CODEWITHSUNDEEP
swift
Chris Karani
Chris Karani

Reputation: 40

Mutating functions and Properties

I have a struct Town

with a population of 11

 struct Town {
    var population: Int = 11 {
        didSet(oldPopulation){
            print("The population has changed to \(population) from \(oldPopulation)")
        }
    }
}

and I have a mutating function

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

I created a zombie class that calls a function that decreases population by 10

final override func terrorizeTown() {
    guard var town = town else {
        return
    }
    town.population <= 0 ? print("no people to terrorize") : town.changePopulation(amount: -10)

    super.terrorizeTown()
}

when I run this i the main.swift file

var myTown = Town()
var fredTheZombie = Zombie()
fredTheZombie.name = "Fred"
fredTheZombie.town = myTown

//myTown.changePopulation(amount: 0)
print(myTown.population)

fredTheZombie.terrorizeTown()
print(myTown.population)

What I don't understand is the results..

11
The population has changed to 1 from 11
Fred is terrorizing a town!
11

Why is it that when I print (myTown.population) again do i receive a value of 11, when I have called a mutating function on the property. I don't understand.. should the result not be 1, why do i get 11?

Upvotes: 0

Views: 461

Answers (1)

matt
matt

Reputation: 534950

It is because the line guard var town = town makes a copy of your Town object. Hence, it is the copy that is mutated.

Upvotes: 1

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