Best xcode4.2 questions in June 2011

Some questions about Automatic Reference Counting in iOS5 SDK

Asked on Thu, 16 Jun 2011 by Luke47 objective-c ios5 automatic-ref-counting xcode4.2
6 votes


I'm currently developing an app for iPad. The development started for iOS 4.2 and is now continuing (and I think will be completed) for iOS 4.3. I just read about ARC in iOS 5, and basically I understood that we will never need to release and retain objects anymore. My questions are:

  • If I decide to upgrade to iOS 5, do I need to remove all [myObject retain] and [myObject release] statements from my code?

  • If I develop a new app for iOS 5 using ARC, will I need to implement some sort of "retro-compatibility" checks? I.e.: will I need to check the version of iOS and call retain and release accordingly? So, basically, is ARC available for all iOS versions or just for iOS 5?

Thank you

Answered by Henrik P.

If I decide to upgrade to iOS 5, do I need to remove all [myObject retain] and [myObject release] statements from my code?

Yes (including dealloc), but XCode 4.2 includes a new "Migrate to Objective-C ARC" tool (in the Edit->Refactor menu), which does that for you.

You enable ARC using a new -fobjc-arc compiler flag. ARC is supported in Xcode 4.2 for Mac OS X v10.6 and v10.7 (64-bit applications) and for iOS 4 and iOS 5. (Weak references are not supported in Mac OS X v10.6 and iOS 4). There is no ARC support in Xcode 4.1. 

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If I develop a new app for iOS 5 using ARC, will I need to implement some sort of "retro-compatibility" checks? I.e.: will I need to check the version of iOS and call retain and release accordingly? So, basically, is ARC available for all iOS versions or just for iOS 5?

No, because ARC does it's magic on compile time and not on run time.

Instead of you having to remember when to use retain, release, and autorelease, ARC evaluates the lifetime requirements of your objects and automatically inserts the appropriate method calls for you at compile time. The compiler also generates appropriate dealloc methods for you.

Further Information on ARC: http://clang.llvm.org/docs/AutomaticReferenceCounting.html