using System;

using System.Collections;

public class Program

{

    public static void Main()

    {

        IEnumerable items = new []{ 1, 2, 3 };

        var c = items.Count();

        Console.WriteLine("counted " + c);

    }

}

​

public static class MyExtensions

{

    public static int Count(this IEnumerable items)

    {

        int c = 0;

        foreach(var i in items) c++;

        return c;

    }

}