using System;

public class Program

{

    public static void Main()

    {

        Thing t = new();

        object x = (object)t;

        Test(x);

    }

    private static void Test<T>(T thing)

    {

        var x = thing switch

            {

                Thing something => something,

                _ => throw new InvalidOperationException()

            };

        Console.WriteLine("Yes");

    }

​

    public class Thing

    {

        public Thing() {}

        public string What => "Thing";

    }

}