New compile error

Swift Programming: The Big Nerd Ranch Guide (2nd E 17. Initialization
1

I am retyping the code & recreating the files in the project as I am going through this chapter (mostly as I have been making my own deviations, comments, etc, as I go through each chapter, so it often no longer looks like the syntax in the book).

In this chapter, I started recreating the Town struct, including the new init() initializers.

Now I am into the section that amends the Monster class(es). However, after retyping the code, I now get a bunch of compile errors around “var town = Town?” and its all to do with the above new initializers I have created.

Here is my code:
Town.swift

import Foundation

struct Town {
var population: Int {
didSet(oldPop) {
print(“Pop changed to (population) from (oldPop)”)
}
}
var noStopLights: Int
let region: String

enum Size{
    
}

// Methods
init(region: String, population: Int, stopLights: Int) {
    self.region = region
    self.population = population
    noStopLights = stopLights
}
init(population: Int, stopLights: Int) {
    self.init(region: "N/A", population: population, stopLights: stopLights)
}

func printDescription() {
    print("Population: \(population). No of Stop Lights: \(noStopLights). Region: \(region)")
}

mutating func changePop(by amount: Int) {
    population += amount
}

}

Monster.swift

import Foundation

class Monster {
var town = Town?()
var name: String
var victimPool: Int {
get {
return town?.population ?? 0
}
set(newVictimPool) {
town?.population = newVictimPool
}
}

// Methods
init(town: Town?, monsterName: String) {
    self.town = town
    name = monsterName
}

func terroriseTown() {
    if town != nil {
        print("\(name) is terrorising the town")
    } else {
        print("\(name) has found a town to terrorise")
    }
}

}

main.swift

import Foundation

// Memberwise Initializers ONLY work on struct’s
var firstTown = Town(region: “NE”, population: 10_000, stopLights: 10)
firstTown.printDescription()

// Manual init functions defined. This 1 only has 2 of 3 properties. 3rd is defaulted in the code
var secondTown = Town(population: 1_000, stopLights: 5)
secondTown.printDescription()

How can I resolve this? Why isn’t the same happening in the book?

From XCode’s tool tips suggestion, if I put “var town = Town?()” most other compile errors disappear, but a compile error remains on this line (only), stating “Cannot invoke initializer for type ‘Town?’ with no arguments”

2

The problem is that in Monster.swift you typed

var town = Town?

instead of

var town: Town?

The first one actually creates a Town, which means you need to provide a valid initializer call for Town, and there are only two of those - one that takes two arguments, and one that takes three.

The second one doesn’t create a Town object, it just creates an uninitialized variable that will be set when the Monster init function is called. Since you aren’t actually creating a Town object when the town variable is defined in this fashion, you don’t need to make an initializer call.

3

JonAuld - you are a star! That fixed it.