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Date: Tue, 28 Jan 2003 12:11:50 -0500
From: Hyman Rosen <hyrosen@mail.com>
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Subject: Re: Anybody in US using ADA ? One silly idea..
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Date: 2003-01-28T12:11:50-05:00
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Dmitry A. Kazakov wrote:
> But that's another thing. Here, Circle cannot use (inherit) the
> methods of Ellipse. It inherits only the abstract methods of
> EliipseInterface and thus, have to implement all of them for scratch.
> This kills the whole idea of inheritance for code reuse.

It's just the way I wrote it here, because I figured Circle
didn't need to store two doubles, just one. It could have
inherited directly from Ellipse if I'd wanted it that way:

class Circle : public Ellipse
{
public:
     struct NotCircle() { }
     Circle(double r) : Ellipse(r, r) { }
     void set(double x, double y) {
         if (x != y) throw NotCircle();
         Ellipse::set(x, y);
     }
};

Someone can sabotage this version though, by taking a
Circle and calling its Ellipse::set method directly.
In my other version, that couldn't happen.