Here's an example of the new syntactic sugar:

    public static double ComputeArea(object shape) {
        switch (shape) {
            case Square s:
                return s.Side * s.Side;
            case Circle c:
                return c.Radius * c.Radius * Math.PI;
            case Rectangle r:
                return r.Height * r.Length;
            default:
                throw new ArgumentException(
                    message: "shape is not recognized",
                    paramName: nameof(shape));
        }
    }

The when clause can be used to deal with special cases (e.g. to avoid division by 0 when a dimension is 0).