[boost] Re: Problem with boost.iterator II

From: David Abrahams (dave_at_[hidden])
Date: 2004-12-09 14:56:47

Bob Bell wrote:
> Dave-
> 
> I was looking over my "sent" items and I think something was wrong with 
> my return address, so I'm resending this with the right address. Sorry 
> for any confusion it may have caused.

Bob,

Please post Boost questions to one of the Boost mailing lists (unless
you want to hire us for consulting services, that is!)

> I've been using the boost iterator adaptor library, and first let me say
> thanks; it's really a great library.

You're welcome :)

> Having said that, however, I'm having a problem. I'm trying to build an
> iterator that uses both boost::filter_iterator and
> boost::transform_iterator, but what happens is that when I combine these
> two adaptors, it seems to lose the iterator category of the original
> iterator. That is, say I build an iterator like this:
> 
> boost::transform_iterator<SomeTransform,
>        boost::filter_iterator<SomeFilter, int*> >
> 
> The resulting iterator only seems to be a forward iterator. My
> understanding is that the iterator category of the base iterator (int*),
> should become the category of the resulting composite. So my first
> question is: is this a correct understanding on my part?

Not according to
http://www.boost.org/libs/iterator/doc/filter_iterator.html#filter-iterator-models

A filter iterator is never more than a forward iterator.

HTH,
-- 
Dave Abrahams
Boost Consulting
http://www.boost-consulting.com