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iOS Swift Closures Functions as First Class Citizens Higher Order Functions

Andreas Skielboe
Andreas Skielboe
846 Points
Posted by Andreas Skielboe
Andreas Skielboe
846 Points

This code works fine in the Playground but Treehouse won't accept my solution..

In the playground I get difference set to the value 2 by passing the function differenceBetweenNumbers and the two integers 5 and 3 to mathOperation.

As far as I can tell this should solve the exercise, but apparently it doesn't.

What am I doing wrong?

/**
 For this code challenge, let’s define a math operation as a function that
 carries out some work on two integers and returns an integer as well. An
 example is the function below, `differenceBetweenNumbers`, which takes two
 integers and calculates the difference between the numbers. After calculating,
 it returns the difference.
 */

func differenceBetweenNumbers(a: Int, b:Int) -> (Int) {
    return a - b
}

// Enter your code below
func mathOperation(mathFunction: ((Int, Int) -> Int), a: Int, b: Int ) -> (Int) {
    return mathFunction(a, b)
}

let difference: Int = mathOperation(differenceBetweenNumbers, a: 5, b: 3)

1 Answer

Andreas Skielboe
Andreas Skielboe
846 Points
Andreas Skielboe
Andreas Skielboe
846 Points

Found the solution in a comment by Michael Reining in this thread: https://teamtreehouse.com/community/closures-makes-no-sense-please-help-me-understand

Turns out I needed to remove the parentheses around the closure and return types such that the function instead reads

func mathOperation(mathFunction: (Int, Int) -> Int, a: Int, b: Int) -> Int {
    return mathFunction(a, b)
}

Furthermore I had to call mathOperation without argument labels:

let difference = mathOperation(differenceBetweenNumbers, 5, 3)

Inspired by the course I also tried using a typealias, but to my disappointment that wasn't accepted by the Challenge Task either.

The Challenge Task code editor definitely could use some updating.