virtuals.cs

using System;
using System.Collections.Generic;

namespace Program {
    public abstract class A {
        protected abstract string Name { get; set; }
        public abstract void Print();
    }

    class B : A {
        protected override string Name { get; set; }
        public B() { Name = "B"; }
        public override void Print() { Console.Write("{0} ", Name); }
    }

    class C1 : B {
        protected override string Name { get; set; }
        public C1() { Name = "C1"; }
        public override void Print() { Console.Write("{0} ", Name); }
    }

    class C2 : B {
        new protected string Name { get; set; }
        public C2() { Name = "C2"; }
        new public void Print() { Console.Write("{0} ", Name); }
    }

    static class Tests {
        public static void Test1() {
            var myC1 = new C1();
            var myC2 = new C2();

            myC1.Print(); ((A)myC1).Print(); myC2.Print(); ((A)myC2).Print();
        }

        public static void Test2() {
            foreach (var o in new List<A> { new C1(), new C2() }) {
                o.Print();
                ((A)o).Print();
            }
        }

        public static void Test3() {
            var f = new Action<A> (x => { x.Print(); ((A)x).Print(); });
            f(new C1()); f(new C2());
        }
    }

    class Program {
        static void Main(string[] argv) {
            Tests.Test1(); Console.WriteLine(); // C1 C1 C2 B
            Tests.Test2(); Console.WriteLine(); // C1 C1 B B
            Tests.Test3(); Console.WriteLine(); // C1 C1 B B
        }
    }
}