bitarena

bitarena is a bitset-accelerated generational arena for stable handles, optimized for fast sweeps over sparse tables (proptest + Miri validated).

• Stable generational handles (Index) (stale after remove)
• Bitset-accelerated iteration (skips 64 empty slots at a time)
• no_std + alloc, optional serde, optional rayon

Quick start

use bitarena::Arena;

let mut arena = Arena::new();

let a = arena.insert("foo");
let b = arena.insert("bar");

assert_eq!(arena.get(a), Some(&"foo"));
assert_eq!(arena[b], "bar");

arena.remove(a);
assert!(arena.get(a).is_none()); // stale index

When it wins

• You keep a long-lived table keyed by stable handles.
• You delete a lot over time (the table gets holey).
• You periodically or frequently sweep the live set (tick/update/expire/GC).

Not a fit

• Your hot loop is packed iteration (ECS archetypes/chunks, dense Vec, DenseSlotMap).
• Your hot loop is a dense sweep over large inline T but only touches a small part of each object (AoS can win).
• You need insertion-order iteration or stable ordering across churn.
• You need more than u32::MAX slots (Index stores the slot as u32).

Performance tips

• Prefer .values().for_each(...) / .sum() when you don’t need keys.
• If T is large, split hot/cold data (or store cold payload out-of-line) so the thing you sweep stays small.

Benchmarks

bitarena is a strict upgrade over thunderdome and slotmap. The only arena that beats it on iteration is dense_slotmap, which pays for its packed array with slower mutations and extra memory. Choose dense_slotmap if your workload is >90% iteration on very sparse data with rare mutations. Choose bitarena for everything else.

Full results + reproduction: BENCHMARKS.md.

Migration

Coming from thunderdome: MIGRATION.md.

Safety

Validated with unit tests, a proptest oracle (tests/oracle_tests.rs), and Miri. Design/invariants: DESIGN.md.

License

MIT (see LICENSE).