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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Should weak counted reference be able to be strengthened?
Date: Fri, 21 Nov 2014 16:28:06 -0600
Organization: Jacob Sparre Andersen Research & Innovation
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Date: 2014-11-21T16:28:06-06:00
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
news:1h5a33dishpky.8m2rngmy7e7x$.dlg@40tude.net...
> On Fri, 21 Nov 2014 18:24:13 +0000 (UTC), Natasha Kerensikova wrote:
>
>> On 2014-11-21, Dmitry A. Kazakov <mailbox@dmitry-kazakov.de> wrote:
>>> On Fri, 21 Nov 2014 15:00:12 +0000 (UTC), Natasha Kerensikova wrote:
>>>
>>>>    type Accessor (Data : not null access constant T) is limited record
>>>>       Parent : Strong_Reference;
>>>>    end record;
>>>
>>> Why do you need accessors? For Ada's crazy implicit dereference?
>>
>> Not for implicit dereference, last time I checked my GNAT FSF didn't
>> handle it well.
>>
>> Rather for the reasons explained in
>> http://www.adacore.com/adaanswers/gems/gem-107-preventing-deallocation-for-reference-counted-types/
>
> Which is misleading. The result should have been an anonymous access. Then
> it could not be copied without a conversion.

So? You still could convert it to any type and cause it to become dangling.

> And there is a safe pattern (in Ada 2005) for handling references without
> any access types and without implicit dereference.

Sure, but it's practically unusable (as occurred in the containers).

>>>> However I agree that the strong reference inside
>>>> Accessor is indeed always on the stack, and guaranteed to never escape
>>>> from the Accessor object.
>>>
>>> Helper types is bad design.
>>
>> I wasn't aware of that.

Me either. ;-) Remember that Dmitry often has unique opinions about software 
design. :-)

                                  Randy.