Hello!

In C# 2.0 has iterator been added and this posting is about that.

Here is a method that has implemented GetEnumerator without using iterator
IEnumerator<T> IEnumerator.GetEnumerator()
{
  return new TreeEnumerator<T>(this);
}
There is also another class called TreeEnumerator which has implemented the
IEnumerator<T> interface.
This is easy to understand.

Below I have a class called BasicCollection<T> which use iterator.

Now to my first question:  This method:
IEnumerator<T> IEnumearble<T>.GetEnumerator()
{
     for (int i = 0;  i<data.Count; i++) yield return data[i];
}
implement the IEnumarable<T> interface and it return an
IEnumerator<T> according to the return type but it doesn't look like that.
Can somebody explain that ?

I test this by writing this code and it writes them out in the same order
that I inserted them into FillList which is correct.
BasicCollection<string> bc = new BasicCollection<string>();
bc.FillList("Twas", "brillig", "and", "the", "slithy", "toves");
foreach(string word in bc);
  Console.WriteLine(word);

Assume I want to write them out in the Reverse sequence I can then write
this method which has been found in a book
public IEnumerable<T> Reverse()
{
   get
   {
      for ( int i = data.Count -1 ; i>= 0;  i--)
        yield return data[i];
   }
}

To test this I can write this test code and it do writes then in the revers
sequence which in correct.
BasicCollection<string> bc = new BasicCollection<string>();
bc.FillList("Twas", "brillig", "and", "the", "slithy", "toves");
foreach(string word in bc.Reverse);
  Console.WriteLine(word);

Now to my second question:
I can't understand this. In the first method that used iterator that was
called GetEnumerator it said yield return data[i];
and this caused a IEnumerator<T> to be returned.
In the second example that uses iterator it said yield return data[i]; and
now it return an IEnumerable<T>
So the same statement will return different interface types.

class   BasicCollection<T>  :  IEnumerable<T>
{
  private List<T> data = new List<T>();

      public void FillList(params T [] items)
     {
         for (int i = 0;  i < items.Length; i++)
            data.Add(items[i]);
     }

   IEnumerator<T> IEnumearble<T>.GetEnumerator()
  {
        for (int i = 0;  i<data.Count; i++) yield return data[i];
  }
}

//Tony