High Order Function : Return types

Support
1

Hey, could there be a difference between these two lines of code ?

  fun demo (name:String) = println("Hi $name")
  fun demo (name:String) = "Hi $name"

I passed in both the demo functions into the HOF (High order function) and one gave result but the other did not.
This is the HOF

fun hof(name : String, myFun : (String) -> Unit)
{
    println("This is my Higher Order Function")
    myFun(name)
}

This is the function call:

hof("Andre", ::demo)
2

:face_with_hand_over_mouth: :face_with_hand_over_mouth: :face_with_hand_over_mouth: :face_with_hand_over_mouth: :face_with_hand_over_mouth: :face_with_hand_over_mouth:

The issue is that println() is explicitly instructed to print out the value from the computation while yet the other demo function without the println simply returns a String value without any action to it

2 Likes
3

Here’s a runnable example:

fun demo1(name: String): Unit = println("Hi $name")
fun demo2(name: String): String = "Hi $name"

fun hof(name: String, myFun: (String) -> Unit) {
    print("This is my higher order function: ")
    myFun(name)
}

fun main() {
    hof("Andre", ::demo1)
    hof("Andre", ::demo2)
}

I made a few changes:

  • Fixed the formatting
  • Added explicit return types to the functions (notice demo1 returns Unit and demo2 returns a String

The reason you get “Hi Andre” printed for demo1 is that you’re calling demo1. On the other hand, the demo2 function only returns a String–it isn’t printing anything to the display. Here’s a runnable example with the higher-order function removed to demonstrate:

//sampleStart
fun demo1(name: String): Unit = println("Hi $name")
fun demo2(name: String): String = "Hi $name"

fun main() {
    val result1: Unit = demo1("name1") // Notice that demo1 doesn't fetch me anything but Unit. It has the side effect of printing.
    println("What demo1 gave me: $result1")

    val result2: String = demo2("name2") // The demo2 function fetches me the String, which I could then choose to print myself.
    println("What demo2 gave me: $result2")
}
//sampleEnd
2 Likes
4

Quite true: Thank you :innocent: