Permanently cast derived class to base

Question

Class A { }
Class B : A { }

B ItemB = new B();
A ItemA = (A)B;

Console.WriteLine(ItemA.GetType().FullName);

Is it possible to do something like a

Answer 1

For amusement, if you wanted to lose all of the derived data you could do this:

   class Program
    {
        [DataContract(Name = "A", Namespace = "http://www.ademo.com")]
        public class A { }
         [DataContract(Name = "A", Namespace = "http://www.ademo.com")]
        public class B : A  {
             [DataMember()]
             public string FirstName;
        }  

    static void Main(string[] args)
    {
        B itemB = new B();
        itemB.FirstName = "Fred";
        A itemA = (A)itemB; 
        Console.WriteLine(itemA.GetType().FullName);
        A wipedA = WipeAllTracesOfB(itemB);
        Console.WriteLine(wipedA.GetType().FullName);
    }

    public static A WipeAllTracesOfB(A a)
    {
        DataContractSerializer serializer = new DataContractSerializer(typeof(A));

        using (MemoryStream ms = new MemoryStream())
        {
            serializer.WriteObject(ms, a);
            ms.Position = 0;

            A wiped = (A)serializer.ReadObject(ms);

            return wiped;
        }
    }
}

If you use the debugger you will see the FirstName is still stored in the field FirstName when it is cast to an A, when you get an A back from WipeAllTracesOfB there is no FirstName, or any trace of B.