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From: matthias_k <nospam@digitalraid.com>
Newsgroups: comp.lang.ada
Subject: Re: Classwide Parameter?
Date: Mon, 11 Oct 2004 19:08:24 +0200
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Date: 2004-10-11T19:08:24+02:00
List-Id: <comp.lang.ada>

Thanks for that answer. However, I'm still having problems (I have 
rewritten the code to be in one single package now):

<snip>
package Graphics is

    type Shape is abstract tagged null record;
    procedure Draw (Obj: Shape'Class);

    type Circle is new Shape with record
       Radius: Float;
       Center: Float;
    end record;
    procedure Draw (Obj: Circle);

    type Square is new Shape with record
       Size: Float;
    end record;
    procedure Draw (Obj: Square);

end;
</snip>

Now, what I want is to have different implementations of the Draw method 
for each Subtype. However, if I run this program:

<snip>
with Graphics;
use Graphics;

procedure Demo is
    type Reference is access all Shape'Class;
    Object: Reference;
begin
    Object := new Circle;
    Draw( Object.all );

    Object := new Square;
    Draw( Object.all );
end;
</snip>

The Shape's Draw method is always called here but it shouldn't. No late 
binding happens. I have tried to make it abstract, but it didn't even 
compile then. What's wrong?

- Matthias