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Date: Mon, 27 Jan 2003 10:08:17 -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: 2003-01-27T10:08:17-05:00
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Dmitry A. Kazakov wrote:
> If I define a method or a free a procedure on Ellipse:
> void Foo (Ellipse& A);
> then the compiler will not substitute a Circle for Ellipse.

Oh, You want to do *that* :-) It's an odd sort of thing to
want to do, but if you did, you wouldn't do it with copy-in/
copy-out, at least in C++. If I had to, I would do it like this,
in typical OO fashion:

struct EllipseInterface
{
     virtual void set(double x, double y) = 0;
     virtual void get(double &x, double &y) const = 0;
};

class Ellipse : public EllipseInterface
{
     double X, Y;
public:
     Ellipse(double x, double y) : X(x), Y(y) { }
     void set(double x, double y) { X = x; Y = y; }
     void get(double &x, double &y) const { x = X; y = Y; }
};

class Circle : public EllipseInterface
{
     double R;
public:
     struct NotCircle { };
     Circle(double r) : R(r) { }
     void set(double x, double y) { R = x == y ? x : throw NotCircle(); }
     void get(double &x, double &y) const { x = R; y = R; }
};

void Foo (EllipseInterface &A);