let x: (Int...) -> Int? = { (a: Int...) in return a.first } typealias Fn = (Array<Int>) -> Optional<Int> print(type(of: x)) // (Array<Int>) -> Optional<Int> print(x as? Fn) // nillet x: (Int...) -> Int? = { (a: Int...) in return a.first } typealias Fn = (Array<Int>) -> Optional<Int> print(type(of: x)) // (Array<Int>) -> Optional<Int> print(x as? Fn) // nil