strong_reference_cycle.swift

// MARK: - Strong reference cycle
class Owner {
    
    let udid: String
    let iin: String
    let name: String
    var business: Business!
    
    init(udid: String, iin: String, name: String) {
        self.udid = udid
        self.iin = iin
        self.name = name
    }
    
    deinit {
        print("owner was deitialized")
    }
    
}

class Business {
    
    let title: String
    var owner: Owner // <- place where we has been mistaken. It must be resoled using 'unowned' reference
    
    init(title: String, owner: Owner) {
        self.title = title
        self.owner = owner
    }
    
    deinit {
        print("business was deitialized")
    }
    
}

var owner: Owner? = Owner(udid: "1st owner", iin: "1", name: "Mike")
owner!.business = Business(title: "1st Corp", owner: owner!)
/*
 Do some work with owner
 */
owner = nil
/*
 No outputs about deinitialization.
 What happend?
 Owner has strong reference to Business.
 Business has strong reference to Owner.
 
 !!! This is strong reference cycle. !!!
 
 We have memory leak now!
 */