[boost] Re: [iterators] request for utility iterator

From: Thomas Witt (witt_at_[hidden])
Date: 2005-02-14 13:47:44

Dave, Thorsten,

David Abrahams wrote:
> "Thorsten Ottosen" <nesotto_at_[hidden]> writes:
> 
> It has been pointed out that this sort of thing would be very much
> easier if, like iterator_facade and iterator_adaptor, all the
> specialized adapters could accept one more optional parameter that
> specifies the most-derived iterator class.  I think that's a good
> idea, but I'm not sure how to do it without making the interface
> overly complicated.  Ideas?  I don't want to go back to the "bad old
> days" of named template parameters.

I can see this being usefull, but deriving from an iterator is such a 
no-no that creating a optonally derivable iterator somehow seems wrong 
to me. We could add another level of indirection and introduce
xxx_iterator_base<Derived, ...> types. And no I don't consider this a 
very bright idea either.

With respect to iterator lib maintenance. Me personally I don't feel 
confident in making changes as I don't have a good feeling on what is 
really needed or what the correct solution will be.

> In fact, the way default types are calculated and specified in the
> iterators library is just too complicated and needs to be re-examined.

This directly relates to what I said before. The whole area of iterator 
categories is so murky currently. IIRC there are outstanding DRs and 
issues that where never really resolved. In general I do agree.

> The whole iterators library needs some attention, but there just
> hasn't been time for me recently.  Jeremy is working on his PhD, and
> Thomas has allowed his professional life to get the better of him ;-).

Yeah having to work for a living really makes your live miserable ;-). 
Seriously I will have more time to deal with these things starting now.
I.e. I am open to input I just currently don't have any good ideas on 
how to improve the whole thing.

With respect to map_xxx iterators I always felt that something like this 
is sorely lacking. IN going ahaed I would much rather like to see an 
iterator_adaptor that iterates over a single/multiple index in a 
collection of tuples than a map iterator.

Thomas

-- 
Thomas Witt
witt_at_[hidden]