# Struct std::collections::hash_set::HashSet

1.0.0 · source ·

    pub struct HashSet<T, S = RandomState> { /* private fields */ }

Expand description

A hash set implemented as a `HashMap` where the value is `()`.

As with the `HashMap` type, a `HashSet` requires that the elements implement the `Eq` and `Hash` traits. This can frequently be achieved by using `#[derive(PartialEq, Eq, Hash)]`. If you implement these yourself, 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 be equal. Violating this property is a logic error.

It is also a logic error for a key to be modified in such a way that the key’s hash, as determined by the `Hash` trait, or its equality, as determined by the `Eq` trait, changes while it is in the map. This is normally only possible through `Cell`, `RefCell`, global state, I/O, or unsafe code.

The behavior resulting from either logic error is not specified, but will be encapsulated to the `HashSet` that observed the logic error and not result in undefined behavior. This could include panics, incorrect results, aborts, memory leaks, and non-termination.

## Examples

    use std::collections::HashSet;
    // Type inference lets us omit an explicit type signature (which
    // would be `HashSet<String>` in this example).
    let mut books = HashSet::new();

    // Add some books.
    books.insert("A Dance With Dragons".to_string());
    books.insert("To Kill a Mockingbird".to_string());
    books.insert("The Odyssey".to_string());
    books.insert("The Great Gatsby".to_string());

    // Check for a specific one.
    if !books.contains("The Winds of Winter") {
        println!("We have {} books, but The Winds of Winter ain't one.",
                 books.len());
    }

    // Remove a book.
    books.remove("The Odyssey");

    // Iterate over everything.
    for book in &books {
        println!("{book}");
    }

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The easiest way to use `HashSet` with a custom type is to derive `Eq` and `Hash`. We must also derive `PartialEq`, which is required if `Eq` is derived.

    use std::collections::HashSet;
    #[derive(Hash, Eq, PartialEq, Debug)]
    struct Viking {
        name: String,
        power: usize,
    }

    let mut vikings = HashSet::new();

    vikings.insert(Viking { name: "Einar".to_string(), power: 9 });
    vikings.insert(Viking { name: "Einar".to_string(), power: 9 });
    vikings.insert(Viking { name: "Olaf".to_string(), power: 4 });
    vikings.insert(Viking { name: "Harald".to_string(), power: 8 });

    // Use derived implementation to print the vikings.
    for x in &vikings {
        println!("{x:?}");
    }

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A `HashSet` with a known list of items can be initialized from an array:

    use std::collections::HashSet;

    let viking_names = HashSet::from(["Einar", "Olaf", "Harald"]);

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## Implementations§

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### impl<T> HashSet<T, RandomState>

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#### pub fn new() -> HashSet<T, RandomState>

Creates an empty `HashSet`.

The hash set is initially created with a capacity of 0, so it will not allocate until it is first inserted into.

##### Examples

    use std::collections::HashSet;
    let set: HashSet<i32> = HashSet::new();

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#### pub fn with_capacity(capacity: usize) -> HashSet<T, RandomState>

Creates an empty `HashSet` with at least the specified capacity.

The hash set will be able to hold at least `capacity` elements without reallocating. This method is allowed to allocate for more elements than `capacity`. If `capacity` is 0, the hash set will not allocate.

##### Examples

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

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### impl<T, S> HashSet<T, S>

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#### 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);

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#### 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}");
    }

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##### Performance

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

source

#### 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);

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#### 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());

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1.6.0 · source

#### 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());

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#### 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` #59618)

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]);

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1.18.0 · source

#### 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]));

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##### Performance

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

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#### 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());

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1.7.0 (const: unstable) · source

#### pub fn with_hasher(hasher: S) -> HashSet<T, S>

Creates a new empty hash set which will use the given hasher to hash keys.

The hash set is also created with the default initial capacity.

Warning: `hasher` is normally randomly generated, and is designed to allow `HashSet`s to be resistant to attacks that cause many collisions and very poor performance. Setting it manually using this function can expose a DoS attack vector.

The `hash_builder` passed should implement the `BuildHasher` trait for the HashMap to be useful, see its documentation for details.

