> They will be slightly slower due to often using indexes instead of raw pointer, which requires a bound check and an addition to get the pointer, and sometimes

> They will be slightly slower due to often using indexes instead of raw pointer, which requires a bound check and an addition to get the pointer, and sometimes a reallocation, but they won't be that slow. This is not a fundamental requirement, though. Assuming arena-like behavior, the index will be constructed/provided by the arena itself, so the bounds check can be safely ellided by-construction. Reallocation cost of the entire arena could be expensive, but if that is a cost you'd want to ammortize down to a new allocation, the arena could be implemented as an extensible list of non-growable arenas: every time an arena is full, you append another. This can be an issue if you don't keep track of deletions/tombstones or can't afford a compaction step to keep memory usage down, but in practice having all of these requirements at once is not as common.