Swift 類型轉(zhuǎn)換

類型轉(zhuǎn)換在Swift4中用于驗證實例的類型。愛掏網(wǎng) - it200.com它用于檢查實例類型是否屬于特定的父類或子類，或者它是否在自己的層次結(jié)構(gòu)中定義。愛掏網(wǎng) - it200.com

Swift 4類型轉(zhuǎn)換提供兩個操作符：

• ‘is’ ：該運算符用于檢查值的類型。愛掏網(wǎng) - it200.com
• ‘as’ ：該運算符用于將類型值轉(zhuǎn)換為不同的類型。愛掏網(wǎng) - it200.com

類型轉(zhuǎn)換還用于檢查實例類型是否符合特定的協(xié)議一致性標準。愛掏網(wǎng) - it200.com它還檢查類的層次結(jié)構(gòu)、其子類和實例，使其成為相同的層次結(jié)構(gòu)。愛掏網(wǎng) - it200.com

示例

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: "Mechanics", equations: "Hertz"),
   Maths(physics: "Fluid Dynamics", formulae: "Giga Hertz")]
let samplechem = Chemistry(physics: "Mechanics", equations: "Hertz")
print("Instance physics is: \(samplechem.physics)")
print("Instance equation is: \(samplechem.equations)")
let samplemaths = Maths(physics: "Fluid Dynamics", formulae: "Giga Hertz")
print("Instance physics is: \(samplemaths.physics)")
print("Instance formulae is: \(samplemaths.formulae)")

輸出：

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

如何進行類型檢查

“is”運算符用于進行類型檢查。愛掏網(wǎng) - it200.com它檢查實例是否屬于特定的子類類型，并在屬于時返回“true”，否則返回“false”。愛掏網(wǎng) - it200.com