The C# IS operator

will return true for tests of Interface implementation and class parentage

    interface IFuddy

    {

       string  test();

    }

    public class testBase: IFuddy

    {

        public string test()

        {

            return "hody";

        }

    }

    public class testA : testBase

    {

        public string atest()

        {

            return "hodydoe";

        }

    }

    public class testB : testBase

    {

        public string btest()

        {

            return "awaywego";

        }

    }

   private void retu(IFuddy f)

        {

            if (f is testA)

            {

                Response.Write((f as testA).atest());

            }

            if (f is testB)

            {

                Response.Write((f as testB).btest());

            }

            if (f is testBase)

            {

                Response.Write("f is testBase");

            }

            if (f is IFuddy)

            {

                Response.Write("f is IFuddy");

            }

        }

      protected void Button12_Click(object sender, EventArgs e)

        {

            testA t1 = new testA();

            testB t2 = new testB();

            retu(t1);

            retu(t2);

        }

Will write:

hodydoe
f is testBase
f is IFuddy
awaywego
f is testBase
f is IFuddy