Struct std::collections::hash_set::HashSet
[−]
[src]
pub struct HashSet<T, S = RandomState> { // some fields omitted }
An implementation of a hash set using the underlying representation of a HashMap where the value is ().
As with the HashMap
`HashMaptype, a
` type, a HashSet
`HashSetrequires that the elements implement the
` requires that the elements
implement the Eq
`Eqand
` and Hash
`Hashtraits. This can frequently be achieved by using
` traits. This can frequently be achieved by
using #[derive(PartialEq, Eq, Hash)]
`#[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
`Hashtrait, or its equality, as determined by the
` trait, or its equality, as
determined by the Eq
`Eqtrait, changes while it is in the set. This is normally only possible through
` trait, changes while it is in the set. This is
normally only possible through Cell
`Cell,
`, RefCell
`RefCell`, global state, I/O, or
unsafe code.
Examples
fn main() { use std::collections::HashSet; // Type inference lets us omit an explicit type signature (which // would be `HashSet<&str>` in this example). let mut books = HashSet::new(); // Add some books. books.insert("A Dance With Dragons"); books.insert("To Kill a Mockingbird"); books.insert("The Odyssey"); books.insert("The Great Gatsby"); // 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); } }use std::collections::HashSet; // Type inference lets us omit an explicit type signature (which // would be `HashSet<&str>` in this example). let mut books = HashSet::new(); // Add some books. books.insert("A Dance With Dragons"); books.insert("To Kill a Mockingbird"); books.insert("The Odyssey"); books.insert("The Great Gatsby"); // 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
`HashSetwith a custom type is to derive
` with a custom type is to derive
Eq
`Eqand
` and Hash
`Hash. We must also derive
`. We must also derive PartialEq
`PartialEq, this will in the future be implied by
`, this will in the
future be implied by Eq
`Eq`.
use std::collections::HashSet; #[derive(Hash, Eq, PartialEq, Debug)] struct Viking<'a> { name: &'a str, power: usize, } let mut vikings = HashSet::new(); vikings.insert(Viking { name: "Einar", power: 9 }); vikings.insert(Viking { name: "Einar", power: 9 }); vikings.insert(Viking { name: "Olaf", power: 4 }); vikings.insert(Viking { name: "Harald", power: 8 }); // Use derived implementation to print the vikings. for x in &vikings { println!("{:?}", x); }
Methods
impl<T: Hash + Eq> HashSet<T, RandomState>
fn new() -> HashSet<T, RandomState>
Creates an empty HashSet.
Examples
fn main() { use std::collections::HashSet; let mut set: HashSet<i32> = HashSet::new(); }use std::collections::HashSet; let mut set: HashSet<i32> = HashSet::new();
fn with_capacity(capacity: usize) -> HashSet<T, RandomState>
Creates an empty HashSet with space for at least n
`n` elements in
the hash table.
Examples
fn main() { use std::collections::HashSet; let mut set: HashSet<i32> = HashSet::with_capacity(10); }use std::collections::HashSet; let mut set: HashSet<i32> = HashSet::with_capacity(10);
impl<T, S> HashSet<T, S> where T: Eq + Hash, S: HashState
fn with_hash_state(hash_state: S) -> HashSet<T, S>
: hasher stuff is unclear
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.
Examples
#![feature(std_misc)] fn main() { use std::collections::HashSet; use std::collections::hash_map::RandomState; let s = RandomState::new(); let mut set = HashSet::with_hash_state(s); set.insert(2); }use std::collections::HashSet; use std::collections::hash_map::RandomState; let s = RandomState::new(); let mut set = HashSet::with_hash_state(s); set.insert(2);
fn with_capacity_and_hash_state(capacity: usize, hash_state: S) -> HashSet<T, S>
: hasher stuff is unclear
Creates an empty HashSet with space for at least capacity
`capacityelements in the hash table, using
`
elements in the hash table, using hasher
`hasher` to hash the keys.
Warning: hasher
`hasheris normally randomly generated, and is designed to allow
` is normally randomly generated, and
is designed to allow HashSet
`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
#![feature(std_misc)] fn main() { use std::collections::HashSet; use std::collections::hash_map::RandomState; let s = RandomState::new(); let mut set = HashSet::with_capacity_and_hash_state(10, s); set.insert(1); }use std::collections::HashSet; use std::collections::hash_map::RandomState; let s = RandomState::new(); let mut set = HashSet::with_capacity_and_hash_state(10, s); set.insert(1);
fn capacity(&self) -> usize
Returns the number of elements the set can hold without reallocating.
Examples
fn main() { use std::collections::HashSet; let set: HashSet<i32> = HashSet::with_capacity(100); assert!(set.capacity() >= 100); }use std::collections::HashSet; let set: HashSet<i32> = HashSet::with_capacity(100); assert!(set.capacity() >= 100);
fn reserve(&mut self, additional: usize)
Reserves capacity for at least additional
`additionalmore elements to be inserted in the
` more elements to be inserted
in the HashSet
`HashSet`. The collection may reserve more space to avoid
frequent reallocations.
Panics
Panics if the new allocation size overflows usize
`usize`.
Examples
fn main() { use std::collections::HashSet; let mut set: HashSet<i32> = HashSet::new(); set.reserve(10); }use std::collections::HashSet; let mut set: HashSet<i32> = HashSet::new(); set.reserve(10);
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
fn main() { 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); }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);
fn iter(&self) -> Iter<T>
An iterator visiting all elements in arbitrary order. Iterator element type is &'a T.
Examples
fn main() { 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); } }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); }
fn difference<'a>(&'a self, other: &'a HashSet<T, S>) -> Difference<'a, T, S>
Visit the values representing the difference.
