[Swift 官方教程]15 析构函数

在实例被回收前调用

析构函数如何工作 (How Deinitialization Works)

Swift 利用"自动引用计数 (Automatic reference counting)" 自动回收不再使用的实例

手动执行一些清理:

deinit{
	   
}

最多只能有一个

超类的解初始化和被自动继承, 如果子类有实现会自动在实现的最后被调用

解初始化实际使用 (Deinitializers in Action)

银行取钱和存钱:

class Bank {
    static var coinsInBank = 10_000
    static func distribute(coins numberOfCoinsRequested: Int) -> Int {
        let numberOfCoinsToVend = min(numberOfCoinsRequested, coinsInBank)
        coinsInBank -= numberOfCoinsToVend
        return numberOfCoinsToVend
    }
    static func receive(coins: Int) {
        coinsInBank += coins
    }
}

赌徒取钱和赢钱:

class Player {
    var coinsInPurse: Int
    init(coins: Int) {
        coinsInPurse = Bank.distribute(coins: coins)
    }
    func win(coins: Int) {
        coinsInPurse += Bank.distribute(coins: coins)
    }
    deinit {
        Bank.receive(coins: coinsInPurse)
    }
}

最后将钱返回给银行

测试1:

var playerOne: Player? = Player(coins: 100)
print("A new player has joined the game with \(playerOne!.coinsInPurse) coins")

print("There are now \(Bank.coinsInBank) coins left in the bank")

测试2:

playerOne!.win(coins: 2_000)
print("PlayerOne won 2000 coins & now has \(playerOne!.coinsInPurse) coins")
print("The bank now only has \(Bank.coinsInBank) coins left")

测试3:

playerOne = nil
print("PlayerOne has left the game")
print("The bank now has \(Bank.coinsInBank) coins")