Welcome to the Treehouse Community

The Treehouse Community is a meeting place for developers, designers, and programmers of all backgrounds and skill levels to get support. Collaborate here on code errors or bugs that you need feedback on, or asking for an extra set of eyes on your latest project. Join thousands of Treehouse students and alumni in the community today. (Note: Only Treehouse students can comment or ask questions, but non-students are welcome to browse our conversations.)

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and a supportive community. Start your free trial today.

iOS Generics in Swift Generic Functions, Parameters and Constraints CSS Background Blend Modes Challenge

Sam Belcher
Sam Belcher
3,719 Points

Generic Functions With Multiple Type Paremeters

I'm confused with why "append" isn't working and I am also not sure how to return a value of type "[U]"

func map<T, U>(array: [T], transformation: (T) -> U) -> [U] {
    var mapArray: [U] = []
    for number in array {
       return mapArray.append(transformation(number))

1 Answer

Magnus Hållberg
Magnus Hållberg
17,232 Points

Its not the append that is the problem, its where you are trying to return. You need to return the array after the new values are appended, now you are trying to appen each new value from the loop. Try to return the array after the loop.