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From: Laurent Guerby <guerby@acm.org>
Subject: Re: Deallocating an object referenced via a classwide access type.
Date: 2000/01/11
Message-ID: <86k8lgmmig.fsf@ppp-112-82.villette.club-internet.fr>#1/1
X-Deja-AN: 571303647
References: <slrn87l2rt.15e.aidan@skinner.demon.co.uk>
X-Trace: front3.grolier.fr 947618924 2744 194.158.112.82 (11 Jan 2000 19:28:44
 GMT)
Organization: Club-Internet (France)
NNTP-Posting-Date: 11 Jan 2000 19:28:44 GMT
Newsgroups: comp.lang.ada
Date: 2000-01-11T19:28:44+00:00
List-Id: <comp.lang.ada>

Aidan wrote:
> I can't use Ada.Unchecked_Deallocation, since My_Thing might be a Foo
> or it might be a New_Foo.

May be I'm missing something obvious about your question and/or the
Ada RM but the code attached at the end of this message works for
AFAIK (I edited your spec so that it compiles ;-). The only thing
special (due to the class wide nature of the Object formal) is that
the Finalize call made as part of the Free call before returning the
memory to the system will be dispatching (you didn't provide Finalize
on Foo but I guess you have one ;-).

--LG

with Ada.Unchecked_Deallocation;
package body Foo_Package is

   procedure Deallocate (Object : in out Foo) is
      procedure Free is new Ada.Unchecked_Deallocation (Foo'Class, Foo_Access);
   begin
      Free (Object.My_Thing);
   end Deallocate;

end Foo_Package;

with Ada.Finalization;
package Foo_Package is

  type Foo is new Ada.Finalization.Controlled with private;

  type Foo_Access is access all Foo'Class;

  type New_Foo is new Foo with private;

private

  type Foo is new Ada.Finalization.Controlled with record
     My_Thing : Foo_Access := null;
  end record;

  procedure Deallocate (Object : in out Foo);

  type New_Foo is new Foo with null record;

end Foo_Package;