How can I call .map() on ImplicitlyUnwrappedOptional?

Question

Optional<T> has map method.

/// If `self == nil`, returns `nil`.  Otherwise, returns `f(self!)`.
func map<U>(f: (T) -> U) -> U?

When we want to convert Int? to UInt64?, we can:

let iVal:Int? = 42
let i64Val = iVal.map { UInt64($0) }

Instead of:

var i64Val:UInt64?
if let iVal = iVal {
    i64Val = UInt64(iVal)
}

Here, ImplicitlyUnwrappedOptional<T> has same method:

/// If `self == nil`, returns `nil`.  Otherwise, returns `f(self!)`.
func map<U>(f: (T) -> U) -> U!

So I tried... and failed :(

let iVal:Int! = 42
let i64Val = iVal.map { UInt64($0) } 
//           ^    ~~~  [!] error: 'Int' does not have a member named 'map'

Here is the question: How can I call this method?

Answer 1

let i64Val = (iVal  as ImplicitlyUnwrappedOptional).map {UInt64($0)}

Answer 2

let iVal:Int! = 42
let i64Val = (iVal as Int?).map { UInt64($0) }

Answer 3

I think the error message clears it up: error: 'Int' does not have a member named 'map'. It says Int not Int! so the value is already unwrapped when trying to call a method.

So just use:

let iVal:Int! = 42
let i64Val = UInt64(iVal)