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iOS Swift Closures Functions as First Class Citizens Higher Order Functions

Vaclav Mlejnsky
Vaclav Mlejnsky
6,832 Points
Posted by Vaclav Mlejnsky
Vaclav Mlejnsky
6,832 Points

Computing difference between numbers with function as a parameter

I am suppose to do this: Using the differenceBetweenNumbers function as an input to mathOperation, compute the difference between any two integers and assign the result to a constant named difference.

I don't understand why I keep getting this error: Make sure you are computing the difference between two integers using the functions created and assigning the result to a constant named difference

But in playground in Xcode everything works just fine.

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

let difference = mathOperation(differenceBetweenNumbers, 8, 1)

4 Answers

Caleb Kleveter
MOD
Caleb Kleveter
Treehouse Moderator 37,862 Points
Caleb Kleveter
Caleb Kleveter
Treehouse Moderator 37,862 Points

Yes except the numbers, I wasn't sure if there was a small typo I didn't see. You might need to change the function:

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

It looks the same to me, but maybe it's not.

Vaclav Mlejnsky
Vaclav Mlejnsky
6,832 Points
Vaclav Mlejnsky
Vaclav Mlejnsky
6,832 Points

All works now. Apparently brackets are problem :)

Caleb Kleveter
MOD
Caleb Kleveter
Treehouse Moderator 37,862 Points
Caleb Kleveter
Caleb Kleveter
Treehouse Moderator 37,862 Points

Try copying and pasting this code, let me know if it works.

let difference = mathOperation(differenceBetweenNumbers, 2, 1)
Vaclav Mlejnsky
Vaclav Mlejnsky
6,832 Points
Vaclav Mlejnsky
Vaclav Mlejnsky
6,832 Points

It doesn't work. Isn't it same as last line of my code?

Corey Dutson
PLUS
Corey Dutson
Courses Plus Student 3,193 Points
Corey Dutson
Corey Dutson
Courses Plus Student 3,193 Points

Glad I found this, because I couldn't figure out why I was getting my answer rejected. for the record, my function signature (which passed step one) was:

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

This threw an error on the second part, and I had to change it to:

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

Note that I had to remove the () off the first Int return. While I understand why now, it shouldn't have passed the first stage, because that was way more confusing to me as a result.