Property Observers

Property observers respond to changes to a property’s value.

var myProperty = 5 {
    willSet {
        print("Will set to \(newValue). It was previously \(myProperty)")
}
    didSet {
        print("Did set to \(myProperty). It was previously \(oldValue)")
    }
}
myProperty = 6
// prints: Will set to 6, It was previously 5
// prints: Did set to 6. It was previously 5