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From: Lutz Donnerhacke <lutz@iks-jena.de>
Newsgroups: comp.lang.ada
Subject: Re: MI ammunition : linked lists
Date: Tue, 11 Nov 2003 12:58:55 +0000 (UTC)
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* Marius Amado Alves wrote:
> 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.

My fault.
 package Base_List2 is new Double_Linked_List (List1.Object); use Base_List2;

> But anyway this does not look like data being shared between lists.

generic
   type Node(<>) is abstract tagged limited private;
package Double_Linked_List is
   type Object is abstract limited new Node with private;
   type List ist limited private;
   ...
private
   type Node_Ptr is access all Object;
   type Object is abstract limited new Node with record
      next, prev : Node_Ptr := Object'Access;
   end record;
   
   type List is limited record
     start, end : Node_Ptr := List'Access;
   end record;
end Double_Linked_List;
   

> It looks like a list of lists, which a different thing entirely.
> Recursive containers.

No, it's a plain mixin.

> Actually in the case of data sharing between containers, I don't think
> you can escape some sort of pointing.

Of course, but you should hide them in the enclosing structure. It's bad
design to collect pointers explicitly.