pub struct HashMap<K, V, S = DefaultHashBuilder>(_);
Expand description
HashMap
implementation that alternates between a vector
and a hashmap to improve performance for low key counts.
Implementations
sourceimpl<K, V> HashMap<K, V, DefaultHashBuilder>
impl<K, V> HashMap<K, V, DefaultHashBuilder>
sourcepub fn new() -> Self
pub fn new() -> Self
Creates an empty HashMap
.
The hash map is initially created with a capacity of 0, so it will not allocate until it is first inserted into.
Examples
use halfbrown::HashMap;
let mut map: HashMap<&str, i32> = HashMap::new();
sourcepub fn with_capacity(capacity: usize) -> Self
pub fn with_capacity(capacity: usize) -> Self
Creates an empty HashMap
with the specified capacity.
The hash map will be able to hold at least capacity
elements without
reallocating. If capacity
is 0, the hash map will not allocate.
Examples
use halfbrown::HashMap;
let mut map: HashMap<&str, i32> = HashMap::with_capacity(10);
sourcepub fn vec_with_capacity(capacity: usize) -> Self
pub fn vec_with_capacity(capacity: usize) -> Self
Same as with capacity with the difference that it, despite of the
requested size always returns a vector. This allows quicker generation
when used in combination with insert_nocheck
.
Examples
use halfbrown::HashMap;
let mut map: HashMap<&str, i32> = HashMap::vec_with_capacity(128);
assert!(map.is_vec());
sourceimpl<K, V, S> HashMap<K, V, S>
impl<K, V, S> HashMap<K, V, S>
sourcepub fn with_hasher(hash_builder: S) -> Self
pub fn with_hasher(hash_builder: S) -> Self
Creates an empty HashMap
which will use the given hash builder to hash
keys.
The created map has the default initial capacity.
Warning: hash_builder
is normally randomly generated, and
is designed to allow HashMaps
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::HashMap;
use hashbrown::hash_map::DefaultHashBuilder;
let s = DefaultHashBuilder::default();
let mut map = HashMap::with_hasher(s);
map.insert(1, 2);
sourcepub fn with_capacity_and_hasher(capacity: usize, hash_builder: S) -> Self
pub fn with_capacity_and_hasher(capacity: usize, hash_builder: S) -> Self
Creates an empty HashMap
with the specified capacity, using hash_builder
to hash the keys.
The hash map will be able to hold at least capacity
elements without
reallocating. If capacity
is 0, the hash map will not allocate.
Warning: hash_builder
is normally randomly generated, and
is designed to allow HashMaps
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::HashMap;
use hashbrown::hash_map::DefaultHashBuilder;
let s = DefaultHashBuilder::default();
let mut map = HashMap::with_capacity_and_hasher(10, s);
map.insert(1, 2);
sourcepub fn hasher(&self) -> &S
pub fn hasher(&self) -> &S
Returns a reference to the map’s BuildHasher
.
Examples
use hashbrown::HashMap;
use hashbrown::hash_map::DefaultHashBuilder;
let hasher = DefaultHashBuilder::default();
let map: HashMap<i32, i32> = HashMap::with_hasher(hasher);
let hasher: &DefaultHashBuilder = map.hasher();
sourcepub fn capacity(&self) -> usize
pub fn capacity(&self) -> usize
Returns the number of elements the map can hold without reallocating.
This number is a lower bound; the HashMap<K, V>
might be able to hold
more, but is guaranteed to be able to hold at least this many.
Examples
use halfbrown::HashMap;
let map: HashMap<i32, i32> = HashMap::with_capacity(100);
assert!(map.capacity() >= 100);
sourcepub fn keys(&self) -> Keys<'_, K, V>ⓘNotable traits for Keys<'a, K, V>impl<'a, K, V> Iterator for Keys<'a, K, V> type Item = &'a K;
pub fn keys(&self) -> Keys<'_, K, V>ⓘNotable traits for Keys<'a, K, V>impl<'a, K, V> Iterator for Keys<'a, K, V> type Item = &'a K;
An iterator visiting all keys in arbitrary order.
The iterator element type is &'a K
.
