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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Rational for not making cursor tagged in Containers
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Date: Tue, 24 Apr 2007 14:21:51 +0200
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Date: 2007-04-24T14:21:51+02:00
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On Tue, 24 Apr 2007 10:58:48 +0200, Georg Bauhaus wrote:

> On Sun, 2007-04-22 at 10:38 +0200, Dmitry A. Kazakov wrote:
> 
>> 'Class is a difficult case. And a general question regarding it is, should
>> it be possible to have it "hyper-dispatching"? [sorry, for inventing new
>> terms on the fly]? I mean T'Class'Class.
> 
> I'm dense, is there any difference between T'Class and T'Class'Class?

If you were allowed to derive from any type to get at the class of, then
you could do:

type Object is ...;
procedure Foo (X : Object'Class);
   -- Does not dispatch on Object'Class

type Meta_Object is new Object'Class with ...;
procedure Bar (X : Meta_Object);
   -- Dispatches on Meta_Object

I cannot think of any useful example for this. Perhaps:

type Node;
type Node_Ptr is access Node;

type Node is new Object'Class with record
   Previous : Node_Ptr;
   Next : Node_Ptr;
end record;

Which is essentially:

type Node (T : Tag) is record
   Previous : Node_Ptr;
   Next : Node_Ptr;
   Value : Object'Class (T);
end record;

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