《浅入浅出Swift》Deinitialization 析构过程

####Initialization

        //析构过程是构造过程的逆向过程，当一个类的实例被释放的时候，在内存中消失前，析构器会被调用
        //swift通过ARC管理内存。
        
        
        //由于swift是ARC管理内存，所以析构过程已经不是那么重要了
        class MyClass{
            var myNum = 0
            init (){
                myNum = 1
            }
            
            deinit {
                myNum = 0
                println("myNum \(myNum)")
            }
        }
        
        var myClass = MyClass()
        println("myClass.myNum = \(myClass.myNum)")
//        myClass = nil
        
        //Deinitializers in Action
        struct Bank {
            //在银行的金币数
            static var coinsInBank = 10_000
            //出售金币
            static func vendCoins(var numberOfCoinsToVend:Int)->Int{
                println("numberOfCoinsToVend = \(numberOfCoinsToVend)")
                println("coinsInBank = \(coinsInBank)")
                numberOfCoinsToVend = min(numberOfCoinsToVend, coinsInBank)
                println("numberOfCoinsToVend = \(numberOfCoinsToVend)")
                coinsInBank -= numberOfCoinsToVend
                return numberOfCoinsToVend
            }
            
            //收到金币
            static func receiveCoins(coins:Int){
                coinsInBank += coins
            }
        }
        
        class Player{
            //硬币钱包
            var coinsInPurse : Int
            //初始化
            init (coins: Int){
                coinsInPurse = Bank.vendCoins(coins)
                println("Player.init.coinsInPurse = \(coinsInPurse)")
            }
            //赢得的钱币
            func winCoins(coins:Int){
                coinsInPurse += Bank.vendCoins(coins)
            }
            //析构过程
            deinit{
                Bank.receiveCoins(coinsInPurse)
            }
        }
        
        //生成一个player，初始化银行出售金币100枚
        var playerOne : Player? = Player(coins:100)
        println("A new player has joined the game with \(playerOne!.coinsInPurse) coins")
        // prints "A new player has joined the game with 100 coins"
        println("There are now \(Bank.coinsInBank) coins left in the bank")
        // 银行剩余9900 coins
        
        playerOne!.winCoins(2_000)
        println("PlayerOne won 2000 coins & now has \(playerOne!.coinsInPurse) coins")
        //赢了2000枚，加上前面的100枚
        println("The bank now only has \(Bank.coinsInBank) coins left")//银行剩余7900
        playerOne = nil
        println("The bank now only has \(Bank.coinsInBank) coins left")//银行剩余10000枚

Reference

• The Swift Programming Language