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From: Dmitry A. Kazakov <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Question about OO programming in Ada
Date: Tue, 02 Dec 2003 09:47:03 +0100
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Date: 2003-12-02T09:47:03+01:00
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On Mon, 01 Dec 2003 16:57:37 +0100, Martin Krischik
<krischik@users.sourceforge.net> wrote:

>Hyman Rosen wrote:
>
>> Jeffrey Carter wrote:
>>  > you cannot create a dangling reference with 'Access.
>> 
>> How not? Just deallocate the object to which the pointer points.
>
>How will you do this without using some form of "Unchecked_"?

Easily if the target is controlled. Consider this:

with Ada.Finalization;
package A is
   type Misty is
      new Ada.Finalization.Limited_Controlled with null record;
   procedure Finalize (X : in out Misty);
end A;

with Text_IO; use Text_IO;
package body A is
   procedure Finalize (X : in out Misty) is
   begin
      Put_Line ("finalized!");
   end Finalize;
end A;

with A;  use A;
with Text_IO;  use Text_IO;
procedure Test is
begin
   Put_Line ("Begin of a scope");
   declare
      type Pointer is access all Misty;
      X : Pointer;
   begin
      X := new Misty; -- This is not dangled!
   end;
   Put_Line ("End of the scope");
end Test;

This program should print;

Begin of a scope
finalized!
End of the scope

All controlled objects allocated by the allocator new, being not
explicity destroyed using Unchecked_Deallocation, will be destroyed
upon finalization of the access type.

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