Re: [boost] lifetime of ranges vs. iterators

From: Arno Schödl (aschoedl_at_[hidden])
Date: 2008-09-01 07:56:16

> >
> > You need to be able to take two adapted iterators and turn them into a
> > range.  Do you want that range to contain redundant data?  I don't.

> Hei, maybe this is all that we need! Let's have a metafunction that
> given an iterator type returns its preferred range type (the
> associated range). The default might be boost.range or even std::pair.
>  The developer of an iterator adaptor, can specialize the metafunction
> so that the associate range is the optimum representation for an
> iterator pair.

> Do you think this would be enough? It seems too simple to me, so
> probably I'm missing something...

I wouldn't know what to do when my iterator_adaptor needs three iterators to the same range. I could store two efficiently as a range and retrieve them when needed by querying range::begin()/end(), but what do I do with the third? Dave's factored iterators go further in the same direction, basically dropping the requirement that the common data must be a range, it can be anything. 

Both proposals have the disadvantage that I need to wrap/unwrap the [common data (Dave)/range (Giovanni)] whenever I change one of the wrapped iterators. I'd rather store the common data explicitly, and have indirections inside the iterators that point to it.

Correct me if I misunderstand one of the two proposals.

Arno

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