error: '([T]) -> U' is not convertible to '(T)

Question

First time working with generics in swift, couldn't figure out how to fix it. I understand what the error is about but couldn't find the right syntax to express what I'm trying to do. How can I pass an array to transformation if the parameter inside is a type T and not an array of T? I came up with this solution:

func map<T, U>(array: T, transformation: (T) -> [U]) -> [U] {

    return transformation(array)
}

func squaredElements(array: [Int]) -> [Int]{
    var squaredArr = [Int]()
    for i in 0...array.count-1{
        squaredArr.append(array[i]*array[i])
    }
    return squaredArr
}

var arr = [1,2,3,4,5]


map(array: arr, transformation: squaredElements)

Does exactly what is asked to the quiz, but in other way. But doesn't solve the question as is asked.

generics.swift

func map<T, U>(array: [T], transformation: (T) -> U) -> [U] {

    return transformation(array)
}


//func squaredElements(array: [Int]) -> [Int]{
//    var squaredArr = [Int]()
//    for i in 0...array.count-1{
//        squaredArr.append(array[i]*array[i])
//    }
//    return squaredArr
//}

Answer 1 · 2017-10-25T11:17:22Z

October 25, 2017 11:17am

Pretty close. It looks like you missed that you are supposed to loop over the array argument and call transformation on each of the elements, then return the transformed items.

Hope this helps!

Answer 2 · 2017-10-25T15:24:26Z

October 25, 2017 3:24pm

Thank you, Caleb. This was very helpful! I don't know why I didn't though about looping inside the generic function!

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

Now it's correct! Thank you again!

Welcome to the Treehouse Community

Looking to learn something new?

Everton Carneiro

Everton Carneiro

error: '([T]) -> U' is not convertible to '(T)

2 Answers

Caleb Kleveter

Caleb Kleveter

Everton Carneiro

Everton Carneiro