swift2 析构过程

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 = nil
print("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"