static void Main2(string[] args)
{
RectangleGood rc = new RectangleGood(2, 3);
Console.WriteLine($"{rc} has area {Area(rc)}");
// should be able to substitute a base type for a subtype
/*Square*/
RectangleGood sq = new SquareGood();
sq.Width = 4;
Console.WriteLine($"{sq} has area {Area(sq)}");
}
static public int Area(RectangleGood r) => r.Width * r.Height;