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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"
}
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