A lot of the information here is about the (relatively stable) hooks the objc runtime gives programmers into its internals. If you’re writing ffi code to interact with the objc runtime, a lot of the functions referenced here are reasonable to call directly in the interop layer

The functions the the runtime exposes are relatively stable API. It’s the implementation details and structure layouts that are subject to change.

I see the article is from 2010. Is that before or after Objective-C 2.0?

Objective-C 2.0 came with 64-bit, IIRC, so 10.6 should be using it.

Objective-C 2.0 was part of 10.5 in 2007. It’s not directly tied to 64-bit support. You’re thinking of features that require the “modern runtime” which is only available on 64-bit Mac. Those features came after ObjC 2.0.

You're right, I mixed those two up. That's a bit too far back for me :)

"Objective-C 2.0" was a marketing term for a bunch of features added in 10.5, some big (e.g. nonfragile ivars, garbage collection) others not so big (e.g. for..in loops, synthesized ivars). The language+runtime has evolved tremendously since then without a new marketing name. Generics and ARC were added, garbage collection and vtable dispatch have been removed.