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From: AdaMagica <christ-usch.grein@t-online.de>
Newsgroups: comp.lang.ada
Subject: Re: discriminant questions
Date: Tue, 20 Sep 2011 04:11:32 -0700 (PDT)
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Date: 2011-09-20T04:11:32-07:00
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On 20 Sep., 09:38, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
wrote:
> On Mon, 19 Sep 2011 19:01:05 -0500, Randy Brukardt wrote:
>
> >>> type Reference_Type (Element : access Integer) is null record;
>
> > The "good reason" for using this construct (beyond the obvious one of being
> > able to use the "implicit dereference" construct is one of lifetime. The
> > access discriminant of this object has the same lifetime as the enclosing
> > object; if that object is returned from a function, that is very short.
>
> That is why this cannot be used for smart pointers. For them the
> relationship is exactly opposite: Element always outlive the pointer except
> the last one.

Excuse me, but that's nonsense. It is a very good reason to use this
construct.
See AdaCore Gem #107:
http://www.adacore.com/2011/06/06/gem-107-preventing-deallocation-for-reference-counted-types/