驗證一個實例的類型'類型轉(zhuǎn)換'在 Swift 語言編程中。它是用來檢查實例類型是否屬于特定超類或子類或其自己的層次結(jié)構(gòu)定義。
Swift 類型轉(zhuǎn)換提供兩個操作符：“is” 檢查值的類型和 'as' 將類型值轉(zhuǎn)換為不同的類型值。 類型轉(zhuǎn)換還檢查實例類型是否符合特定的協(xié)議一致性標(biāo)準(zhǔn)。
定義一個類層次結(jié)構(gòu)
類型轉(zhuǎn)換用于檢查實例的類型或者它屬于特定類型。此外，檢查類和它的子類層次結(jié)構(gòu)來檢查并轉(zhuǎn)換這些實例，使之作為一個相同的層次結(jié)構(gòu)。
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)")
當(dāng)我們使用 playground 運行上面的程序，得到以下結(jié)果。
Instance physics is: solid physicsInstance equation is: HertzInstance physics is: Fluid DynamicsInstance formulae is: Giga Hertz
類型檢查
進行類型檢查，用 'is' 操作符。在 'is' 操作符檢查類型實例是否屬于特定的子類型，如果它屬于該實例返回“true”，否則將返回“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: "solid physics", equations: "Hertz"),
Maths(physics: "Fluid Dynamics", 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: "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)")
var chemCount = 0
var mathsCount = 0
for item in sa {
if item is Chemistry {
++chemCount
} else if item is Maths {
++mathsCount
}
}
println("Subjects in chemistry contains /(chemCount) topics and maths contains /(mathsCount) topics")
當(dāng)我們使用 playground 運行上面的程序，得到以下結(jié)果。
Instance physics is: solid physicsInstance equation is: HertzInstance physics is: Fluid DynamicsInstance formulae is: Giga HertzSubjects in chemistry contains 2 topics and maths contains 3 topics
向下轉(zhuǎn)換
向下類型轉(zhuǎn)換的子類型可以有兩個操作符（如：as? 和 as!）。as? 當(dāng)值是nil，返回一個可選值。它是用來檢查成功向下轉(zhuǎn)型。
“as!” 返回強制解包裹，如可選鏈，向下轉(zhuǎn)換返回 nil 值。它用來觸發(fā)運行時錯誤在向下轉(zhuǎn)型出現(xiàn)故障時
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"),
Chemistry(physics: "Thermo physics", equations: "Decibels"),
Maths(physics: "Astro Physics", formulae: "MegaHertz"),
Maths(physics: "Differential Equations", formulae: "Cosine Series")]
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)")
var chemCount = 0
var mathsCount = 0
for item in sa {
if let print = item as? Chemistry {
println("Chemistry topics are: '/(print.physics)', /(print.equations)")
} else if let example = item as? Maths {
println("Maths topics are: '/(example.physics)', /(example.formulae)")
}
}
當(dāng)我們使用 playground 運行上面的程序，得到以下結(jié)果。
Instance physics is: solid physicsInstance equation is: HertzInstance physics is: Fluid DynamicsInstance formulae is: Giga HertzChemistry topics are: 'solid physics', HertzMaths topics are: 'Fluid Dynamics', Giga HertzChemistry topics are: 'Thermo physics', DecibelsMaths topics are: 'Astro Physics', MegaHertzMaths topics are: 'Differential Equations', Cosine Series
類型轉(zhuǎn)換：任何與任何對象
為了表示實例屬于任何類型包括函數(shù)類型，使用“Any”關(guān)鍵字
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 sa = [
Chemistry(physics: "solid physics", equations: "Hertz"),
Maths(physics: "Fluid Dynamics", 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: "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)")
var chemCount = 0
var mathsCount = 0
for item in sa {
if let print = item as? Chemistry {
println("Chemistry topics are: '/(print.physics)', /(print.equations)")
} else if let example = item as? Maths {
println("Maths topics are: '/(example.physics)', /(example.formulae)")
}
}
var exampleany = [Any]()
exampleany.append(12)
exampleany.append(3.14159)
exampleany.append("Example for Any")
exampleany.append(Chemistry(physics: "solid physics", equations: "Hertz"))
for print in exampleany {
switch print {
case let someInt as Int:
println("Integer value is /(someInt)")
case let someDouble as Double where someDouble > 0:
println("Pi value is /(someDouble)")
case let someString as String:
println("/(someString)")
case let phy as Chemistry:
println("Topics '/(phy.physics)', /(phy.equations)")
default:
println("None")
}
}
當(dāng)我們使用 playground 運行上面的程序，得到以下結(jié)果。
Instance physics is: solid physicsInstance equation is: HertzInstance physics is: Fluid DynamicsInstance formulae is: Giga HertzChemistry topics are: 'solid physics', HertzMaths topics are: 'Fluid Dynamics', Giga HertzChemistry topics are: 'Thermo physics', DecibelsMaths topics are: 'Astro Physics', MegaHertzMaths topics are: 'Differential Equations', Cosine SeriesInteger value is 12Pi value is 3.14159Example for AnyTopics 'solid physics', HertzAnyObject
為了表示是任何類型的類實例，使用AnyObject“關(guān)鍵字
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: "solid physics", equations: "Hertz"),
Maths(physics: "Fluid Dynamics", 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: "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)")
var chemCount = 0
var mathsCount = 0
for item in saprint {
if let print = item as? Chemistry {
println("Chemistry topics are: '/(print.physics)', /(print.equations)")
} else if let example = item as? Maths {
println("Maths topics are: '/(example.physics)', /(example.formulae)")
}
}
var exampleany = [Any]()
exampleany.append(12)
exampleany.append(3.14159)
exampleany.append("Example for Any")
exampleany.append(Chemistry(physics: "solid physics", equations: "Hertz"))
for print in exampleany {
switch print {
case let someInt as Int:
println("Integer value is /(someInt)")
case let someDouble as Double where someDouble > 0:
println("Pi value is /(someDouble)")
case let someString as String:
println("/(someString)")
case let phy as Chemistry:
println("Topics '/(phy.physics)', /(phy.equations)")
default:
println("None")
}
}
當(dāng)我們使用 playground 運行上面的程序，得到以下結(jié)果。
Instance physics is: solid physicsInstance equation is: HertzInstance physics is: Fluid DynamicsInstance formulae is: Giga HertzChemistry topics are: 'solid physics', HertzMaths topics are: 'Fluid Dynamics', Giga HertzChemistry topics are: 'Thermo physics', DecibelsMaths topics are: 'Astro Physics', MegaHertzMaths topics are: 'Differential Equations', Cosine SeriesInteger value is 12Pi value is 3.14159Example for AnyTopics 'solid physics', Hertz
