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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Why are Ada compilers difficult to write ?
Date: Thu, 28 Jun 2018 20:26:29 +0200
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Xref: reader02.eternal-september.org comp.lang.ada:53411
Date: 2018-06-28T20:26:29+02:00
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On 2018-06-28 16:43, J-P. Rosen wrote:
> Le 28/06/2018 à 14:08, Vincent a écrit :
>> 1. The "Owning Object Aspect" changes the semantics of Access types in Ada.
> Yes. This would be a different kind of pointer, safer but less powerful.
> For example, it would not be possible to write a circular list with
> them. So it is not intended to replace current access types, it would be
> something different.

I used this strategy in my implementation of linked lists, e.g. when an 
element is inserted into a list then the original access type is set to 
null.

I don't think this is a universal enough approach to deserve a special 
class of types. Then, I don't know SPARK good enough, but I wonder why 
it is not possible to simply contract subprograms like list insert to 
leave a single access (maybe single circular access) to each list 
element? It does not look difficult to prove.

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