When and why should I use willSet/didSet willSet is called just before the value is stored. didSet is called immediately after the new value is stored. Consider your example with outputs: var variable1 : Int = 0 { didSet{ print(“didSet called”) } willSet(newValue){ print(“willSet called”) } } print(“we are going to add 3”) variable1 = … Read more
Although Kotlin doesn’t provide a built-in Swift-style solution for property changes observation, you can still do it in several ways depending on what your goal is. There is observable(…) delegate (in stdlib) that allows you to handle the property changes. Usage example: var foo: String by Delegates.observable(“bar”) { property, old, new -> println(“$property has changed … Read more
If you use defer inside of an initializer, for updating any optional properties or further updating non-optional properties that you’ve already initialized and after you’ve called any super.init() methods, then your willSet, didSet, etc. will be called. I find this to be more convenient than implementing separate methods that you have to keep track of … Read more
The point seems to be that sometimes, you need a property that has automatic storage and some behavior, for instance to notify other objects that the property just changed. When all you have is get/set, you need another field to hold the value. With willSet and didSet, you can take action when the value is … Read more