การตรวจสอบชนิดด้วย is

ตัวดำเนินการ is

class Animal {
    let name: String
    init(name: String) { self.name = name }
}
class Dog: Animal {
    func bark() -> String { return name + " says Woof" }
}
class Cat: Animal {
    func meow() -> String { return name + " says Meow" }
}
let a: Animal = Dog(name: "Rex")
print(a is Dog)
print(a is Cat)

การตรวจสอบการเป็นสมาชิกของชนิดย่อย

class Animal {
    let name: String
    init(name: String) { self.name = name }
}
class Dog: Animal {
    func bark() -> String { return name + " says Woof" }
}
class Cat: Animal {
    func meow() -> String { return name + " says Meow" }
}
let a: Animal = Dog(name: "Rex")
print(a is Animal)
print(a is Dog)

การใช้ is ในเงื่อนไข

class Animal {
    let name: String
    init(name: String) { self.name = name }
}
class Dog: Animal {
    func bark() -> String { return name + " says Woof" }
}
class Cat: Animal {
    func meow() -> String { return name + " says Meow" }
}
let a: Animal = Cat(name: "Mia")
if a is Cat {
    print("It is a cat")
} else {
    print("Not a cat")
}

การนับชนิดในคอลเลกชัน

class Animal {
    let name: String
    init(name: String) { self.name = name }
}
class Dog: Animal {
    func bark() -> String { return name + " says Woof" }
}
class Cat: Animal {
    func meow() -> String { return name + " says Meow" }
}
let zoo: [Animal] = [Dog(name: "Rex"), Cat(name: "Mia"), Dog(name: "Buddy")]
let dogCount = zoo.filter { $0 is Dog }.count
print("Dogs:", dogCount)

การใช้ is กับโพรโทคอล

protocol Flyer {}
class Bird: Flyer {}
class Fish {}
let creatures: [Any] = [Bird(), Fish()]
for c in creatures { print(c is Flyer) }

is เทียบกับ as?

class Animal {
    let name: String
    init(name: String) { self.name = name }
}
class Dog: Animal {
    func bark() -> String { return name + " says Woof" }
}
class Cat: Animal {
    func meow() -> String { return name + " says Meow" }
}
let a: Animal = Dog(name: "Rex")
print("Check only:", a is Dog)
if let d = a as? Dog { print("Use it:", d.bark()) }

การป้องกันด้วย is

class Animal {
    let name: String
    init(name: String) { self.name = name }
}
class Dog: Animal {
    func bark() -> String { return name + " says Woof" }
}
class Cat: Animal {
    func meow() -> String { return name + " says Meow" }
}
func onlyForCats(_ a: Animal) {
    guard a is Cat else {
        print("Skipping non-cat")
        return
    }
    print("Processing a cat")
}
onlyForCats(Cat(name: "Mia"))
onlyForCats(Dog(name: "Rex"))

การรวม is ใน switch

class Animal {
    let name: String
    init(name: String) { self.name = name }
}
class Dog: Animal {
    func bark() -> String { return name + " says Woof" }
}
class Cat: Animal {
    func meow() -> String { return name + " says Meow" }
}
let items: [Any] = [Dog(name: "Rex"), 42, "hello"]
for item in items {
    switch item {
    case is Dog: print("a dog")
    case is Int: print("an integer")
    default: print("something else")
    }
}

is ตรวจสอบชนิดขณะทำงาน

class Animal {
    let name: String
    init(name: String) { self.name = name }
}
class Dog: Animal {
    func bark() -> String { return name + " says Woof" }
}
class Cat: Animal {
    func meow() -> String { return name + " says Meow" }
}
let declaredAsAnimal: Animal = Dog(name: "Rex")
print("Runtime is Dog:", declaredAsAnimal is Dog)

การตรวจสอบก่อนแปลงชนิดแบบบังคับ

class Animal {
    let name: String
    init(name: String) { self.name = name }
}
class Dog: Animal {
    func bark() -> String { return name + " says Woof" }
}
class Cat: Animal {
    func meow() -> String { return name + " says Meow" }
}
let a: Animal = Dog(name: "Rex")
if a is Dog {
    let d = a as! Dog
    print(d.bark())
}

ตัวอย่างสรุปการตรวจสอบชนิด

class Animal {
    let name: String
    init(name: String) { self.name = name }
}
class Dog: Animal {
    func bark() -> String { return name + " says Woof" }
}
class Cat: Animal {
    func meow() -> String { return name + " says Meow" }
}
let zoo: [Animal] = [Dog(name: "Rex"), Cat(name: "Mia")]
for a in zoo {
    if a is Dog { print("dog:", a.name) }
    if a is Cat { print("cat:", a.name) }
}

ตรวจสอบอย่างรวดเร็ว

ทบทวน: การตรวจสอบชนิดด้วย is

class Animal {
    let name: String
    init(name: String) { self.name = name }
}
class Dog: Animal {
    func bark() -> String { return name + " says Woof" }
}
class Cat: Animal {
    func meow() -> String { return name + " says Meow" }
}
let zoo: [Animal] = [Dog(name: "Rex"), Cat(name: "Mia"), Dog(name: "Buddy")]
print("Cats:", zoo.filter { $0 is Cat }.count)
print("Dogs:", zoo.filter { $0 is Dog }.count)