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在Swift语言中，感叹号是什么意思？
Swift编程语言指南包含以下示例： class Person { let name: String init(name: String) { self.name = name } var apartment: Apartment? deinit { println("\(name) is being deinitialized") } } class Apartment { let number: Int init(number: Int) { self.number = number } var tenant: Person? deinit { println("Apartment #\(number) is being deinitialized") } } …