CODEWITHSUNDEEP
kotlin
yras8
yras8

Reputation: 459

Function references as objects Kotlin

Suppose I have

fun getRealGrade(x: Double) = x
fun getGradeWithPenalty(x: Double) = x - 1

fun getScoringFunction(isCheater: Boolean): (Double) -> Double {
    if (isCheater) {
        return ::getGradeWithPenalty
    }

    return ::getRealGrade
}

What is the use of (Double) -> Double in getScoringfunction?

If I dont undestand the syntax correct me isCheater val is boolean here, and function returns double but what does this (Double) do?

What I get is:

fun sayHello() {
    println("Hello")
}

In this example sayHello has a type of () -> Unit

Upvotes: 0

Views: 51

Answers (1)

Rubydesic
Rubydesic

Reputation: 3476

The function doesn't return a (Double), it returns a (Double) -> Double, i.e. it returns a function. The function that it returns takes a double and returns a double.

You would use it like this

fun main() {
    val scoreFunction: (Double) -> Double = getScoringFunction(true); // returns the cheater scoring function
    val score = scoreFunction(10) // score = 9, they were graded with penalty
}

In your second example, the return type is Unit. In Kotlin, a function that returns no value is said to return Unit, a singleton object. () -> Unit is a function that takes no parameters and returns no value.

Upvotes: 2

Related Questions