C# in Depth

Advanced generics91}{}return new CountingEnumerator();IEnumerator IEnumerable.GetEnumerator(){return GetEnumerator();}CImplementsIEnumerableexplicitlyclass CountingEnumerator : IEnumerator{int current = -1;public bool MoveNext(){current++;return current < 10;}public int Current{get { return current; }}object IEnumerator.Current{get { return Current; }}public void Reset(){current = -1;}public void Dispose(){}}...CountingEnumerable counter = new CountingEnumerable();foreach (int x in counter){Console.WriteLine(x);}DImplementsIEnumerator.CurrentimplicitlyEImplementsIEnumerator.CurrentexplicitlyProves thatenumerabletype worksClearly this isn’t useful in terms of the result, but it shows the little hoops you haveto go through in order to implement generic enumeration appropriately—at least ifyou’re doing it all longhand. (And that’s without making an effort to throw exceptionsif Current is accessed at an inappropriate time.) If you think that listing 3.9looks like a lot of work just to print out the numbers 0 to 9, I can’t help but agreewith you—and there’d be even more code if we wanted to iterate through anythinguseful. Fortunately we’ll see in chapter 6 that C# 2 takes a large amount of the workaway from enumerators in many cases. I’ve shown the “full” version so you canappreciate the slight wrinkles that have been introduced by the design decision forIEnumerable to extend IEnumerable.FLicensed to Rhona Hadida