EducaSwift

Class

We've only seen struct types of objects so far, but we can use class as well. If we declare a class we can see the first difference: if there is any not assigned variable, then you need to implement an init for it.

class Person {
    var fullName: String
    
    init(fullName: String) {
        self.fullName = fullName
    }
}

But there are more differences that are important to understand, actually, one of the most common questions on iOS developer interviews is "What's the difference between a class and an struct?.

Class vs Struct

The main difference between class and struct is that the first one is a reference type, and the second one is a value type. But, what does this mean? Let's explore this in an example.

First I'll define a class, I'll create two instances, myPerson and myPersonCopy, then when I change the name of the myPersonCopy it will also change myPerson name, because it keeps a reference, due to they are in the same memory address.

class Person {
    var fullName: String
    
    init(fullName: String) {
        self.fullName = fullName
    }
}

var myPerson = Person(fullName: "Pablo")
var myPersonCopy = myPerson

myPersonCopy.fullName = "Andrea"

print(myPerson.fullName)

However, this is not the case if we use a struct.

struct Person {
    var fullName: String
}

var myPerson = Person(fullName: "Pablo")
var myPersonCopy = myPerson

myPersonCopy.fullName = "Andrea"

print(myPerson.fullName)

When we use a struct, myPersonCopy is actually a copy of myPerson, any change on myPersonCopy won't affect to myPerson. They are in different memory addresses.

When should I used then?

In general we'll use struct to declare our objects, specially for models and views. However, since struct cannot mutate theirselfs (not in a safe way), for these cases we will use class.

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