When should you use switch statements rather than if?

Paul Hudson    @twostraws    October 6th 2021

Updated for Xcode 15

Swift developers can use both switch and if to check multiple values in their code, and often there isn’t a hard reason why you should choose one rather than the other. That being said, there are three reasons why you might want to consider using switch rather than if:

1. Swift requires that its switch statements are exhaustive, which means you must either have a case block for every possible value to check (e.g. all cases of an enum) or you must have a default case. This isn’t true for if and else if, so you might accidentally miss a case.
2. When you use switch to check a value for multiple possible results, that value will only be read once, whereas if you use if it will be read multiple times. This becomes more important when you start using function calls, because some of these can be slow.
3. Swift’s switch cases allow for advanced pattern matching that is unwieldy with if.

There’s one more situation, but it’s a little fuzzier: broadly speaking, if you want to check the same value for three or more possible states, you’ll find folks prefer to use switch rather than if for legibility purposes if nothing else – it becomes clearer that we’re checking the same value repeatedly, rather than writing different conditions.

PS: I’ve covered the fallthrough keyword because it’s important to folks coming from other programming languages, but it’s fairly rare to see it used in Swift – don’t worry if you’re struggling to think up scenarios when it might be useful, because honestly most of the time it isn’t!

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