NEW: Subscribe to Hacking with Swift+ and accelerate your learning! >>

Copying objects

The third difference between classes and structs is how they are copied. When you copy a struct, both the original and the copy are different things – changing one won’t change the other. When you copy a class, both the original and the copy point to the same thing, so changing one does change the other.

For example, here’s a simple Singer class that has a name property with a default value:

class Singer {
    var name = "Taylor Swift"
}

If we create an instance of that class and prints its name, we’ll get “Taylor Swift”:

var singer = Singer()
print(singer.name)

Now let’s create a second variable from the first one and change its name:

var singerCopy = singer
singerCopy.name = "Justin Bieber"

Because of the way classes work, both singer and singerCopy point to the same object in memory, so when we print the singer name again we’ll see “Justin Bieber”:

print(singer.name)

On the other hand, if Singer were a struct then we would get “Taylor Swift” printed a second time:

struct Singer {
    var name = "Taylor Swift"
}
Hacking with Swift is sponsored by Instabug

SPONSORED Are you tired of wasting time debugging your Swift app? Instabug’s SDK is here to help you minimize debugging time by providing you with complete device details, network logs, and reproduction steps with every bug report. All data is attached automatically, and it only takes a line of code to setup. Start your free trial now and get 3 months off exclusively for the Hacking with Swift Community.

Start your free trial!

Sponsor Hacking with Swift and reach the world's largest Swift community!

BUY OUR BOOKS
Buy Pro Swift Buy Swift Design Patterns Buy Testing Swift Buy Hacking with iOS Buy Swift Coding Challenges Buy Swift on Sundays Volume One Buy Server-Side Swift (Vapor Edition) Buy Advanced iOS Volume One Buy Advanced iOS Volume Two Buy Advanced iOS Volume Three Buy Hacking with watchOS Buy Hacking with tvOS Buy Hacking with macOS Buy Dive Into SpriteKit Buy Swift in Sixty Seconds Buy Objective-C for Swift Developers Buy Server-Side Swift (Kitura Edition) Buy Beyond Code

Was this page useful? Let us know!

Average rating: 4.3/5

Link copied to your pasteboard.