Ok, I tried to further understand this code. It's really messed up and tangled. Would not consider it a best practice. You should not define classes with lateinit vars to only use them from outside that class. Also, using interfaces like Iterator for no good apparent reason is hard to grasp.

Why do you instanciate your WhatTheBoolFuck class twice? Once directly and then on it, you apply some code. Then again, inside that code. I don't get this. I also do not like that there is no clear responsibility for this class. What is it for, what does it do?

This solution has me stumped. I totally don't get how this works.

I feel like as a kotlin exercise this misses the point of nullability in kotlin. for any type T whe can have T? or nullable T and this is a core feature of kotlin the the language is built to support. so in using optional you are using javas hacky tool that is designed to do what kotlin natively does.

Same, i used Continuation.resumeWithException, and the programme always truns wrong untill i removed it.

dont_use_try_and_catch

Such information should be present in the description.

There is a typo in the empty solution.

Line 11: implemention -> implementation

Yes.

It can consume huge amount of memory, right?

I find your solution of pred to be both amazingly simple and elegant.