ok, I was asking because there's some properties on the class I'd rather not be public, but maybe I'll have to live with it

You can have the extension function be just a thin "helper wrapper" around an

internal

function on the class.

when I made the functions it calls internal, I get java.lang.NoSuchMethodErrors when running tests

That... should not happen! 😄

yeah, the IDE says it's fine, but then the tests blow up

technically speaking, you may be able to implement the curiously recurring template pattern here, since you need a few classes to implement this behavior

it is

Ah, in that case never mind

🙂

can’t exactly ask consumers to properly implement leaf classes in that case

yeah, but I have it working the way that I want it to now

you can do it without an extension function.

class Foo {
    fun foo(block: Foo.() -> Unit) = this.block()
}

That does not account for subclassing, where you want the correct type to be passed into the lambda.

I just wanted to point out that its possible to do it without an extension method. If subclasses are involved, he could override the method in the subclass