Swift Academy · Lesson

Type Casting: is, as?, as! and as

Checking and converting types safely with Swift's casting operators.

What is Type Casting?

Type casting lets you check or convert an instance to a different class in its hierarchy.

class Animal { var name: String = "Animal" }
class Dog: Animal { func bark() { print("Woof") } }
let a: Animal = Dog()
print(a.name)

Use is to check whether an instance is of a certain subclass.

let a: Animal = Dog()
if a is Dog {
  print("It's a dog")
}