Jimmy questions

• Can cocoa framework hide an ivar declaration in their public header file?
• What's the harm of retain self in block?(Objective-C, GCD)
• Why does google suggest to use trailing underscores when naming iVars in Objective-C?
• Is there any problem using self.property = nil in dealloc?
• Why would ABAddressbookRef need to be created for each thread?
• How to identify a NSData's image format?
• What's the harm of property override in Objective-C?

Jimmy answers