Examples
use halfbrown::HashMap;
let mut map = HashMap::new();
map.insert("a", 1);
map.insert("b", 2);
map.insert("c", 3);
for key in map.keys() {
println!("{}", key);
}
sourcepub fn values(&self) -> Values<'_, K, V>ⓘNotable traits for Values<'a, K, V>impl<'a, K, V> Iterator for Values<'a, K, V> type Item = &'a V;
pub fn values(&self) -> Values<'_, K, V>ⓘNotable traits for Values<'a, K, V>impl<'a, K, V> Iterator for Values<'a, K, V> type Item = &'a V;
An iterator visiting all values in arbitrary order.
The iterator element type is &'a V
.
Examples
use halfbrown::HashMap;
let mut map = HashMap::new();
map.insert("a", 1);
map.insert("b", 2);
map.insert("c", 3);
for val in map.values() {
println!("{}", val);
}
sourcepub fn values_mut(&mut self) -> ValuesMut<'_, K, V>ⓘNotable traits for ValuesMut<'a, K, V>impl<'a, K, V> Iterator for ValuesMut<'a, K, V> type Item = &'a mut V;
pub fn values_mut(&mut self) -> ValuesMut<'_, K, V>ⓘNotable traits for ValuesMut<'a, K, V>impl<'a, K, V> Iterator for ValuesMut<'a, K, V> type Item = &'a mut V;
An iterator visiting all values mutably in arbitrary order.
The iterator element type is &'a mut V
.
Examples
use halfbrown::HashMap;
let mut map = HashMap::new();
map.insert("a", 1);
map.insert("b", 2);
map.insert("c", 3);
for val in map.values_mut() {
*val = *val + 10;
}
for val in map.values() {
println!("{}", val);
}
sourcepub fn iter(&self) -> Iter<'_, K, V>ⓘNotable traits for Iter<'a, K, V>impl<'a, K, V> Iterator for Iter<'a, K, V> type Item = (&'a K, &'a V);
pub fn iter(&self) -> Iter<'_, K, V>ⓘNotable traits for Iter<'a, K, V>impl<'a, K, V> Iterator for Iter<'a, K, V> type Item = (&'a K, &'a V);
An iterator visiting all key-value pairs in arbitrary order.
The iterator element type is (&'a K, &'a V)
.
Examples
use halfbrown::HashMap;
let mut map = HashMap::new();
map.insert("a", 1);
map.insert("b", 2);
map.insert("c", 3);
for (key, val) in map.iter() {
println!("key: {} val: {}", key, val);
}
sourcepub fn iter_mut(&mut self) -> IterMut<'_, K, V>ⓘNotable traits for IterMut<'a, K, V>impl<'a, K, V> Iterator for IterMut<'a, K, V> type Item = (&'a K, &'a mut V);
pub fn iter_mut(&mut self) -> IterMut<'_, K, V>ⓘNotable traits for IterMut<'a, K, V>impl<'a, K, V> Iterator for IterMut<'a, K, V> type Item = (&'a K, &'a mut V);
An iterator visiting all key-value pairs in arbitrary order,
with mutable references to the values.
The iterator element type is (&'a K, &'a mut V)
.
Examples
use halfbrown::HashMap;
let mut map = HashMap::new();
map.insert("a", 1);
map.insert("b", 2);
map.insert("c", 3);
// Update all values
for (_, val) in map.iter_mut() {
*val *= 2;
}
for (key, val) in &map {
println!("key: {} val: {}", key, val);
}
sourcepub fn len(&self) -> usize
pub fn len(&self) -> usize
Returns the number of elements in the map.
Examples
use halfbrown::HashMap;
let mut a = HashMap::new();
assert_eq!(a.len(), 0);
a.insert(1, "a");
assert_eq!(a.len(), 1);
sourcepub fn is_empty(&self) -> bool
pub fn is_empty(&self) -> bool
Returns true
if the map contains no elements.
