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)));

Implementations on Foreign Types§

Implementors§