Extension methods on Interfaces

 

class Program
{
    [STAThread]
    public static void Main()
    {
        IFoo myFoo = new Foo();
        myFoo.DoFoo();  //Class Foo does DoFoo()
        myFoo.DoBar();  //Class FooExtensions does DoBar()
    }
}
internal interface IFoo
{
    void DoFoo();
}
internal class Foo : IFoo
{
    public void DoFoo()
    {
        Console.WriteLine("Class Foo does DoFoo()");
    }
}
internal static class FooExtensions
{
    public static void DoBar(this IFoo obj)
    {
        Console.WriteLine("Class FooExtensions does DoBar()");
    }
}