The function returns the result before processing the completionHandler of another function, how to fix it?

Question

I ran into such a problem, and I can't figure out what are the ways to solve this problem.

First, let's say I have the following function

func summ(x: Int, y: Int, completionHandler: @escaping (Int) -> ()) {
    let result: Int = x + y
    completionHandler(result)
}

Next, in another function, we want to somehow process the result of the above function and return the processed value.

func summ(x: Int, y: Int, completionHandler: @escaping (Int) -> ()) {
    let result: Int = x + y
    completionHandler(result)
}


func getResult(x: Int, y: Int) -> (String) {
    let resultString: String = ""

    summ(x, y) { result in
        resultString = "Result: \(String(result))" 
    }

    return resultString
}

But when I call let resultString = getResult(x = 15, y = 10) I just get an empty string. When trying to find an error, I realized that in this method it creates let resultString: String = "" and then immediately returns this variable return resultString, and only After that completionHandler starts working

MARK - The solution below does not suit me, because the methods that I indicated above are just an example, in a real project, I need to return the correct value from the function in order to use it further.

let resultString: String = ""

func summ(x: Int, y: Int, completionHandler: @escaping (Int) -> ()) {
    let result: Int = x + y
    completionHandler(result)
}


func getResult(x: Int, y: Int) {
    summ(x, y) { result in
        resultString = "Result: \(String(result))"
        self.resultString = resultString
    }
}

score 0 · Accepted Answer · answered Nov 28 '21 at 00:55

So it is returning "" because the sum func takes time to complete. In the getResult func since the sum func takes time to finished u will always return "" in the getResult func. So instead the getResult should look something like this.

func getResult(x: Int, y: Int, completion: (String) -> Void) {
  let resultString: String = ""

  summ(x, y) { result in
    resultString = "Result: \(String(result))" 
    completion(resultString)
  }

}

The function returns the result before processing the completionHandler of another function, how to fix it?

1 Answers1