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From: AdaMagica <christoph.grein@eurocopter.com>
Newsgroups: comp.lang.ada
Subject: Re: Enforcing initialization protocol for protected type
Date: Fri, 11 Sep 2009 08:25:56 -0700 (PDT)
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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.

subtype ConRec is Rec (new Disc);

If I understand the RM correctly, the discriminant of objects of the
constrained subtype is no coextensions; it will be deallocated when
the subtype goes out of scope.