Re: [boost] Re: Iterator Adaptor Poll

From: Thomas Witt (witt_at_[hidden])
Date: 2002-07-29 03:33:49

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Dave,

On Monday 29 July 2002 01:59, David Abrahams wrote:
> From: "Thomas Witt" <witt_at_[hidden]>
> It's really hard to carry on this discussion without a definition of your
> Adapter/LeanIterator concepts.

I will try to provide some code/text later.

>
> I'm not claiming that it's the right solution. However, at least read-only
> access to the state is often useful, and I wouldn't want to prohibit it.
>

Agreed.

> It's hard to say without seeing more details. There are lots of viable
> approaches, though. Have you thought about using a GenVoca arrangement?

No, I haven't got around to learn about GenVoca yet. Is there a paper 
available somewhere?

> > Ok maybe I was exaggerating a bit, but with the current design it is
> > impossible to implement a cycle or joining iterator that has natural
> > const/non-const interaction.
>
> Because you end up using a different type for the policies class in the
> const version?

Yes, the basic problem is that you have to store iterators in the policies 
object so that they can be returned to the user later(wrapping around, moving 
to the next sequence). Either you use different policies types or you store 
non-const iterators even for the const iterator. The first option results in 
incompatible iterators, the second in a const iterator that can not be 
generated from a const container.

- --Thomas

- -- 
Dipl.-Ing. Thomas Witt
Institut fuer Verkehrswesen, Eisenbahnbau und -betrieb, Universitaet Hannover
voice: [phone] - 4273, fax: [phone]
http://www.ive.uni-hannover.de
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