Swift Functional Programming - Second Edition

An example

Let's suppose that we have an outlet and we want to observe its changes:

@IBOutlet weak var textFieldUserName: UITextField! 

We can create a SignalProducer as follows:

let userNameSignalProducer = textFieldUserName.rac_textSignal().toSignalProducer.map {     text in     text as! String } 

The rac_textSignal method is a ReactiveCocoa extension for UITextField that can be used to create the signal producer.

Then, we can start our SignalProducer as follows:

userNameSignalProducer.startWithNext {      results in     print("User name:\(results)") } 

This will print any changes in our textField to the console.

Also, we can execute operations such as map, flatMap, filter, and reduce on this signal producer, which we covered in Chapter 6, Map, Filter, ...