Tuples in Swift, Advanced Usage and Best Practices



There's no Tuple type available in Swift. If you wonder why that is, think about it: every tuple is a totally different type, depending on the types within it. So instead of defining a generic tuple requirement, you define the specific but generic incarnation of the tuple you intend to use:

func wantsTuple<T1, T2>(_ tuple: (T1, T2)) -> T1 {
    return tuple.0

wantsTuple(("a", "b")) // "a"
wantsTuple((1, 2)) // 1

You can also use tuples in typealiases, thus allowing subclasses to fill out your types with details. This looks fairly useless and complicated, but I've already had a use case where I need to do exactly this.

class BaseClass<A,B> {
    typealias Element = (A, B)
    func add(_ elm: Element) {

class IntegerClass<B> : BaseClass<Int, B> {

let example = IntegerClass<String>()
example.add((5, ""))
// Prints (5, "")

You can also define a typealias with generic parameters like in this example where we introduce a custom Either type:

typealias MyEither<A, B> = (left: A, right: B)