NEW: Master Swift design patterns with my latest book! >>

How to use local variable observers

Written by Paul Hudson    @twostraws

You should already be familiar with the concept of property observers in Swift – those willSet and didSet blocks you can attach to property on classes and structs. Well, those same blocks can be attached to local and global variables as well, allowing you to respond to changes easily.

The syntax is identical: create your variable, give it an initial value, then provide willSet and/or didSet closures inside braces, like this:

var name = "Taylor Swift" {
    didSet {
        print("Name changed to \(name)!")
    }
}

name = "Justin Bieber"

That will print “Name changed to Justin Bieber!” when run.

Available from iOS 8.0

Did this solution work for you? Please pass it on!

Other people are reading…

About the Swift Knowledge Base

This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.

Hacking with watchOS

Transfer your Swift skills to watchOS the easy way, and learn to build real-world apps in the process!

Click here to visit the Hacking with Swift store >>