.cs

                string GetShapeDescription1(Shape shape)
                {
                    if (shape is Circle)
                        return $"found a circle with radius {(shape as Circle).Radius}";
                    if (shape is Rectangle)
                        return $"Found {(shape as Rectangle).Height }x {(shape as Rectangle).Width} rectangle";

                    throw new System.Exception(nameof(shape));
                }