上一章Swift教程请查看：swift可选链式调用
在Swift 语言中“类型转换”用于验证实例类型，它用于检查实例类型是否属于某个特定的超类或子类，或者它是在自己的层次结构中定义的。
Swift类型转换提供了两个操作符：“is”来检查值的类型和，“as”将类型值转换为不同的类型，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。
定义类层次结构类型转换用于检查实例的类型，以确定它是否属于特定的类类型。此外，它还检查类的层次结构及其子类，以检查和转换这些实例，使其成为相同的层次结构。
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: "流体动力学", formulae: "Giga Hertz")]
let samplechem = Chemistry(physics: "solid physics", equations: "Hertz")
print("物理实例: \(samplechem.physics)")
print("实例方程: \(samplechem.equations)")
let samplemaths = Maths(physics: "Fluid Dynamics", formulae: "Giga Hertz")
print("物理实例: \(samplemaths.physics)")
print("表达式实例: \(samplemaths.formulae)")
类型检查使用’ is’ 操作符进行类型检查。’ is’ 类型检查操作符检查实例是否属于特定的子类类型，如果属于该实例则返回’ true’ ，否则将返回’ false’ 。
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: "固体物理", equations: "Hertz"),
Maths(physics: "流体动力学", formulae: "Giga Hertz"),
Chemistry(physics: "热物理", equations: "Decibels"),
Maths(physics: "宇宙物理学", formulae: "MegaHertz"),
Maths(physics: "微分方程", formulae: "余弦级数")]
let samplechem = Chemistry(physics: "固体物理", equations: "Hertz")
print("物理实例: \(samplechem.physics)")
print("实例方程: \(samplechem.equations)")
let samplemaths = Maths(physics: "流体动力学", formulae: "Giga Hertz")
print("物理实例: \(samplemaths.physics)")
print("表达式实例: \(samplemaths.formulae)")
var chemCount = 0
var mathsCount = 0
for item in sa {
if item is Chemistry {
++chemCount
} else if item is Maths {
++mathsCount
}
}
print("Subjects, chemistry: \(chemCount), math: \(mathsCount)")
向下类型转换可以使用两个操作符(as?和as!)”as?当该值返回nil时，返回一个可选值，它用于检查成功的向下强制转换。
“as!当向下强制转换返回空值时，将返回可选链接中讨论的强制展开，它用于在向下转换失败时触发运行时错误：
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: "AA", equations: "Hertz"),
Maths(physics: "BB", formulae: "Giga Hertz"),
Chemistry(physics: "CC", equations: "Decibels"),
Maths(physics: "DD", formulae: "MegaHertz"),
Maths(physics: "EE", formulae: "Cosine Series")]
let samplechem = Chemistry(physics: "AA", equations: "Hertz")
print("物理实例: \(samplechem.physics)")
print("方程实例: \(samplechem.equations)")
let samplemaths = Maths(physics: "BB", formulae: "Giga Hertz")
print("物理实例: \(samplemaths.physics)")
print("表达式: \(samplemaths.formulae)")
var chemCount = 0
var mathsCount = 0
for item in sa {
if let print = item as? Chemistry {
print("Chemistry: '\(print.physics)', \(print.equations)")
} else if let example = item as? Maths {
print("Maths: '\(example.physics)', \(example.formulae)")
}
}
类型转换：any和任何对象关键字“Any”用于表示属于任何类型(包括函数类型)的实例。
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: "固体物理", equations: "Hertz"),
Maths(physics: "流体动力学", formulae: "Giga Hertz"),
Chemistry(physics: "热力", equations: "Decibels"),
Maths(physics: "宇宙学", formulae: "MegaHertz"),
Maths(physics: "微分方程", formulae: "Cosine Series")]
let samplechem = Chemistry(physics: "固体物理", equations: "Hertz")
print("a: \(samplechem.physics)")
print("b: \(samplechem.equations)")
let samplemaths = Maths(physics: "流体动力学", formulae: "Giga Hertz")
print("a: \(samplemaths.physics)")
print("b: \(samplemaths.formulae)")
var chemCount = 0
var mathsCount = 0
for item in sa {
if let print = item as? Chemistry {
print("Chemistry: '\(print.physics)', \(print.equations)")
} else if let example = item as? Maths {
print("Maths: '\(example.physics)', \(example.formulae)")
}
}
var exampleany = [Any]()
exampleany.append(12)
exampleany.append(3.14159)
exampleany.append("Any实例")
exampleany.append(Chemistry(physics: "固体物理", equations: "Hertz"))
for print in exampleany {
switch print {
case let someInt as Int:
print("Integer: \(someInt)")
case let someDouble as Double where someDouble > 0:
print("Pi: \(someDouble)")
case let someString as String:
print("\(someString)")
case let phy as Chemistry:
print("Topics '\(phy.physics)', \(phy.equations)")
default:
print("None")
}
}
AnyObject【swift类型转换 – Swift最新教程】要表示任何类类型的实例，使用’ AnyObject’ 关键字。
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 saprint: [AnyObject] = [Chemistry(physics: "固体物理", equations: "Hertz"),
Maths(physics: "流体动力学", formulae: "Giga Hertz"),
Chemistry(physics: "Thermo physics", equations: "Decibels"),
Maths(physics: "Astro Physics", formulae: "MegaHertz"),
Maths(physics: "Differential Equations", formulae: "Cosine Series")]
let samplechem = Chemistry(physics: "固体物理", equations: "Hertz")
print("Instance: \(samplechem.physics)")
print("Instance: \(samplechem.equations)")
let samplemaths = Maths(physics: "流体动力学", formulae: "Giga Hertz")
print("Instance: \(samplemaths.physics)")
print("Instance: \(samplemaths.formulae)")
var chemCount = 0
var mathsCount = 0
for item in saprint {
if let print = item as? Chemistry {
print("Chemistry: '\(print.physics)', \(print.equations)")
} else if let example = item as? Maths {
print("Maths: '\(example.physics)', \(example.formulae)")
}
}
var exampleany = [Any]()
exampleany.append(12)
exampleany.append(3.14159)
exampleany.append("AnyObject")
exampleany.append(Chemistry(physics: "固体物理", equations: "Hertz"))
for print in exampleany {
switch print {
case let someInt as Int:
print("v: \(someInt)")
case let someDouble as Double where someDouble > 0:
print("Pi: \(someDouble)")
case let someString as String:
print("\(someString)")
case let phy as Chemistry:
print("Topics '\(phy.physics)', \(phy.equations)")
default:
print("None")
}
}
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