Mark unused parameters in Kotlin

Question

I am defining some functions to be used as callbacks and not all of them use all their parameters.

How can I mark unused parameters so that the compiler won't give me warnings about them?

Answer 1

With the @Suppress annotation You can suppress any diagnostics on any declaration or expression.

Examples: Suppress warning on parameter:

fun foo(a: Int, @Suppress("UNUSED_PARAMETER") b: Int) = a 

Suppress all UNUSED_PARAMETER warnings inside declaration

@Suppress("UNUSED_PARAMETER") fun foo(a: Int,  b: Int) {   fun bar(c: Int) {} }  @Suppress("UNUSED_PARAMETER") class Baz {     fun foo(a: Int,  b: Int) {         fun bar(c: Int) {}     } } 

Additionally IDEA's intentions(Alt+Enter) can help you to suppress any diagnostics:

Answer 2

If your parameter is in a lambda, you can use an underscore to omit it. This removes the unused parameter warnings. It will also prevent IllegalArgumentException in the case that the parameter was null and was marked non-null.

See https://kotlinlang.org/docs/reference/lambdas.html#underscore-for-unused-variables-since-11