What does the type ((Int) -> Int) mean in Swift?

Question

I was going through Apple\'s introduction to Swift and came across such example:

func makeIncrementer() -> ((Int) -> Int) {

    func addOne(number: In         


        

Answer 1

It indicates that the function returns a function and that returned function takes an Int as an input parameter and returns an Int as well.

Defining functions within functions is perfectly legal in Swift.