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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: discriminant questions
Date: Fri, 23 Sep 2011 11:48:50 +0200
Organization: cbb software GmbH
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Date: 2011-09-23T11:48:50+02:00
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On Fri, 23 Sep 2011 05:23:38 -0400, Stephen Leake wrote:

> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
> 
>> Consider a generic
>> implementation of removing all elements of the container using iterators:
>>
>>    This := Container.First;
>>    while This /= Null_Iterator loop
>>        Next := This.Next;
>>        This.Delete;
>>        This := Next;
>>    end loop;
>>
>> This may work or not depending on the semantics of Delete. E.g. for a
>> circular list, it will loop forever.
> 
> No, it will produce an invalid dereference; for a one element circular
> list, This.Next = This, so Next is invalid after This.Delete.

If the element is only in this list and freed upon delete, then Next is
dangling.

However a common schema is that elements of lists are actually never freed,
but rather moved to the list of unused element to reuse, when a new element
is needed. For this implementation the above loops.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de