pub trait Key: Copy {
type MapStorage<V>: MapStorage<Self, V>;
type SetStorage: SetStorage<Self>;
}Expand description
The trait for a key that can be used to store values in a
Map or Set.
This can be derived automatically from enums. The following is a simple key which has no nested keys:
use fixed_map::Key;
#[derive(Clone, Copy, Key)]
enum MyKey {
First,
Second,
}Composite keys are when keys structurally includes other keys. They have
slightly worse performance than simple keys because they can’t be simply
arranged as arrays internally. bool below here implements Key and
using it in one key constructs a composite key. It’s a simple form of key
since it can only inhabit two values - true or false. Option<K> can
also be used as a composite key:
use fixed_map::Key;
#[derive(Clone, Copy, Key)]
enum MyKey {
First(bool),
Second(Option<bool>),
}Some composite keys require dynamic storage since they can inhabit a large
number of values, and preferrably should be avoided in favor of using a
HashMap directly. But if you absolutely have to you can enable the map
feature:
use fixed_map::Key;
#[derive(Clone, Copy, Key)]
enum MyKey {
First(u32),
Second,
}Ordering
Keys provide their own ordering semantics instead of relying on the
PartialOrd and Ord traits.
Therefore keys when stored in a collection such as Map and Set are
always ordered in declaration order. This allows those containers
themselves to be ordered if the underlying key supports, it similarly to how
BTreeMap and BTreeSet works.
use fixed_map::{Key, Set};
#[derive(Clone, Copy, Key)]
enum MyKey {
First,
Second,
Third,
}
let mut a = Set::new();
a.insert(MyKey::First);
let mut b = Set::new();
b.insert(MyKey::Third);
let mut c = Set::new();
c.insert(MyKey::First);
c.insert(MyKey::Third);
assert!(a < b);
assert!(c < b);
assert!(a < c);The same example with BTreeSet:
use std::collections::BTreeSet;
#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
enum MyKey {
First,
Second,
Third,
}
let mut a = BTreeSet::new();
a.insert(MyKey::First);
let mut b = BTreeSet::new();
b.insert(MyKey::Third);
let mut c = BTreeSet::new();
c.insert(MyKey::First);
c.insert(MyKey::Third);
assert!(a < b);
assert!(c < b);
assert!(a < c);Required Associated Types§
sourcetype MapStorage<V>: MapStorage<Self, V>
type MapStorage<V>: MapStorage<Self, V>
The Map storage implementation to use for the key
implementing this trait.
sourcetype SetStorage: SetStorage<Self>
type SetStorage: SetStorage<Self>
The Set storage implementation to use for the key
implementing this trait.