ARC (Automatic Reference Counting)

https://docs.swift.org/swift-book/LanguageGuide/AutomaticReferenceCounting.html

1. class Person {
2. let name: String
3. init(name: String) { self.name = name }
4. var apartment: Apartment?
5. deinit { print("\(name) is being deinitialized") }
6. }
8. class Apartment {
9. let unit: String
10. init(unit: String) { self.unit = unit }
11. var tenant: Person?
12. deinit { print("Apartment \(unit) is being deinitialized") }
13. }

Weak References

    Property observers aren’t called when ARC sets a weak reference to. nil.

1. class Person {
2. let name: String
3. init(name: String) { self.name = name }
4. var apartment: Apartment?
5. deinit { print("\(name) is being deinitialized") }
6. }
8. class Apartment {
9. let unit: String
10. init(unit: String) { self.unit = unit }
11. weak var tenant: Person?
12. deinit { print("Apartment \(unit) is being deinitialized") }
13. }
14. 
    

Unowned References

Use an unowned reference only when you are sure that the reference always refers to an instance that has not been deallocated.

If you try to access the value of an unowned reference after that instance has been deallocated, you’ll get a runtime error.

https://www.raywenderlich.com/959-arc-and-memory-management-in-swift