Trait std::hash::Hash
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 { ... }
}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
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
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());Object Safety
This trait is not object safe.
Implementors
impl Hash for AsciiCharimpl Hash for std::cmp::Orderingimpl Hash for Infallibleimpl Hash for ErrorKindimpl Hash for IpAddrimpl Hash for Ipv6MulticastScopeimpl Hash for SocketAddrimpl Hash for Whichimpl Hash for std::sync::atomic::Orderingimpl Hash for boolimpl Hash for charimpl Hash for i8impl Hash for i16impl Hash for i32impl Hash for i64impl Hash for i128impl Hash for isizeimpl Hash for !impl Hash for strimpl Hash for u8impl Hash for u16impl Hash for u32impl Hash for u64impl Hash for u128impl Hash for ()impl Hash for usizeimpl Hash for Layoutimpl Hash for TypeIdimpl Hash for CStrimpl Hash for CStringimpl Hash for OsStrimpl Hash for OsStringimpl Hash for Errorimpl Hash for FileTypeimpl Hash for PhantomPinnedimpl Hash for Ipv4Addrimpl Hash for Ipv6Addrimpl Hash for SocketAddrV4impl Hash for SocketAddrV6impl Hash for NonZeroI8impl Hash for NonZeroI16impl Hash for NonZeroI32impl Hash for NonZeroI64impl Hash for NonZeroI128impl Hash for NonZeroIsizeimpl Hash for NonZeroU8impl Hash for NonZeroU16impl Hash for NonZeroU32impl Hash for NonZeroU64impl Hash for NonZeroU128impl Hash for NonZeroUsizeimpl Hash for RangeFullimpl Hash for UCredAvailable on Unix only.impl Hash for Pathimpl Hash for PathBufimpl Hash for PrefixComponent<'_>impl Hash for Alignmentimpl Hash for Stringimpl Hash for ThreadIdimpl Hash for Durationimpl Hash for Instantimpl Hash for SystemTimeimpl<'a> Hash for Component<'a>impl<'a> Hash for Prefix<'a>impl<'a> Hash for Location<'a>impl<B> Hash for Cow<'_, B>
where
B: Hash + ToOwned + ?Sized,impl<B, C> Hash for ControlFlow<B, C>
where
B: Hash,
C: Hash,impl<Dyn> Hash for DynMetadata<Dyn>
where
Dyn: ?Sized,impl<F> Hash for F
where
F: FnPtr,impl<Idx> Hash for Range<Idx>
where
Idx: Hash,impl<Idx> Hash for RangeFrom<Idx>
where
Idx: Hash,impl<Idx> Hash for RangeInclusive<Idx>
where
Idx: Hash,impl<Idx> Hash for RangeTo<Idx>
where
Idx: Hash,impl<Idx> Hash for RangeToInclusive<Idx>
where
Idx: Hash,impl<K, V, A> Hash for BTreeMap<K, V, A>
where
K: Hash,
V: Hash,
A: Allocator + Clone,impl<P> Hash for Pin<P>
where
P: Deref,
<P as Deref>::Target: Hash,impl<T> Hash for Bound<T>
where
T: Hash,impl<T> Hash for Option<T>
where
T: Hash,impl<T> Hash for Poll<T>
where
T: Hash,impl<T> Hash for *const T
where
T: ?Sized,impl<T> Hash for *mut T
where
T: ?Sized,impl<T> Hash for &T
where
T: Hash + ?Sized,impl<T> Hash for &mut T
where
T: Hash + ?Sized,impl<T> Hash for [T]
where
T: Hash,impl<T> Hash for (T₁, T₂, …, Tₙ)
where
T: Hash + ?Sized,This trait is implemented for tuples up to twelve items long.
impl<T> Hash for Reverse<T>
where
T: Hash,impl<T> Hash for PhantomData<T>
where
T: ?Sized,impl<T> Hash for Discriminant<T>impl<T> Hash for ManuallyDrop<T>
where
T: Hash + ?Sized,impl<T> Hash for Saturating<T>
where
T: Hash,impl<T> Hash for Wrapping<T>
where
T: Hash,impl<T> Hash for NonNull<T>
where
T: ?Sized,impl<T, A> Hash for Box<T, A>
where
T: Hash + ?Sized,
A: Allocator,impl<T, A> Hash for BTreeSet<T, A>
where
T: Hash,
A: Allocator + Clone,impl<T, A> Hash for LinkedList<T, A>
where
T: Hash,
A: Allocator,impl<T, A> Hash for VecDeque<T, A>
where
T: Hash,
A: Allocator,impl<T, A> Hash for Rc<T, A>
where
T: Hash + ?Sized,
A: Allocator,impl<T, A> Hash for Arc<T, A>
where
T: Hash + ?Sized,
A: Allocator,impl<T, A> Hash for Vec<T, A>
where
T: Hash,
A: Allocator,The hash of a vector is the same as that of the corresponding slice, as required by the core::borrow::Borrow implementation.
use std::hash::BuildHasher;
let b = std::collections::hash_map::RandomState::new();
let v: Vec<u8> = vec![0xa8, 0x3c, 0x09];
let s: &[u8] = &[0xa8, 0x3c, 0x09];
assert_eq!(b.hash_one(v), b.hash_one(s));impl<T, E> Hash for Result<T, E>
where
T: Hash,
E: Hash,impl<T, const N: usize> Hash for [T; N]
where
T: Hash,The hash of an array is the same as that of the corresponding slice, as required by the Borrow implementation.
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));impl<T, const N: usize> Hash for Simd<T, N>
where
LaneCount<N>: SupportedLaneCount,
T: SimdElement + Hash,impl<Y, R> Hash for CoroutineState<Y, R>
where
Y: Hash,
R: Hash,© 2010 The Rust Project Developers
Licensed under the Apache License, Version 2.0 or the MIT license, at your option.
https://doc.rust-lang.org/std/hash/trait.Hash.html