Swift编程中的一些类型转换方法详解.doc

Swift编程中的一些类型转换方法详解 验证一个实例的类型类型转换在 Swift 语言编程中。它是用来检查实例类型是否属于特定超类或子类或其自己的层次结构定义。 Swift 类型转换提供两个操作符：“is” 检查值的类型和 as 将类型值转换为不同的类型值。 类型转换还检查实例类型是否符合特定的协议一致性标准。 定义一个类层次结构 类型转换用于检查实例的类型或者它属于特定类型。此外，检查类和它的子类层次结构来检查并转换这些实例，使之作为一个相同的层次结构。 复制代码 代码如下: class Subjects { var physics: String init(physics: String) { self.physics = physics } } class Chemistry: Subjects { var equations: String init(physics: String, equations: String) { self.equations = equations super.init(physics: physics) } } class Maths: Subjects { var formulae: String init(physics: String, formulae: String) { self.formulae = formulae super.init(physics: physics) } } let sa = [ Chemistry(physics: solid physics, equations: Hertz), Maths(physics: Fluid Dynamics, formulae: Giga Hertz)] let samplechem = Chemistry(physics: solid physics, equations: Hertz) println(Instance physics is: \(samplechem.physics)) println(Instance equation is: \(samplechem.equations)) let samplemaths = Maths(physics: Fluid Dynamics, formulae: Giga Hertz) println(Instance physics is: \(samplemaths.physics)) println(Instance formulae is: \(samplemaths.formulae)) 当我们使用 playground 运行上面的程序，得到以下结果。 Instance physics is: solid physicsInstance equation is: HertzInstance physics is: Fluid DynamicsInstance formulae is: Giga Hertz 类型检查 进行类型检查，用 is 操作符。在 is 操作符检查类型实例是否属于特定的子类型，如果它属于该实例返回“true”，否则将返回“false”。 复制代码 代码如下: class Subjects { var physics: String init(physics: String) { self.physics = physics } } class Chemistry: Subjects { var equations: String init(physics: String, equations: String) { self.equations = equations super.init(physics: physics) } } class Maths: Subjects { var formulae: String init(physics: String, formulae: String) { self.formulae = formulae super.init(physics: physics) } } let sa = [ Chemistry(physics: solid physics, e