didset

When I override the function noise , the function gets replaced by the new one. But when I override a property with an observer, the old and new value gets both executed. In playground: class Vehicle { func noise(sound: String) { println("Vehicle sound sounds like \(sound)") } } class Train: Vehicle { override func noise(sound: String) { println("A train does: \(sound)") } } Output: var oldTrain = Train() bulletTrain.noise("tjoek tjoek") // Prints: "A train does: tjoek tjoek" But when I do the same with an property with an observer: In playground: class Foo { var something: Int! { didSet {

What is the difference between willSet - didSet , and get - set , when working with this inside a property? From my point of view, both of them can set a value for a property. When, and why, should I use willSet - didSet , and when get - set ? I know that for willSet and didSet , the structure looks like this: var variable1 : Int = 0 { didSet { println (variable1) } willSet(newValue) { .. } } var variable2: Int { get { return variable2 } set (newValue){ } } Maxim Shoustin When and why should I use willSet/didSet willSet is called just before the value is stored. didSet is called immediately

Question Apple's docs specify that: willSet and didSet observers are not called when a property is first initialized. They are only called when the property’s value is set outside of an initialization context. Is it possible to force these to be called during initialization? Why? Let's say I have this class class SomeClass { var someProperty: AnyObject { didSet { doStuff() } } init(someProperty: AnyObject) { self.someProperty = someProperty doStuff() } func doStuff() { // do stuff now that someProperty is set } } I created the method doStuff , to make the processing calls more concise, but I'd