C# IEnumerable和IEnumerator的區別，如何?

IEnumerable介面和IEnumerator介面是.NET中非常重要的介面，二者有何區別？

    1. 簡單來說IEnumerable是一個聲明式的介面，聲明實現該介面的類就是“可迭代的enumerable”,但並沒用說明如何?迭代器(iterator).其代碼實現為：

         public interface IEnumerable
         {
                IEnumerator GetEnumerator();
          }
    2. 而IEnumerator介面是實現式介面，它聲明實現該介面的類就可以作為一個迭代器iterator.其代碼實現為：

        public interface IEnumerator
       {
                object Current { get; }

                bool MoveNext();
                void Reset();
        }

   3.一個collection要支援Foreach進行遍曆，就必須實現IEnumerable,並一某種方式返回迭代器對象:IEnumerator.

   那麼又如何?這兩個介面呢？ 其代碼如下：

  假設有一個Person類，其有兩個屬性FirstName和LastName

  public class Person
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public Person(string firstName, string lastName)
        {
            this.FirstName = firstName;
            this.LastName = lastName;
        }
    }

另外通過People類來實現IEnumerable和IEnumerator介面.

//實現IEnumerable介面

public class People :IEnumerable

{

   public Person [] pers;

   public People(Person [] ps)

    {

      this.pers = ps;

    }

    public IEnumerator GetEnumerator()

    {

         //foreach(Person p in pers)

         // {

             //  yield return p;

          // }

      return new People1(pers);

      }

}

  //實現IEnumerator介面

   public class People1 : IEnumerator
    {
        public Person[] pers;
        public People1(Person[] per)
        {
            this.pers = per;
        }
        int position = -1;

        public bool MoveNext()
        {
            position++;
            return position < pers.Length;
        }
        public void Reset()
        {
            position=-1;
        }
        public object Current
        {
            get
            {
               try
               {
                   return pers[position];
               }
                catch(IndexOutOfRangeException ex)
                {
                    throw new InvalidOperationException();
                }
            }
        }
    }