frozenset

frozenset() for Rust

What is frozenset?

frozenset is a library crate for Rust that provides the FrozenMap and FrozenSet types, which are wrappers around HashMap and HashSet. These types implement Hash, and are therefore suitable for use as keys in other HashMaps and HashSets.

Why would I want to use frozenset?

frozenset is useful when you want to use a HashMap or HashSet as a key in another HashMap or HashSet. This is not possible with the standard library types, because they do not implement Hash.

Frozen sets have already been shown to be useful in other languages - in Python, frozenset() is considered so useful that it is a built-in, globally-accessible type.

How do I use frozenset?

Easy! Just add frozenset to your Cargo.toml:

[dependencies]
frozenset = "0.1"

Ensure that frozenset::Freeze is in scope, and call .freeze() on your HashMap or HashSet:

use std::collections::HashMap;

use frozenset::Freeze;

let map: HashMap<i32, i32> = [(1, 2), (3, 4)].into();
let frozen_map = map.freeze();
// Now you can use `frozen_map` as a key in another `HashMap` or `HashSet`!
let mut map_of_maps = HashMap::new();
map_of_maps.insert(frozen_map, 7i32);

Why is frozenset only 0.2.2?

frozenset is currently in a pre-release state. It is not yet considered stable, and I may add/change any functionality I do not yet consider complete.