ambiguouscovariant.swift

[Int(1)] is [String] // false
[Int]() is [String] // true
[Int?.none] is [String] //false
[Int?.some(1)] is [String?] // false
[Int?.none] is [String?] // true

[Int(1)] as? [String] // nil
[Int]() as? [String] // []
[Int?.none] as? [String] // nil
[Int?.some(1)] as? [String?] // nil
[Int?.none] as? [String?] // [nil]

let a1 = [Int?.none] as? [Int??]
let a2 = [Int?.none] as [Int??]

switch a1!.first! {
case .none:
    print("come here")
case .some(.none):
    fatalError()
case .some(.some):
    fatalError()
}

switch a2.first! {
case .none:
    fatalError()
case .some(.none):
    print("come here")
case .some(.some):
    fatalError()
}