Why does Apple recommend to use dispatch_once for implementing the singleton pattern under ARC?What's the exact reason for using dispatch_once in the shared instance accessor of a singleton under ARC? + (MyClass *)sharedInstance { // Static local predicate must be initialized to 0 static MyClass *sharedInstance = nil; static dispatch_once_t onceToken = 0; dispatch_once(&onceToken, ^{ sharedInstance = [[MyClass alloc] init]; // Do any other initialisation stuff here }); return sharedInstance
