Wouldn't this be better served with defaults?

    // constructor
    func init (a, b, c) {
        if (!a) a = 0;
        if (!b) b = 0;
        if (!c) c = 0;
        x = a; y = b; z = c;
    }

Like

    func init (a=0, b=0, c=0) {
        x = a; y = b; z = c;
    }