Examples
use halfbrown::HashMap;
let mut a = HashMap::new();
assert!(a.is_empty());
a.insert(1, "a");
assert!(!a.is_empty());
sourcepub fn drain(&mut self) -> Drain<'_, K, V>ⓘNotable traits for Drain<'a, K, V>impl<'a, K, V> Iterator for Drain<'a, K, V> type Item = (K, V);
pub fn drain(&mut self) -> Drain<'_, K, V>ⓘNotable traits for Drain<'a, K, V>impl<'a, K, V> Iterator for Drain<'a, K, V> type Item = (K, V);
Clears the map, returning all key-value pairs as an iterator. Keeps the allocated memory for reuse.
Examples
use halfbrown::HashMap;
let mut a = HashMap::new();
a.insert(1, "a");
a.insert(2, "b");
for (k, v) in a.drain().take(1) {
assert!(k == 1 || k == 2);
assert!(v == "a" || v == "b");
}
assert!(a.is_empty());
sourceimpl<K, V, S> HashMap<K, V, S> where
K: Eq + Hash,
S: BuildHasher,
impl<K, V, S> HashMap<K, V, S> where
K: Eq + Hash,
S: BuildHasher,
sourcepub fn reserve(&mut self, additional: usize)
pub fn reserve(&mut self, additional: usize)
Reserves capacity for at least additional
more elements to be inserted
in the HashMap
. The collection may reserve more space to avoid
frequent reallocations.
Panics
Panics if the new allocation size overflows usize
.
Examples
use halfbrown::HashMap;
let mut map: HashMap<&str, i32> = HashMap::new();
map.reserve(10);
sourcepub fn shrink_to_fit(&mut self)
pub fn shrink_to_fit(&mut self)
Shrinks the capacity of the map 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 halfbrown::HashMap;
let mut map: HashMap<i32, i32> = HashMap::with_capacity(100);
map.insert(1, 2);
map.insert(3, 4);
assert!(map.capacity() >= 100);
map.shrink_to_fit();
assert!(map.capacity() >= 2);
sourcepub fn entry(&mut self, key: K) -> Entry<'_, K, V, S>
pub fn entry(&mut self, key: K) -> Entry<'_, K, V, S>
Gets the given key’s corresponding entry in the map for in-place manipulation.
Examples
use halfbrown::HashMap;
let mut letters = HashMap::new();
for ch in "a short treatise on fungi".chars() {
let counter = letters.entry(ch).or_insert(0);
*counter += 1;
}
assert_eq!(letters[&'s'], 2);
assert_eq!(letters[&'t'], 3);
assert_eq!(letters[&'u'], 1);
assert_eq!(letters.get(&'y'), None);
sourcepub fn get<Q: ?Sized>(&self, k: &Q) -> Option<&V> where
K: Borrow<Q>,
Q: Hash + Eq,
pub fn get<Q: ?Sized>(&self, k: &Q) -> Option<&V> where
K: Borrow<Q>,
Q: Hash + Eq,
Returns a reference to the value corresponding to the key.
The key may be any borrowed form of the map’s key type, but
Hash
and Eq
on the borrowed form must match those for
the key type.
Examples
use halfbrown::HashMap;
let mut map = HashMap::new();
map.insert(1, "a");
assert_eq!(map.get(&1), Some(&"a"));
assert_eq!(map.get(&2), None);
sourcepub fn contains_key<Q: ?Sized>(&self, k: &Q) -> bool where
K: Borrow<Q>,
Q: Hash + Eq,
pub fn contains_key<Q: ?Sized>(&self, k: &Q) -> bool where
K: Borrow<Q>,
Q: Hash + Eq,
Returns true
if the map contains a value for the specified key.
The key may be any borrowed form of the map’s key type, but
Hash
and Eq
on the borrowed form must match those for
the key type.
Examples
use halfbrown::HashMap;
let mut map = HashMap::new();
map.insert(1, "a");
assert_eq!(map.contains_key(&1), true);
assert_eq!(map.contains_key(&2), false);
sourcepub fn get_mut<Q: ?Sized>(&mut self, k: &Q) -> Option<&mut V> where
K: Borrow<Q>,
Q: Hash + Eq,
pub fn get_mut<Q: ?Sized>(&mut self, k: &Q) -> Option<&mut V> where
K: Borrow<Q>,
Q: Hash + Eq,
Returns a mutable reference to the value corresponding to the key.
