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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Enforcing initialization protocol for protected type
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Date: Fri, 11 Sep 2009 18:27:38 +0200
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Date: 2009-09-11T18:27:38+02:00
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On Fri, 11 Sep 2009 08:25:56 -0700 (PDT), AdaMagica wrote:

> On 11 Sep., 11:03, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
> wrote:
>> On Thu, 10 Sep 2009 22:01:17 -0700 (PDT), AdaMagica wrote:
>>> On 7 Sep., 22:19, Maciej Sobczak <see.my.homep...@gmail.com> wrote:
>>>> This, however, opens another question: controlled finalization of
>>>> protected types to release the state object, if it was allocated
>>>> dynamically. Oops.
>>
>>> Use an access discriminant of an anonymous type and you will get a
>>> coextension that is reclaimed automatically when the object goes out
>>> of scope, see RM 3.10(14.3/2,14.4/2) [or in the newest draft of the
>>> Amendment 2, (14.1/3,14.4/3), which is a bit clearer].
>>
>>> See also RM 3.7(1.c/2..1.e/2).
>>
>> Hmm, what do you mean by that? When the discriminant's type is an anonymous
>> access it is still declared at the declaration point of the type. It is not
>> the declaration point of an object. So if the discriminant is obtained by
>> the allocator new it will not be destroyed when the object leaves the
>> scope. It will when the type does. If these scopes are different, the
>> compiler will complain that the type in the allocator has a deeper level.
> 
> type Disc is ...
> 
> type Rec (D: access Disc) is record ...
> 
> Obj: Rec (new Disc);
> 
> The discriminant (a coextension of the object) will be deallocated
> when Obj goes out of scope.

OK I see. Anyway I would not use this design pattern because it would be a
source of countless errors very difficult to track down.

P.S. It looks like a language design bug. If allowed then at least it
should have been like:

   Obj: subtype Rec (new Disc);
      -- An anonymous subtype is declared for Obj

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