Crate multi_map

multi-map

MultiMap is like a std::collection::HashMap, but allows you to use either of two different keys to retrieve items.

The keys have two distinct types - K1 and K2 - which may be the same. Accessing on the primary K1 key is via the usual get, get_mut and remove_alt methods, while accessing via the secondary K2 key is via new get_alt, get_mut_alt and remove_alt methods. The value is of type V.

Internally, two HashMaps are created - a main one on <K1, (K2, V)> and a second one on <K2, K1>. The (K2, V) tuple is so that when an item is removed using the K1 key, the appropriate K2 value is available so the K2->K1 map can be removed from the second MultiMap, to keep them in sync.

Using two HashMaps instead of one naturally brings a slight performance and memory penalty. Notably, indexing by K2 requires two HashMap lookups.

extern crate multi_map;
use multi_map::MultiMap;

#[derive(Hash,Clone,PartialEq,Eq)]
enum ThingIndex {
    IndexOne,
    IndexTwo,
    IndexThree,
};

let mut map = MultiMap::new();
map.insert(1, ThingIndex::IndexOne, "Chicken Fried Steak");
map.insert(2, ThingIndex::IndexTwo, "Blueberry Pancakes");

assert!(*map.get_alt(&ThingIndex::IndexOne).unwrap() == "Chicken Fried Steak");
assert!(*map.get(&2).unwrap() == "Blueberry Pancakes");
assert!(map.remove_alt(&ThingIndex::IndexTwo).unwrap() == "Blueberry Pancakes");

Macros

multimap

Create a MultiMap from a list of key-value tuples

Structs

MultiMap