How to do it...

Let's start by entering the following code into the playground:

class Person { 
     
    let givenName: String 
    let middleName: String 
    let familyName: String 
    var countryOfResidence: String = "UK" 
     
    init(givenName: String, middleName: String, familyName: String) { 
        self.givenName = givenName 
        self.middleName = middleName 
        self.familyName = familyName 
    } 
     
    var displayString: String { 
        return "\(fullName()) - Location: \(countryOfResidence)" 
    } 
     
    func fullName() -> String { 
        return "\(givenName) \(middleName) \(familyName)" 
    } 
} 
 
final class Friend: Person { 
    var whereWeMet: String? 
     
    override var displayString: String { 
        return "\(super.displayString) - \(whereWeMet ?? "Don't know where we met")" 
    } 
} 
 
final class Family: Person { 
    let relationship: String 
     
    init(givenName: String, middleName: String, familyName: String = "Moon", 
    relationship: String) { 
        self.relationship = relationship 
        super.init(givenName: givenName, middleName: middleName, familyName:    
        familyName) 
    } 
     
    override var displayString: String { 
        return "\(super.displayString) - \(relationship)" 
    } 
} 
 
let steve = Person(givenName: "Steven", middleName: "Paul", familyName: "Jobs") 
let dan = Friend(givenName: "Daniel", middleName: "James", familyName: "Woodel") 
dan.whereWeMet = "Worked together at BBC News" 
let finnley = Family(givenName: "Finnley", middleName: "David", relationship: "Son") 
let dave = Family(givenName: "Dave", middleName: "deRidder", familyName: "Jones", relationship: "Father-In-Law") 
dave.countryOfResidence = "US" 
 
print(steve.displayString) // Steven Paul Jobs 
print(dan.displayString) // Daniel James Woodel - Worked together at BBC News 
print(finnley.displayString) // Finnley David Moon - Son