Extension methods example C#

Using this technique you can add methods to existing types. Say you want a method in the type string which returns the characters in the string in the reverse order
 You could probably
1>Inherit from the class System.String, (suppose you called this inherited class as MyStringExtension )add the new method called Reverse() to the inherited class. Then declare a variable of the type MyStringExtension instead of declaring it a string. Then call the method Reverse() on it.
OR
2>Take the faster route and declare an extension method on the type string.

In the code below I have declared an extension method on the type string, that just returns the string  "Dilbert" when called.

Adding an extension method to the type string

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

namespace ExtensionMethodExample

{

    class Program

    {

        static void Main(string[] args)

        {

            string s="";
            //Here ReplaceDilbert() is an extension method on the type string

            Console.WriteLine(s.ReplaceDilbert());

            //Displays Dilbert

        }       

    }

    static class StringExtension

    {

        //This method must be static

        public static string ReplaceDilbert(this string s)//notice there is a this keyword

        {

            return "Dilbert";

        }

    }

}

Adding an extension method to the type float

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

namespace ExtensionMethodExample

{

    class Program

    {

        static void Main(string[] args)

        {

            float f= 10;

            Console.WriteLine(f.GetInverse());

            //Displays 0.1

        }       

    }

    //This class must be static

    static class StringExtension

    {

        //This method must be static

        public static float GetInverse(this float f)//notice there is a this keyword

        {

            return 1 / f;

        }

    }

}

You can define your extension method in a different class or namespace, just make sure that it (the class and namespace containing the extension method) is accessible to the calling code.