Inheritance is a mechanism in object-oriented programming that allows you to define a new class based on an existing class, in which the new class inherits all the properties and methods of the existing class. In Swift, you can use the class keyword to define a class, and the super keyword to refer to the superclass.
Here is an example of a Vehicle class that contains basic properties and methods that describe a vehicle:
class Vehicle {
var brand: String
var model: String
var year: Int
init(brand: String, model: String, year: Int) {
self.brand = brand
self.model = model
self.year = year
}
func startEngine() {
print("Starting the engine of \(brand) \(model)")
}
func stopEngine() {
print("Stopping the engine of \(brand) \(model)")
}
func drive() {
print("Driving \(brand) \(model)")
}
}
Now, let's say we want to create a Car class that is a subclass of Vehicle. We can do this by using the class keyword followed by the subclass name, and then specifying the superclass name using a colon and the superclass name:
class Car: Vehicle {
var numWheels: Int
init(numWheels: Int, brand: String, model: String, year: Int) {
self.numWheels = numWheels
super.init(brand: brand, model: model, year: year)
}
func honk() {
print("Honking the horn of \(brand) \(model)")
}
}
In this subclass, we've added a new property numWheels, and a new method honk(). We've also added an init method that takes in arguments for both the subclass and superclass properties, and calls the superclass init method using super.init(). This ensures that the superclass properties are initialized before the subclass properties.
Now, we can create a Car object:
let myCar = Car(numWheels: 4, brand: "Toyota", model: "Camry", year: 2020)
We can access the superclass methods and properties using the super keyword:
myCar.startEngine() // prints "Starting the engine of Toyota Camry"
myCar.stopEngine() // prints "Stopping the engine of Toyota Camry"
myCar.drive() // prints "Driving Toyota Camry"
And, we can access the subclass properties and methods:
myCar.honk() // prints "Honking the horn of Toyota Camry"
print(myCar.numWheels) // prints 4