Map with Optional Unwrapping in Swift

Question

Say I had the below api :

func paths() -> [String?] {
    return ["test", nil, "Two"]
}

And I was using this in a method where I needed [String], hence I had to unwrap it using the simple map function. I'm currently doing :

func cleanPaths() -> [String] {
    return paths.map({$0 as! String})
}

Here, the force-cast will cause an error. So technically I need to unwrap the Strings in the paths array. I'm having some trouble doing this and seem to be getting silly errors. Can someone help me out here?

Answer 1

compactMap() can do this for you in one step:

let paths:[String?] = ["test", nil, "Two"]

let nonOptionals = paths.compactMap{$0}

nonOptionals will now be a String array containing ["test", "Two"].

Previously flatMap() was the proper solution, but has been deprecated for this purpose in Swift 4.1

Answer 2

You should filter first, and map next:

return paths.filter { $0 != .None }.map { $0 as! String }

but using flatMap as suggested by @BradLarson is a just better

Answer 3

Perhaps what you want to is a filter followed by a map:

func cleanPaths() -> [String] {
    return paths()
            .filter {$0 != nil}
            .map {$0 as String!}
}

let x = cleanPaths()
println(x) // ["test", "two"]