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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Pop function
Date: Thu, 15 Dec 2011 20:14:41 +0100
Organization: cbb software GmbH
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Date: 2011-12-15T20:14:41+01:00
List-Id: <comp.lang.ada>

On Thu, 15 Dec 2011 18:34:53 +0000, Simon Wright wrote:

> Here, for example, if I write
> 
>       L : aliased T_List;
>       ...
>    begin
>       ...
>       J := Pop (L'Access);
> 
> I'm going to get a crash at runtime because I'm trying to deallcate
> memory that was never allocated.

Another reason to have it an explicit access type, BTW. If L were access to
specific pool you would not be able to declare L on the stack.

> I have in the past implemented lists where the 'head' element was just
> another member which -- by convention -- wasn't part of the list.

I tried:

   type Item is access Element_Type;
   type List is new Item;

and then to separate elements and lists in operations. E.g.

   procedure Delete (Container : in out List; Element : in out Item);

Item becomes null, Container set to the new head.

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