Question

As a beginning iPhone programmer, what is the best practice for writing apps to be used either with iOS 5 or older versions? Specifically, should I continue using the release/retain of data, or should I ignore that? Does it matter?

Answer 1

It’s up to you. You can write apps using ARC (Automatic Reference Counting), and Xcode will write “glue code” to allow your ARC enabled apps to run on iOS 4, no modifications required. However, certain things wont work, and most noticeably many libraries you might wish to use will (sometimes) throw up innumerable errors and you will be unable to use them until the developers release an update which is compatible with ARC.

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Edit: I recently discovered that you can turn off ARC on a per-file basis. See pixelfreak‘s answer. So, my advice still stands, but now the 3rd-party libraries shouldn’t need to be updated to work with ARC.

Here’s what Apple says about opting out of ARC for specific files:

When you migrate a project to use ARC, the -fobjc-arc compiler flag is
set as the default for all Objective-C source files. You can disable
ARC for a specific class using the -fno-objc-arc compiler flag for
that class. In Xcode, in the target Build Phases tab, open the Compile
Sources group to reveal the source file list. Double-click the file
for which you want to set the flag, enter -fno-objc-arc in the pop-up
panel, then click Done.

See the full transition guide here.