Some questions about Automatic Reference Counting in iOS5 SDK

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

Yes, but XCode 4.2 includes a new “Migrate to Objective-C ARC” tool (in the Edit->Refactor menu), which does that for you. Calling dealloc is a different story. As mentioned in the comments the clang reference states that you should keep your the dealloc method:

Rationale: even though ARC destroys instance variables automatically, there are still legitimate reasons to write a dealloc method, such as freeing non-retainable resources. Failing to call [super dealloc] in such a method is nearly always a bug.

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.

–

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 its 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

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