Struct AHashSet

pub struct AHashSet<T, S = RandomState>(/* private fields */);

A HashSet using RandomState to hash the items. (Requires the std feature to be enabled.)

Implementations

impl<T> AHashSet<T, RandomState>

pub fn new() -> Self

This crates a hashset using RandomState::new. See the documentation in [RandomSource] for notes about key strength.

pub fn with_capacity(capacity: usize) -> Self

This crates a hashset with the specified capacity using RandomState::new. See the documentation in [RandomSource] for notes about key strength.

impl<T, S> AHashSet<T, S>

where S: BuildHasher,

pub fn with_hasher(hash_builder: S) -> Self

pub fn with_capacity_and_hasher(capacity: usize, hash_builder: S) -> Self

Methods from Deref<Target = HashSet<T, S>>

pub fn capacity(&self) -> usize

Returns the number of elements the set can hold without reallocating.

Examples

use std::collections::HashSet;
let set: HashSet<i32> = HashSet::with_capacity(100);
assert!(set.capacity() >= 100);

pub fn iter(&self) -> Iter<'_, T>

An iterator visiting all elements in arbitrary order. The iterator element type is &'a T.

Examples

use std::collections::HashSet;
let mut set = HashSet::new();
set.insert("a");
set.insert("b");

// Will print in an arbitrary order.
for x in set.iter() {
    println!("{x}");
}

Performance

In the current implementation, iterating over set takes O(capacity) time instead of O(len) because it internally visits empty buckets too.

pub fn len(&self) -> usize

Returns the number of elements in the set.

Examples

use std::collections::HashSet;

let mut v = HashSet::new();
assert_eq!(v.len(), 0);
v.insert(1);
assert_eq!(v.len(), 1);

pub fn is_empty(&self) -> bool

Returns true if the set contains no elements.

Examples

use std::collections::HashSet;

let mut v = HashSet::new();
assert!(v.is_empty());
v.insert(1);
assert!(!v.is_empty());

pub fn drain(&mut self) -> Drain<'_, T>

Clears the set, returning all elements as an iterator. Keeps the allocated memory for reuse.

If the returned iterator is dropped before being fully consumed, it drops the remaining elements. The returned iterator keeps a mutable borrow on the set to optimize its implementation.

Examples

use std::collections::HashSet;

let mut set = HashSet::from([1, 2, 3]);
assert!(!set.is_empty());

// print 1, 2, 3 in an arbitrary order
for i in set.drain() {
    println!("{i}");
}

assert!(set.is_empty());

pub fn extract_if<F>(&mut self, pred: F) -> ExtractIf<'_, T, F>

where F: FnMut(&T) -> bool,

🔬This is a nightly-only experimental API. (hash_extract_if)

Creates an iterator which uses a closure to determine if a value should be removed.

If the closure returns true, then the value is removed and yielded. If the closure returns false, the value will remain in the list and will not be yielded by the iterator.

If the returned ExtractIf is not exhausted, e.g. because it is dropped without iterating or the iteration short-circuits, then the remaining elements will be retained. Use retain with a negated predicate if you do not need the returned iterator.

Examples

Splitting a set into even and odd values, reusing the original set:

#![feature(hash_extract_if)]
use std::collections::HashSet;

let mut set: HashSet<i32> = (0..8).collect();
let extracted: HashSet<i32> = set.extract_if(|v| v % 2 == 0).collect();

let mut evens = extracted.into_iter().collect::<Vec<_>>();
let mut odds = set.into_iter().collect::<Vec<_>>();
evens.sort();
odds.sort();

assert_eq!(evens, vec![0, 2, 4, 6]);
assert_eq!(odds, vec![1, 3, 5, 7]);

pub fn retain<F>(&mut self, f: F)

where F: FnMut(&T) -> bool,

Retains only the elements specified by the predicate.

In other words, remove all elements e for which f(&e) returns false. The elements are visited in unsorted (and unspecified) order.

Examples

use std::collections::HashSet;

let mut set = HashSet::from([1, 2, 3, 4, 5, 6]);
set.retain(|&k| k % 2 == 0);
assert_eq!(set, HashSet::from([2, 4, 6]));

Performance

In the current implementation, this operation takes O(capacity) time instead of O(len) because it internally visits empty buckets too.

pub fn clear(&mut self)

Clears the set, removing all values.

Examples

use std::collections::HashSet;

let mut v = HashSet::new();
v.insert(1);
v.clear();
assert!(v.is_empty());

pub fn hasher(&self) -> &S

Returns a reference to the set’s BuildHasher.

