Trait comfy_core::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§

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());

Object Safety§

This trait is not object safe.

Trait comfy_core::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,

Object Safety§

Implementors§

impl Hash for ElementState

impl Hash for comfy_core::KeyCode

impl Hash for comfy_core::MouseButton

impl Hash for RenderTargetId

impl Hash for comfy_core::TextureHandle

impl Hash for Uniform

impl Hash for VirtualKeyCode

impl Hash for AsciiChar

impl Hash for core::cmp::Ordering

impl Hash for Infallible

impl Hash for IpAddr

impl Hash for Ipv6MulticastScope

impl Hash for SocketAddr

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

impl Hash for ErrorKind

impl Hash for CheckedCastError

impl Hash for PodCastError

impl Hash for AboveOrBelow

impl Hash for egui::data::input::Key

impl Hash for Order

impl Hash for SizeHint

impl Hash for OperatingSystem

impl Hash for TextStyle

impl Hash for ViewportClass

impl Hash for WriteStyle

impl Hash for TextureId

impl Hash for FontFamily

impl Hash for TextureFilter

impl Hash for EulerRot

impl Hash for ComponentError

impl Hash for QueryOneError

impl Hash for ColorType

impl Hash for ExtendedColorType

impl Hash for ImageFormatHint

impl Hash for LimitErrorKind

impl Hash for ParameterErrorKind

impl Hash for UnsupportedErrorKind

impl Hash for image::flat::Error

impl Hash for NormalForm

impl Hash for ImageFormat

impl Hash for WhenToStart

impl Hash for OutputDestination

impl Hash for PlaybackState

impl Hash for StartTime

impl Hash for EqFilterKind

impl Hash for TrackId

impl Hash for Level

impl Hash for LevelFilter

impl Hash for RecursiveMode

impl Hash for WatcherKind

impl Hash for AccessKind

impl Hash for AccessMode

impl Hash for CreateKind

impl Hash for DataChange

impl Hash for EventKind

impl Hash for Flag

impl Hash for MetadataKind

impl Hash for ModifyKind

impl Hash for RemoveKind

impl Hash for RenameMode

impl Hash for SpinStrategy

impl Hash for Ime

impl Hash for winit::event::MouseButton

impl Hash for TouchPhase

impl Hash for DeviceEventFilter

impl Hash for WindowType

impl Hash for CursorGrabMode

impl Hash for CursorIcon

impl Hash for ResizeDirection

impl Hash for bool

impl Hash for char

impl Hash for i8

impl Hash for i16

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

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