How to check lambda emptiness in Kotlin

Question

How to check if there is a lambda in Kotlin? For example, I have a signature, for example

onError:(Throwable) -> Unit = {} 

How can I distinguish this default value comes to the body or the value applied to this function?

Answer 1

You cannot check if the lambda body is empty (therefore it does not contain the source code), but you can check if the lambda is your default value by creating a constant for this value and using this default value. Than you can also check if the value is the default value:

 fun main(args: Array<String>) { foo() foo { } foo { println("Bar") } } private val EMPTY: (Throwable) -> Unit = {} fun foo(onError: (Throwable) -> Unit = EMPTY) { if (onError === EMPTY) { // the default value is used } else { // a lambda was defined - no default value used } }