Past (… – 4.3)
Previously in Objective-C, we were often writing both an @property keyword in our interface (.h file), as well as a @synthesize keyword in our implementation (.m file). New in Xcode 4.4 (and the new LLVM clang compiler), we no longer need to synthesize our properties. They are done for us when we compile our code!
Present ( 4.4 – [4.6.2])
Instance variables are now prefixed with the “_” character, which you can still access within the class itself.
Full article: http://brianflove.com/2012/10/08/synthesize-by-default-with-xcode-4-4/