Update, 22 Oct 2015: The ReactiveCocoa core team recently decided to increment their major version alongside Swift. So while ReactiveCocoa 4 will use Swift 2, conceptually it stays very close to its Swift 1.2 counterpart, ReactiveCocoa 3. The required code changes are illustrated in my ReactiveCocoa 4 migration example. Despite its somewhat unwieldy name, the Model-View-ViewModel (MVVM) architectu