using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Threading;

using System.Diagnostics;

public class Program

{

    public static void Main()

    {

        Stopwatch watch = Stopwatch.StartNew();

        Console.WriteLine("Main begin");

        Console.WriteLine("In Main - Before calling GetStrs");

        IEnumerable<string> strs;

        strs = GetStrs();

        // strs = GetStrs().ToList();

        Console.WriteLine("In Main - After calling GetStrs");

        Console.WriteLine("In Main - Determining strs count");

        int strCount = strs.Count();

        Console.WriteLine("In Main - strCount: " + strCount);

        Console.WriteLine("In Main - Iterating strs");

        foreach(string s in strs)

        {

            Console.WriteLine("In Main - Iterating strs - " + s);

        }

        Console.WriteLine("In Main - strs iteration complete"); 

        watch.Stop();

        Console.WriteLine("Main took: " + watch.Elapsed.TotalSeconds + " seconds");

    }

    private static IEnumerable<string> GetStrs()

    {

        Console.WriteLine("GetStrs begin");

        Thread.Sleep(1000);

        yield return "line1";

        Thread.Sleep(1000);

        yield return "line2";

        Thread.Sleep(1000);     

        Console.WriteLine("GetStrs end");

    }

​

}

​

​