Question

I have to make apps for that work on both iOS 4 and iOS 5. The iOS 5.0 SDK has nice features like ARC, storyboard etc, which are not available in iOS 4.

My question is: In order to make an app optimized for iOS 4 and 5 what should do? Should I develop an app in a classic way without ARC, storyboard etc?

For instance, how can I switch off automatic garbage collection for iOS 4? If I do, of course iOS 5 will not benefit from having ARC. Also, if you mark reference as weak/string – that will not compile for iOS4, won’t it?

Answer 1

As Andrey indicates in his comments, while automatic reference counting was introduced with the LLVM Compiler 3.0 that came with Xcode 4.2 and the iOS 5.0 SDK, you can use it in applications that target back to iOS 4.0. There’s no good reason not to use it for applications that will run on iOS 4.0+. Also, it’s different from garbage collection, as I explain in this answer.

__weak pointers are only available for applications that use ARC and target iOS 5.0 and greater. For iOS 4.0, you’ll need to fall back to using __unsafe_unretained as a pointer type when you want to avoid retain cycles.

However, storyboarding is not available for applications targeting anything earlier than iOS 5.0. It’s a nice convenience, but I don’t personally use it for anything. Jonathan Wight has, and he has some complaints about its current implementation, so you might not be missing much if you gave that feature a pass.