Struct comemo::Prehashed

pub struct Prehashed<T: ?Sized> { /* private fields */ }

A wrapper type with precomputed hash.

This is useful if you want to pass large values of T to memoized functions. Especially recursive structures like trees benefit from intermediate prehashed nodes.

Note that for a value v of type T, hash(v) is not necessarily equal to hash(Prehashed::new(v)). Writing the precomputed hash into a hasher’s state produces different output than writing the value’s parts directly. However, that seldomly matters as you are typically either dealing with values of type T or with values of type Prehashed<T>, not a mix of both.

Equality

Because comemo uses high-quality 128 bit hashes in all places, the risk of a hash collision is reduced to an absolute minimum. Therefore, this type additionally provides PartialEq and Eq implementations that compare by hash instead of by value. For this to be correct, your hash implementation must feed all information relevant to the PartialEq impl to the hasher.

Implementations

impl<T: Hash + 'static> Prehashed<T>

pub fn new(item: T) -> Self

Compute an item’s hash and wrap it.

pub fn into_inner(self) -> T

Return the wrapped value.

pub fn update<F, U>(&mut self, f: F) -> Uwhere F: FnOnce(&mut T) -> U,

Update the wrapped value and recompute the hash.

Trait Implementations

impl<T: Clone + ?Sized> Clone for Prehashed<T>

fn clone(&self) -> Prehashed<T>

Returns a copy of the value.

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

Performs copy-assignment from source.

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

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

Formats the value using the given formatter.

impl<T: Default + Hash + 'static> Default for Prehashed<T>

fn default() -> Self

Returns the “default value” for a type.

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

type Target = T

The resulting type after dereferencing.

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

Dereferences the value.

impl<T: Hash + 'static> From<T> for Prehashed<T>

fn from(value: T) -> Self

Converts to this type from the input type.

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

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

Feeds this value into the given Hasher.

impl<T: Ord + ?Sized> Ord for Prehashed<T>

fn cmp(&self, other: &Self) -> Ordering

This method returns an Ordering between self and other.

impl<T: ?Sized> PartialEq for Prehashed<T>

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: PartialOrd + ?Sized> PartialOrd for Prehashed<T>

fn partial_cmp(&self, other: &Self) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

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

This method tests less than (for self and other) and is used by the < operator.

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

This method tests less than or equal to (for self and other) and is used by the <= operator.

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

This method tests greater than (for self and other) and is used by the > operator.

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

This method tests greater than or equal to (for self and other) and is used by the >= operator.

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

impl<T: ?Sized> Eq for Prehashed<T>