Examples

use std::collections::HashSet;
use std::hash::RandomState;

let hasher = RandomState::new();
let set: HashSet<i32> = HashSet::with_hasher(hasher);
let hasher: &RandomState = set.hasher();

pub fn reserve(&mut self, additional: usize)

Reserves capacity for at least additional more elements to be inserted in the HashSet. The collection may reserve more space to speculatively avoid frequent reallocations. After calling reserve, capacity will be greater than or equal to self.len() + additional. Does nothing if capacity is already sufficient.

Panics

Panics if the new allocation size overflows usize.

Examples

use std::collections::HashSet;
let mut set: HashSet<i32> = HashSet::new();
set.reserve(10);
assert!(set.capacity() >= 10);

pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError>

Tries to reserve capacity for at least additional more elements to be inserted in the HashSet. The collection may reserve more space to speculatively avoid frequent reallocations. After calling try_reserve, capacity will be greater than or equal to self.len() + additional if it returns Ok(()). Does nothing if capacity is already sufficient.

Errors

If the capacity overflows, or the allocator reports a failure, then an error is returned.

Examples

use std::collections::HashSet;
let mut set: HashSet<i32> = HashSet::new();
set.try_reserve(10).expect("why is the test harness OOMing on a handful of bytes?");

pub fn shrink_to_fit(&mut self)

Shrinks the capacity of the set as much as possible. It will drop down as much as possible while maintaining the internal rules and possibly leaving some space in accordance with the resize policy.

Examples

use std::collections::HashSet;

let mut set = HashSet::with_capacity(100);
set.insert(1);
set.insert(2);
assert!(set.capacity() >= 100);
set.shrink_to_fit();
assert!(set.capacity() >= 2);

pub fn shrink_to(&mut self, min_capacity: usize)

Shrinks the capacity of the set with a lower limit. It will drop down no lower than the supplied limit while maintaining the internal rules and possibly leaving some space in accordance with the resize policy.

If the current capacity is less than the lower limit, this is a no-op.

Examples

use std::collections::HashSet;

let mut set = HashSet::with_capacity(100);
set.insert(1);
set.insert(2);
assert!(set.capacity() >= 100);
set.shrink_to(10);
assert!(set.capacity() >= 10);
set.shrink_to(0);
assert!(set.capacity() >= 2);

pub fn difference<'a>( &'a self, other: &'a HashSet<T, S>, ) -> Difference<'a, T, S>

Visits the values representing the difference, i.e., the values that are in self but not in other.

Examples

use std::collections::HashSet;
let a = HashSet::from([1, 2, 3]);
let b = HashSet::from([4, 2, 3, 4]);

// Can be seen as `a - b`.
for x in a.difference(&b) {
    println!("{x}"); // Print 1
}

let diff: HashSet<_> = a.difference(&b).collect();
assert_eq!(diff, [1].iter().collect());

// Note that difference is not symmetric,
// and `b - a` means something else:
let diff: HashSet<_> = b.difference(&a).collect();
assert_eq!(diff, [4].iter().collect());

pub fn symmetric_difference<'a>( &'a self, other: &'a HashSet<T, S>, ) -> SymmetricDifference<'a, T, S>

Visits the values representing the symmetric difference, i.e., the values that are in self or in other but not in both.

Examples

use std::collections::HashSet;
let a = HashSet::from([1, 2, 3]);
let b = HashSet::from([4, 2, 3, 4]);

// Print 1, 4 in arbitrary order.
for x in a.symmetric_difference(&b) {
    println!("{x}");
}

let diff1: HashSet<_> = a.symmetric_difference(&b).collect();
let diff2: HashSet<_> = b.symmetric_difference(&a).collect();

assert_eq!(diff1, diff2);
assert_eq!(diff1, [1, 4].iter().collect());

pub fn intersection<'a>( &'a self, other: &'a HashSet<T, S>, ) -> Intersection<'a, T, S>

Visits the values representing the intersection, i.e., the values that are both in self and other.

When an equal element is present in self and other then the resulting Intersection may yield references to one or the other. This can be relevant if T contains fields which are not compared by its Eq implementation, and may hold different value between the two equal copies of T in the two sets.

Examples

use std::collections::HashSet;
let a = HashSet::from([1, 2, 3]);
let b = HashSet::from([4, 2, 3, 4]);

// Print 2, 3 in arbitrary order.
for x in a.intersection(&b) {
    println!("{x}");
}

let intersection: HashSet<_> = a.intersection(&b).collect();
assert_eq!(intersection, [2, 3].iter().collect());

pub fn union<'a>(&'a self, other: &'a HashSet<T, S>) -> Union<'a, T, S>

Visits the values representing the union, i.e., all the values in self or other, without duplicates.

