swift – 如何在ImplicitlyUnwrappedOptional上调用.map()？

可选< T>有地图方法.

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

当我们要转换Int？到UInt64？,我们可以：

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

代替：

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

这里,ImplicitlyUnwrappedOptional< T>有相同的方法：

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

所以我试过……但失败了:(

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

这是一个问题：我怎么称呼这种方法？

解决方法

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