bimap-rs

bimap-rs is a pure-Rust library for bijective maps — two-way mappings where every left value pairs with exactly one right value and vice versa. Published as the bimap crate, it offers hash-based (BiHashMap) and tree-based (BiBTreeMap) variants, has no required dependencies, and supports optional Serde serialization and no_std usage through feature flags.

What You Get

• BiHashMap for O(1) average bidirectional lookups
• BiBTreeMap for ordered, range-friendly bidirectional maps
• Zero required dependencies with std enabled by default
• Optional Serde and no_std support via feature flags

Common Use Cases

• Maintaining a two-way mapping between IDs and names
• Interning values while keeping a reverse lookup available
• Associating enum variants with codes in both directions

Under The Hood

Architecture

The crate is organized around a shared design in lib.rs with two backends: hash.rs implements BiHashMap over standard HashMaps and btree.rs implements BiBTreeMap over BTreeMaps, both maintaining paired left-to-right and right-to-left indexes. mem.rs manages the shared-ownership storage that keeps the two directions consistent, and serde.rs provides optional (de)serialization.

Tech Stack

Pure Rust (edition 2018) with no required dependencies; serde is the only optional dependency, gated behind a feature flag. std is enabled by default but can be disabled for no_std targets.

Code Quality

The library is carefully engineered to mirror standard-library map ergonomics, with feature-gated serde and no_std paths and documentation hosted on docs.rs. Its clean module separation and focus on a single well-defined abstraction make the code approachable and dependable, backed by tens of millions of downloads.

API Design

The API mirrors HashMap and BTreeMap deliberately: insert pairs, then call get_by_left or get_by_right. Because the naming and semantics follow the standard library, existing Rust developers are productive almost immediately with minimal new concepts to learn.