[Pitch] Parameter Packs

[filip-sakel]

@hborla

for-in loops are kinda hard to think about under the repetition pattern model. I think what you really want is just a body of code that is repeated for each value in the expanded pattern. Maybe that suggests we should find a different way to express iteration, or maybe we should just let you call the binding the same name as the pack if you're expanding a pack directly.

I don’t necessarily agree with this. The element type of packs could be considered the union of all types making up the pack. Since the types making up the pack are unknown in the generic context, they could be opaque types that expose the constraints placed on the parameter pack’s elements. In pseudo Swift

typealias H = (Bool, Int, String)

H.Element.self // (Bool | Int | String).self

func hello<pack Values>(values: expand Values) {
  (expand Values).Element.self // some Any
}

To be clear, I’m not proposing a union feature, just exploring a conceptual model for the type of pack elements.