# Struct hashbrown::hash_set::HashSet

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    pub struct HashSet<T, S = DefaultHashBuilder, A: Allocator + Clone = Global> { /* 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.

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

It is also a logic error for the `Hash` implementation of a key to panic. This is generally only possible if the trait is implemented manually. If a panic does occur then the contents of the `HashSet` may become corrupted and some items may be dropped from the table.

## Examples

    use hashbrown::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);
    }

The easiest way to use `HashSet` with a custom type is to derive `Eq` and `Hash`. We must also derive `PartialEq`. This will in the future be implied by `Eq`.

    use hashbrown::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);
    }

A `HashSet` with fixed list of elements can be initialized from an array:

    use hashbrown::HashSet;

    let viking_names: HashSet<&'static str> =
        [ "Einar", "Olaf", "Harald" ].iter().cloned().collect();
    // use the values stored in the set

## Implementations

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### impl<T> HashSet<T, DefaultHashBuilder>

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#### pub fn new() -> Self

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 hashbrown::HashSet;
    let set: HashSet<i32> = HashSet::new();

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#### pub fn with_capacity(capacity: usize) -> Self

Creates an empty `HashSet` with the specified capacity.

The hash set will be able to hold at least `capacity` elements without reallocating. If `capacity` is 0, the hash set will not allocate.

##### Examples

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

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### impl<T: Hash + Eq, A: Allocator + Clone> HashSet<T, DefaultHashBuilder, A>

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#### pub fn new_in(alloc: A) -> Self

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 hashbrown::HashSet;
    let set: HashSet<i32> = HashSet::new();

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#### pub fn with_capacity_in(capacity: usize, alloc: A) -> Self

Creates an empty `HashSet` with the specified capacity.

The hash set will be able to hold at least `capacity` elements without reallocating. If `capacity` is 0, the hash set will not allocate.

##### Examples

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

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### impl<T, S, A: Allocator + Clone> HashSet<T, S, A>

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#### pub fn capacity(&self) -> usize

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

##### Examples

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

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#### pub fn iter(&self) -> Iter<'_, T>ⓘNotable traits for Iter<'a, K>`impl<'a, K> Iterator for Iter<'a, K> type Item = &'a K;`

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

##### Examples

    use hashbrown::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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#### pub fn len(&self) -> usize

Returns the number of elements in the set.

##### Examples

    use hashbrown::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 hashbrown::HashSet;

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

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#### pub fn drain(&mut self) -> Drain<'_, T, A>ⓘNotable traits for Drain<'_, K, A>`impl<K, A: Allocator + Clone> Iterator for Drain<'_, K, A> type Item = K;`

Clears the set, returning all elements in an iterator.

##### Examples

    use hashbrown::HashSet;

    let mut set: HashSet<_> = [1, 2, 3].iter().cloned().collect();
    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 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` such that `f(&e)` returns `false`.

##### Examples

    use hashbrown::HashSet;

    let xs = [1,2,3,4,5,6];
    let mut set: HashSet<i32> = xs.iter().cloned().collect();
    set.retain(|&k| k % 2 == 0);
    assert_eq!(set.len(), 3);

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#### pub fn drain_filter<F>(&mut self, f: F) -> DrainFilter<'_, T, F, A>ⓘNotable traits for DrainFilter<'_, K, F, A>`impl<K, F, A: Allocator + Clone> Iterator for DrainFilter<'_, K, F, A> where
F: FnMut(&K) -> bool, type Item = K;` where
F: FnMut(&T) -> bool,

Drains elements which are true under the given predicate, and returns an iterator over the removed items.

In other words, move all elements `e` such that `f(&e)` returns `true` out into another iterator.

When the returned DrainedFilter is dropped, any remaining elements that satisfy the predicate are dropped from the set.

##### Examples

    use hashbrown::HashSet;

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

    let mut evens = drained.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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#### pub fn clear(&mut self)

Clears the set, removing all values.

