Swift Choosing Specific Value by Condition - swift

Question

I am applying a simple inheritance project using Swift. However, after completing my code, getting this error all the time.This project creates vehicle class and has 2 child classes as Car and Bicycle.
Car has speed depending on its chosen gear.
So I implement a gearBox dictionary which has gear as key and speed as value.
I am not sure if I could assign speed value by controlling its gear in my Car class.
Any help would be appreciated.
MY ERROR
Playground execution failed: error: psionix.playground:19:34: error: use of 'self' in property access 'speed' before super.init initializes self
super.init(speedVehicle: speed)
^
MY CODE
//: Playground - noun: a place where people can play
import UIKit
class Vehicle{
var speed : Double
init(speedVehicle:Double){
speed = speedVehicle
}
func printDescription(){
print("Vehicle has \(speed) km/h speed by default.")
}
}
class Car : Vehicle{
var speedCar :Double
let gearBox : [Int : Double] = [1:10.5, 2:23.3, 3:33.4, 4:45.0, 5:51.2]
init(){
super.init(speedVehicle: speed)
}
func calculateTravelTime(distance:Double, gearCar:Int)->Double{
var travelTime : Double
travelTime = distance/speedCar
for (gear, speed) in gearBox{
if(gear == gearCar){
speedCar = speed
}
}
return travelTime
}
override func printDescription() {
print("My Car has \(gearBox.count) gears and has \(speedCar) km/h speed.")
}
}
class Bicycle : Vehicle{
var hasBasket : Bool
var distance : Double // in km
var speedBicycle : Double
init(hasBasket: Bool){
super.init(speedVehicle: speed)
self.hasBasket = hasBasket
}
func calculateTravelTime(speed:Double)->Double{
let time = (distance/speed)
print("Bicycle travel time is: \(time)")
return time
}
override func printDescription() {
if(hasBasket == true){
print("My Bicycle has \(speedBicycle) km/h speed and its has a basket.")
}
else{
print("My Bicycle has \(speedBicycle) km/h speed and its has no basket.")
}
}
}
let myVehicle = Vehicle(speedVehicle:3.0)
myVehicle.printDescription()
let myCar = Car()
print("My car travel time is \(myCar.calculateTravelTime(distance: 100.0, gearCar:3)) hours.")
myCar.printDescription()
let myBicycle = Bicycle(hasBasket:true)
print("My bicycle travel time is \(myBicycle.calculateTravelTime(speed: 10)) hours.")
myBicycle.printDescription()

Answer 1

The problem is you are trying to call the initializer of your superclass without actually providing all necessary values as input arguments to super.init(speed:). You need to change your init methods to provide a speed value.
class Car : Vehicle{
...
init(speed: Double){
super.init(speedVehicle: speed)
}
}
class Bicycle : Vehicle{
...
init(speed: Double,hasBasket: Bool){
super.init(speedVehicle: speed)
self.hasBasket = hasBasket
}
}
And do the same for all your Vehicle subclasses. Moreover, the speedCar property is not needed, since Car already has a speed property inherited from Vehicle, same for speedBicycle in Bicycle.
If you want all your subclass instances to have the same speed, just set up a default value in the init method like so:
class Car : Vehicle{
...
init(){
let carSpeed = 50.0
super.init(speedVehicle: carSpeed)
//you could even do super.init(speedVehicle: 50), I just used a variable for clarity
}
}
Moreover, you should never iterate through a dictionary to find a certain key, you can safely access values using subscripting. If the key doesn't exist, the value will simply be nil.
func calculateTravelTime(distance:Double, gearCar:Int)->Double{
if let currentSpeed = gearBox[gear] {
speedCar = currentSpeed
}
return distance/speedCar
}

Answer 2

You are init your Bicycle and Car, before you set it speed. Add speed before you called super.init method
Edit this
init(hasBasket: Bool){
speedBicycle = 0
super.init(speedVehicle: speedBicycle)
self.hasBasket = hasBasket
}
And This
init(){
speedCar = 0
super.init(speedVehicle: speedCar)
}

Answer 3

It makes sense that any Vehicle has an initial speed of either a user desired value, or 0 by default. Same happens with a Car, and since a Car is a Vehicle, you don't need two different speeds.
This would be my refined approach:
import Foundation
class Vehicle: CustomStringConvertible {
var speedInKmH: Double
init(speedInKmH: Double = 0) {
self.speedInKmH = speedInKmH
}
var description: String {
return "Vehicle has \(speedInKmH) km/h speed by default."
}
}
struct GearBox {
var gear: Int
var speedInKmH: Double
}
class Car: Vehicle {
let gearBox: [GearBox] = [GearBox(gear: 1, speedInKmH: 10.5), GearBox(gear: 3, speedInKmH: 33.4), GearBox(gear: 5, speedInKmH: 51.2),
GearBox(gear: 2, speedInKmH: 23.3), GearBox(gear: 4, speedInKmH: 45.0)]
func travelTimeInHoursWith(distanceInKm: Double, gear: Int) -> Double {
if let matchedGearBox = gearBox.filter({ $0.gear == gear }).first {
self.speedInKmH = matchedGearBox.speedInKmH
}
return distanceInKm / speedInKmH
}
override var description: String {
return "My Car has \(self.gearBox.count) gears and has \(self.speedInKmH) km/h speed."
}
}
let toyota = Car()
print(toyota.travelTimeInHoursWith(distanceInKm: 22, gear: 4))
print(toyota)
I did some improvements to make it clear, you can take my code as example and modify your other implemented class/classes