Module core::hash

Generic hashing support.

This module provides a generic way to compute the hash of a value. The simplest way to make a type hashable is to use #[derive(Hash)]:

Examples

fn main() { use std::hash::{Hash, SipHasher, 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!(hash(&person1) != hash(&person2)); fn hash<T: Hash>(t: &T) -> u64 { let mut s = SipHasher::new(); t.hash(&mut s); s.finish() } }

use std::hash::{Hash, SipHasher, 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!(hash(&person1) != hash(&person2));

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

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

fn main() { use std::hash::{Hash, Hasher, SipHasher}; struct Person { id: u32, #[allow(dead_code)] 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!(hash(&person1), hash(&person2)); fn hash<T: Hash>(t: &T) -> u64 { let mut s = SipHasher::new(); t.hash(&mut s); s.finish() } }

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

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!(hash(&person1), hash(&person2));

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

Structs

BuildHasherDefault	A structure which implements BuildHasher for all Hasher types which also implement Default.
SipHasher	An implementation of SipHash 2-4.

Traits

BuildHasher	A BuildHasher is typically used as a factory for instances of Hasher which a HashMap can then use to hash keys independently.
Hash	A hashable type.
Hasher	A trait which represents the ability to hash an arbitrary stream of bytes.