Why is this an issue?

Kotlin uses the data type Unit to represent the absence of a value in a function or an expression. It corresponds to the type void in Java or unknown in JavaScript. While Void is available in Kotlin, it is a Java platform type and not equivalent to Java void but java.lang.Void.

Use Unit instead of Void because it represents the absence of a value in Kotlin.

What is the potential impact?

Wrong logic

Void is not equivalent to Java void but java.lang.Void.

Unnecessary platform dependency

Void is a platform type available only in the Java Runtime Environment.

How to fix it

Replace Void with Unit.

Code examples

Noncompliant code example

typealias NoValueFunction = () -> Void // Noncompliant, `Void` used

interface NoValueFunctions {
    fun voidFunction1(): Void // Noncompliant, `Void` used
    fun voidFunction2(): Void // Noncompliant, `Void` used
}

Compliant solution

typealias NoValueFunction = () -> Unit // Compliant, `Unit` used

interface NoValueFunctions {
    fun unitFunction1(): Unit // Compliant, `Unit` used
    fun unitFunction2() // Compliant, `Unit` used implicitly
}

Resources

Documentation

• Kotlin Docs, Unit-returning functions