Trait geng::prelude::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.


let a: Authority = "HELLO.com".parse().unwrap();
let b: Authority = "hello.coM".parse().unwrap();

let mut s = DefaultHasher::new();
a.hash(&mut s);
let a = s.finish();

let mut s = DefaultHasher::new();
b.hash(&mut s);
let b = s.finish();

assert_eq!(a, b);

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impl Hash for PathAndQuery

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impl Hash for Scheme

Case-insensitive hashing

URLs hash like their serialization.

source §

impl<V, A> Hash for TArr<V, A>
where V: Hash, A: Hash,

source §

impl<Y, R> Hash for CoroutineState<Y, R>
where Y: Hash, R: Hash,

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Trait geng::prelude::Hash

§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

Object Safety§

Implementors§

impl Hash for CursorType

impl Hash for geng::Key

impl Hash for geng::MouseButton

impl Hash for AnsiColor

impl Hash for geng::prelude::cli::prelude::clap::builder::styling::Color

impl Hash for ValueHint

impl Hash for ContextKind

impl Hash for geng::prelude::cli::prelude::clap::error::ErrorKind

impl Hash for geng::prelude::futures::io::ErrorKind

impl Hash for PollNext

impl Hash for AsciiChar

impl Hash for core::cmp::Ordering

impl Hash for Infallible

impl Hash for core::net::ip_addr::IpAddr

impl Hash for Ipv6MulticastScope

impl Hash for SocketAddr

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

impl Hash for DistanceMode

impl Hash for gilrs::ev::Axis

impl Hash for AxisOrBtn

impl Hash for Button

impl Hash for IpAddrRange

impl Hash for IpNet

impl Hash for IpSubnets

impl Hash for Condition

impl Hash for CullFace

impl Hash for DepthFunc

impl Hash for StencilOpFunc

impl Hash for ugli::error::Error

impl Hash for Filter

impl Hash for WrapMode

impl Hash for AttributeType

impl Hash for Origin

impl Hash for geng::prelude::log::Level

impl Hash for geng::prelude::log::LevelFilter

impl Hash for geng::prelude::ron::Number

impl Hash for Value

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 geng::prelude::cli::prelude::clap::builder::OsStr

impl Hash for geng::prelude::cli::prelude::clap::builder::Str

impl Hash for ValueRange

impl Hash for Ansi256Color

impl Hash for Effects

impl Hash for Reset

impl Hash for RgbColor

impl Hash for geng::prelude::cli::prelude::clap::builder::styling::Style

impl Hash for geng::prelude::cli::prelude::clap::Id

impl Hash for geng::prelude::fmt::Error

impl Hash for CString

impl Hash for String

impl Hash for Layout

§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,