How to do it...

Amend the currentUserName property definition to be the following:

class UserManager { 
    var currentUserName: String = "Emmanuel Goldstein" { 
        willSet (newUserName) { 
            print("Goodbye to \(currentUserName)") 
            print("I hear \(newUserName) is on their way!") 
        } 
        didSet (oldUserName) { 
            print("Welcome to \(currentUserName)") 
            print("I miss \(oldUserName) already!") 
        } 
    } 
} 

Now, we can create an instance of the UserManager and change the current username, which will generate the friendly messages:

let manager = UserManager() 
 
manager.currentUserName = "Dade Murphy" 
// Goodbye to Emmanuel Goldstein 
// I hear Dade Murphy is on their way! 
// Welcome to Dade Murphy 
// I miss Emmanuel Goldstein already! 
 
manager.currentUserName = "Kate Libby" 
// Goodbye to Dade Murphy 
// I hear Kate Libby is on their way! 
// Welcome to Kate Libby 
// I miss Dade Murphy already!