Explore ClojureDart-style hash maps

[jeaye]

Hey Juanpe! I hope you're doing well.

At Clojure Conj this year, the ClojureDart folks showed off a data structure change they made to their persistent maps which allowed for 100x speedups to operations like merging.

• Here are some actual numbers: https://gist.github.com/cgrand/6303edaa04951fe3c20d18fa60a7c4d9
• They have a blog post about it here: https://buttondown.com/tensegritics-curiosities/archive/accelerating-maps-with-join-with/
• The implementation is here: https://github.com/Tensegritics/ClojureDart/blob/a10c5f7c6933c8abe3f3360b89c47436bff4ecd9/clj/src/cljd/core.cljd#L4789
• Conj 2025 talk: https://www.youtube.com/watch?v=ZLYnOTCRBbg

I don't have more details right now, but if we can get this into immer, that could be huge.

[arximboldi]

Ohhh thank you! I've sometimes had in mind that it would be so cool to have fast merging for hash maps, but didn't know how to achieve it for the general case. I wonder if this affects other operations (read, iteration) or memory use...

[jeaye]

Dropping a note here that I've updated this ticket to include a link to the Conj 2025 talk, now that it's been uploaded. Happy new year!