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iOS Swift Closures Functions as First Class Citizens Higher Order Functions

Tony Luo
Tony Luo
14,224 Points
Posted by Tony Luo
Tony Luo
14,224 Points

Higher Order Functions - Why isn't my code passing in the online editor but works as expected in the playground?

This works fine in the playground, not sure why it isn't working on Treehouse

higherOrderFunctions.swift 
/** 
  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(mathStuff: (Int, Int) -> Int, a: Int, b: Int) -> (Int) {
  return mathStuff(a, b);
}

let difference = mathOperation(differenceBetweenNumbers, 5, 5)

3 Answers

Holger Liesegang
Holger Liesegang
50,595 Points
Holger Liesegang
Holger Liesegang
50,595 Points

Hi Tony,

you might want to use func mathOperation(mathStuff: (Int, Int) -> Int, a: Int, b: Int) -> (Int) { return mathStuff(a, b); without the open and close brackets around Int like so:

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

let difference = mathOperation(differenceBetweenNumbers, 5, 5)
Tony Luo
Tony Luo
14,224 Points
Tony Luo
Tony Luo
14,224 Points

Hmm that ended up working. What is strange though is that the differenceBetweenNumbers function was able to pass the test no problem, even though the return type was wrapped in parens.

Thanks Holger!

Chris Jones
STAFF
Chris Jones
Treehouse Guest Teacher
Chris Jones
Chris Jones
Treehouse Guest Teacher

Tony, I'm in the same boat as you. I do want to note that I am using Xcode 7 Beta 3 locally.

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

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

mathOperation(differenceBetweenNumbers, a: 4, b: 2)

This works just fine in a playground but will not pass in the code challenge. Maybe Pasan Premaratne has an answer?

Tony Luo
Tony Luo
14,224 Points
Tony Luo
Tony Luo
14,224 Points

Hi Chris, I ended up making modifications that Holger suggested and I was able to pass the checks.

Try removing the labels a and b from your last line of code. I am using xcode 6.4 and it is showing an error in my playground.

Jonas Simkus
Jonas Simkus
10,814 Points
Jonas Simkus
Jonas Simkus
10,814 Points

It worked for me when I removed "a" and "b" from mathOperation(differenceBetweenNumbers, a: 4, b: 2).

But then this line of code is incorrect, but only with incorrect line of code you can pass "THE Challenge".

mathOperation(differenceBetweenNumbers, 4, 2)

Unless, you do this for "mathOperation" function

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