ARC 强属性枚举错误

ARC 强属性枚举错误是 iOS 开发中常见的问题之一。在使用 ARC（Automatic Reference Counting）自动引用计数机制时，如果在强属性的枚举中使用了相互引用，就会导致循环引用的问题。这会导致内存泄漏，最终导致应用程序的性能下降和内存消耗增加。

swift
class Person {
    var name: String
    var car: Car?
    
    init(name: String) {
        self.name = name
        print("\(name) is being initialized")
    }
    
    deinit {
        print("\(name) is being deinitialized")
    }
}
class Car {
    var model: String
    var owner: Person?
    
    init(model: String) {
        self.model = model
        print("\(model) is being initialized")
    }
    
    deinit {
        print("\(model) is being deinitialized")
    }
}
var john: Person?
var mercedes: Car?
john = Person(name: "John")
mercedes = Car(model: "Mercedes")
john?.car = mercedes
mercedes?.owner = john
john = nil
mercedes = nil

swift
class Person {
    var name: String
    weak var car: Car?
    
    // ...
}

swift
class Car {
    var model: String
    unowned var owner: Person?
    
    // ...
}