Examples

use std::collections::HashSet;
let a = HashSet::from([1, 2, 3]);
let b = HashSet::from([4, 2, 3, 4]);

// Print 1, 2, 3, 4 in arbitrary order.
for x in a.union(&b) {
    println!("{x}");
}

let union: HashSet<_> = a.union(&b).collect();
assert_eq!(union, [1, 2, 3, 4].iter().collect());

pub fn contains<Q>(&self, value: &Q) -> bool

where T: Borrow<Q>, Q: Hash + Eq + ?Sized,

Returns true if the set contains a value.

The value may be any borrowed form of the set’s value type, but Hash and Eq on the borrowed form must match those for the value type.

Examples

use std::collections::HashSet;

let set = HashSet::from([1, 2, 3]);
assert_eq!(set.contains(&1), true);
assert_eq!(set.contains(&4), false);

pub fn get<Q>(&self, value: &Q) -> Option<&T>

where T: Borrow<Q>, Q: Hash + Eq + ?Sized,

Returns a reference to the value in the set, if any, that is equal to the given value.

The value may be any borrowed form of the set’s value type, but Hash and Eq on the borrowed form must match those for the value type.

Examples

use std::collections::HashSet;

let set = HashSet::from([1, 2, 3]);
assert_eq!(set.get(&2), Some(&2));
assert_eq!(set.get(&4), None);

pub fn get_or_insert(&mut self, value: T) -> &T

🔬This is a nightly-only experimental API. (hash_set_entry)

Inserts the given value into the set if it is not present, then returns a reference to the value in the set.

Examples

#![feature(hash_set_entry)]

use std::collections::HashSet;

let mut set = HashSet::from([1, 2, 3]);
assert_eq!(set.len(), 3);
assert_eq!(set.get_or_insert(2), &2);
assert_eq!(set.get_or_insert(100), &100);
assert_eq!(set.len(), 4); // 100 was inserted

pub fn get_or_insert_with<Q, F>(&mut self, value: &Q, f: F) -> &T

where T: Borrow<Q>, Q: Hash + Eq + ?Sized, F: FnOnce(&Q) -> T,

🔬This is a nightly-only experimental API. (hash_set_entry)

Inserts a value computed from f into the set if the given value is not present, then returns a reference to the value in the set.

Examples

#![feature(hash_set_entry)]

use std::collections::HashSet;

let mut set: HashSet<String> = ["cat", "dog", "horse"]
    .iter().map(|&pet| pet.to_owned()).collect();

assert_eq!(set.len(), 3);
for &pet in &["cat", "dog", "fish"] {
    let value = set.get_or_insert_with(pet, str::to_owned);
    assert_eq!(value, pet);
}
assert_eq!(set.len(), 4); // a new "fish" was inserted

pub fn entry(&mut self, value: T) -> Entry<'_, T, S>

🔬This is a nightly-only experimental API. (hash_set_entry)

Gets the given value’s corresponding entry in the set for in-place manipulation.

Examples

#![feature(hash_set_entry)]

use std::collections::HashSet;
use std::collections::hash_set::Entry::*;

let mut singles = HashSet::new();
let mut dupes = HashSet::new();

for ch in "a short treatise on fungi".chars() {
    if let Vacant(dupe_entry) = dupes.entry(ch) {
        // We haven't already seen a duplicate, so
        // check if we've at least seen it once.
        match singles.entry(ch) {
            Vacant(single_entry) => {
                // We found a new character for the first time.
                single_entry.insert()
            }
            Occupied(single_entry) => {
                // We've already seen this once, "move" it to dupes.
                single_entry.remove();
                dupe_entry.insert();
            }
        }
    }
}

assert!(!singles.contains(&'t') && dupes.contains(&'t'));
assert!(singles.contains(&'u') && !dupes.contains(&'u'));
assert!(!singles.contains(&'v') && !dupes.contains(&'v'));

pub fn is_disjoint(&self, other: &HashSet<T, S>) -> bool

Returns true if self has no elements in common with other. This is equivalent to checking for an empty intersection.

Examples

use std::collections::HashSet;

let a = HashSet::from([1, 2, 3]);
let mut b = HashSet::new();

assert_eq!(a.is_disjoint(&b), true);
b.insert(4);
assert_eq!(a.is_disjoint(&b), true);
b.insert(1);
assert_eq!(a.is_disjoint(&b), false);

pub fn is_subset(&self, other: &HashSet<T, S>) -> bool

Returns true if the set is a subset of another, i.e., other contains at least all the values in self.

