-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.https://developer.apple.com/library/ios/#releasenotes/ObjectiveC/RN-TransitioningToARC/Introduction/Introduction.html