Extension Method

ExtensionMethod

using System.Linq;
using System.Text;
using System;

namespace CustomExtensions
{
    //Extension methods must be defined in a static class 
    public static class StringExtension
    {
        // This is the extension method. 
        // The first parameter takes the "this" modifier
        // and specifies the type for which the method is defined. 
        public static int WordCount(this String str)
        {
            return str.Split(new char[] {' ', '.','?'}, StringSplitOptions.RemoveEmptyEntries).Length;
        }
    }
}
namespace Extension_Methods_Simple
{
    //Import the extension method namespace. 
    using CustomExtensions;
    class Program
    {
        static void Main(string[] args)
        {
            string s = "The quick brown fox jumped over the lazy dog.";
            //  Call the method as if it were an  
            //  instance method on the type. Note that the first 
            //  parameter is not specified by the calling code. 
            int i = s.WordCount();
            System.Console.WriteLine("Word count of s is {0}", i);
        }
    }
}

/********************************* Distinct 1 **************************************/

public static IEnumerable<T> Distinct<T>(this IEnumerable<T> collection, Func<T, T, Boolean> comparer)
{
    return collection.Distinct(new LinqExtensions.Comparer<T>(comparer));
}

/********************************* Distinct 2 **************************************/

public static class EnumerableExtensions
{
    public static IEnumerable<TKey> Distinct<T, TKey>(this IEnumerable<T> source, Func<T, TKey> selector)
    {
        return source.GroupBy(selector).Select(x => x.Key);
    }
}