Swift学习笔记(十三)析构过程

析构过程

在一个类的实例被释放之前，析构函数被立即调用。用关键字deinit来标示析构函数，类似于初始化函数用init来标示。析构函数只适用于类类型。

析构过程原理

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

示例

deinit {
    // 执行析构过程
}

析构函数是在实例释放发生前一步被自动调用。不允许主动调用自己的析构函数。子类继承了父类的析构函数，并且在子类析构函数实现的最后，父类的析构函数被自动调用。即使子类没有提供自己的析构函数，父类的析构函数也总是被调用。

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 {//Player实例被销毁时调用
        Bank.receiveCoins(coinsInPurse)
    }
}
var playerOne: Player? = Player(coins: 100)
println("A new player has joined the game with (playerOne!.coinsInPurse) coins")
// 输出 "A new player has joined the game with 100     coins"
println("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)
println("PlayerOne won 2000 coins & now has (playerOne!.coinsInPurse) coins")
// 输出 "PlayerOne won 2000 coins & now has 2100 coins"
println("The bank now only has (Bank.coinsInBank) coins left")
// 输出 "The bank now only has 7900 coins left"
playerOne = nil  //置为nil时析构函数被调用
println("PlayerOne has left the game")
// 输出 "PlayerOne has left the game"
println("The bank now has (Bank.coinsInBank) coins")
// 输出 "The bank now has 10000 coins"

（编辑：李大同）

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