ARC之解决对象之间的循环强引用（Swift）

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直接上代码，具体看代码中的注释
////  ViewController.swift//  Refrence////  Created by Mac on 8/24/15.//  Copyright © 2015 fevershen. All rights reserved.//import UIKitclass ViewController: UIViewController {        // 解决对象之间的循环强引用造成的内存泄漏        // 1.弱引用， 2.无主引用， 3.无主引用以及显示展开(隐式解析)的可选属性    override func viewDidLoad() {        super.viewDidLoad()        //        var john: Person//        var number73: Apartment//        john = Person(name: "John Appleseed")//        number73 = Apartment(number: 73)//        john.apartment = number73//        number73.tenant = john//                //        var lina: Customer?//        lina = Customer(name: "Lina Appleseed")//        lina!.card = CreditCard(number: 1234_5678_9012_3456, customer: lina!)                let country = Country(name: "Canada", captialName: "Ottawa")        print("\(country.name)'s capital city is called \(country.capitalCity.name)")                // 可选类型并不会自动初始化为 nil， 因此，使用前必须赋值        let str: String? = nil        if (str != nil) {            print("===" + str!)        } else {            print("---")        }            }        // 1.    // 人和公寓的关系都是可选的， 这里用 weak 就可以了    class Person {        var name: String        init (name: String) {            self.name = name            print("\(name) init")        }        var apartment: Apartment?        deinit {            print("\(name) deinit")        }    }        class Apartment {        let number: Int        init (number: Int) {            self.number = number            print("Apartment \(number) init")        }                // 都不加 weak 将形成循环强引用，两个都不能被析构        weak var tenant: Person?        deinit {            print("Apartment \(number) deinit")        }    }    // 2.    // 客户的信用卡是可选的，但是信用卡必须要有客户（非可选），因此这里要用到 unowner    class Customer {        let name: String        var card: CreditCard?        init(name: String) {            self.name = name            print("Customer \(name) init")        }        deinit {            print("Customer \(name) deinit")        }    }        class CreditCard {        let number: Int                // 卡必须有主人， 无主引用是永远有值的        unowned let customer: Customer        init(number: Int, customer: Customer) {            self.number = number            self.customer = customer            print("CreditCard #\(number) init")        }        deinit {            print("CreditCard #\(number) deinit")        }    }        // 3.    class Country {        let name: String                // 可选类型并不会自动初始化为 nil， 因此，使用前必须赋值        // 这里的意义在于通过一条语句同时创建两个实例        var capitalCity: City! = nil        init(name: String, captialName: String) {            print("Country is initing")            self.name = name                        // 下面这条语句是将 Country 的实例做为参数传递给 City 来创建 City 的实例，表面上看 Country 本身还没有实例完成，实际上由于该类中 City 的属性为加 ! 的方式，因此，一旦 Country 的实例在构造函数中给 name 属性赋值，整个初始化过程就完成了，下面的打印信息为虚的            self.capitalCity = City(name: captialName, country: self)            print("Country is inited")        }        deinit {            print("Country is deinited")        }    }        class City {        let name: String        unowned let country: Country        init(name: String, country: Country) {            print("City is initing")            self.name = name            self.country = country            print("City is inited")        }        deinit {            print("City is deinited")        }    }}
3.打印结果：
Country is initing
City is initing
City is inited
Country is inited
Canada's capital city is called Ottawa
---
Country is deinited
City is deinited
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