在Swift的某些情况下，弱引用有什么区别？

Question

例如，有：

class Person {
   let name: String
   init(name: String) {
     self.name = name
     print("\(name) is being initialized")
   }
   deinit {
     print("\(name) is being deinitialized")
  }
}

//案例1：

var reference1: Person? = Person(name: "John Appleseed")
weak var reference2: Person?
weak var reference3: Person?
reference2 = reference1
reference3 = reference1
reference1 = nil
print(reference1 ?? "nil") // nil
print(reference2 ?? "nil") // Person
print(reference3 ?? "nil") // Person

//Case 2:
var reference1: Person? = Person(name: "John Appleseed")
weak var reference2: Person? = reference1
weak var reference3: Person? = reference1
reference1 = nil
print(reference1 ?? "nil") // nil
print(reference2 ?? "nil") // nil
print(reference3 ?? "nil") // nil

我想问一下，为什么弱参考在案件中有所不同？感谢帮助。