##### Examples

    use std::collections::HashSet;
    use std::collections::hash_map::RandomState;

    let s = RandomState::new();
    let mut set = HashSet::with_hasher(s);
    set.insert(2);

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1.7.0 · source

#### pub fn with_capacity_and_hasher(capacity: usize, hasher: S) -> HashSet<T, S>

Creates an empty `HashSet` with at least the specified capacity, using `hasher` to hash the keys.

The hash set will be able to hold at least `capacity` elements without reallocating. This method is allowed to allocate for more elements than `capacity`. If `capacity` is 0, the hash set will not allocate.

Warning: `hasher` is normally randomly generated, and is designed to allow `HashSet`s to be resistant to attacks that cause many collisions and very poor performance. Setting it manually using this function can expose a DoS attack vector.

The `hash_builder` passed should implement the `BuildHasher` trait for the HashMap to be useful, see its documentation for details.

##### Examples

    use std::collections::HashSet;
    use std::collections::hash_map::RandomState;

    let s = RandomState::new();
    let mut set = HashSet::with_capacity_and_hasher(10, s);
    set.insert(1);

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1.9.0 · source

#### pub fn hasher(&self) -> &S

Returns a reference to the set’s `BuildHasher`.

##### Examples

    use std::collections::HashSet;
    use std::collections::hash_map::RandomState;

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

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source§

### impl<T, S> HashSet<T, S>where T: Eq + Hash, S: BuildHasher,

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#### 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);

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1.57.0 · source

#### 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?");

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#### 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);

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1.56.0 · source

#### 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);

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#### 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());

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#### 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());

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#### 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());

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#### 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());

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#### 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);

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1.9.0 · source

#### 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);

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

🔬This is a nightly-only experimental API. (`hash_set_entry` #60896)

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

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#### pub fn get_or_insert_owned<Q>(&mut self, value: &Q) -> &T where T: Borrow<Q>, Q: Hash + Eq + ToOwned<Owned = T> + ?Sized,

🔬This is a nightly-only experimental API. (`hash_set_entry` #60896)

Inserts an owned copy of 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<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_owned(pet);
        assert_eq!(value, pet);
    }
    assert_eq!(set.len(), 4); // a new "fish" was inserted

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#### 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` #60896)

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

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#### 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);

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#### 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);

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#### 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);

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#### 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);

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1.9.0 · source

#### 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);

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#### 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);

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1.9.0 · source

#### 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);

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## Trait Implementations§

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### impl<T, S> BitAnd<&HashSet<T, S>> for &HashSet<T, S>where T: Eq + Hash + Clone, S: BuildHasher + Default,

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

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

##### Examples

    use std::collections::HashSet;

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

    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());

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#### type Output = HashSet<T, S>

The resulting type after applying the `&` operator.
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### impl<T, S> BitOr<&HashSet<T, S>> for &HashSet<T, S>where T: Eq + Hash + Clone, S: BuildHasher + Default,

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

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

##### Examples

    use std::collections::HashSet;

    let a = HashSet::from([1, 2, 3]);
    let b = HashSet::from([3, 4, 5]);

    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());

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#### type Output = HashSet<T, S>

The resulting type after applying the `|` operator.
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### impl<T, S> BitXor<&HashSet<T, S>> for &HashSet<T, S>where T: Eq + Hash + Clone, S: BuildHasher + Default,

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

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

##### Examples

    use std::collections::HashSet;

    let a = HashSet::from([1, 2, 3]);
    let b = HashSet::from([3, 4, 5]);

    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());

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#### type Output = HashSet<T, S>

The resulting type after applying the `^` operator.
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### impl<T, S> Clone for HashSet<T, S>where T: Clone, S: Clone,

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#### fn clone(&self) -> Self

Returns a copy of the value. Read more
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#### fn clone_from(&mut self, other: &Self)

Performs copy-assignment from `source`. Read more
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### impl<T, S> Debug for HashSet<T, S>where T: Debug,

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

Formats the value using the given formatter. Read more
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### impl<T, S> Default for HashSet<T, S>where S: Default,

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#### fn default() -> HashSet<T, S>

Creates an empty `HashSet<T, S>` with the `Default` value for the hasher.

