As we move away from the traditional paradigm of typing or touching one step at a time to interact with programs, users expect apps to adapt and not need constant hand-holding. People today expect their devices to do much more than just follow commands. They expect devices to react and adapt. Reactive programming, a new term for asynchronous processing, requires new app architectures, and you'll learn how these are already built into iOS and macOS in many places.   

As part of this more complex environment, you'll move beyond Cocoa and Cocoa Touch to incorporate data from Amazon Web Services (AWS), JavaScript Object Notation (JSON), and other formats, and standards. Together with the concepts of reactive programming and RxSwift,these tools help you build more powerful and useful apps that have wide appeal and use.