一个迭代器的示例

    public class Weeks : System.Collections.IEnumerable
    {

        private string[] _weeks = new string[] { "", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday" };


        #region IEnumerable 成员

        System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
        {
            foreach (string str in _weeks)
            {
                yield return str;                 //yield  关键字用于指定返回的一个或多个值。到达 yield return 语句时，会保存当前位置。下次调用迭代器时将从此位置重新开始执行。
            }
        }

        #endregion
    }