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

Posted by james gamber
james gamber
7,727 Points

generics in swift 3 challenge task 1 of 1

Generics in Swift 3 Challenge Task 1 of 1

In the editor define a function named map with two generic type parameters, T and U. The function takes two arguments - array of type [T], and transformation of type (T) -> U. The function returns an array of type U.

The goal of the function is to apply the transformation operation on the array passed in as argument to return a new array containing the values transformed. For example given the array [1,2,3,4,5] as first argument, and a square function as the transformation argument, the result should be [1, 4, 9, 16, 25].

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

func square(array: Array<Int>) ->Array<Int> { var sq : Array<Int> = []

for item in array {
    sq.append( item * item )
}

return sq

}

works in payground

but treehouse shows error Bummer! Make sure your second argument has the external name transformation and type (T) -> U

generics.swift 
func map<T, U>(array: [T], transformation: ([T])->[U])->[U] {
    return transformation(array)
}

func square(array: Array<Int>) ->Array<Int> {
    var sq : Array<Int> = []

    for item in array {
        sq.append( item * item )
    }

    return sq
}

2 Answers

David Papandrew
David Papandrew
8,386 Points
David Papandrew
David Papandrew
8,386 Points

James,

I kept my notes for this module because I struggled with it and knew that I might need to refer back to the code challenge answers.

Here's the solution that worked for me:

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

    for item in array {
        let newValue = transformation(item)
        transformedArray.append(newValue)
    }

    return transformedArray
}

func squared(_ number: Int) -> Int {
    return number * number
}
james gamber
james gamber
7,727 Points

Thanks that works.

I was trying to pass the array to the function, rather than operate on one element of the array with each func call to squared.

Adam Teale
Adam Teale
10,989 Points
Adam Teale
Adam Teale
10,989 Points

yes the question could be a little clearer