O'Reilly's Programming iOS 5 says (maybe in a looser sense), that "an NSString is a CFString". But is it true that at least NSString * will point to some memory chunk with an isa, while CFStringRef probably does not?
Not exactly the same; they are Toll-Free Bridged. This Apple Doc should explain in more detail.
Here is even more detail from iOS 5 Programming Pushing The Limits on Google Books.
来源：https://stackoverflow.com/questions/12641189/nsstring-is-exactly-the-same-as-cfstring