Collections

Last Updated: 2001

Supported by the System.Collection namespace.

Note: You may write "for... each" but the compiler converts this to IEnumerator.

IEnumerable

public interface IEnumerable {
    IEnumerator GetEnumerator();
}

public interface IEnumerator {
    object current {get;}
    bool MoveNext();
    bool Reset();
}

• Forward only access
   
• When implemented, the collection can be used with "for... each".
   
• The built-in Array type supports this already:
   
      string[] myList = new string[3]  {"Hello", "Welcome", "Goodnight"};
      IEnumerator i;
      i = myList.GetEnumerator();
      while (i.MoveNext() == true) Console.WriteString(i.Current.ToString());
  
      (same as
      for each (object x in myList)
          Console.WriteString(x.ToString());
      )
   
• If its following the rules, we're enumerating a "snap shot" of the array rather than live data. In reality, each item has a version string and if it changes an InvalidOperationException gets thrown.
   
• We start "BOF", so we much MoveNext before referencing Current.
   
• Current is of type object, so be prepared to cast.