One bug I saw came from picking an integer id as “one more than the largest id of the current elements we have.” This worked fine until they added support for d

One bug I saw came from picking an integer id as “one more than the largest id of the current elements we have.” This worked fine until they added support for deleting elements, which also worked fine most of the time. A common disadvantage of integer keys is that programs will have bugs and use a foo_id as a bar_id. If most ids are small integers then it is likely that a valid foo_id may be a valid bar_id, whereas uuids probably won’t collide. This can be somewhat mitigated with a sufficiently strong type system. Even in a dynamic language like lisp you can represent your ids as e.g. (foo . <id>), and only need to get the tags right on the boundary. An advantage of integer ids is density: if your ids are likely close together, there are probably some better or more compressed data structures you can use.