# Objective
Since #18704 is done, we can track the length of unique entity row
collections with only a `u32` and identify an index within that
collection with only a `NonMaxU32`. This leaves an opportunity for
performance improvements.
## Solution
- Use `EntityRow` in sparse sets.
- Change table, entity, and query lengths to be `u32` instead of
`usize`.
- Keep `batching` module `usize` based since that is reused for events,
which may exceed `u32::MAX`.
- Change according `Range<usize>` to `Range<u32>`. This is more
efficient and helps justify safety.
- Change `ArchetypeRow` and `TableRow` to wrap `NonMaxU32` instead of
`u32`.
Justifying `NonMaxU32::new_unchecked` everywhere is predicated on this
safety comment in `Entities::set`: "`location` must be valid for the
entity at `index` or immediately made valid afterwards before handing
control to unknown code." This ensures no entity is in two table rows
for example. That fact is used to argue uniqueness of the entity rows in
each table, archetype, sparse set, query, etc. So if there's no
duplicates, and a maximum total entities of `u32::MAX` none of the
corresponding row ids / indexes can exceed `NonMaxU32`.
## Testing
CI
---------
Co-authored-by: Christian Hughes <9044780+ItsDoot@users.noreply.github.com>
# Objective
This is a followup to #18704 . There's lots more followup work, but this
is the minimum to unblock #18670, etc.
This direction has been given the green light by Alice
[here](https://github.com/bevyengine/bevy/pull/18704#issuecomment-2853368129).
## Solution
I could have split this over multiple PRs, but I figured skipping
straight here would be easiest for everyone and would unblock things the
quickest.
This removes the now no longer needed `identifier` module and makes
`Entity::generation` go from `NonZeroU32` to `struct
EntityGeneration(u32)`.
## Testing
CI
---------
Co-authored-by: Mark Nokalt <marknokalt@live.com>
