I'm having trouble with the calling a function with a function argument. I have reviewed the documentation for swift.

Question

This is for the test at the end of swift closures. I have tried everything I know but it doesn't work.
``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(mathFunc: (a: Int, b: Int) -> Int ) {
  return mathFunc(a, b)
}
```

Christopher Augg · Accepted Answer

Hello Randal,
This can be a tough one to understand for sure. I will go through it step by step. The first part of the instructions says, "Write a function called mathOperation that takes a math operation (as defined in the editor) as the first input, two integers on which we carry out the math operation, and a return type of Int."
We are given the following code to start with:
```Swift
func differenceBetweenTwoNumbers(a : Int, b : Int) -> Int {
    return a - b
}
```
This function takes two integers and returns the difference of a - b as an Int.
So we need to write a function named mathOperation that takes 3 parameters. 
The first parameter for mathOperation is a function that takes the same parameters as the math operation function named differenceBetweenTwoNumbers (Two Ints) as well as the same return type (an Int). The name of this parameter function is arbitrary so we can just call it calculate.
```Swift
func mathOperation(calculate : (Int, Int) -> Int, secondParam, thirdParam) -> returnType {}
```
The second and third parameters are integers labeled a and b respectively.
```Swift
func mathOperation(calculate : (Int, Int) -> Int, a: Int, b: Int) -> returnType {}
```
And this method should also return an Int. It does so by returning a function call on the function passed into mathOperation along with the required integers.
```Swift
func mathOperation( calculate : (Int, Int) -> Int, a: Int, b: Int ) -> Int {
    return calculate(a,b)
}
```
+ And now we can call the math operation method, pass in the difference function along with two integers and it will return the difference to us as a constant.
```Swift
let difference = mathOperation(differenceBetweenTwoNumbers, 50, 10)
```
```HigherOrderFunctions.swift
func differenceBetweenTwoNumbers(a : Int, b : Int) -> Int {
    return a - b
}
func mathOperation( calculate : (Int, Int) -> Int, a: Int, b: Int ) -> Int {
    return calculate(a,b)
}
let difference = mathOperation(differenceBetweenTwoNumbers, 50, 10)
```
I hope this helps.
Regards,
Chris

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randal beck

randal beck

I'm having trouble with the calling a function with a function argument. I have reviewed the documentation for swift.

1 Answer

Christopher Augg

Christopher Augg

randal beck

randal beck