using System;

public class Program

{

    public static void Main()

    {

        var c = new Collection();

        foreach(var o in c)

        {

            Console.WriteLine(o);

        }

    }

    public class Collection

    {

        private int state = 0;

        public Collection GetEnumerator()

        {

            return this;

        }

        public override string ToString()

        {

            return state.ToString();

        }

        public int Current { get { return state; } }

        public bool MoveNext()

        {

            return state++ < 10;

        }

    }

}

​

​