If I pass a method reference from Java to a Kotlin...

# announcements

[tenprint]

If I pass a method reference from Java to a Kotlin function, what do I put for parameter type?
E.g.

MyJavaClass {
  MyKotlinClass myKotlinClass;

  void myMethod() { ... }

  ... myKotlinClass.foo(this::myMethod);
}

What should be the parameter in fun foo( ? ) ?

[diesieben07]

You can just use a normal Kotlin function, as they are a "functional interface" from Java's point of view. If you however need void as a return type, you need to use something like Runnable or Consumer from java.util.function or make your own functional interface.

[Evan R.]

My guess is it would be either () -> Unit or () -> Nothing

[Evan R.]

I can verify later if you like

[diesieben07]

() -> Unit requires you to do return kotlin.Unit.getINSTANCE() (or something) from Java

[streetsofboston]

It won’t be () -> Nothing. This type is a function/lambda that never returns normally (either it loops forever or it always throws an exception).

[tenprint]

When I tried () -> Unit I had to do weird stuff in my Java function like return Unit.INSTANCE

[tenprint]

For now I created a single function interface in the kotlin class and am using that as the parameter type. This compiles. But open to any improvements