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From: John G. Volan <John_Volan@ccmail.dayton.saic.com>
Subject: Re: Real OO
Date: 1996/03/30
Message-ID: <4jkgti$kb7@dayuc.dayton.saic.com>#1/1
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references: <DoLo83.tA@assip.csasyd.oz> <65h8jGx-3RB@herold.franken.de>
 <4jf54u$o14@Sahara.enmu.edu> <4jh5cr$101s@watnews1.watson.ibm.com>
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Date: 1996-03-30T00:00:00+00:00
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In article <4jh5cr$101s@watnews1.watson.ibm.com>
Norman H. Cohen, ncohen@watson.ibm.com writes:
>No, the proper solution is to add the classwide function
>
>   function Geometry_Of
>      (Graphic: Graphic_Type'Class) return Shape_Pointer_Type is
>   begin
>      return Graphic.Shape;
>   end Geometry_Of;
>
>(and possibly a Set_Geometry_Of procedure).  Then, to test whether
>Graphic_Type instances G1 and G2 have congruent polygons, we write
>
>   Congruent (Geometry_Of(G1).all, Geometry_Of(G2).all)

Actually, I think you might be able get by with:

    function Geometry_Of
        (Graphic: Graphic_Type'Class) return Shape_Type'Class is
    begin
        return Graphic.Shape.all;
    end Geometry_Of;
    
I believe this would be a return-by-reference function, so I don't think
there would be any extra copying involved.  Of course, this only
provides a "constant" view of the referenced Shape, so you couldn't
then pass it into an "in out" parameter for instance. But you would be
able to do:

    Congruent (Geometry_Of(G1), Geometry_Of(G2))
    
Note you could use the result of a call to Geometry_Of in this way even
if Shape_Type happened to be limited (although you wouldn't be able to
save the result in a variable, for instance).

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