using System;

using System.Collections.Generic;

using System.Diagnostics;

using System.Linq;

​

namespace ConsoleApp

{

    public static class IEnumerableExtensions

    {

        public static IEnumerable<T> Do<T>(this IEnumerable<T> data, Action<T> predicate)

        {

            foreach (T value in data)

            {

                predicate(value);

                yield return value;

            }

        }

    }

​

    public class Program

    {

        public static void Main(string[] args)

        {

            var sw = new Stopwatch();

            sw.Start();

            var query = Enumerable.Range(1, 10)

                .Where(num => num % 2 == 0)

                .Do(num => Console.WriteLine("Processing {0} : {0} * 2 = {1}", num, num * 2));

                //.ToList();

            foreach (var num in query)

            {

                Console.WriteLine(num);

            }

​

            Console.WriteLine("Elasped Time: " + sw.ElapsedTicks);

            Console.WriteLine("Done. You can continue working.");

        }

    }

}