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What’s the difference between a struct and a tuple?

Paul Hudson    @twostraws   

Updated for Xcode 12.0

Swift’s tuples let us store several different named values inside a single variable, and a struct does much the same – so what’s the difference, and when should you choose one over the other?

When you’re just learning, the difference is simple: a tuple is effectively just a struct without a name, like an anonymous struct. This means you can define it as (name: String, age: Int, city: String) and it will do the same thing as the following struct:

struct User {
    var name: String
    var age: Int
    var city: String
}

However, tuples have a problem: while they are great for one-off use, particularly when you want to return several pieces of data from a single function, they can be annoying to use again and again.

Think about it: if you have several functions that work with user information, would you rather write this:

func authenticate(_ user: User) { ... }
func showProfile(for user: User) { ... }
func signOut(_ user: User) { ... }

Or this:

func authenticate(_ user: (name: String, age: Int, city: String)) { ... }
func showProfile(for user: (name: String, age: Int, city: String)) { ... }
func signOut(_ user: (name: String, age: Int, city: String)) { ... }

Think about how hard it would be to add a new property to your User struct (very easy indeed), compared to how hard it would be to add another value to your tuple everywhere it was used? (Very hard, and error-prone!)

So, use tuples when you want to return two or more arbitrary pieces of values from a function, but prefer structs when you have some fixed data you want to send or receive multiple times.

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