in this area. I don't know why you won't, but I've stopped trying now. Cheers, -- Dave Abrahams Boost Consulting www.boost-consulting.com