Trait nohash_hasher::IsEnabled
source · pub trait IsEnabled { }Expand description
Types which are safe to use with NoHashHasher.
This marker trait is an option for types to enable themselves for use
with NoHashHasher. In order to be safe, the Hash impl needs to
satisfy the following constraint:
One of the
Hasher::write_{u8,u16,u32,u64,usize,i8,i16,i32,i64,isize}methods is invoked exactly once.
The best way to ensure this is to write a custom Hash impl even when
deriving Hash for a simple newtype of a single type which itself
implements IsEnabled may work as well.
Example
#[derive(PartialEq, Eq)]
struct SomeType(u32);
impl std::hash::Hash for SomeType {
fn hash<H: std::hash::Hasher>(&self, hasher: &mut H) {
hasher.write_u32(self.0)
}
}
impl nohash_hasher::IsEnabled for SomeType {}
let mut m = nohash_hasher::IntMap::default();
m.insert(SomeType(1), 't');
m.insert(SomeType(0), 'f');
assert_eq!(Some(&'t'), m.get(&SomeType(1)));
assert_eq!(Some(&'f'), m.get(&SomeType(0)));