示例1：
class E{public IEnumerable MyGetEnumerator1(){yield return 1;}public IEnumerable<int> MyGetEnumerator2(){yield return 1;yield return 2;}public IEnumerator MyGetEnumerator3(){yield return 1;yield return 2;yield return 3;}public IEnumerator<int> MyGetEnumerator4(){yield return 1;yield return 2;yield return 3;yield return 4;} public IEnumerator GetEnumerator(){yield return 1;yield return 2;yield return 3;yield return 4;}}E e = new E(); foreach (var item in e.MyGetEnumerator1()) Console.WriteLine(item);foreach (var item in e.MyGetEnumerator2())Console.WriteLine(item);//报错：foreach statement cannot operate on variables of type 'IEnumerator' because 'IEnumerator' does not contain a public instance or extension definition for 'GetEnumerator' foreach (var item in e.MyGetEnumerator3()) Console.WriteLine(item);//报错：同上 foreach (var item in e.MyGetEnumerator4()) Console.WriteLine(item);//当GetEnumerator()的返回类型为IEnumerator或IEnumerator<int>时都能正常运行，当为IEnumerable或IEnumerable<int>时，则报错：1、'IEnumerable' does not contain a definition for 'Current'，2、foreach requires that the return type 'IEnumerable' of 'E.GetEnumerator()' must have a suitable public 'MoveNext' method and public 'Current' property foreach (var item in e) Console.WriteLine(item);
