swift2 析构过程

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Swift 会自动释放不再需要的实例以释放资源。Swift 通过自动引用计数（ARC）处理实例的内存管理。

通常当你的实例被释放时不需要手动地去清理。但是，当使用自己的资源时，你可能需要进行一些额外的清理。

例如，如果创建了一个自定义的类来打开一个文件，并写入一些数据，你可能需要在类实例被释放之前关闭该文件。

在类的定义中，每个类最多只能有一个析构函数。析构函数不带任何参数，在写法上不带括号：

deinit {    // 执行析构过程}

实例：

struct Bank {    static var coinsInBank = 10_000    static func vendCoins(var numberOfCoinsToVend: Int) -> Int {        numberOfCoinsToVend = min(numberOfCoinsToVend, coinsInBank)        coinsInBank -= numberOfCoinsToVend        return numberOfCoinsToVend    }    static func receiveCoins(coins: Int) {        coinsInBank += coins    }}class Player {    var coinsInPurse: Int    init(coins: Int) {        coinsInPurse = Bank.vendCoins(coins)    }    func winCoins(coins: Int) {        coinsInPurse += Bank.vendCoins(coins)    }    deinit {        Bank.receiveCoins(coinsInPurse)    }}var playerOne: Player? = Player(coins: 100)print("A new player has joined the game with \(playerOne!.coinsInPurse) coins")// 输出 "A new player has joined the game with 100  coins"print("There are now \(Bank.coinsInBank) coins left   in the bank")// 输出 "There are now 9900 coins left in the bank"playerOne!.winCoins(2_000)print("PlayerOne won 2000 coins & now has \(playerOne!.coinsInPurse) coins")// 输出 "PlayerOne won 2000 coins & now has 2100 coins"print("The bank now only has \(Bank.coinsInBank) coins left")// 输出 "The bank now only has 7900 coins left"playerOne = nilprint("PlayerOne has left the game")// 输出 "PlayerOne has left the game"print("The bank now has \(Bank.coinsInBank) coins")// 输出 "The bank now has 10000 coins"

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