Swift Closure why does calling function return error?

Question

just learning about closures and nesting functions. Given the nested function below:

func printerFunction() -> (Int) -> () {
    var runningTotal = 0
    func printInteger(number: Int) {
        runningTotal += 10
        println("The running total is: \(runningTotal)")
    }
    return printInteger
}

Why does calling the func itself have an error, but when I assign the func to a constant have no error? Where is printAndReturnIntegerFunc(2) passing the 2 Int as a parameter to have a return value?

printerFunction(2) // error
let printAndReturnIntegerFunc = printerFunction() 
printAndReturnIntegerFunc(2) // no error. where is this 2 going??

Answer 1

First of all you are getting error here printerFunction(2) because printerFunction can not take any argument and If you want to give an argument then you can do it like:

func printerFunction(abc: Int) -> (Int) -> (){


}

And this will work fine:

printerFunction(2)

After that you are giving reference of that function to another variable like this:

let printAndReturnIntegerFunc = printerFunction() 

which means the type of printAndReturnIntegerFunc is like this:

that means It accept one Int and it will return void so this will work:

printAndReturnIntegerFunc(2)

Answer 2

(1) The function signature of printerFunction is () -> (Int) -> () which means it takes no parameter and returns another function, thats why when you try to call printerFunction(2) with a parameter gives you an Error.
(2) And the signature of the returned function is (Int) -> () which means it takes one parameter of Int and returns Void. So printAndReturnIntegerFunc(2) works