FAQ по ARC

How do blocks work in ARC?

Blocks “just work” when you pass blocks up the stack in ARC mode, such as in a return. You don’t have to call Block Copy any more.

The one thing to be aware of is that NSString * __block myString is retained in ARC mode, not a possibly dangling pointer. To get the previous behavior, use __block NSString * __unsafe_unretained myString or (better still) use __block NSString * __weak myString.

Is ARC slow?

It depends on what you’re measuring, but generally “no.” The compiler efficiently eliminates many extraneous retain/release calls and much effort has been invested in speeding up the Objective-C runtime in general. In particular, the common “return a retain/autoreleased object” pattern is much faster and does not actually put the object into the autorelease pool, when the caller of the method is ARC code.

One issue to be aware of is that the optimizer is not run in common debug configurations, so expect to see a lot more retain/release traffic at -O0 than at -Os.

Can I opt out of ARC for specific files?

-fobjc-arc

-fno-objc-arc 

Is GC (Garbage Collection) deprecated on the Mac?

Garbage collection is deprecated in OS X Mountain Lion v10.8, and will be removed in a future version of OS X.