From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00 autolearn=ham
	autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,56131a5c3acc678e
X-Google-Attributes: gid103376,public
X-Google-ArrivalTime: 2003-12-04 00:51:33 PST
Path: 
 archiver1.google.com!news2.google.com!fu-berlin.de!uni-berlin.de!tar-atanamir.cbb-automation.DE!not-for-mail
From: Dmitry A. Kazakov <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Question about OO programming in Ada
Date: Thu, 04 Dec 2003 09:55:31 +0100
Message-ID: <2prtsvgmt5lt3u1ulb5dvh8ba5nulfl3l3@4ax.com>
References: <8urxb.19482$sb4.18182@newsread2.news.pas.earthlink.net>
 <ygAxb.8265$lF6.7551@nwrdny01.gnilink.net>
 <1792884.HtYz4Yv8lY@linux1.krischik.com>
 <bhjosvgrsg4mokscld2057arufu8pv1ndn@4ax.com> <uhe0idzbm.fsf@wanadoo.fr>
 <mghrsvguffpi8v7m6vamr8k4j38j8ufvkp@4ax.com> <m3y8tut6b3.fsf@insalien.org>
 <b0prsv8mp1a2qtadss47j7fpgg6nqumj8u@4ax.com>
 <1070466281.168920@master.nyc.kbcfp.com> <ud6b5eexz.fsf@wanadoo.fr>
 <1070490862.478119@master.nyc.kbcfp.com> <PfudnS_16cQ3EVOi4p2dnA@comcast.com>
NNTP-Posting-Host: tar-atanamir.cbb-automation.de (212.79.194.116)
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
X-Trace: news.uni-berlin.de 1070527892 71774861 212.79.194.116 ([77047])
X-Newsreader: Forte Agent 1.8/32.548
Xref: archiver1.google.com comp.lang.ada:3125
Date: 2003-12-04T09:55:31+01:00
List-Id: <comp.lang.ada>

On Wed, 03 Dec 2003 20:23:53 -0500, "Robert I. Eachus"
<rieachus@comcast.net> wrote:

>Hyman Rosen wrote:
>
>> Not on a pointer field within the object, but on the object itself.
>
>I'm very confused about why Hyman is confused.  Making a copy of an 
>access value in Ada, and calling Free for both the original and the copy 
>is bad juju.  Calling Free twice, or twenty times and passing the only 
>the original access object is never a problem.

It is worth to write a sample code to the problem:

with Ada.Finalization;
package B is
   type Object is
      new Ada.Finalization.Limited_Controlled with
   record
      Got_It : Boolean := False; -- Prevents recursion
   end record;
   procedure Finalize (X : in out Object);
end B;

with Ada.Unchecked_Deallocation;
with Text_IO;  use Text_IO;
package body B is
   type Object_Ptr is access all Object'Class;
   procedure Free is
      new Ada.Unchecked_Deallocation (Object'Class, Object_Ptr);
   procedure Finalize (X : in out Object) is
      Ptr : Object_Ptr := X'Unchecked_Access;
   begin
      if not X.Got_It then
         X.Got_It := True;
         Put_Line ("Deallocation");
         Free (Ptr);
      end if;
   end Finalize;
end B;

Intended to mend this:

with B; use B;
with Text_IO; use Text_IO;
procedure Test1 is
begin
   Put_Line ("Begin of the scope");
   declare
      type Pointer is access Object;
      X : Pointer;
   begin
      X := new Object; -- This is not dangled!
   end;
   Put_Line ("End of the scope");
end Test1;

The point is that calling Free from Finalize is revolting. This would
not be necessary if finalization of the type Pointer called
deallocator in addition to a call to Finalize.

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