/// <summary>
/// 集合的接口
/// </summary>
  public interface ICollection
  {
    int Count { get; }
    /// <summary>
    /// 获取迭代器
    /// </summary>
    /// <returns>迭代器</returns>
    Iterator GetIterator();
  }
  /// <summary>
  /// 迭代器接口
  /// </summary>
  public interface Iterator
  {
    bool MoveNext();

    object Current { get; }
  }

  public class List : ICollection
  {
    private const int MAX = 10;
    private object[] items;
    public List()
    { 
      items = new object[MAX];
    }
    public object this[int i]
    {
      get { return items[i]; }
      set { this.items[i] = value; }
    }
    #region ICollection Members

    public int Count
    {
      get { return items.Length; }
    }

    public Iterator GetIterator()
    {
      return new ListIterator(this);
    }

    #endregion
  }
  public class ListIterator : Iterator
  {
    private int index = 0;
    private ICollection list;
    public ListIterator(ICollection list)
    {
      this.list = list;
      index = 0;
    }
    #region Iterator Members

    public bool MoveNext()
    {
      if (index + 1 > list.Count)
        return false;
      else
      { 
        index++;
        return true;
      }
    }

    public object Current
    {
      get { return list[index]; }
    }

    #endregion
  }
  /// <summary>
  /// 测试
  /// </summary>
  public class Program
  {
    static void Main()
    {
      ICollection list = new List();
      Iterator iterator = list.GetIterator();
      while (iterator.MoveNext())
      {
        object current = iterator.Current;
      }
    }
}

public static void Main()
{      
      ArrayList list = new ArrayList();
      list.Add(1);
      list.Add(2);
      list.Add(3);
      foreach (object item in list)
      {
        Console.WriteLine(item.ToString());
      }
}

.method private hidebysig static void Main() cil managed
{
  .entrypoint
  .maxstack 2
  .locals init (
    [0] class [mscorlib]System.Collections.ArrayList list,
    [1] object item,
    [2] class [mscorlib]System.Collections.IEnumerator CS$5$0000,
    [3] class [mscorlib]System.IDisposable CS$0$0001)
  L_0000: newobj instance void [mscorlib]System.Collections.ArrayList::.ctor()
  L_0005: stloc.0 
  L_0006: ldloc.0 
  L_0007: ldc.i4.1 
  L_0008: box int32
  L_000d: callvirt instance int32 [mscorlib]System.Collections.ArrayList::Add(object)
  L_0012: pop 
  L_0013: ldloc.0 
  L_0014: ldc.i4.2 
  L_0015: box int32
  L_001a: callvirt instance int32 [mscorlib]System.Collections.ArrayList::Add(object)
  L_001f: pop 
  L_0020: ldloc.0 
  L_0021: ldc.i4.3 
  L_0022: box int32
  L_0027: callvirt instance int32 [mscorlib]System.Collections.ArrayList::Add(object)
  L_002c: pop 
  L_002d: ldloc.0 
  L_002e: callvirt instance class [mscorlib]System.Collections.IEnumerator [mscorlib]System.Collections.ArrayList::GetEnumerator()
  L_0033: stloc.2 
  L_0034: br.s L_0048
  L_0036: ldloc.2 
  L_0037: callvirt instance object [mscorlib]System.Collections.IEnumerator::get_Current()
  L_003c: stloc.1 
  L_003d: ldloc.1 
  L_003e: callvirt instance string [mscorlib]System.Object::ToString()
  L_0043: call void [mscorlib]System.Console::WriteLine(string)
  L_0048: ldloc.2 
  L_0049: callvirt instance bool [mscorlib]System.Collections.IEnumerator::MoveNext()
  L_004e: brtrue.s L_0036
  L_0050: leave.s L_0063
  L_0052: ldloc.2 
  L_0053: isinst [mscorlib]System.IDisposable
  L_0058: stloc.3 
  L_0059: ldloc.3 
  L_005a: brfalse.s L_0062
  L_005c: ldloc.3 
  L_005d: callvirt instance void [mscorlib]System.IDisposable::Dispose()
  L_0062: endfinally 
  L_0063: call string [mscorlib]System.Console::ReadLine()
  L_0068: pop 
  L_0069: ret 
  .try L_0034 to L_0052 finally handler L_0052 to L_0063
}