Browse Questions
  • Codable is a type alias for Encodable & Decodable.
  • You can add observers to stored properties you define, and to inherited stored or computed properties by overriding them in a subclass.
  • Delegate protocols must inherit from AnyObject to restrict protocol conformance to classes, allowing delegate properties to be marked with the weak keyword.
  • Subscribe to keyboard notifications to adjust your layout when the keyboard appears or hides, so it doesn't cover your input fields.

Answer: You can add observers to stored properties you define, and to inherited stored or computed properties by overriding them in a subclass.

Property kindCan add observers?
Stored var you define✅ Yes
Inherited stored property (via override)✅ Yes
Inherited computed property (via override)✅ Yes
Computed property you define❌ No — put the logic in its set
let constant❌ No — it never changes

Code Example:

class Vehicle {
    var currentSpeed = 0.0
    var description: String { "traveling at \(currentSpeed) mph" }
}

class Car: Vehicle {
    var gear = 1

    // Observing an inherited stored property
    override var currentSpeed: Double {
        didSet {
            gear = Int(currentSpeed / 10) + 1
        }
    }
}

let car = Car()
car.currentSpeed = 35
print(car.gear) // 4

Key Points:

  • An overriding property observer cannot also provide its own setter — choose one or the other.
  • You cannot add observers to an inherited read-only computed property, since it is never set.
  • The superclass's own observers still run; the subclass's observers run around them.

Further reading