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iOS Swift Closures Functions as First Class Citizens Higher Order Functions

Jason Teo
PLUS
Jason Teo
Courses Plus Student 8,398 Points

I can't solve this.

Any help? Thanks!

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

2 Answers

Martin Wildfeuer
PLUS
Martin Wildfeuer
Courses Plus Student 11,071 Points

First of all, the return type of mathOperation is wrong. mathOperation should only return a single Int, and so does differenceBetweenNumbers. Therefore mathOperation should have a return type of -> Int instead of -> (Int,Int) -> (Int).

Moreover, it is not a good idea to name the first parameter of your mathOperation function differenceBetweenNumbers. That is because there already is a function named differenceBetweenNumbers. Within the scope of your mathOperation function, you are "shadowing" the outside function name with the parameter name, thus it is not possible to call the "outside" function anymore.

That might not be a problem with this example, but in general you should not use the same name for variables/constants/parameters and functions. so the correct function should look something like this:

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

Hope this helps! Happy coding :)

Martin Wildfeuer
Martin Wildfeuer
Courses Plus Student 11,071 Points

The call looks good! Make sure your mathOperation return type doesn't have parenthesis, like in my answer. Though this is not wrong, code check here seems to be picky about it.