using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

namespace ForeachDemo

{

    class Program

    {

        static void Main()

        {

            Mylist list = new Mylist();

            MyList2 list2 = new MyList2();

            foreach (string str in list)

            {

                Console.WriteLine(str);

            }

            Console.WriteLine("==========================================");

            foreach (string str in list2)

            {

                Console.WriteLine(str);

            }

        }

    }

    class Mylist : IEnumerable                                                                  //通过yield return 来返回,实现IEnumerable接口

    {

        static string[] testString= { "", "", "", "" ,""};

        public IEnumerator GetEnumerator()

        {

            foreach (string str in testString)

            {

                yield return  str;

            }

        }

    }

    class MyList2 : IEnumerable                                                                 //实现自己的IEnumerator来实现

    {

        static string[] testString2 = { "", "", "", "", "" };

        public IEnumerator GetEnumerator()

        {

            return new MyEnumerator();

        }

        private class MyEnumerator : IEnumerator

        {

            int index = -;

            public object Current

            {

                get

                {

                    return testString2[index];

                }

            }

            public bool MoveNext()

            {

                if (++index >= testString2.Length)

                {

                    return false;

                }

                else

                {

                    return true;

                }

            }

            public void Reset()

            {

                index = -;

            }

        }

    }

}