Trait identity_hash::IdentityHashable
source · pub trait IdentityHashable { }Expand description
Types which are safe to use with IdentityHasher.
This marker trait is an option for types to enable themselves for use
with IdentityHasher. 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 new type 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 identity_hash::IdentityHashable for SomeType {}
let mut m = identity_hash::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)));