class Person { let name: String var apartment: Apartment? init(name: String) { self.name = name } deinit { print("Person deinit") } } class Apartment { let unit: String weak var tenant: Person? // weak breaks the cycle init(unit: String) { self.unit = unit } deinit { print("Apartment deinit") } } do { var john: Person? = Person(name: "John") var unit: Apartment? = Apartment(unit: "4A") john!.apartment = unit unit!.tenant = john john = nil // Person deinit unit = nil // Apartment deinit }