For example:

enum Filter {
  case filter1
  case filter2
  ...
}

let allCases: [Filter?] = [.filter1, .filter2, ..., nil]

The problem is there are could be a lot of cases and CaseIterable returns [Filter] (nonoptional values only). How to solve this issue properly?

>Solution :

If you make your enum conform to CaseIterable you could easily create an array of optional values

enum Filter: CaseIterable {
  case filter1
  case filter2
}

let allCases: [Filter?] = Filter.allCases + [nil]

or add it as a computed property

extension Filter {
    var optionalValues: [Filter?] {
        Self.allCases + [nil]
    }
}