Trait tract_core::internal::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)].

Implementations of hash should ensure that the data they pass to the Hasher are prefix-free. That is, unequal values 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§

source

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

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§

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::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());

Trait tract_core::internal::Hash

Required Methods§

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

Provided Methods§

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

Implementors§

impl Hash for PadMode

impl Hash for AxisOp

impl Hash for InOut

impl Hash for KernelFormat

impl Hash for PaddingSpec

impl Hash for AttrOrInput

impl Hash for Cost

impl Hash for Validation

impl Hash for ProtoFusedSpec

impl Hash for QParamKind

impl Hash for DataFormat

impl Hash for Reducer

impl Hash for InputMapping

impl Hash for StateInitializer

impl Hash for DatumType

impl Hash for QParams

impl Hash for TDim

impl Hash for core::cmp::Ordering

impl Hash for Infallible

impl Hash for Which

impl Hash for core::sync::atomic::Ordering

impl Hash for std::io::error::ErrorKind

impl Hash for IpAddr

impl Hash for Ipv6MulticastScope

impl Hash for SocketAddr

impl Hash for Level

impl Hash for LevelFilter

impl Hash for BinOp

impl Hash for RoundingPolicy

impl Hash for InputStoreSpec

impl Hash for OutputStoreSpec

impl Hash for SliceInfoElem

impl Hash for bool

impl Hash for char

impl Hash for i8

impl Hash for i16

impl Hash for i32

impl Hash for i64

impl Hash for i128

impl Hash for isize

impl Hash for !

impl Hash for str

impl Hash for u8

impl Hash for u16

impl Hash for u32

impl Hash for u64

impl Hash for u128

impl Hash for ()

impl Hash for usize

impl Hash for InletId

impl Hash for OutletId

impl Hash for ShapeFact

impl Hash for TypedFact

impl Hash for DynSlice

impl Hash for FiniteReshape

impl Hash for Gather

impl Hash for GatherElements

impl Hash for GatherNd

impl Hash for MultiBroadcastTo

impl Hash for OneHot

impl Hash for Pad

impl Hash for tract_core::ops::array::Range

impl Hash for ScatterElements

impl Hash for ScatterNd

impl Hash for tract_core::ops::array::Slice

impl Hash for Tile

impl Hash for TypedConcat

impl Hash for MergeOpUnicast

impl Hash for TypedBinOp

impl Hash for Cast

impl Hash for ConvUnary

impl Hash for Im2Col

impl Hash for DeconvUnary

impl Hash for ConcretePoolGeometry