Presented with no comment beyond read all the other comments and answers to understand why you probably don’t want to do this:
use std::{collections::HashMap, hash};
#[derive(Debug, Copy, Clone)]
struct DontUseThisUnlessYouUnderstandTheDangers(f64);
impl DontUseThisUnlessYouUnderstandTheDangers {
fn key(&self) -> u64 {
self.0.to_bits()
}
}
impl hash::Hash for DontUseThisUnlessYouUnderstandTheDangers {
fn hash<H>(&self, state: &mut H)
where
H: hash::Hasher,
{
self.key().hash(state)
}
}
impl PartialEq for DontUseThisUnlessYouUnderstandTheDangers {
fn eq(&self, other: &DontUseThisUnlessYouUnderstandTheDangers) -> bool {
self.key() == other.key()
}
}
impl Eq for DontUseThisUnlessYouUnderstandTheDangers {}
fn main() {
let a = DontUseThisUnlessYouUnderstandTheDangers(0.1);
let b = DontUseThisUnlessYouUnderstandTheDangers(0.2);
let c = DontUseThisUnlessYouUnderstandTheDangers(0.3);
let mut map = HashMap::new();
map.insert(a, 1);
map.insert(b, 2);
println!("{:?}", map.get(&a));
println!("{:?}", map.get(&b));
println!("{:?}", map.get(&c));
}
Basically, if you want to treat a f64
as a set of bits that have no meaning, well, we can treat them as an equivalently sized bag of bits that know how to be hashed and bitwise-compared.
Don’t be surprised when one of the 16 million NaN
values doesn’t equal another one.