CODEWITHSUNDEEP
swiftoverriding
Rytis Razmus
Rytis Razmus

Reputation: 35

override func doesn't work

I'm learning swift from a book and typed an example of structs and classes. However the example does not work like it should because the program won't decrease the population whenever a zombie is called. I know this is a stupid question but I just can't understand why. Can somebody explain what's wrong? So here's the code:

main.swift

import Foundation

var myTown = Town()
myTown.changePopulation(by:500)

let fredTheZombie = Zombie()
fredTheZombie.town = myTown
fredTheZombie.terrorizeTown()
fredTheZombie.town?.printDescription()
myTown.printDescription()

Town.swift

import Foundation

struct Town {
var population = 5422
var numberOfStopLights = 4

func printDescription() {
    print("Population: \(myTown.population), number of stoplights: \ .    (myTown.numberOfStopLights).")
}
 mutating func changePopulation(by amount: Int){
    population += amount
}
}

Monster.swift

import Foundation

class Monster{
var town: Town?
var name = "Monster"

func terrorizeTown(){
    if town != nil{
        print("\(name) is terrorazing a town!")
    }
    else{
        print("\(name) hasn't found a town to terrorize yet...")
    }
}
}

Zombie.swift

import Foundation

class Zombie: Monster {

override func terrorizeTown() { 
town?.changePopulation(by: -10)
super.terrorizeTown() 
}
}

Upvotes: 1

Views: 476

Answers (2)

simonWasHere
simonWasHere

Reputation: 1340

If you change Town from a struct to a class it will work.

A struct is copied each time you assign it, so when you put zombie.town = myTown it is not the same town, the zombie has a copy of the town and the original town is not changed when the zombie's town is updated. A class will work the way you expect it to.

Upvotes: 1

Andreas Oetjen
Andreas Oetjen

Reputation: 10199

Since Town is a struct, it will be copied when you assign it to your zombie. Therefore, fredTheZombie.terrorizeTown() terrorizes a copy of myTown - so myTown keeps it's value.

What you want is a class, which will be transferred by reference when you assign it to your monster -- so you only have one Town:

class Town {
    var population = 5422
    var numberOfStopLights = 4

    func printDescription() {
        print("Population: \(myTown.population), number of stoplights: \ .    (myTown.numberOfStopLights).")
    }
    func changePopulation(by amount: Int){
        population += amount
    }
}

Upvotes: 1

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