Swift Quick Syntax Reference

Chapter    35

Property Observers

You can observe the state of a property with the willSet and didSet keywords. You can use these in the property declaration to assign an action that will occur when a property is about to change and when a property value just changed. Listing 35-1 shows how you would add an action that prints a message to the console log whenever the age property value is about to change and after the age value has changed.

Listing 35-1. Property Observers

class Person {    var name: String = "Name"    var age:Int = 0{    willSet{        println("age value is about to change to \(newValue)")    }    didSet{        println("age value just changed to \(self.age)")    }    }    func profile() -> String {        return "I'm \(self.name) ...