Welcome to the Treehouse Community

Want to collaborate on code errors? Have bugs you need feedback on? Looking for an extra set of eyes on your latest project? Get support with fellow developers, designers, and programmers of all backgrounds and skill levels here with the Treehouse Community!

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today.

Start your free trial

iOS Closures in Swift First Class Functions Higher Order Functions

Remove Vowels from the String

I don't get it why the compiler stills says 'Make sure removeVowels' function accepts String and return a String.

My method signature is correct.

// Enter your code below
extension String {
  func transform(_ function: (String) -> String) -> String {
    return function(self)

  func removeVowels(from value: String) -> String {
    let vowels: [Character] = ["a", "e", "i", "o", "u"]
    var removeVowels: String = ""

    for character in value.characters {
        if vowels.contains(character) {

    return removeVowels

2 Answers

Jeff McDivitt
Jeff McDivitt
23,970 Points

This is how I completed this task; although yours looks like it will do the same thing

extension String{

    func transform(_ argument : (String) -> String) -> String {
        return  argument(self)

func removeVowels(from value: String) -> String {
    var output = ""

    for char in value.characters {
        if !(char == "a" || char == "A" || char == "e" || char == "e"
            || char == "i" || char == "I" || char == "o" || char == "O"
            || char == "u" || char == "U") {
    return output

Jeff McDivitt Thank you so much. I thought the instruction wants me to create a function inside the extension of the String.