Swift 類(lèi)型轉(zhuǎn)換提供兩個(gè)操作符：“is” 檢查值的類(lèi)型和 'as' 將類(lèi)型值轉(zhuǎn)換為不同的類(lèi)型值。類(lèi)型轉(zhuǎn)換還檢查實(shí)例類(lèi)型是否符合特定的協(xié)議一致性標(biāo)準(zhǔn)。

定義一個(gè)類(lèi)層次結(jié)構(gòu)

類(lèi)型轉(zhuǎn)換用于檢查實(shí)例的類(lèi)型或者它屬于特定類(lèi)型。此外，檢查類(lèi)和它的子類(lèi)層次結(jié)構(gòu)來(lái)檢查并轉(zhuǎn)換這些實(shí)例，使之作為一個(gè)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(yùn)行上面的程序，得到以下結(jié)果。

Instance physics is: solid physics
Instance equation is: Hertz
Instance physics is: Fluid Dynamics
Instance formulae is: Giga Hertz

類(lèi)型檢查

進(jìn)行類(lèi)型檢查，用 'is' 操作符。在 'is' 操作符檢查類(lèi)型實(shí)例是否屬于特定的子類(lèi)型，如果它屬于該實(shí)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 上一篇：Swift 可選鏈下一篇：Swift 方法

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Swift 類(lèi)型轉(zhuǎn)換

定義一個(gè)類(lèi)層次結(jié)構(gòu)

類(lèi)型檢查