When should you use an array, a set, or a tuple in Swift?

Paul Hudson    @twostraws    August 22nd 2021

Updated for Xcode 14.0 beta 1

Because arrays, sets, and tuples work in slightly different ways, it’s important to make sure you choose the right one so your data is stored correctly and efficiently.

Remember: arrays keep the order and can have duplicates, sets are unordered and can’t have duplicates, and tuples have a fixed number of values of fixed types inside them.

So:

• If you want to store a list of all words in a dictionary for a game, that has no duplicates and the order doesn’t matter so you would go for a set.
• If you want to store all the articles read by a user, you would use a set if the order didn’t matter (if all you cared about was whether they had read it or not), or use an array if the order did matter.
• If you want to store a list of high scores for a video game, that has an order that matters and might contain duplicates (if two players get the same score), so you’d use an array.
• If you want to store items for a todo list, that works best when the order is predictable so you should use an array.
• If you want to hold precisely two strings, or precisely two strings and an integer, or precisely three Booleans, or similar, you should use a tuple.

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