1.4.0 · source§

### impl<'a, T, S> Extend<&'a T> for HashSet<T, S>where T: 'a + Eq + Hash + Copy, S: BuildHasher,

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

Extends a collection with the contents of an iterator. Read more
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#### fn extend_one(&mut self, item: &'a T)

🔬This is a nightly-only experimental API. (`extend_one` #72631)
Extends a collection with exactly one element.
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#### fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (`extend_one` #72631)
Reserves capacity in a collection for the given number of additional elements. Read more
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### impl<T, S> Extend<T> for HashSet<T, S>where T: Eq + Hash, S: BuildHasher,

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

Extends a collection with the contents of an iterator. Read more
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#### fn extend_one(&mut self, item: T)

🔬This is a nightly-only experimental API. (`extend_one` #72631)
Extends a collection with exactly one element.
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#### fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (`extend_one` #72631)
Reserves capacity in a collection for the given number of additional elements. Read more
1.56.0 · source§

### impl<T, const N: usize> From<[T; N]> for HashSet<T, RandomState>where T: Eq + Hash,

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

##### Examples

    use std::collections::HashSet;

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

Run
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### impl<T, S> FromIterator<T> for HashSet<T, S>where T: Eq + Hash, S: BuildHasher + Default,

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#### fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> HashSet<T, S>

Creates a value from an iterator. Read more
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### impl<'a, T, S> IntoIterator for &'a HashSet<T, S>

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#### type Item = &'a T

The type of the elements being iterated over.
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#### type IntoIter = Iter<'a, T>

Which kind of iterator are we turning this into?
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#### fn into_iter(self) -> Iter<'a, T> ⓘ

Creates an iterator from a value. Read more
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### impl<T, S> IntoIterator for HashSet<T, S>

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#### fn into_iter(self) -> IntoIter<T> ⓘ

Creates a consuming iterator, that is, one that moves each value out of the set in arbitrary order. The set cannot be used after calling this.

##### Examples

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

    // Not possible to collect to a Vec<String> with a regular `.iter()`.
    let v: Vec<String> = set.into_iter().collect();

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

Run
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#### type Item = T

The type of the elements being iterated over.
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#### type IntoIter = IntoIter<T>

Which kind of iterator are we turning this into?
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### impl<T, S> PartialEq for HashSet<T, S>where T: Eq + Hash, S: BuildHasher,

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

This method tests for `self` and `other` values to be equal, and is used by `==`.
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#### 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.
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### impl<T, S> Sub<&HashSet<T, S>> for &HashSet<T, S>where T: Eq + Hash + Clone, S: BuildHasher + Default,

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

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

##### Examples

    use std::collections::HashSet;

    let a = HashSet::from([1, 2, 3]);
    let b = HashSet::from([3, 4, 5]);

    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());

Run
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#### type Output = HashSet<T, S>

The resulting type after applying the `-` operator.
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### impl<T, S> Eq for HashSet<T, S>where T: Eq + Hash, S: BuildHasher,

## Auto Trait Implementations§

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### impl<T, S> RefUnwindSafe for HashSet<T, S>where S: RefUnwindSafe, T: RefUnwindSafe,

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### impl<T, S> Send for HashSet<T, S>where S: Send, T: Send,

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### impl<T, S> Sync for HashSet<T, S>where S: Sync, T: Sync,

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### impl<T, S> Unpin for HashSet<T, S>where S: Unpin, T: Unpin,

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### impl<T, S> UnwindSafe for HashSet<T, S>where S: UnwindSafe, T: UnwindSafe,

## Blanket Implementations§

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### impl<T> Any for Twhere T: 'static + ?Sized,

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#### fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more
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### impl<T> Borrow<T> for Twhere T: ?Sized,

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#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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### impl<T> BorrowMut<T> for Twhere T: ?Sized,

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#### fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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### impl<T> From<T> for T

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#### fn from(t: T) -> T

Returns the argument unchanged.

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### impl<T, U> Into<U> for Twhere U: From<T>,

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#### fn into(self) -> U

Calls `U::from(self)`.

That is, this conversion is whatever the implementation of `From<T> for U` chooses to do.

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### impl<T> ToOwned for Twhere T: Clone,

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#### type Owned = T

The resulting type after obtaining ownership.
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#### fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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#### fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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### impl<T, U> TryFrom<U> for Twhere U: Into<T>,

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#### type Error = Infallible

The type returned in the event of a conversion error.
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#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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### impl<T, U> TryInto<U> for Twhere U: TryFrom<T>,

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#### type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.