deft ferry
enum E {
A,
B,
C,
}
type EnumMap<Enum: Sized, Value: Default>
fn main() {
let mut map = EnumMap<E, f64>::default();
map[E::B] = 2.0;
assert_eq!(
map as Vec,
vec![
(E::A, 0.0),
(E::B, 2.0),
(E::C, 0.0),
]
);
}
does this hypothetical EnumMap type exist? or do i have to create it myself? and if i do have to create it myself, how to i do that?
does a Map for Enums exist?
dense onyxBOT
jaunty trout
That was the wrong crate, sorry
dense onyxBOT
jaunty trout
That's the one I was looking for. It's the closest I found at a glance
gilded imp
I would just make a method on the enum that does match and returns the "value" it represents
jaunty trout
I agree with that, I'd use an enum mapping in situations where the mapping values are dependent on runtime values
gilded imp
enum E {
A,
B,
C,
}
impl E {
fn value(&self) -> f64 {
match self {
E::A => 0.0,
E::B => 2.0,
E::C => 0.0,
}
}
}```plus the compiler is going to optimize this a lot better than an entire hashmap
also if youre thinking about maybe doing this instead:rs match self { E::B => 2.0, _ => 0.0, }dont do that. you would lose out on the advantages of exhaustive pattern matching.
if you added a new variant to E, its nice to have the compiler just notify about every location where you need to also account for the change.
jaunty trout
I mean, one of the advantages of enum-map is that it doesn't do allocation - it uses an array
(And supports nesting of enums, enum Foo { A, B(bool) } becomes a length-3 array with distinct options for A, B(false), and B(true))
deft ferry
I agree with that, I'd use an enum mapping in situations where the mapping value...
yes, i tried to get across the fact that the runtime value is unknown to the compiler.
does the enum_map crate have a default feature?