How can I have Hashable element type for an Array that is wrapped value for optional

Question

I am looking the correct syntax of this code:

extension Optional where Wrapped == Array<Element> where Element == Hashable {

}

The elements of Array are Hashable.

Answer 1

You can either constrain every member, or use a typealias. But you can't use properties unless you use the typealias solution.

typealias OptionalHashableArray<Hashable: Swift.Hashable> = [Hashable]?

extension OptionalHashableArray {
  var ?: String { "?" }
}

([] as Optional).?

extension Optional {
  func ?<Hashable: Swift.Hashable>() -> String
  where Wrapped == [Hashable] {
    "?"
  }
}

[AnyHashable]?.none.?()