Tuples with default values idea

Evolution Pitches
1

Got this rough idea of allowing default values in tuples:

typealias T = (Int, Double, String = "")
T(1, 2)             // ✅

func foo(_ v: (Int, Double, String = "")) {}
foo((1, 2))         // ✅

typealias R = (x: Int, y: Double = 2, z: String)
R(x: 1, z: "3")     // ✅

func foo(_ v: (x: Int, y: Double = 2, z: String)) {}
foo((x: 1, z: "3")) // ✅

Worth having this in Swift?

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2

My general thinking around tuples is that when you start doing things like assigning names to them (typealias T = ...) or trying to reach for other behavior to add to them, it's really just time to make it a dedicated struct.

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3

The tuple may be provided by the API and the API author may not need to give it a typealias name or an added functionality. OTOH the user of this API may have such a need, and he or she can't change the tuple to a struct.

4

Fun fact: default arguments used to be part of the tuple's type in the Swift 2 days, when functions would semantically always have a single input value, which could be a tuple. This caused no end of trouble!

However, you can probably do what you want with a macro. Have the expansion emit a function that takes the parameters with defaults and forms a tuple value from those arguments. Or even just write that function by hand.

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