Swift: inherited objects - ios

Question

I am getting a strange message when I use a derived class for a function with the base class as argument:
class Vehicle: Object, Mappable, Hashable, Equatable {
...
}
class Car: Vehicle {
...
}
class TransportFactory: NSObject{
func doSomethingWithVehicles(vehicles:[Vehicle]){
...
}
}
class CarFactory: TransportFactory{
let myCars = [Car]()
doSomethingWithVehicles(myCars)
}
This results in: "Cannot convert value of type '[Car]' to expected argument type '[Vehicle]'"
Object is a class (Realm), Mappable a protocol (AlamofireMapper), Hashable and Equatable a protocol from Foundation

Answer 1

You're declaring myCars without a type and assigning it an Array containing your Car class, so type inference is literally giving you an Array with your class object inside. Try:
let myCars = [Car]()
self.doSomethingWithVehicles(myCars)
This is why I prefer the Array<Car> syntax rather than the [Car]. I feel the code is clearer/safer, as let myCars = Array<Car> would have just not compiled.

Answer 2

You need to wrap doSomethingWithVehicles in a function, you can't just have it hanging out in the class scope:
class Vehicle: NSObject {
// ...
}
class Car: Vehicle {
// ...
}
class TransportFactory: NSObject {
func doSomethingWithVehicles(vehicles:[Vehicle]){
// ...
}
}
class CarFactory: TransportFactory {
let myCars = [Car]()
func someFunc() {
self.doSomethingWithVehicles(myCars)
}
}
myCars can be at the class scope because it is a class variable.

Answer 3

import Foundation
class Vehicle: NSObject{
}
class Car: Vehicle {
}
class TransportFactory: NSObject{
func doSomethingWithVehicles(vehicles:[Vehicle]){
print("Number of vehicles:", vehicles.count)
}
}
class CarFactory: TransportFactory {
let myCars = [Car]()
}
let carFactory = CarFactory()
carFactory.doSomethingWithVehicles(carFactory.myCars)
/* print out
Number of vehicles: 0
*/