Trait Hash

1.0.0 · Source

pub trait Hash {
    // Required method
    fn hash<H>(&self, state: &mut H)
       where H: Hasher;

    // Provided method
    fn hash_slice<H>(data: &[Self], state: &mut H)
       where H: Hasher,
             Self: Sized { ... }
}

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)].

Violating this property is a logic error. The behavior resulting from a logic error is not specified, but users of the trait must ensure that such logic errors do not result in undefined behavior. This means that unsafe code must not rely on the correctness of these methods.

§Prefix collisions

Implementations of hash should ensure that the data they pass to the Hasher are prefix-free. That is, values which are not equal should cause two different sequences of values to be written, and neither of the two sequences should be a prefix of the other.

For example, the standard implementation of Hash for &str passes an extra 0xFF byte to the Hasher so that the values ("ab", "c") and ("a", "bc") hash differently.

§Portability

Due to differences in endianness and type sizes, data fed by Hash to a Hasher should not be considered portable across platforms. Additionally the data passed by most standard library types should not be considered stable between compiler versions.

This means tests shouldn’t probe hard-coded hash values or data fed to a Hasher and instead should check consistency with Eq.

Serialization formats intended to be portable between platforms or compiler versions should either avoid encoding hashes or only rely on Hash and Hasher implementations that provide additional guarantees.

Required Methods§

1.0.0 · Source

fn hash<H>(&self, state: &mut H)
where H: Hasher,

Feeds this value into the given Hasher.

§Examples

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

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

Provided Methods§

1.3.0 · Source

fn hash_slice<H>(data: &[Self], state: &mut H)
where H: Hasher, Self: Sized,

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::hash::{DefaultHasher, 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());

Dyn Compatibility§

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Trait HashCopy item path

§Implementing Hash

§Hash and Eq

§Prefix collisions

§Portability

Required Methods§

fn hash<H>(&self, state: &mut H)where H: Hasher,

§Examples

Provided Methods§

fn hash_slice<H>(data: &[Self], state: &mut H)where H: Hasher, Self: Sized,

§Examples

Dyn Compatibility§

Implementors§

impl Hash for CreationStrategy

impl Hash for AccessControllerPartitionOffset

impl Hash for AccessRule

impl Hash for AccountLockerPartitionOffset

impl Hash for AccountPartitionOffset

impl Hash for AlwaysVisibleGlobalNodesVersion

impl Hash for AttachedModuleId

impl Hash for AuthZoneField

impl Hash for BasicRequirement

impl Hash for BlueprintPayloadDef

impl Hash for BootLoaderField

impl Hash for ComponentField

impl Hash for ComponentRoyaltyPartitionOffset

impl Hash for CompositeRequirement

impl Hash for ConsensusManagerCollection

impl Hash for ConsensusManagerFeature

impl Hash for ConsensusManagerField

impl Hash for ConsensusManagerPartitionOffset

impl Hash for CurveType

impl Hash for DatabaseUpdate

impl Hash for DefaultDepositRule

impl Hash for Emitter

impl Hash for EntityType

impl Hash for FungibleBucketField

impl Hash for FungibleProofField

impl Hash for FungibleResourceManagerCollection

impl Hash for FungibleResourceManagerFeature

impl Hash for FungibleResourceManagerField

impl Hash for FungibleResourceManagerPartitionOffset

impl Hash for FungibleVaultCollection

impl Hash for FungibleVaultFeature

impl Hash for FungibleVaultField

impl Hash for FungibleVaultPartitionOffset

impl Hash for GenericSubstitution

impl Hash for IdentityV1MinorVersion

impl Hash for IntentHash

impl Hash for LocalRef

impl Hash for LocalTypeId

impl Hash for ManifestAddress

impl Hash for ManifestBucketBatch

impl Hash for ManifestComponentAddress

impl Hash for ManifestExpression

impl Hash for ManifestGlobalAddress

impl Hash for ManifestNonFungibleLocalId

impl Hash for ManifestPackageAddress

impl Hash for ManifestProofBatch

impl Hash for ManifestResourceAddress

impl Hash for ManifestResourceOrNonFungible

impl Hash for MetadataPartitionOffset

impl Hash for MethodAccessibility

impl Hash for ModuleId

impl Hash for MultiResourcePoolPartitionOffset

impl Hash for NonFungibleBucketField

impl Hash for NonFungibleIdType

impl Hash for NonFungibleLocalId

impl Hash for NonFungibleProofField

impl Hash for NonFungibleResourceManagerCollection

impl Hash for NonFungibleResourceManagerFeature

impl Hash for NonFungibleResourceManagerField

impl Hash for NonFungibleResourceManagerGeneric

impl Hash for NonFungibleResourceManagerPartitionOffset

impl Hash for NonFungibleVaultCollection

impl Hash for NonFungibleVaultFeature

impl Hash for NonFungibleVaultField

impl Hash for NonFungibleVaultPartitionOffset

impl Hash for OneResourcePoolPartitionOffset

impl Hash for OwnerRole

Trait Hash

§Implementing `Hash`

§`Hash` and `Eq`

fn hash<H>(&self, state: &mut H)
where H: Hasher,

fn hash_slice<H>(data: &[Self], state: &mut H)
where H: Hasher, Self: Sized,