The key may be any borrowed form of the map’s key type, but
Hash
and Eq
on the borrowed form must match those for
the key type.
Examples
use halfbrown::HashMap;
let mut map = HashMap::new();
map.insert(1, "a");
if let Some(x) = map.get_mut(&1) {
*x = "b";
}
assert_eq!(map[&1], "b");
sourcepub fn insert(&mut self, k: K, v: V) -> Option<V> where
S: Default,
pub fn insert(&mut self, k: K, v: V) -> Option<V> where
S: Default,
Inserts a key-value pair into the map.
If the map did not have this key present, None
is returned.
If the map did have this key present, the value is updated, and the old
value is returned. The key is not updated, though; this matters for
types that can be ==
without being identical. See the module-level
documentation for more.
Examples
use halfbrown::HashMap;
let mut map = HashMap::new();
assert_eq!(map.insert(37, "a"), None);
assert_eq!(map.is_empty(), false);
map.insert(37, "b");
assert_eq!(map.insert(37, "c"), Some("b"));
assert_eq!(map[&37], "c");
sourcepub fn remove<Q: ?Sized>(&mut self, k: &Q) -> Option<V> where
K: Borrow<Q>,
Q: Hash + Eq,
pub fn remove<Q: ?Sized>(&mut self, k: &Q) -> Option<V> where
K: Borrow<Q>,
Q: Hash + Eq,
Removes a key from the map, returning the value at the key if the key was previously in the map.
The key may be any borrowed form of the map’s key type, but
Hash
and Eq
on the borrowed form must match those for
the key type.
Examples
use halfbrown::HashMap;
let mut map = HashMap::new();
map.insert(1, "a");
assert_eq!(map.remove(&1), Some("a"));
assert_eq!(map.remove(&1), None);
sourcepub fn remove_entry<Q: ?Sized>(&mut self, k: &Q) -> Option<(K, V)> where
K: Borrow<Q>,
Q: Hash + Eq,
pub fn remove_entry<Q: ?Sized>(&mut self, k: &Q) -> Option<(K, V)> where
K: Borrow<Q>,
Q: Hash + Eq,
Removes a key from the map, returning the stored key and value if the key was previously in the map.
The key may be any borrowed form of the map’s key type, but
Hash
and Eq
on the borrowed form must match those for
the key type.
Examples
use halfbrown::HashMap;
let mut map = HashMap::new();
map.insert(1, "a");
assert_eq!(map.remove_entry(&1), Some((1, "a")));
assert_eq!(map.remove(&1), None);
sourcepub fn retain<F>(&mut self, f: F) where
F: FnMut(&K, &mut V) -> bool,
pub fn retain<F>(&mut self, f: F) where
F: FnMut(&K, &mut V) -> bool,
Retains only the elements specified by the predicate.
In other words, remove all pairs (k, v)
such that f(&k, &mut v)
returns false
.
The elements are visited in unsorted (and unspecified) order.
Examples
use halfbrown::HashMap;
let mut map: HashMap<i32, i32> = (0..8).map(|x| (x, x*10)).collect();
map.retain(|&k, _| k % 2 == 0);
assert_eq!(map.len(), 4);
sourcepub fn insert_nocheck(&mut self, k: K, v: V)
pub fn insert_nocheck(&mut self, k: K, v: V)
Inserts element, this ignores check in the vector map if keys are present - it’s a fast way to build a new map when uniqueness is known ahead of time.
sourceimpl<K, V, S> HashMap<K, V, S> where
S: BuildHasher,
K: Eq + Hash,
impl<K, V, S> HashMap<K, V, S> where
S: BuildHasher,
K: Eq + Hash,
sourcepub fn raw_entry_mut(&mut self) -> RawEntryBuilderMut<'_, K, V, S>
pub fn raw_entry_mut(&mut self) -> RawEntryBuilderMut<'_, K, V, S>
Creates a raw entry builder for the HashMap
.
Raw entries provide the lowest level of control for searching and manipulating a map. They must be manually initialized with a hash and then manually searched. After this, insertions into a vacant entry still require an owned key to be provided.
