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

Paul Hudson    @twostraws   

Updated for Xcode 13.2

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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