What is callback function?

Ans : A callback function is a function that is passed as an argument to another function, to be “called back” at a later time.

Code for Example :

func printValue(index: Int, element: Int) {

    print("index = \(index), Element = \(element)")

}

func each(array: [Int], callback: (Int, Int) -> Void) {

    for i in 0..<array.count {

        callback(i, array[i])

    }

}

each(array: [1, 2, 3, 4, 5],callback: printValue)

Here each function type is ( [Int], (Int, Int) -> Void ) .
Here callback function type is ( (Int, Int) -> Void ) .

Callback function mostly used when we want to pass block of code that should be executed in another function execution complete.