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"