##### Examples

    use hashbrown::HashSet;

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

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

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#### pub const fn with_hasher(hasher: S) -> Self

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 hashbrown::HashSet;
    use hashbrown::hash_map::DefaultHashBuilder;

    let s = DefaultHashBuilder::default();
    let mut set = HashSet::with_hasher(s);
    set.insert(2);

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

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

The hash set will be able to hold at least `capacity` elements without reallocating. 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 hashbrown::HashSet;
    use hashbrown::hash_map::DefaultHashBuilder;

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

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### impl<T, S, A> HashSet<T, S, A> where
A: Allocator + Clone,

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#### pub fn allocator(&self) -> &A

Returns a reference to the underlying allocator.

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#### pub fn with_hasher_in(hasher: S, alloc: A) -> Self

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.

##### Examples

    use hashbrown::HashSet;
    use hashbrown::hash_map::DefaultHashBuilder;

    let s = DefaultHashBuilder::default();
    let mut set = HashSet::with_hasher(s);
    set.insert(2);

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#### pub fn with_capacity_and_hasher_in(capacity: usize, hasher: S, alloc: A) -> Self

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

The hash set will be able to hold at least `capacity` elements without reallocating. 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.

##### Examples

    use hashbrown::HashSet;
    use hashbrown::hash_map::DefaultHashBuilder;

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

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

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

##### Examples

    use hashbrown::HashSet;
    use hashbrown::hash_map::DefaultHashBuilder;

    let hasher = DefaultHashBuilder::default();
    let set: HashSet<i32> = HashSet::with_hasher(hasher);
    let hasher: &DefaultHashBuilder = set.hasher();

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

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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 avoid frequent reallocations.

##### Panics

Panics if the new allocation size overflows `usize`.

##### Examples

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

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#### 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 given `HashSet<K,V>`. The collection may reserve more space to avoid frequent reallocations.

##### Errors

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

##### Examples

    use hashbrown::HashSet;
    let mut set: HashSet<i32> = HashSet::new();
    set.try_reserve(10).expect("why is the test harness OOMing on 10 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 hashbrown::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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#### 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.

Panics if the current capacity is smaller than the supplied minimum capacity.

##### Examples

    use hashbrown::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 Self) -> Difference<'a, T, S, A>ⓘNotable traits for Difference<'a, T, S, A>`impl<'a, T, S, A> Iterator for Difference<'a, T, S, A> where
T: Eq + Hash,
S: BuildHasher,
A: Allocator + Clone, type Item = &'a T;`

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

##### Examples

    use hashbrown::HashSet;
    let a: HashSet<_> = [1, 2, 3].iter().cloned().collect();
    let b: HashSet<_> = [4, 2, 3, 4].iter().cloned().collect();

    // 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 Self
) -> SymmetricDifference<'a, T, S, A>ⓘNotable traits for SymmetricDifference<'a, T, S, A>`impl<'a, T, S, A> Iterator for SymmetricDifference<'a, T, S, A> where
T: Eq + Hash,
S: BuildHasher,
A: Allocator + Clone, type Item = &'a T;`

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

##### Examples

    use hashbrown::HashSet;
    let a: HashSet<_> = [1, 2, 3].iter().cloned().collect();
    let b: HashSet<_> = [4, 2, 3, 4].iter().cloned().collect();

    // 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 Self) -> Intersection<'a, T, S, A>ⓘNotable traits for Intersection<'a, T, S, A>`impl<'a, T, S, A> Iterator for Intersection<'a, T, S, A> where
T: Eq + Hash,
S: BuildHasher,
A: Allocator + Clone, type Item = &'a T;`

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

##### Examples

    use hashbrown::HashSet;
    let a: HashSet<_> = [1, 2, 3].iter().cloned().collect();
    let b: HashSet<_> = [4, 2, 3, 4].iter().cloned().collect();

    // 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 Self) -> Union<'a, T, S, A>ⓘNotable traits for Union<'a, T, S, A>`impl<'a, T, S, A> Iterator for Union<'a, T, S, A> where
T: Eq + Hash,
S: BuildHasher,
A: Allocator + Clone, type Item = &'a T;`

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

##### Examples

    use hashbrown::HashSet;
    let a: HashSet<_> = [1, 2, 3].iter().cloned().collect();
    let b: HashSet<_> = [4, 2, 3, 4].iter().cloned().collect();

