Inspired by indexmap-rs/equivalent, providing Equivalent and Comparable, which are Rust traits for key comparison in maps, but flips K and Q.

• Why this crate?

  Rust's compiler cannot infur types in some cases(by using indexmap-rs/equivalent) and users have to add turbofish, the details can be found in https://github.com/indexmap-rs/equivalent/issues/5 or https://github.com/crossbeam-rs/crossbeam/pull/1132.

These may be used in the implementation of maps where the lookup type Q may be different than the stored key type K.

• K: Equivalent<Q>, Q: ?Sized checks for equality, similar to the HashMap<K, V> constraint K: Borrow<Q>, Q: Eq.
• K: Comparable<Q>, Q: ?Sized checks the ordering, similar to the BTreeMap<K, V> constraint K: Borrow<Q>, Q: Ord.

These traits are not used by the maps in the standard library, but they may add more flexibility in third-party map implementations, especially in situations where a strict K: Borrow<Q> relationship is not available.

Installation

[dependencies]
equivalent-flipped = "0.1"

Pedigree

This code is inspired and modified based on indexmap-rs/equivalent, and reference to @cuviper attempts on https://github.com/indexmap-rs/indexmap/issues/253#issuecomment-1459160166

License

equivalent-flipped is under the terms of both the MIT license and the Apache License (Version 2.0).

See LICENSE-APACHE, LICENSE-MIT for details.

Copyright (c) 2024 Al Liu.