Posted by smartmic 12/21/2025
- Immer (C++) appears to be roughly equivalent to Immutable.js ( https://immutable-js.com/ ): a set of specialized data structures
- Immer (JS), on the other hand, uses JS Proxies to wrap plain values, traps attempted mutations, and then replays them to return a safely immutable updated final result
As far as I know, Michel Weststrate came up with the name independently (although I can't 100% confirm that).
(source: I didn't create Immer (JS), but I started using it in Redux Toolkit in 2018, am quoted in the docs about how much I love it, spent the last couple months doing performance optimization work that got shipped in Immer 11.x, and just put up some more bugfix PRs today. I'm a secondary maintainer at this point.)
(Of course, they might have more in common, I don't know.)
An example:
DE: Er schwor, ihr auf immer treu zu sein.
EN: He swore to be eternally faithful to her.
2019 (102 points, 56 comments) https://news.ycombinator.com/item?id=20947222
2016 (144 points, 46 comments) https://news.ycombinator.com/item?id=13049843
[1] https://sinusoid.es/immer/memory.html#classimmer_1_1gc__heap
I am currently fighting the JIT to understand why a simple flags check (ANDing two bytes and comparing to 0) makes the code 2.5x slower. This is my first c# project so right now I am just throwing things at the compilrr to see what sticks. If anyone knows where I can get help, that would be much appreciated. Dont look too closely on the benchmarks. I managed to make two of them an absolutely best case for ImmutableList (especially SetItem which should degrage linearly with size but now is O(1))
https://github.com/bjoli/RrbList/tree/main/src/Collections
Another thing I havent figured out is how to setup docfx to just pull my XML comments and generate API documentation.
Besides performance, the API is very well thought.