pub trait Hash: PointeeSized { // Required method fn hash<H: Hasher>(&self, state: &mut H); // Provided method fn hash_slice<H: Hasher>(data: &[Self], state: &mut H) where 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.
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§
Provided Methods§
1.3.0 · Sourcefn hash_slice<H: Hasher>(data: &[Self], state: &mut H)where Self: Sized,
fn hash_slice<H: Hasher>(data: &[Self], state: &mut H)where 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
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.
Implementors§
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 IntErrorKind
impl Hash for core::sync::atomic::Ordering
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 Layout
impl Hash for TypeId
impl Hash for ByteStr
impl Hash for CStr
impl Hash for Error
impl Hash for PhantomPinned
impl Hash for Ipv4Addr
impl Hash for Ipv6Addr
impl Hash for SocketAddrV4
impl Hash for SocketAddrV6
impl Hash for RangeFull
impl Hash for Location<'_>
impl Hash for Alignment
impl Hash for Duration
impl<'a> Hash for PhantomContravariantLifetime<'a>
impl<'a> Hash for PhantomCovariantLifetime<'a>
impl<'a> Hash for PhantomInvariantLifetime<'a>
impl<B: Hash, C: Hash> Hash for ControlFlow<B, C>
impl<Dyn: PointeeSized> Hash for DynMetadata<Dyn>
impl<F: FnPtr> Hash for F
impl<Idx: Hash> Hash for core::ops::Range<Idx>
impl<Idx: Hash> Hash for core::ops::RangeFrom<Idx>
impl<Idx: Hash> Hash for core::ops::RangeInclusive<Idx>
impl<Idx: Hash> Hash for RangeTo<Idx>
impl<Idx: Hash> Hash for RangeToInclusive<Idx>
impl<Idx: Hash> Hash for core::range::Range<Idx>
impl<Idx: Hash> Hash for core::range::RangeFrom<Idx>
impl<Idx: Hash> Hash for core::range::RangeInclusive<Idx>
impl<Ptr: Deref<Target: Hash>> Hash for Pin<Ptr>
impl<T> Hash for PhantomContravariant<T>where T: ?Sized,
impl<T> Hash for PhantomCovariant<T>where T: ?Sized,
impl<T> Hash for PhantomInvariant<T>where T: ?Sized,
impl<T> Hash for Discriminant<T>
impl<T> Hash for NonZero<T>where T: ZeroablePrimitive + Hash,
impl<T, const N: usize> Hash for Simd<T, N>
impl<T: PointeeSized> Hash for PhantomData<T>
impl<T: PointeeSized> Hash for NonNull<T>
impl<T: Hash + ?Sized> Hash for ManuallyDrop<T>
impl<T: Hash> Hash for Bound<T>
impl<T: Hash> Hash for Option<T>
impl<T: Hash> Hash for Poll<T>
impl<T: Hash> Hash for [T]
impl<T: Hash> Hash for (T₁, T₂, …, Tₙ)
This trait is implemented for tuples up to twelve items long.
impl<T: Hash> Hash for Reverse<T>
impl<T: Hash> Hash for Saturating<T>
impl<T: Hash> Hash for Wrapping<T>
impl<T: Hash, E: Hash> Hash for Result<T, E>
impl<T: Hash, const N: usize> Hash for [T; N]
The hash of an array is the same as that of the corresponding slice, as required by the Borrow implementation.