Examples
fn main() { use std::collections::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).cloned().collect(); assert_eq!(diff, [1].iter().cloned().collect()); // Note that difference is not symmetric, // and `b - a` means something else: let diff: HashSet<_> = b.difference(&a).cloned().collect(); assert_eq!(diff, [4].iter().cloned().collect()); }use std::collections::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).cloned().collect(); assert_eq!(diff, [1].iter().cloned().collect()); // Note that difference is not symmetric, // and `b - a` means something else: let diff: HashSet<_> = b.difference(&a).cloned().collect(); assert_eq!(diff, [4].iter().cloned().collect());
fn symmetric_difference<'a>(&'a self, other: &'a HashSet<T, S>) -> SymmetricDifference<'a, T, S>
Visit the values representing the symmetric difference.
Examples
fn main() { use std::collections::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).cloned().collect(); let diff2: HashSet<_> = b.symmetric_difference(&a).cloned().collect(); assert_eq!(diff1, diff2); assert_eq!(diff1, [1, 4].iter().cloned().collect()); }use std::collections::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).cloned().collect(); let diff2: HashSet<_> = b.symmetric_difference(&a).cloned().collect(); assert_eq!(diff1, diff2); assert_eq!(diff1, [1, 4].iter().cloned().collect());
fn intersection<'a>(&'a self, other: &'a HashSet<T, S>) -> Intersection<'a, T, S>
Visit the values representing the intersection.
Examples
fn main() { use std::collections::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 diff: HashSet<_> = a.intersection(&b).cloned().collect(); assert_eq!(diff, [2, 3].iter().cloned().collect()); }use std::collections::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 diff: HashSet<_> = a.intersection(&b).cloned().collect(); assert_eq!(diff, [2, 3].iter().cloned().collect());
fn union<'a>(&'a self, other: &'a HashSet<T, S>) -> Union<'a, T, S>
Visit the values representing the union.
Examples
fn main() { use std::collections::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 diff: HashSet<_> = a.union(&b).cloned().collect(); assert_eq!(diff, [1, 2, 3, 4].iter().cloned().collect()); }use std::collections::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 diff: HashSet<_> = a.union(&b).cloned().collect(); assert_eq!(diff, [1, 2, 3, 4].iter().cloned().collect());
fn len(&self) -> usize
Returns the number of elements in the set.
Examples
fn main() { use std::collections::HashSet; let mut v = HashSet::new(); assert_eq!(v.len(), 0); v.insert(1); assert_eq!(v.len(), 1); }use std::collections::HashSet; let mut v = HashSet::new(); assert_eq!(v.len(), 0); v.insert(1); assert_eq!(v.len(), 1);
fn is_empty(&self) -> bool
Returns true if the set contains no elements.
Examples
fn main() { use std::collections::HashSet; let mut v = HashSet::new(); assert!(v.is_empty()); v.insert(1); assert!(!v.is_empty()); }use std::collections::HashSet; let mut v = HashSet::new(); assert!(v.is_empty()); v.insert(1); assert!(!v.is_empty());
fn drain(&mut self) -> Drain<T>
: matches collection reform specification, waiting for dust to settle
Clears the set, returning all elements in an iterator.
fn clear(&mut self)
Clears the set, removing all values.
Examples
fn main() { use std::collections::HashSet; let mut v = HashSet::new(); v.insert(1); v.clear(); assert!(v.is_empty()); }use std::collections::HashSet; let mut v = HashSet::new(); v.insert(1); v.clear(); assert!(v.is_empty());
fn contains<Q: ?Sized>(&self, value: &Q) -> bool where T: Borrow<Q>, Q: Hash + Eq
Returns true
`true` if the set contains a value.
The value may be any borrowed form of the set's value type, but
Hash
`Hashand
` and Eq
`Eq` on the borrowed form must match those for
the value type.
Examples
fn main() { use std::collections::HashSet; let set: HashSet<_> = [1, 2, 3].iter().cloned().collect(); assert_eq!(set.contains(&1), true); assert_eq!(set.contains(&4), false); }use std::collections::HashSet; let set: HashSet<_> = [1, 2, 3].iter().cloned().collect(); assert_eq!(set.contains(&1), true); assert_eq!(set.contains(&4), false);
fn is_disjoint(&self, other: &HashSet<T, S>) -> bool
Returns true
`trueif the set has no elements in common with
` if the set has no elements in common with other
`other`.
This is equivalent to checking for an empty intersection.
Examples
fn main() { use std::collections::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); }use std::collections::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);
fn is_subset(&self, other: &HashSet<T, S>) -> bool
Returns true
`true` if the set is a subset of another.
Examples
fn main() { use std::collections::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); }use std::collections::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);
fn is_superset(&self, other: &HashSet<T, S>) -> bool
Returns true
`true` if the set is a superset of another.
Examples
fn main() { use std::collections::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); }use std::collections::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);
fn insert(&mut self, value: T) -> bool
Adds a value to the set. Returns true
`true` if the value was not already
present in the set.
Examples
fn main() { 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); }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);
fn remove<Q: ?Sized>(&mut self, value: &Q) -> bool where T: Borrow<Q>, Q: Hash + Eq
Removes a value from the set. Returns true
`true` if the value was
present in the set.
The value may be any borrowed form of the set's value type, but
Hash
`Hashand
` and Eq
`Eq` on the borrowed form must match those for
the value type.
Examples
fn main() { use std::collections::HashSet; let mut set = HashSet::new(); set.insert(2); assert_eq!(set.remove(&2), true); assert_eq!(set.remove(&2), false); }use std::collections::HashSet; let mut set = HashSet::new(); set.insert(2); assert_eq!(set.remove(&2), true); assert_eq!(set.remove(&2), false);