strong.swift

// MARK: - strong reference counting
var customer1stRef: Customer? = nil
var customer2ndRef: Customer? = nil

customer1stRef = Customer(udid: "1st", name: "Maxim")
/*
 print: 1st initialized
 */
customer2ndRef = customer1stRef
customer1stRef = nil

/*
 Customer class instance don't deallocated after nil set to customer1stRef.
 That happened because it has a strong reference in customer2ndRef
 */

customer2ndRef = nil
/*
 print: 1st deinitialized
 */