Virtual methods implementation example from acticle by Eric Lippert http://blogs.msdn.com/b/ericlippert/archive/2011/03/17/implementing-the-virtual-method-pattern-in-c-part-one.aspx

VirtualMethodsImplementation.cs

using System;

// Example from acticle by Eric Lippert http://blogs.msdn.com/b/ericlippert/archive/2011/03/17/implementing-the-virtual-method-pattern-in-c-part-one.aspx

namespace VirtualMethodsImplementation
{
    internal sealed class VTable
    {
        public readonly Func<Animal, string> Complain;
        public readonly Func<Animal, string> MakeNoise;

        public VTable(Func<Animal, string> complain, Func<Animal, string> makeNoise)
        {
            Complain = complain;
            MakeNoise = makeNoise;
        }
    }


    internal abstract class Animal
    {
        public VTable VTable;

        public static string MakeNoise_(Animal _this)
        {
            return "";
        }
    }


    internal class Giraffe : Animal
    {
        private static readonly VTable GiraffeVTable = new VTable(Giraffe.Complain_, Animal.MakeNoise_);

        public bool SoreThroat { get; set; }

        public static string Complain_(Animal _this)
        {
            return (_this as Giraffe).SoreThroat ? "What a pain in the neck!" : "No complaints today.";
        }

        public static Giraffe Create()
        {
            Giraffe giraffe = new Giraffe();
            giraffe.VTable = Giraffe.GiraffeVTable;
            return giraffe;
        }
    }


    internal class Cat : Animal
    {
        private static readonly VTable CatVTable = new VTable(Cat.Complain_, Cat.MakeNoise_);

        public bool Hungry { get; set; }

        public static string Complain_(Animal _this)
        {
            return (_this as Cat).Hungry ? "GIVE ME THAT TUNA!" : "I HATE YOU ALL!";
        }

        public static string MakeNoise_(Animal _this)
        {
            return "MEOW MEOW MEOW MEOW MEOW MEOW";
        }

        public static Cat Create()
        {
            Cat cat = new Cat();
            cat.VTable = Cat.CatVTable;
            return cat;
        }
    }


    internal class Dog : Animal
    {
        private static readonly VTable DogVTable = new VTable(Dog.Complain_, Animal.MakeNoise_);

        public bool Small { get; set; }

        public static string Complain_(Animal _this)
        {
            return "Our regressive state tax code is... SQUIRREL!";
        }

        public static string MakeNoise_(Dog _this)
        {
            return _this.Small ? "yip" : "WOOF";
        }

        public static Dog Create()
        {
            Dog dog = new Dog();
            dog.VTable = Dog.DogVTable;
            return dog;
        }
    }

    internal static class Program
    {
        public static void Main(string[] args)
        {
            string s;
            Animal animal = Giraffe.Create();
            s = animal.VTable.Complain(animal);  // no complaints
            s = animal.VTable.MakeNoise(animal); // no noise
            animal = Cat.Create();
            s = animal.VTable.Complain(animal);  // I hate you
            s = animal.VTable.MakeNoise(animal); // meow!
            Dog dog = Dog.Create();
            animal = dog;
            s = animal.VTable.Complain(animal);  // squirrel!
            s = animal.VTable.MakeNoise(animal); // no noise
            s = Dog.MakeNoise_(dog); // yip!
        }
    }
}