Sets are collections of values just like arrays, except they have two differences:
You can create sets directly from arrays, like this:
let colors = Set(["red", "green", "blue"])
When you look at the value of
colors inside the playground output you’ll see it doesn’t match the order we used to create it. It’s not really a random order, it’s just unordered – Swift makes no guarantees about its order. Because they are unordered, you can’t read values from a set using numerical positions like you can with arrays.
If you try to insert a duplicate item into a set, the duplicates get ignored. For example:
let colors2 = Set(["red", "green", "blue", "red", "blue"])
colors2 set will still only include red, green, and blue once.
Need to know Objective-C fast?
I wrote a book dedicated to teaching Objective-C to developers who already know Swift – it's the fastest way to get up to speed!