Extension Methods in C#

Extension Methods in C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ExtensionMethodsSample
{
    using MyExtensionMethod;
    class Program
    {
         static void Main(string[] args)
        {
            string firstName = "Anish";
            var res = firstName.MySampleExtensionMethod();
            Console.ReadLine();
        }
    }
}

namespace MyExtensionMethod
{
    public static class MyExtensionMethod {

         public static string MySampleExtensionMethod(this string inputString)
        {
            return inputString.ToUpperInvariant();
        }
    }

}

The method and class should be static.

Practical Use

using System;
using System.Collections.Generic;
using System.Text;
using System.Linq;

namespace EnumExtension
{
    // Define an extension method in a non-nested static class.
    public static class Extensions
    {        
        public static Grades minPassing = Grades.D;
        public static bool Passing(this Grades grade)
        {
            return grade >= minPassing;
        }
    }

    public enum Grades { F = 0, D=1, C=2, B=3, A=4 };
    class Program
    {       
        static void Main(string[] args)
        {
            Grades g1 = Grades.D;
            Grades g2 = Grades.F;
            Console.WriteLine("First {0} a passing grade.", g1.Passing() ? "is" : "is not");
            Console.WriteLine("Second {0} a passing grade.", g2.Passing() ? "is" : "is not");

            Extensions.minPassing = Grades.C;
            Console.WriteLine("\r\nRaising the bar!\r\n");
            Console.WriteLine("First {0} a passing grade.", g1.Passing() ? "is" : "is not");
            Console.WriteLine("Second {0} a passing grade.", g2.Passing() ? "is" : "is not");
        }
    }
  }
/* Output:
    First is a passing grade.
    Second is not a passing grade.

    Raising the bar!

    First is not a passing grade.
    Second is not a passing grade.
 */