In the video, the dudes makes the variables mutable, but to avoid concurrency problems, he ends up cloning it in every thread.
One can wonder why not just using immutable functional concepts instead. :)
Discussion
Haha didn't mean to put you down the wrong path. Took a peek at my playlist from months ago.... back then everything was helpful even if a little wrong it was exposure to syntax for me. But yea, stay safe, stay immutable 😄