It's pretty easy to try out: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=6bfcdc0a94fcbb45cc430ab139a962cb https://play.rust-lang.org

It's pretty easy to try out: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=6bfcdc0a94fcbb45cc430ab139a962cb https://play.rust-lang.org/?version=stable&mode=debug&editio... Now, if you have an enum such as `serde_json::Value` which is kind of recursive with its `Map` variant, and you have a ton of dynamic JSON parsing in your code, these numbers really add up. And serde_json uses `BTreeMap` (I was wrong in my previous message) by default which is even smaller than `HashMap`. The learning here is to avoid dynamic JSON parsing if you can. And if needing it, but not caring the insertion order, avoid the `preserve_order` feature flag. The other learning here is that there is no map structure that fits to all purposes. They all have their pros and cons and you should choose the right one for the problem.