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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: How to get Ada to ?cross the chasm??
Date: Wed, 9 May 2018 10:37:21 +0200
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Xref: reader02.eternal-september.org comp.lang.ada:52151
Date: 2018-05-09T10:37:21+02:00
List-Id: <comp.lang.ada>

On 09/05/2018 09:23, Paul Rubin wrote:
> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
>> Yes, but my argument is that it only hides the logical error. The
>> reference that is semantically weak acts as a strong one preventing
>> collection of an unused object. Circular references are never right.
> 
> I don't see the issue here.  Circular linked lists are a venerable data
> structure of which there are many assembly code examples in Knuth vol 1
> from the 1960s.

Sure, but references in such a list should never be used for memory 
management. This is because a list is not an object/container, it a pair 
of steps down on the abstraction ladder.

> Similarly, graphs are data and some of them have
> cycles.  Some algorithms might have trouble with cyclic data, but others
> handle it ok.

Graphs are exemplary for the need of a careful design with weak and 
strong references. BTW, reference counted nodes have an advantage that 
you can decide if the subgraph is shared with another task, and not to 
clone it before updating if it is not. My point is that all such 
situations are subject for careful design (of memory management in 
particular). GC is only an obstacle here.

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