I have a function that takes the following as a parameter:

validator: ValidationContext.(String?) -> ValidationMessage?

So I think I need to provide a function that takes in a

ValidationContext

and gives out a

ValidationMessage

, but what is up with the

.(String?)

. I don’t understand what the signature of my function should be.

The type of that

validator

variable is "A lambda where

ValidationContext

is the receiver, with one parameter of type

String?

(nullable string), returning a `ValidationMessage?`"

So that means I would make an extension function on ValidationContext like this?

fun ValidationContext.myValidator(myString: String?): ValidationMessage?

?

It doesn't _ have_ to be a lambda, you could also pass a function reference

::myValidator