Trait sp_std::hash::Hash1.0.0[][src]

pub trait Hash {
    fn hash<H>(&self, state: &mut H)
    where
        H: Hasher
; fn hash_slice<H>(data: &[Self], state: &mut H)
    where
        H: Hasher
, { ... } }
Expand description

A hashable type.

Types implementing Hash are able to be hashed with an instance of Hasher.

Implementing Hash

You can derive Hash with #[derive(Hash)] if all fields implement Hash. The resulting hash will be the combination of the values from calling hash on each field.

#[derive(Hash)]
struct Rustacean {
    name: String,
    country: String,
}

If you need more control over how a value is hashed, you can of course implement the Hash trait yourself:

use std::hash::{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);
    }
}

Hash and Eq

When implementing both Hash and Eq, it is important that the following property holds:

k1 == k2 -> hash(k1) == hash(k2)

In other words, if two keys are equal, their hashes must also be equal. HashMap and HashSet both rely on this behavior.

Thankfully, you won’t need to worry about upholding this property when deriving both Eq and Hash with #[derive(PartialEq, Eq, Hash)].

Required methods

Feeds this value into the given Hasher.

Examples

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

let mut hasher = DefaultHasher::new();
7920.hash(&mut hasher);
println!("Hash is {:x}!", hasher.finish());

Provided methods

Feeds a slice of this type into the given Hasher.

This method is meant as a convenience, but its implementation is also explicitly left unspecified. It isn’t guaranteed to be equivalent to repeated calls of hash and implementations of Hash should keep that in mind and call hash themselves if the slice isn’t treated as a whole unit in the PartialEq implementation.

For example, a VecDeque implementation might naïvely call as_slices and then hash_slice on each slice, but this is wrong since the two slices can change with a call to make_contiguous without affecting the PartialEq result. Since these slices aren’t treated as singular units, and instead part of a larger deque, this method cannot be used.

Examples

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

let mut hasher = DefaultHasher::new();
let numbers = [6, 28, 496, 8128];
Hash::hash_slice(&numbers, &mut hasher);
println!("Hash is {:x}!", hasher.finish());

Implementations on Foreign Types

The hash of an array is the same as that of the corresponding slice, as required by the Borrow implementation.

#![feature(build_hasher_simple_hash_one)]
use std::hash::BuildHasher;

let b = std::collections::hash_map::RandomState::new();
let a: [u8; 3] = [0xa8, 0x3c, 0x09];
let s: &[u8] = &[0xa8, 0x3c, 0x09];
assert_eq!(b.hash_one(a), b.hash_one(s));

Implementors

impl Hash for WithdrawReasons

impl Hash for ReturnFlags

impl Hash for Public

impl Hash for Signature

impl<Header: Hash + HeaderT> Hash for RemoteCallRequest<Header> where
    Header::Hash: Hash

impl<Header: Hash + HeaderT> Hash for RemoteHeaderRequest<Header> where
    Header::Hash: Hash,
    Header::Number: Hash

impl<Header: Hash + HeaderT> Hash for RemoteReadRequest<Header> where
    Header::Hash: Hash

impl<Header: Hash + HeaderT> Hash for RemoteReadChildRequest<Header> where
    Header::Hash: Hash

impl<Header: Hash + HeaderT> Hash for RemoteBodyRequest<Header>

impl<T: Hash> Hash for SlotDuration<T>

impl Hash for WasmExecutionMethod

impl Hash for IfDisconnected

impl Hash for ProtocolId

impl Hash for SetId

impl Hash for IncomingIndex

impl Hash for TelemetryEndpoints

impl Hash for Public

impl Hash for Signature

impl Hash for Public

impl Hash for Signature

impl Hash for Public

impl Hash for Signature

impl Hash for DeriveJunction

impl Hash for AccountId32

impl Hash for Dummy

impl Hash for KeyTypeId

impl Hash for CryptoTypeId

impl Hash for CryptoTypePublicPair

impl Hash for Public

impl Hash for Signature

impl Hash for Public

impl Hash for Signature

impl Hash for Public

impl Hash for Signature

impl Hash for HttpRequestId

impl Hash for OffchainOverlayedChange

impl Hash for Bytes

impl Hash for Keyring

impl Hash for Keyring

impl Hash for UintAuthorityId

impl Hash for TestSignature

impl<AccountId: Hash, AccountIndex: Hash> Hash for MultiAddress<AccountId, AccountIndex>

impl Hash for StorageKey

impl Hash for TrackedStorageKey

impl Hash for PrefixedStorageKey

impl Hash for StorageData

impl Hash for ChildInfo

impl Hash for ChildTrieParentKeyId

impl<V: Hash> Hash for StorageQuery<V>