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@H_197_18@deinit@H_197_18@来标示析构函数，类似于初始化函数用@H_197_18@init@H_197_18@来标示。析构函数只适用于类类型。@H_197_18@

析构过程原理

Swift @H_197_18@会自动释放不再需要的实例以释放资源@H_197_18@Swift @H_197_18@通过自动引用计数（@H_197_18@ARC@H_197_18@）处理实例的内存管理@H_197_18@

示例@H_197_18@

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。@H_197_18@

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"