Inheritance - RaduG/swift_learning GitHub Wiki

Classes can inherit from other classes in Swift in a single inheritance model. There is no absolute base class (a class from which all types are derived).

class Vehicle {
  var currentSpeed: Double = 0.0
  let topSpeed: Double
  let name: String

  init(topSpeed: Double, name: String) {
    self.topSpeed = topSpeed
    self.name = name
  }

  func accellerate(by speed: Double) {
    self.currentSpeed = min(self.currentSpeed + speed, self.topSpeed)
  }

  func decellerate(by speed: Double) {
    self.currentSpeed = max(self.currentSpeed - speed, 0.0)
  }

  func description() -> String {
    return "\(name): \(currentSpeed) / \(topSpeed)"
  }
}


class Bicycle: Vehicle {
    init(topSpeed: Double) {
        super.init(topSpeed: topSpeed, name: "Bicycle")
    }
}

let bicycle = Bicycle(topSpeed: 25)
print(bicycle.description())
bicycle.accellerate(by: 20)
print(bicycle.description())
bicycle.accellerate(by: 20)
print(bicycle.description())

Overriding methods

class Bicycle: Vehicle {
    init(topSpeed: Double) {
        super.init(topSpeed: topSpeed, name: "Bicycle")
    }

    override func description() -> String {
        return "Human-powered \(super.description())"
    }
}

Overriding properties

• If overriding a computed property, both the getter and the setter need to be provided (if implemented by the base class)
• Use property observers to add observers to an inherited property. Overridden observers and getter/setter are mutually exclusive

class Car: Vehicle {
  var gear: Int = 0

  init(topSpeed: Double) {
    super.init(topSpeed: topSpeed, name: "Car")
  }

  override func description() -> String {
    return "\(super.description()) in gear \(gear)"
  }
}

class AutomaticCar: Car {
  override var currentSpeed: Double {
    didSet {
      if Int(currentSpeed) == 0 {
        self.gear = 0
      } else {
        self.gear = Int(currentSpeed / 10) + 1
      }
    }
  }
}