At MacCrazy’s blog, there is a post about the Fast Enumberation, which was introduced in the Objective-C 2.0. Han9kin mentioned that he didn’t see much performance improvement with it.
So, I asked to the Apple’s Obj-C mailing list if there was any document which showed the difference of the performance between the Fast Enumeration and general NSEnumerator. ( Also, just like C/C++, you can iterate a collection using its index.
They reply to my inquiry, and here is the link for the answer.