Crate assoc

AssocListExt is a trait extension that allows you to work with Vec<(K, V)> as if it were a map. It provides APIs for querying, adding, and removing key-value pairs, as well as an Entry API. It places no constraints on the keys other than PartialEq.

use assoc::AssocListExt;

#[derive(PartialEq, Debug)]
enum MyKey {
    A,
    B,
    C,
}

let mut map = vec![(MyKey::A, 1), (MyKey::B, 2)];
map.entry(MyKey::C).or_insert(3);
assert_eq!(map.get(&MyKey::C), Some(&3));
map.entry(MyKey::A).and_modify(|e| *e += 1).or_insert(9);
assert_eq!(map.get(&MyKey::A), Some(&2));

Why?

std::collections offers two maps: HashMap and BTreeMap. HashMap requires that its keys implement Hash and Eq while BTreeMap requires that its keys implement Ord and Eq. Hash and Ord enable efficient implementations of mapping data structures; however, they are not necessary for general mapping data structures. std::collections falls short when working with keys that cannot implement Hash or Ord.

For example, the following snippet fails to compile because Hash is not implemented for MyKey:

use std::collections::HashMap;

#[derive(PartialEq, Eq, Debug)]
enum MyKey {
    A,
    B,
    C,
}

let map = vec![(MyKey::A, 1), (MyKey::B, 2)]
    .into_iter()
    .collect::<HashMap<MyKey, u64>>();

Strictly speaking, a map’s keys should implement Eq, which is why this crate provides a AssocListStrictExt as well. This trait extension behaves like AssocListExt but requires K: Eq.

Modules

vec	See the module level documentation for an overview.

Traits

AssocListExt	A trait extension that allows vectors to be treated as association lists.
AssocListStrictExt	This has the same API as AssocListExt but with the additional constraint K: Eq.