Module hash

Generic hashing support.

This module provides a generic way to compute the hash of a value. Hashes are most commonly used with HashMap and HashSet.

The simplest way to make a type hashable is to use #[derive(Hash)]:

Examples

use std::hash::{DefaultHasher, Hash, Hasher};

#[derive(Hash)]
struct Person {
    id: u32,
    name: String,
    phone: u64,
}

let person1 = Person {
    id: 5,
    name: "Janet".to_string(),
    phone: 555_666_7777,
};
let person2 = Person {
    id: 5,
    name: "Bob".to_string(),
    phone: 555_666_7777,
};

assert!(calculate_hash(&person1) != calculate_hash(&person2));

fn calculate_hash<T: Hash>(t: &T) -> u64 {
    let mut s = DefaultHasher::new();
    t.hash(&mut s);
    s.finish()
}

If you need more control over how a value is hashed, you need to implement the Hash trait:

use std::hash::{DefaultHasher, Hash, Hasher};

struct Person {
    id: u32,
    name: String,
    phone: u64,
}

impl Hash for Person {
    fn hash<H: Hasher>(&self, state: &mut H) {
        self.id.hash(state);
        self.phone.hash(state);
    }
}

let person1 = Person {
    id: 5,
    name: "Janet".to_string(),
    phone: 555_666_7777,
};
let person2 = Person {
    id: 5,
    name: "Bob".to_string(),
    phone: 555_666_7777,
};

assert_eq!(calculate_hash(&person1), calculate_hash(&person2));

fn calculate_hash<T: Hash>(t: &T) -> u64 {
    let mut s = DefaultHasher::new();
    t.hash(&mut s);
    s.finish()
}

Re-exports

pub use self::random::DefaultHasher;

pub use self::random::RandomState;

Modules

random 🔒

This module exists to isolate RandomState and DefaultHasher outside of the collections module without actually publicly exporting them, so that parts of that implementation can more easily be moved to the alloc crate.

Structs

BuildHasherDefault

Used to create a default BuildHasher instance for types that implement Hasher and Default.

SipHasherDeprecated

An implementation of SipHash 2-4.

Traits

BuildHasher

A trait for creating instances of Hasher.

Hash

A hashable type.

Hasher

A trait for hashing an arbitrary stream of bytes.

Derive Macros

Hash

Derive macro generating an impl of the trait Hash.