Hands-On Design Patterns with Swift

Unowned references

You can use unowned references when you can guarantee that the owner of another object will never exist when the reference is deallocated. Let's look at the following example:

class CreditCard {    let number: String    let expiry: String    unowned let owner: Person        init(owner: Person) {        self.owner = owner        self.number = "XXXXXXXXXXXXXXXX"        self.expiry = "XX/YY"    }}class Person {    let name: String    var cards: [CreditCard] = []    init(name: String) {        self.name = name    }}

In this example, one person can have many credit cards. Each card needs to have an owner, which is immutable.

Let's look that how to use such an API:

let me = Person(name: "John Smith")let card = CreditCard(owner: me)let otherCard = CreditCard(owner: me)me.cards = [card, ...