Raw entries are useful for such exotic situations as:
- Hash memoization
- Deferring the creation of an owned key until it is known to be required
- Using a search key that doesn’t work with the Borrow trait
- Using custom comparison logic without newtype wrappers
Because raw entries provide much more low-level control, it’s much easier
to put the HashMap
into an inconsistent state which, while memory-safe,
will cause the map to produce seemingly random results. Higher-level and
more foolproof APIs like entry
should be preferred when possible.
In particular, the hash used to initialized the raw entry must still be
consistent with the hash of the key that is ultimately stored in the entry.
This is because implementations of HashMap
may need to recompute hashes
when resizing, at which point only the keys are available.
Raw entries give mutable access to the keys. This must not be used to modify how the key would compare or hash, as the map will not re-evaluate where the key should go, meaning the keys may become “lost” if their location does not reflect their state. For instance, if you change a key so that the map now contains keys which compare equal, search may start acting erratically, with two keys randomly masking each other. Implementations are free to assume this doesn’t happen (within the limits of memory-safety).
sourcepub fn raw_entry(&self) -> RawEntryBuilder<'_, K, V, S>
pub fn raw_entry(&self) -> RawEntryBuilder<'_, K, V, S>
Creates a raw immutable entry builder for the HashMap
.
Raw entries provide the lowest level of control for searching and manipulating a map. They must be manually initialized with a hash and then manually searched.
This is useful for
- Hash memoization
- Using a search key that doesn’t work with the Borrow trait
- Using custom comparison logic without newtype wrappers
Unless you are in such a situation, higher-level and more foolproof APIs like
get
should be preferred.
Immutable raw entries have very limited use; you might instead want raw_entry_mut
.
Trait Implementations
sourceimpl<K, V, S> FromIterator<(K, V)> for HashMap<K, V, S> where
K: Eq + Hash,
S: BuildHasher + Default,
impl<K, V, S> FromIterator<(K, V)> for HashMap<K, V, S> where
K: Eq + Hash,
S: BuildHasher + Default,
sourceimpl<K, Q: ?Sized, V, S> Index<&'_ Q> for HashMap<K, V, S> where
K: Eq + Hash + Borrow<Q>,
Q: Eq + Hash,
S: BuildHasher,
impl<K, Q: ?Sized, V, S> Index<&'_ Q> for HashMap<K, V, S> where
K: Eq + Hash + Borrow<Q>,
Q: Eq + Hash,
S: BuildHasher,
sourceimpl<K, V, S> IntoIterator for HashMap<K, V, S>
impl<K, V, S> IntoIterator for HashMap<K, V, S>
sourceimpl<'a, K, V, S> IntoIterator for &'a HashMap<K, V, S>
impl<'a, K, V, S> IntoIterator for &'a HashMap<K, V, S>
Auto Trait Implementations
impl<K, V, S> RefUnwindSafe for HashMap<K, V, S> where
K: RefUnwindSafe,
S: RefUnwindSafe,
V: RefUnwindSafe,
impl<K, V, S> Send for HashMap<K, V, S> where
K: Send,
S: Send,
V: Send,
impl<K, V, S> Sync for HashMap<K, V, S> where
K: Sync,
S: Sync,
V: Sync,
impl<K, V, S> Unpin for HashMap<K, V, S> where
K: Unpin,
S: Unpin,
V: Unpin,
impl<K, V, S> UnwindSafe for HashMap<K, V, S> where
K: UnwindSafe,
S: UnwindSafe,
V: UnwindSafe,
Blanket Implementations
sourceimpl<T> BorrowMut<T> for T where
T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
const: unstable · sourcefn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
Mutably borrows from an owned value. Read more
sourceimpl<T> ToOwned for T where
T: Clone,
impl<T> ToOwned for T where
T: Clone,
type Owned = T
type Owned = T
The resulting type after obtaining ownership.
sourcefn clone_into(&self, target: &mut T)
fn clone_into(&self, target: &mut T)
toowned_clone_into
)Uses borrowed data to replace owned data, usually by cloning. Read more