dispatch.cs

using System;

class Base
{
	public virtual string Method()
	{
		return "base method";
	}
}

class Derived : Base
{
	public override string Method()
	{
		return "derived method";
	}
}

static class Extensions
{
	public static string Extension(this Base x)
	{
		return "base extension";
	}
	
	public static string Extension(this Derived x)
	{
		return "derived extension";
	}
}

public class Program
{
	public static void Main()
	{
		Base a = new Base();
		Base b = new Derived();
		Console.WriteLine(a.Method());      // prints "base method"
		Console.WriteLine(b.Method());      // prints "derived method"
		Console.WriteLine(a.Extension());   // prints "base extension"
		Console.WriteLine(b.Extension());   // prints "base extension" (not "derived extension!!")
	}
}