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From: Florian Weimer <fw@deneb.enyo.de>
Newsgroups: comp.lang.ada
Subject: Re: A hole in Ada type safety
Date: Sun, 08 May 2011 10:46:05 +0200
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Date: 2011-05-08T10:46:05+02:00
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* Dmitry A. Kazakov:

> I mean a schema which could be usable for Ada. I see many problems, apart
> from tasking. If you want to refer components, you need to add the parent's
> count to the component's count in order to prevent its zeroing.

The component wouldn't have its own count.  A reference to a component
would consist of a pointer to the component, combined with a pointer
to the reference counters for the outmost object.

> When you create a reference you have to check if the counts already
> exist somewhere.  Since nothing is allocated in the object, where
> get that information from?

You would only be able to create a reference from prefixes which
contain references at certain points.  For everything else, you'd have
to use access values, as before.

> IMO weak references are quite useless if do not support notifications (when
> the last strong reference is removed). I.e. you need a list of weak
> reference holders.

I think they are supposed to be used for parent pointers in trees, for
instance, to avoid the cycle issue.  Not so much for finalization.