If you want to go one step further, a lot of game development uses a generational index, where the index is both a value and a generation, allowing you to know whether the index you currently have stored references an object that has already been destroyed and replaced by another object. Basically every ECS framework I’ve ever seen uses this pattern.
I was originally introduced to the idea by this RustConf 2018 keynote: https://kyren.github.io/2018/09/14/rustconf-talk.html. It’s rather dense though.
I did find this random article that outlines just the concept of generational indices pretty concisely: https://lucassardois.medium.com/generational-indices-guide-8e3c5f7fd594
That same keynote is linked in the last paragraph! :) The slotmap crate is also one option for generational indexes.
