StrongReference.swift

class Car {
    private let brand: String
    var owner: Owner?

    init(brand: String) {
        self.brand = brand
    }

    deinit { print("Car deallocated") }
}

class Owner {
    private let name: String
    var car: Car?

    init(name: String) {
        self.name = name
    }

    deinit { print("Owner deallocated") }
}

var owner: Owner? = Owner(name: "Ayush")
var car: Car? = Car(brand: "Tata")

owner?.car = car
car?.owner = owner