using System;

using System.Linq;

using System.Collections.Generic;

​

public static class ExtensionMethods

{

    //public static IEnumerable<T> Filter<T>(this IEnumerable<string> myArray)

    //public static int[] Filter(this IEnumerable<string> someArray)

    public static IEnumerable<int> Filter(this IEnumerable<string> someArray, Func<int,bool> func)

    {

        someArray.Select(i => Convert.ToInt32(i)).Where(i => func(i));

        return null;

    }

​

}

​

public class Program

{

​

    public static void Main()

    {

        // https://www.youtube.com/watch?v=v_cgQzp8YHQ

        Console.WriteLine("Hello World");

        /*

        Extension methods let us to add methods to existing types without creating a new  derivated type

        */

        var myArray = new int[] {1,2,3,4,5,6,7,8,9};

        // Where is a extension method 

        //var evenNumbers = myArray.Where(x => x % 2 == 0);

        //var evenNumbers = myArray.Select(x => $"Item number : {x}");

        // use an class extension method 

        var myArrayString = new string[] {"1","2","3"};

        var evenNumbers = myArrayString.Filter().Select(x => $"Item number: {x}");

        Console.WriteLine($"Even numbers are : {string.Join(',' , evenNumbers)}");

    }

}