    // 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: ?Sized>(&self, value: &Q) -> bool where
T: Borrow<Q>,
Q: Hash + Eq,

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 hashbrown::HashSet;

    let set: HashSet<_> = [1, 2, 3].iter().cloned().collect();
    assert_eq!(set.contains(&1), true);
    assert_eq!(set.contains(&4), false);

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#### pub fn get<Q: ?Sized>(&self, value: &Q) -> Option<&T> where
T: Borrow<Q>,
Q: Hash + Eq,

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 hashbrown::HashSet;

    let set: HashSet<_> = [1, 2, 3].iter().cloned().collect();
    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

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

##### Examples

    use hashbrown::HashSet;

    let mut set: HashSet<_> = [1, 2, 3].iter().cloned().collect();
    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: ?Sized>(&mut self, value: &Q) -> &T where
T: Borrow<Q>,
Q: Hash + Eq + ToOwned<Owned = T>,

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

    use hashbrown::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: ?Sized, F>(&mut self, value: &Q, f: F) -> &T where
T: Borrow<Q>,
Q: Hash + Eq,
F: FnOnce(&Q) -> T,

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

    use hashbrown::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 entry(&mut self, value: T) -> Entry<'_, T, S, A>

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

##### Examples

    use hashbrown::HashSet;
    use hashbrown::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'));

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#### pub fn is_disjoint(&self, other: &Self) -> bool

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

##### Examples

    use hashbrown::HashSet;

    let a: HashSet<_> = [1, 2, 3].iter().cloned().collect();
    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: &Self) -> bool

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

##### Examples

    use hashbrown::HashSet;

    let sup: HashSet<_> = [1, 2, 3].iter().cloned().collect();
    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: &Self) -> bool

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

##### Examples

    use hashbrown::HashSet;

    let sub: HashSet<_> = [1, 2].iter().cloned().collect();
    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.

If the set did not have this value present, `true` is returned.

If the set did have this value present, `false` is returned.

##### Examples

    use hashbrown::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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#### pub fn insert_unique_unchecked(&mut self, value: T) -> &T

Insert a value the set without checking if the value already exists in the set.

Returns a reference to the value just inserted.

This operation is safe if a value does not exist in the set.

However, if a value exists in the set already, the behavior is unspecified: this operation may panic, loop forever, or any following operation with the set may panic, loop forever or return arbitrary result.

That said, this operation (and following operations) are guaranteed to not violate memory safety.

This operation is faster than regular insert, because it does not perform lookup before insertion.

This operation is useful during initial population of the set. For example, when constructing a set from another set, we know that values are unique.

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#### 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 hashbrown::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: ?Sized>(&mut self, value: &Q) -> bool where
T: Borrow<Q>,
Q: Hash + Eq,

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 hashbrown::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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#### pub fn take<Q: ?Sized>(&mut self, value: &Q) -> Option<T> where
T: Borrow<Q>,
Q: Hash + Eq,

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 hashbrown::HashSet;

    let mut set: HashSet<_> = [1, 2, 3].iter().cloned().collect();
    assert_eq!(set.take(&2), Some(2));
    assert_eq!(set.take(&2), None);

## Trait Implementations

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

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

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

##### Examples

    use hashbrown::HashSet;

    let a: HashSet<_> = vec![1, 2, 3].into_iter().collect();
    let b: HashSet<_> = 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 = HashSet<T, S, Global>

The resulting type after applying the `&` operator.

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

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

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

##### Examples

    use hashbrown::HashSet;

    let a: HashSet<_> = vec![1, 2, 3].into_iter().collect();
    let b: HashSet<_> = 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 = HashSet<T, S, Global>

The resulting type after applying the `|` operator.

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### impl<T, S> BitXor<&HashSet<T, S, Global>> 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 hashbrown::HashSet;

    let a: HashSet<_> = vec![1, 2, 3].into_iter().collect();
    let b: HashSet<_> = 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 = HashSet<T, S, Global>

The resulting type after applying the `^` operator.

