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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: discriminant questions
Date: Tue, 20 Sep 2011 09:38:15 +0200
Organization: cbb software GmbH
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Date: 2011-09-20T09:38:15+02:00
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On Mon, 19 Sep 2011 19:01:05 -0500, Randy Brukardt wrote:

> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
> news:148cxoyabima2.16mz6xwdph2hj.dlg@40tude.net...
>> On Sat, 17 Sep 2011 15:55:15 -0700 (PDT), ytomino wrote:
> ...
>>> This code is same as:
>>>
>>> type Reference_Type (Element : access Integer) is null record;
>>
>> It is not same, and I don't see the purpose of using this construct. In 
>> any case it cannot serve as a good basis for smart pointers.
> 
> 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.

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