Explain what is going on in the code block?

Question

Kotlin

What is the use of :: in the second line? I know that in Java it is a reference to a static method in a lambda. Shorter syntax. What is this used for in Kotlin?

Answer 1

This notation is similar to
takeIf { it.isNotEmpty() }
Colon in Kotlin means getting a reference to a function/property. The List::isEmpty line in particular returns a reference of type (List<Int>) -> Boolean. The takeIf argument is a function type (T) -> Boolean, in this case List<Int> -> Boolean.