Iterating enums containing nested associated enums

Swift’s CaseIterable protocol automatically generates an array with all cases for a given enum that doesn’t contain any cases with associated values.

So, the below won’t work:

enum Category: CaseIterable {
    case all
    case none
    case level(Level)
}

With the error:

Type ‘Category’ does not conform to protocol ‘CaseIterable’

It still won’t work if the associated values are restricted to CaseIterable enums.

enum Level: CaseIterable {
    case one, two, three
}

Howerver, you can still somewhat cleanly achieve an iteration of all the values by assembling the parent allCases static property manually.

enum Level: CaseIterable {
    case one, two, three
}

enum Category: CaseIterable {
    static var allCases: [Category] {
        [.all, .none] + Level.allCases.map { Category.level($0) }
    }

    case all
    case none
    case level(Level)
}

Category.allCases.forEach { print($0) }
/* Output:
all
none
level(__lldb_expr_16.Level.one)
level(__lldb_expr_16.Level.two)
level(__lldb_expr_16.Level.three)
*/

In this case it won’t automatically account for new cases in the parent, though.