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From: Marius Amado Alves <amado.alves@netcabo.pt>
Newsgroups: comp.lang.ada
Subject: Re: MI ammunition : linked lists
Date: Tue, 11 Nov 2003 12:24:32 +0000
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Date: 2003-11-11T12:24:32+00:00

On Tue, 2003-11-11 at 09:32, Lutz Donnerhacke wrote:
> ...
>   type Base is limited tagged record
>     d : Datum;
>   end record;
>   
>   package Base_List1 is new Double_Linked_List (Base);  use Base_List1;
>   package Base_List2 is new Double_Linked_List (List1); use Base_List2;

I think you've failed to define List1 before using it here. But anyway
this does not look like data being shared between lists. It looks like a
list of lists, which a different thing entirely. Recursive containers. A
fascinating subject, because there is so many ways to do it, depending
on many factors, the principal perhaps being the features of the
container library used. I also abhor pointers, and prefer static
polymorphism. I discuss this in AI-302, and possibly in Ada-Europe 2004.
Actually in the case of data sharing between containers, I don't think
you can escape some sort of pointing. But you can avoid access types.
With the proper container library, you can select one container to be
the "master" (not in the ARM sense), and then make the elements of a
second container reference the elements of the master in terms of
iterators or whatever types the master provides for element
identification.