[koito17]

What Apple calls "ARC", the rest of the word simply calls "RC". Unlike in Objective-C, the vast majority of RC implementations do not need the developer to modify refcounts by hand. It was already "automatic", so to speak.

Moreover, ARC itself indeed modifies refcounts atomically. If it didn't, you would not be able to reliably determine the liveness of an object shared between threads. Now ask yourself whether atomically updating dozens of integers is faster than flipping a bit across a table of pointers.

[pjmlp]

Basically Apple turned Objective-C's GC failure to deal with C semantics, picked COM's approach to smart pointers, and made a market message out of it into ARC, for people that never dealt with this kind of stuff before.

Like in many things where "Apple did it first".