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iOS Swift Closures Functions as First Class Citizens Capturing Variables

Kishan S
Kishan S
15,410 Points
Posted by Kishan S
Kishan S
15,410 Points

Why do we use parentheses here?

func printerFunction () -> (Int) -> () {
   func printInteger(number:Int)  {
        println("Passed: \(number)")
   }
    return printInteger
}

/////////////////////////////////////////////////////////////////////////////////////////
//   Why do we have to use parentheses here to assign the function to the constant???? //
/////////////////////////////////////////////////////////////////////////////////////////

let printAndIntegerFunc = printerFunction()

And Not Here ??

func printString(aString: String) {
    println("Print String: \(aString)")
}

/////////////////////
//  Why not here?  //
/////////////////////

let someFunction = printString

3 Answers

nathankrishnan
nathankrishnan
26,276 Points

Kishan Sundar I understand what you mean. Let me first clarify why the parenthesis is used in the printerFunction example.

printerFunction is a function with no parameters, that returns a function that takes in an int as a parameter and returns void. In:

let printAndIntegerFunc = printerFunction()

We are assigning the constant to what printerFunction returns: a function that takes in an int as a parameter and returns void. In other words, we are assigning the execution of the printerFunction to a constant. The execution of the printerFunction returns the inner function: printInteger. That is why this is possible:

printAndReturnIntegerFunc(2)

We are able to pass in the integer value of 2 into the printInteger function, which is the inner function that is invoked when printerFunction is executed.

In the other example you posted from the video, the parenthesis aren't used when declaring the function to the constant because we are assigning the function itself, not the execution of the function, to the constant.

Christian Dangaard
Christian Dangaard
3,378 Points
Christian Dangaard
Christian Dangaard
3,378 Points

This explanation makes sense, thank you also.

Kishan S
Kishan S
15,410 Points
Kishan S
Kishan S
15,410 Points

Why do we have to use parentheses here to assign the function to the constant?? [first code snippet] and Why don't we use parentheses on the [Second code snippet] ??

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

I'm not seeing how Pasan is using parentheses to assign the function to the constant.