Extension Methods: Calling on an object instance

In C#, static methods could only be called through their respective type references.  The power of Extensions Methods lies in the fact they could be called on an object instance.  In fact, they could ONLY be called on an object instance.  This ability is vital for implementing Linq in C# 3.0.

    1 using System;

    2 using System.Collections.Generic;

    3 using System.Linq;

    4 using System.Text;

    5 

    6 namespace TestBed

    7 {

    8 

    9     public class TestExtensionMethods

   10     {

   11         public static void Main()

   12         {

   13 

   14             string val = "Vyas";

   15 

   16             //Static method of string class called through the class

   17             Console.WriteLine("Is Internered: {0}", string.IsInterned(val));

   18 

   19             //Static method called through an instance

   20             //Intellisense does not display it

   21             //Error: Member 'string.IsInterned(string)' cannot be 

   22             //accessed with an instance reference; 

   23             //qualify it with a type name instead

   24             //Console.WriteLine(val.IsInterned(val));

   25 

   26 

   27             //The ability for a static method to be called through an instance

   28             Console.WriteLine(val.Reverse());

   29 

   30             //Does not compile

   31             //Error: 'string' does not contain a definition for 'Reverse'

   32             //Console.WriteLine(string.Reverse(val));

   33             Console.Read();

   34         }

   35 

   36     }

   37 

   38     public static class StringUtils

   39     {

   40         public static string Reverse(this string arg)

   41         {

   42             char [] reversed;

   43             Array.Reverse(reversed = arg.ToCharArray());

   44             return new string(reversed);

   45 

   46         }

   47     }

   48 

   49 

   50 }