//yield return用于无缝实现迭代模式。

 public class YieldReturn
    {
        //yield return用于无缝实现迭代模式。
   
        string[] strArr;
        public YieldReturn(params string[] arr)
        {
            strArr = new string[arr.Length];
            arr.CopyTo(strArr, 0);
            
        }
        
       
        //-------一个枚举对象可以对应多个枚举
        /// <summary>
        /// 反序输出
        /// </summary>
        public IEnumerable<string> Reverse
        {
            get
            {
                for (int i = strArr.Length - 1; i >= 0; i--)
                    yield return strArr[i];
            }
        }
        /// <summary>
        /// 顺序输出
        /// </summary>
        public IEnumerable<string> PosEven
        {
            get
            {
                for (int i=0;i<strArr.Length; i++)
                    yield return strArr[i];
            }
        }
        public IEnumerable<string> Concat
        {
            get
            {
                foreach (string s in Reverse)
                    yield return s;
                foreach (string s in PosEven)
                    yield return s;
            }
        }
        
    }
 实现：
      public static void yieldreturn()
        {
            YieldReturn yr = new YieldReturn("aaa", "bbb", "ccc");
            Console.WriteLine("-----Reverse:");
            foreach (string s in yr.Reverse)
                Console .WriteLine (s);
            Console.WriteLine("-----PosEven:");
            foreach (string s in yr.PosEven)
                Console.WriteLine(s);
            Console.WriteLine("-----Concat:");
            foreach (string s in yr.Concat)
                Console.WriteLine(s);
        }