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### impl<T: Clone, S: Clone, A: Allocator + Clone> Clone for HashSet<T, S, A>

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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, source: &Self)

Performs copy-assignment from `source`. Read more

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### impl<T, S, A> Debug for HashSet<T, S, A> where
T: Debug,
A: Allocator + Clone,

source

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

Formats the value using the given formatter. Read more

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### impl<T, S, A> Default for HashSet<T, S, A> where
S: Default,
A: Default + Allocator + Clone,

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#### fn default() -> Self

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

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

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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

source

#### fn extend_one(&mut self, item: A)

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

Extends a collection with exactly one element.

source

#### 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. Read more

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### impl<T, S, A> Extend<T> for HashSet<T, S, A> where
T: Eq + Hash,
S: BuildHasher,
A: Allocator + Clone,

source

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

Extends a collection with the contents of an iterator. Read more

source

#### fn extend_one(&mut self, item: A)

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

Extends a collection with exactly one element.

source

#### 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. Read more

source

### impl<T, A, const N: usize> From<[T; N]> for HashSet<T, DefaultHashBuilder, A> where
T: Eq + Hash,
A: Default + Allocator + Clone,

source

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

##### Examples

    use hashbrown::HashSet;

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

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### impl<T, S, A> From<HashMap<T, (), S, A>> for HashSet<T, S, A> where
A: Allocator + Clone,

source

#### fn from(map: HashMap<T, (), S, A>) -> Self

Converts to this type from the input type.

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

source

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

Creates a value from an iterator. Read more

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### impl<'a, T, S, A: Allocator + Clone> IntoIterator for &'a HashSet<T, S, A>

#### 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?

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#### fn into_iter(self) -> Iter<'a, T>ⓘNotable traits for Iter<'a, K>`impl<'a, K> Iterator for Iter<'a, K> type Item = &'a K;`

Creates an iterator from a value. Read more

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### impl<T, S, A: Allocator + Clone> IntoIterator for HashSet<T, S, A>

source

#### fn into_iter(self) -> IntoIter<T, A>ⓘNotable traits for IntoIter<K, A>`impl<K, A: Allocator + Clone> Iterator for IntoIter<K, A> type Item = K;`

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 hashbrown::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);
    }

#### type Item = T

The type of the elements being iterated over.

#### type IntoIter = IntoIter<T, A>

Which kind of iterator are we turning this into?

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### impl<T, S, A> PartialEq<HashSet<T, S, A>> for HashSet<T, S, A> where
T: Eq + Hash,
S: BuildHasher,
A: Allocator + Clone,

source

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

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

1.0.0 · source

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

This method tests for `!=`.

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### impl<T, S> Sub<&HashSet<T, S, Global>> 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 hashbrown::HashSet;

    let a: HashSet<_> = vec![1, 2, 3].into_iter().collect();
    let b: HashSet<_> = 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 = HashSet<T, S, Global>

The resulting type after applying the `-` operator.

source

### impl<T, S, A> Eq for HashSet<T, S, A> where
T: Eq + Hash,
S: BuildHasher,
A: Allocator + Clone,

## Auto Trait Implementations

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

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

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

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

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

## Blanket Implementations

source

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

source

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

Gets the `TypeId` of `self`. Read more

source

### impl<T> Borrow<T> for T where
T: ?Sized,

const: unstable · source

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

Immutably borrows from an owned value. Read more

source

### impl<T> BorrowMut<T> for T where
T: ?Sized,

const: unstable · source

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

Mutably borrows from an owned value. Read more

source

### impl<T> From<T> for T

const: unstable · source

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

Returns the argument unchanged.

source

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

const: unstable · source

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

Calls `U::from(self)`.

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

source

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

#### type Owned = T

The resulting type after obtaining ownership.

source

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

Creates owned data from borrowed data, usually by cloning. Read more

source

#### fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more

source

### impl<T, U> TryFrom<U> for T where
U: Into<T>,

#### type Error = Infallible

The type returned in the event of a conversion error.

const: unstable · source

#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.

source

### impl<T, U> TryInto<U> for T where
U: TryFrom<T>,

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

The type returned in the event of a conversion error.

const: unstable · source

#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.