Struct xorf::HashProxy

pub struct HashProxy<T, H, F> where
    T: Hash,
    H: Hasher + Default,
    F: Filter<u64>,  { /* fields omitted */ }

Arbitrary key type proxy for Xor filters.

A HashProxy exposes a Filter trait for arbitrary key types, using a Filter<u64> as an underlying keystore. The performance and collision rate of the HashProxy filter depends on the choice of Hasher and underlying Filter. A HashProxy is immutable once constructed.

use std::collections::hash_map::DefaultHasher;
use xorf::{Filter, HashProxy, Xor8};

const SAMPLE_SIZE: usize = 1_000_000;
let rng = rand::thread_rng();
let passwords: Vec<String> = (0..SAMPLE_SIZE)
    .map(|_| rng.sample_iter(&Alphanumeric).take(30).collect())
    .collect();

let pw_filter: HashProxy<String, DefaultHasher, Xor8> = HashProxy::from(&passwords);

for password in passwords {
    assert!(pw_filter.contains(&password));
}

While a HashProxy persists type information about the keys it is constructed with, in most cases the key type parameter can be elided. For example, the pw_filter defined above can also be defined as

let pw_filter: HashProxy<_, DefaultHasher, Xor8> = HashProxy::from(&passwords);

Because of HashProxys' key type parameter, the existence of a key can only be checked using types a HashProxy is constructed with.

use std::collections::hash_map::DefaultHasher;
use std::hash::{Hash, Hasher};
use xorf::{Filter, HashProxy, Xor8};

let fruits = vec!["apple", "banana", "tangerine", "watermelon"];
let fruits: HashProxy<_, DefaultHasher, Xor8> = HashProxy::from(&fruits);

let mut hasher = DefaultHasher::default();
"tangerine".hash(&mut hasher);
let tangerine_hash = hasher.finish();

assert!(fruits.contains(&tangerine_hash)); // doesn't work!

Serializing and deserializing HashProxys can be enabled with the serde feature.

Trait Implementations

impl<T, H, F> Filter<T> for HashProxy<T, H, F> where
    T: Hash,
    H: Hasher + Default,
    F: Filter<u64>, 

fn contains(&self, key: &T) -> bool

Returns true if the underlying filter contains the specified key.

fn len(&self) -> usize

Returns the number of fingerprints in the filter.

impl<'_, T, H, F> From<&'_ [T]> for HashProxy<T, H, F> where
    T: Hash,
    H: Hasher + Default,
    F: Filter<u64> + From<Vec<u64>>, 

fn from(keys: &[T]) -> Self

Performs the conversion.

impl<'_, T, H, F> From<&'_ Vec<T>> for HashProxy<T, H, F> where
    T: Hash,
    H: Hasher + Default,
    F: Filter<u64> + From<Vec<u64>>, 

fn from(v: &Vec<T>) -> Self

Performs the conversion.