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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Implicit dereferences rational question
Date: Mon, 19 May 2014 16:51:56 -0500
Organization: Jacob Sparre Andersen Research & Innovation
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Date: 2014-05-19T16:51:56-05:00
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"Victor Porton" <porton@narod.ru> wrote in message 
news:llb1aa$gth$1@speranza.aioe.org...
> Robert A Duff wrote:
>> Victor Porton <porton@narod.ru> writes:
>>
>>> Why implicit dereferences use only access discriminants, not arbitrary
>>> access fields?
>>
>> It helps prevent dangling pointers.
>
> In which way limiting to discriminants may prevent dangling pointers?

Discriminants have a lengthy set of accessibility rules, which turn out to 
be exactly what's needed for limiting dangling pointers. In particular, it's 
almost never the case that one can make a copy of an access discriminant, 
while that's easy for a "arbitrary access field".

                                        Randy.