Examples

use std::collections::HashSet;

let sup = HashSet::from([1, 2, 3]);
let mut set = HashSet::new();

assert_eq!(set.is_subset(&sup), true);
set.insert(2);
assert_eq!(set.is_subset(&sup), true);
set.insert(4);
assert_eq!(set.is_subset(&sup), false);

pub fn is_superset(&self, other: &HashSet<T, S>) -> bool

Returns true if the set is a superset of another, i.e., self contains at least all the values in other.

Examples

use std::collections::HashSet;

let sub = HashSet::from([1, 2]);
let mut set = HashSet::new();

assert_eq!(set.is_superset(&sub), false);

set.insert(0);
set.insert(1);
assert_eq!(set.is_superset(&sub), false);

set.insert(2);
assert_eq!(set.is_superset(&sub), true);

pub fn insert(&mut self, value: T) -> bool

Adds a value to the set.

Returns whether the value was newly inserted. That is:

• If the set did not previously contain this value, true is returned.
• If the set already contained this value, false is returned, and the set is not modified: original value is not replaced, and the value passed as argument is dropped.

Examples

use std::collections::HashSet;

let mut set = HashSet::new();

assert_eq!(set.insert(2), true);
assert_eq!(set.insert(2), false);
assert_eq!(set.len(), 1);

pub fn replace(&mut self, value: T) -> Option<T>

Adds a value to the set, replacing the existing value, if any, that is equal to the given one. Returns the replaced value.

Examples

use std::collections::HashSet;

let mut set = HashSet::new();
set.insert(Vec::<i32>::new());

assert_eq!(set.get(&[][..]).unwrap().capacity(), 0);
set.replace(Vec::with_capacity(10));
assert_eq!(set.get(&[][..]).unwrap().capacity(), 10);

pub fn remove<Q>(&mut self, value: &Q) -> bool

where T: Borrow<Q>, Q: Hash + Eq + ?Sized,

Removes a value from the set. Returns whether the value was present in the set.

The value may be any borrowed form of the set’s value type, but Hash and Eq on the borrowed form must match those for the value type.

Examples

use std::collections::HashSet;

let mut set = HashSet::new();

set.insert(2);
assert_eq!(set.remove(&2), true);
assert_eq!(set.remove(&2), false);

pub fn take<Q>(&mut self, value: &Q) -> Option<T>

where T: Borrow<Q>, Q: Hash + Eq + ?Sized,

Removes and returns the value in the set, if any, that is equal to the given one.

The value may be any borrowed form of the set’s value type, but Hash and Eq on the borrowed form must match those for the value type.

Examples

use std::collections::HashSet;

let mut set = HashSet::from([1, 2, 3]);
assert_eq!(set.take(&2), Some(2));
assert_eq!(set.take(&2), None);

Trait Implementations

impl<T, S> BitAnd<&AHashSet<T, S>> for &AHashSet<T, S>

where T: Eq + Hash + Clone, S: BuildHasher + Default,

fn bitand(self, rhs: &AHashSet<T, S>) -> AHashSet<T, S>

Returns the intersection of self and rhs as a new AHashSet<T, S>.

Examples

use ahash::AHashSet;

let a: AHashSet<_> = vec![1, 2, 3].into_iter().collect();
let b: AHashSet<_> = vec![2, 3, 4].into_iter().collect();

let set = &a & &b;

let mut i = 0;
let expected = [2, 3];
for x in &set {
    assert!(expected.contains(x));
    i += 1;
}
assert_eq!(i, expected.len());

type Output = AHashSet<T, S>

The resulting type after applying the & operator.

impl<T, S> BitOr<&AHashSet<T, S>> for &AHashSet<T, S>

where T: Eq + Hash + Clone, S: BuildHasher + Default,

fn bitor(self, rhs: &AHashSet<T, S>) -> AHashSet<T, S>

Returns the union of self and rhs as a new AHashSet<T, S>.

Examples

use ahash::AHashSet;

let a: AHashSet<_> = vec![1, 2, 3].into_iter().collect();
let b: AHashSet<_> = vec![3, 4, 5].into_iter().collect();

let set = &a | &b;

let mut i = 0;
let expected = [1, 2, 3, 4, 5];
for x in &set {
    assert!(expected.contains(x));
    i += 1;
}
assert_eq!(i, expected.len());

type Output = AHashSet<T, S>

The resulting type after applying the | operator.

impl<T, S> BitXor<&AHashSet<T, S>> for &AHashSet<T, S>

where T: Eq + Hash + Clone, S: BuildHasher + Default,

fn bitxor(self, rhs: &AHashSet<T, S>) -> AHashSet<T, S>

Returns the symmetric difference of self and rhs as a new AHashSet<T, S>.

