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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Issue with GNAT GPL 2009 and GtkAda
Newsgroups: comp.lang.ada
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Date: Fri, 26 Jun 2009 11:07:11 +0200
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Date: 2009-06-26T11:07:11+02:00
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On Fri, 26 Jun 2009 10:39:45 +0200, Alex R. Mosteo wrote:

> Dmitry A. Kazakov wrote:
> 
>> On Thu, 25 Jun 2009 05:06:08 -0400, Stephen Leake wrote:
>> 
>>> Another thought: whenever I have trouble with anonymous access types,
>>> I replace them with the corresponding named access type, and the
>>> problem goes away. That may indicate a conmpiler bug, but I've always
>>> had to much to do to find out.
>> 
>> Yes, but that is not necessarily a compiler bug. It is quite simple to
>> create a serious problem to oneself:
>> 
>> declare
>>    Ptr : access T := new T;
>> begin
>>    ...
>>    External_Ptr := Ptr.all'Uchecked_Access; -- Copy the pointer
>>    ...
>> end;  -- Now External_Ptr is dangling, because the object is freed.
>  
> If I understand correctly, this is because the type of Ptr goes out of 
> scope?

Yes

> I strongly suspect that Gnat does not behave this way, but I should test it.

Here is a test:

with Ada.Finalization;
with Ada.Text_IO;  use Ada.Text_IO;

procedure Test_Anonymous_Access is
   package P is
      type T is new Ada.Finalization.Controlled with null record;
      overriding procedure Finalize (X : in out T);
   end P;
   package body P is
      procedure Finalize (X : in out T) is
      begin
         Put_Line ("Finalized");
      end Finalize;
   end P;
   use P;
begin
   declare
      X : access T := new T;
   begin
      Put_Line ("Created");
   end;
   Put_Line ("Left the scope");
end Test_Anonymous_Access;

It should print:

Created
Finalized
Left the scope

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