Struct prehash::Prehashed

pub struct Prehashed<T: ?Sized, H = u64> { /* private fields */ }

A value (of type T) stored along with a precomputed hash (of type H, which defaults to u64).

When a hash of this value is requested, the stored precomputed hash is hashed instead of the value itself. However, when an equality test is requested, the contained value is used.

Prehashed values are unaware of the hash algorithm used to compute the hash. Algorithms may misbehave if used with Prehashed values created by different hashers.

Example

See the crate-level documentation.

Implementations

impl<T: ?Sized, H> Prehashed<T, H>

pub fn as_parts(pre: &Self) -> (&T, &H)

Returns references to the value and its precomputed hash.

Invocation

This is an associated function, so it is invoked like Prehashed::as_parts(prehashed). This is so this method does not interfere with automatic dereferencing as the contained value.

Notes

If the value or hash are interiorly mutable, it is possible to cause a mismatch between the precomputed hash and the value. This may cause certain algorithms to malfunction.

pub fn as_inner(pre: &Self) -> &T

Returns a reference to the contained value.

Invocation

This is an associated function, so it is invoked like Prehashed::as_inner(prehashed). This is so this method does not interfere with automatic dereferencing as the contained value.

Notes

If the value is interiorly mutable, it is possible to cause a mismatch between the precomputed hash and the value. This may cause certain algorithms to malfunction.

pub fn as_hash(pre: &Self) -> &H

Returns a reference to the contained hash.

Invocation

This is an associated function, so it is invoked like Prehashed::as_hash(prehashed). This is so this method does not interfere with automatic dereferencing as the contained value.

Notes

If the hash is interiorly mutable, it is possible to cause a mismatch between the precomputed hash and the value. This may cause certain algorithms to malfunction.

impl<T, H> Prehashed<T, H>

pub const fn new(value: T, hash: H) -> Self

Creates a new Prehashed object from the specified value and precomputed hash.

pub fn into_parts(pre: Self) -> (T, H)

Deconstructs the Prehashed object into the value and its precomputed hash.

These parts can be passed to new to reconstruct the original Prehashed object.

Invocation

This is an associated function, so it is invoked like Prehashed::into_parts(prehashed). This is so this method does not interfere with automatic dereferencing as the contained value.

pub fn into_inner(pre: Self) -> T

Deconstructs the Prehashed object and returns the contained value.

The precomputed hash is discarded.

Invocation

This is an associated function, so it is invoked like Prehashed::into_inner(prehashed). This is so this method does not interfere with automatic dereferencing as the contained value.

impl<T: Hash> Prehashed<T, u64>

pub fn with_default(value: T) -> Self

Available on crate feature std only.

Constructs a Prehashed object by hashing a value with the default hasher.

Security

Consider using with_builder if collision-based denial of service attacks are a potential concern.

pub fn with_hasher<H: Default + Hasher>(value: T) -> Self

Constructs a Prehashed object by hashing a value with a default instance of the specified Hasher type, H.

Invocation

You will need to use “turbofish operator” to invoke this method: Prehashed::with_hasher::<Hasher>(value)

Security

Consider using with_builder if collision-based denial of service attacks are a potential concern.

pub fn with_builder<B: BuildHasher + ?Sized>(value: T, build: &B) -> Self

Constructs a Prehashed object by hashing a value with a hasher created the specified builder.

impl<T: PartialEq + ?Sized, H: Eq> Prehashed<T, H>

pub fn fast_eq(lhs: &Self, rhs: &Self) -> bool

Compares two Prehashed values for equality, using the precomputed hash to quickly test for inequality.

Invocation

This is an associated function, so it is invoked like Prehashed::fast_eq(a, b). This is so this method does not interfere with automatic dereferencing as the contained value.

Notes

The PartialEq implementation for Prehashed does not check the hash value for early inequality because this would slow down algorithms which execute a deep equality test only once a hash equality test has indicated possible equivalence. In that sense, fast_eq strictly slower if the hashes have already been tested for equality.

Trait Implementations

impl<T: ?Sized, H> AsRef<T> for Prehashed<T, H>

fn as_ref(&self) -> &T

Converts this type into a shared reference of the (usually inferred) input type.

impl<T: Copy + ?Sized, H: Copy> Clone for Prehashed<T, H>

fn clone(&self) -> Self

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T: Debug + ?Sized, H: Debug> Debug for Prehashed<T, H>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<T: ?Sized, H> Deref for Prehashed<T, H>

type Target = T

The resulting type after dereferencing.

fn deref(&self) -> &Self::Target

Dereferences the value.

impl<T: Display + ?Sized, H> Display for Prehashed<T, H>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<T: ?Sized, H: Hash> Hash for Prehashed<T, H>

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

Feeds this value into the given Hasher.

impl<T: PartialEq + ?Sized, H> PartialEq<Prehashed<T, H>> for Prehashed<T, H>

fn eq(&self, other: &Self) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<T: PartialEq + ?Sized, H> PartialEq<T> for Prehashed<T, H>

fn eq(&self, other: &T) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<T: Copy + ?Sized, H: Copy> Copy for Prehashed<T, H>

impl<T: Eq + ?Sized, H> Eq for Prehashed<T, H>