There's more...

Now that we have a PersonName struct, let's amend our Person class so that it can use it:

class Person { 
     
    let birthName: PersonName 
    var currentName: PersonName 
    var countryOfResidence: String 
     
    init(name: PersonName, countryOfResidence: String = "UK") { 
        birthName = name 
        currentName = name 
        self.countryOfResidence = countryOfResidence 
    } 
     
    var displayString: String { 
        return "\(currentName.fullName()) - Location: \(countryOfResidence)" 
    } 
} 

We've added the birthName and currentName properties of our new PersonName struct type, and we initiate them with the same value when the Person object is initiated. Since a person's birth name won't change, we define it as a constant, but their current name can change, so it's defined as a variable.

Now, let's create a new Person object:

var name = PersonName(givenName: "Alissa", middleName: "May", familyName: "Jones") 
let alissa = Person(name: name) 
print(alissa.currentName.fullName()) // Alissa May Jones 

Since our PersonName struct has value semantics, we can use this to enforce the behavior that we expect our model to have. We would expect to not be able to change a person's birth name, and if you try, you will find that the compiler won't let you.

As we discussed earlier, changing the family name mutates the struct, and so a new copy is made. However, we defined birthName as a constant, which can't be changed, so the only way we would be able to change the family name would be to change our definition of birthName from let to var:

alissa.birthName.change(familyName: "Moon") // Does not compile. Compiler tells you to change let to var 

When we change the currentName to have a new family name, which we can do, since we defined it as a var, it changes the currentName property, but not the birthName property, even though these were assigned from the same source:

print(alissa.birthName.fullName()) // Alissa May Jones 
print(alissa.currentName.fullName()) // Alissa May Jones 
alissa.currentName.change(familyName: "Moon") 
print(alissa.birthName.fullName()) // Alissa May Jones 
print(alissa.currentName.fullName()) // Alissa May Moon 

We have used a combination of objects and structs to create a model that enforces our expected behavior.