Examples

use ahash::AHashSet;

let a: AHashSet<_> = vec![1, 2, 3].into_iter().collect();
let b: AHashSet<_> = vec![3, 4, 5].into_iter().collect();

let set = &a ^ &b;

let mut i = 0;
let expected = [1, 2, 4, 5];
for x in &set {
    assert!(expected.contains(x));
    i += 1;
}
assert_eq!(i, expected.len());

type Output = AHashSet<T, S>

The resulting type after applying the ^ operator.

impl<T: Clone, S: Clone> Clone for AHashSet<T, S>

fn clone(&self) -> AHashSet<T, S>

Returns a copy of the value.

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

Performs copy-assignment from source.

impl<T, S> Debug for AHashSet<T, S>

where T: Debug, S: BuildHasher,

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

Formats the value using the given formatter.

impl<T, S> Deref for AHashSet<T, S>

type Target = HashSet<T, S>

The resulting type after dereferencing.

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

Dereferences the value.

impl<T, S> DerefMut for AHashSet<T, S>

fn deref_mut(&mut self) -> &mut Self::Target

Mutably dereferences the value.

impl<'a, T, S> Extend<&'a T> for AHashSet<T, S>

where T: 'a + Eq + Hash + Copy, S: BuildHasher,

fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I)

Extends a collection with the contents of an iterator.

fn extend_one(&mut self, item: A)

🔬This is a nightly-only experimental API. (extend_one)

Extends a collection with exactly one element.

fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (extend_one)

Reserves capacity in a collection for the given number of additional elements.

impl<T, S> Extend<T> for AHashSet<T, S>

where T: Eq + Hash, S: BuildHasher,

fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I)

Extends a collection with the contents of an iterator.

fn extend_one(&mut self, item: A)

🔬This is a nightly-only experimental API. (extend_one)

Extends a collection with exactly one element.

fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (extend_one)

Reserves capacity in a collection for the given number of additional elements.

impl<T, const N: usize> From<[T; N]> for AHashSet<T>

where T: Eq + Hash,

fn from(arr: [T; N]) -> Self

Examples

use ahash::AHashSet;

let set1 = AHashSet::from([1, 2, 3, 4]);
let set2: AHashSet<_> = [1, 2, 3, 4].into();
assert_eq!(set1, set2);

impl<T> From<HashSet<T, RandomState>> for AHashSet<T>

fn from(item: HashSet<T, RandomState>) -> Self

Converts to this type from the input type.

impl<T> FromIterator<T> for AHashSet<T, RandomState>

where T: Eq + Hash,

fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> AHashSet<T>

This crates a hashset from the provided iterator using RandomState::new. See the documentation in [RandomSource] for notes about key strength.

impl<T> Into<HashSet<T, RandomState>> for AHashSet<T>

fn into(self) -> HashSet<T, RandomState>

Converts this type into the (usually inferred) input type.

impl<'a, T, S> IntoIterator for &'a AHashSet<T, S>

type Item = &'a T

The type of the elements being iterated over.

type IntoIter = Iter<'a, T>

Which kind of iterator are we turning this into?

fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value.

impl<T, S> IntoIterator for AHashSet<T, S>

type Item = T

The type of the elements being iterated over.

type IntoIter = IntoIter<T>

Which kind of iterator are we turning this into?

fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value.

impl<T, S> PartialEq for AHashSet<T, S>

where T: Eq + Hash, S: BuildHasher,

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

Tests for self and other values to be equal, and is used by ==.

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

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

impl<T, S> Sub<&AHashSet<T, S>> for &AHashSet<T, S>

where T: Eq + Hash + Clone, S: BuildHasher + Default,

fn sub(self, rhs: &AHashSet<T, S>) -> AHashSet<T, S>

Returns the difference of self and rhs as a new AHashSet<T, S>.

Examples

use ahash::AHashSet;

let a: AHashSet<_> = vec![1, 2, 3].into_iter().collect();
let b: AHashSet<_> = vec![3, 4, 5].into_iter().collect();

let set = &a - &b;

let mut i = 0;
let expected = [1, 2];
for x in &set {
    assert!(expected.contains(x));
    i += 1;
}
assert_eq!(i, expected.len());

type Output = AHashSet<T, S>

The resulting type after applying the - operator.

impl<T, S> Eq for AHashSet<T, S>

where T: Eq + Hash, S: BuildHasher,