Alternate/custom key types
Any type that implements the Eq
and Hash
traits can be a key in HashMap
.
This includes:
bool
(though not very useful since there is only two possible keys)int
,uint
, and all variations thereofString
and&str
(protip: you can have aHashMap
keyed byString
and call.get()
with an&str
)
Note that f32
and f64
do not implement Hash
,
likely because floating-point precision errors
would make using them as hashmap keys horribly error-prone.
All collection classes implement Eq
and Hash
if their contained type also respectively implements Eq
and Hash
.
For example, Vec<T>
will implement Hash
if T
implements Hash
.
You can easily implement Eq
and Hash
for a custom type with just one line:
#[derive(PartialEq, Eq, Hash)]
The compiler will do the rest. If you want more control over the details,
you can implement Eq
and/or Hash
yourself.
This guide will not cover the specifics of implementing Hash
.
To play around with using a struct
in HashMap
,
let's try making a very simple user logon system: