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References: <mailman.4.1045140569.13246.comp.lang.ada@ada.eu.org>
From: porton@ex-code.com (Victor Porton)
Subject: Re: Pitfall: freeing access discriminants
Newsgroups: comp.lang.ada
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Date: Thu, 13 Feb 2003 18:38:38 +0500
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Date: 2003-02-13T13:47:54+00:00
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In article <mailman.4.1045140569.13246.comp.lang.ada@ada.eu.org>,
	"Grein, Christoph" <christoph.grein@eurocopter.com> writes:
> This works, but you have to be careful with the allocation pools.
> Also access discriminants can never be null, so if you deallocate the object it 
> is accessing, ...
> 
> Ok, here you are safe since you finalize the whole object.
> 
> with Ada.Finalization;
> 
> package Acc_Dis is
> 
>   type T (D: access Integer) is
>     new Ada.Finalization.Limited_Controlled with null record;
> 
>   procedure Finalize (Object: in out T);
> 
>   V: T (new Integer'(5));
> 
> end Acc_Dis;
> with Ada.Unchecked_Deallocation;
> 
> package body Acc_Dis is
> 
>   procedure Finalize (Object: in out T) is
>     type Integer_Ptr is access all Integer;
>     procedure Free is new Ada.Unchecked_Deallocation (Integer, Integer_Ptr);
>     P: Integer_Ptr := Integer_Ptr (Object.D);
>   begin
>     Free (P);
>   end Finalize;
> 
> end Acc_Dis;

Oops, I've found that this in not safe and even may lead to erraneous 
execution!! Because of storage pools for Integer_Ptr may be different 
from storage pool used by "new".