Manual Reference Counting (aka Manual Retain Release) is obsolete in the sense that there's no reason for most people to use it, but it is still completely supported, and Apple themselves still have huge MRC codebases, including AppKit itself. Automatic Reference Counting (ARC) uses the same underlying reference counting mechanism, it just inserts the retain/release calls for you at compile time. (There's slightly more to it than that, especially around ARC's ability to optimize, but it's not too far off.)
The author has already clarified that Objective-C "garbage collection" wasn't really what he meant, but the distinction between ARC and MRC only makes sense in the context of the ObjC compiler itself. From the "outside", esp. for compiled binaries (like the system frameworks), ObjC classes always just use reference counting.
The author has already clarified that Objective-C "garbage collection" wasn't really what he meant, but the distinction between ARC and MRC only makes sense in the context of the ObjC compiler itself. From the "outside", esp. for compiled binaries (like the system frameworks), ObjC classes always just use reference counting.