using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        int item = -1;

        After(ForEach(Sample(10), v => item = v), () => Console.WriteLine(item));

        Console.WriteLine(item);

        After(ForEach(Sample(10), v => item = v).ToList(), () => Console.WriteLine(item));

        Console.WriteLine(item);

    }

​

    static IEnumerable<int> Sample(int count)

    {

        Console.WriteLine("Sample Invoked");

        for (int i = 0; i < count; i++)

            yield return i;

    }

​

    static IEnumerable<int> ForEach(IEnumerable<int> items, Action<int> action)

    {

        Console.WriteLine("ForEach Invoked:");

        foreach (int item in items)

        {

            action(item);

            yield return item;

        }

    }

​

    static void After(IEnumerable<int> items, Action action)

    {

        action();

    }

}