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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: A few questions
Date: Thu, 19 Nov 2015 15:15:15 -0600
Organization: JSA Research & Innovation
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Xref: news.eternal-september.org comp.lang.ada:28470
Date: 2015-11-19T15:15:15-06:00
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
news:1wew1bio4hygc.xotxd22aq47g.dlg@40tude.net...
> On Wed, 18 Nov 2015 16:27:31 -0600, Randy Brukardt wrote:
...
>> If you think allowing erroneous execution is somehow safe, you're in the
>> wrong language forum.
>
> The point was that keeping the iteration state in the container is more
> erroneous that keeping it outside in the iterator object. E.g. some
> implementations store last found element, deploy caching and book-keeping
> things in the container. That far less safe than keeping that stuff 
> outside
> the container, e.g. in the iterator object.

Sorry, missed your point originally. I don't think it's possible (in 
general) to keep the iteration information within the container, as that 
would mean that you could only do one iteration at a time. Which would be a 
nasty abstraction break (inner iterations on the same container would have 
to fail in that case, but for no good reason).

That is, if the iterator info is part of the container, then
        for E of C loop
            for F of C loop
               ...
            end loop;
       end loop;

cannot work. (The inner loop often occurs in some routine called from the 
body of the loop, it wouldn't be obvious like this is.)

                               Randy.