moogle is an alternative to BTreeMap with a lot of desirable properties for game-like simulations. These include determinism, symmetry, and uniqueness of associations between keys/values.
Its interface is fairly close to Rust's builtin map interface. I haven't profiled it yet, but based on its implementation, I'd expect it to be within an order of magnitude of BTreeMap in all respects.
Specifically: moogle provides an internal bimap type with four public specializations. Each is equivalent to a different kind of junction table.
The four specializations are below:
OneToOne: maps Optional<T> to Optional<T>OneToSet: maps Optional<T> to BTreeSet<T>SetToOne: maps BTreeSet<T> to Optional<T>SetToSet: maps BTreeSet<T> to BTreeSet<T>The bimap is based on BTreeMap, meaning it preserves Ord of elements and is deterministic. Elements are required to be PartialEq, Ord and Copy. (Some examples of types satisfying these requirements are numeric IDs and UUIDs.)
Each specialization can be viewed in a forwards direction (using the .fwd() accessor) and a backwards direction (using the .bwd() accessor) -- for instance, OneToSet<usize, char> corresponds to a BTreeMap<usize, BTreeSet<char>> and a BTreeMap<char, usize> that are always kept in sync.
(What does "kept in sync" mean? Formally: insert()ing on one automatically insert()s on the other, and each pair (a, b) in one has a corresponding pair (b, a) in the other.)
Set-based specializations provide an Entry-like interface for insertions, as well as a .items() iterator that averts that interface.