https://www.youtube.com/watch?v=lCVtRZTM9pI

RetainCycle.swift

import UIKit

/*

 class Person {
 let name: String
 init(name: String) {
 self.name = name
 }
 
 deinit {
 print("\(name) is be deinit ")
 }
 }
 
 class Apertment {
 let number: Int
 // weak wont increase reference count
 weak var tenant: Person?
 
 init(number: Int) {
 self.number = number
 }
 }
 
 var bob :Person? = Person(name: "Bob")
 
 // constant
 let apt: Apertment? = Apertment(number: 123)
 apt?.tenant = bob
 bob = nil
 if(apt?.tenant == nil) {
 print("Oops bob is left")
 }
 print("end")
 

 */


class Person {
    let name: String
    weak var apartment: Apertment?
//    var apartment: Apertment?
    init(name: String) {
        self.name = name
    }
    
    deinit {
        print("\(name) is be deinit ")
    }
}

class Apertment {
    let number: Int
    // if weak wont increase reference count
    weak var tenant: Person?
//    var tenant: Person?
    
    init(number: Int) {
        self.number = number
    }
    
    deinit {
        print("Apertment \(number) is be deinit ")
    }
}

var bob :Person? = Person(name: "Bob")

var apt: Apertment? = Apertment(number: 123)
apt?.tenant = bob
bob?.apartment = apt
bob = nil
apt = nil