GeezerVison is showing docs.rs — HashMap in algorithm - Rust pub struct HashMap<K, V, S = RandomState, A = Global>{ /* private fields */ }
Expand descriptionA hash map implemented with quadratic probing and SIMD lookup.
The default hashing algorithm is currently foldhash, though this is
subject to change at any point in the future. This hash function is very
fast for all types of keys, but this algorithm will typically not protect
against attacks such as HashDoS.
The hashing algorithm can be replaced on a per-HashMap basis using the
default, with_hasher, and with_capacity_and_hasher methods. Many
alternative algorithms are available on crates.io, such as the fnv crate.
It is required that the keys implement the Eq and Hash traits, although
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 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.
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 HashMap may become corrupted and
some items may be dropped from the table.
§Examples
use hashbrown::HashMap;
// Type inference lets us omit an explicit type signature (which
// would be `HashMap<String, String>` in this example).
let mut book_reviews = HashMap::new();
// Review some books.
book_reviews.insert(
"Adventures of Huckleberry Finn".to_string(),
"My favorite book.".to_string(),
);
book_reviews.insert(
"Grimms' Fairy Tales".to_string(),
"Masterpiece.".to_string(),
);
book_reviews.insert(
"Pride and Prejudice".to_string(),
"Very enjoyable.".to_string(),
);
book_reviews.insert(
"The Adventures of Sherlock Holmes".to_string(),
"Eye lyked it alot.".to_string(),
);
// Check for a specific one.
// When collections store owned values (String), they can still be
// queried using references (&str).
if !book_reviews.contains_key("Les Misérables") {
println!("We've got {} reviews, but Les Misérables ain't one.",
book_reviews.len());
}
// oops, this review has a lot of spelling mistakes, let's delete it.
book_reviews.remove("The Adventures of Sherlock Holmes");
// Look up the values associated with some keys.
let to_find = ["Pride and Prejudice", "Alice's Adventure in Wonderland"];
for &book in &to_find {
match book_reviews.get(book) {
Some(review) => println!("{}: {}", book, review),
None => println!("{} is unreviewed.", book)
}
}
// Look up the value for a key (will panic if the key is not found).
println!("Review for Jane: {}", book_reviews["Pride and Prejudice"]);
// Iterate over everything.
for (book, review) in &book_reviews {
println!("{}: \"{}\"", book, review);
}
HashMap also implements an Entry API, which allows
for more complex methods of getting, setting, updating and removing keys and
their values:
use hashbrown::HashMap;
// type inference lets us omit an explicit type signature (which
// would be `HashMap<&str, u8>` in this example).
let mut player_stats = HashMap::new();
fn random_stat_buff() -> u8 {
// could actually return some random value here - let's just return
// some fixed value for now
42
}
// insert a key only if it doesn't already exist
player_stats.entry("health").or_insert(100);
// insert a key using a function that provides a new value only if it
// doesn't already exist
player_stats.entry("defence").or_insert_with(random_stat_buff);
// update a key, guarding against the key possibly not being set
let stat = player_stats.entry("attack").or_insert(100);
*stat += random_stat_buff();
The easiest way to use HashMap with a custom key type is to derive Eq and Hash.
We must also derive PartialEq.
use hashbrown::HashMap;
#[derive(Hash, Eq, PartialEq, Debug)]
struct Viking {
name: String,
country: String,
}
impl Viking {
/// Creates a new Viking.
fn new(name: &str, country: &str) -> Viking {
Viking { name: name.to_string(), country: country.to_string() }
}
}
// Use a HashMap to store the vikings' health points.
let mut vikings = HashMap::new();
vikings.insert(Viking::new("Einar", "Norway"), 25);
vikings.insert(Viking::new("Olaf", "Denmark"), 24);
vikings.insert(Viking::new("Harald", "Iceland"), 12);
// Use derived implementation to print the status of the vikings.
for (viking, health) in &vikings {
println!("{:?} has {} hp", viking, health);
}
A HashMap with fixed list of elements can be initialized from an array:
use hashbrown::HashMap;
let timber_resources: HashMap<&str, i32> = [("Norway", 100), ("Denmark", 50), ("Iceland", 10)]
.into_iter().collect();
// use the values stored in map
Implementations§
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.
§HashDoS resistance
The hash_builder normally use a fixed key by default and that does
not allow the HashMap to be protected against attacks such as HashDoS.
Users who require HashDoS resistance should explicitly use
std::collections::hash_map::RandomState
as the hasher when creating a HashMap, for example with
with_hasher method.
§Examples
use hashbrown::HashMap;
let mut map: HashMap<&str, i32> = HashMap::new();
assert_eq!(map.len(), 0);
assert_eq!(map.capacity(), 0);
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.
§HashDoS resistance
The hash_builder normally use a fixed key by default and that does
not allow the HashMap to be protected against attacks such as HashDoS.
Users who require HashDoS resistance should explicitly use
std::collections::hash_map::RandomState
as the hasher when creating a HashMap, for example with
with_capacity_and_hasher method.
§Examples
use hashbrown::HashMap;
let mut map: HashMap<&str, i32> = HashMap::with_capacity(10);
assert_eq!(map.len(), 0);
assert!(map.capacity() >= 10);
Creates an empty HashMap using the given allocator.
The hash map is initially created with a capacity of 0, so it will not allocate until it
is first inserted into.
§HashDoS resistance
The hash_builder normally use a fixed key by default and that does
not allow the HashMap to be protected against attacks such as HashDoS.
Users who require HashDoS resistance should explicitly use
std::collections::hash_map::RandomState
as the hasher when creating a HashMap, for example with
with_hasher_in method.
§Examples
use hashbrown::HashMap;
use bumpalo::Bump;
let bump = Bump::new();
let mut map = HashMap::new_in(&bump);
// The created HashMap holds none elements
assert_eq!(map.len(), 0);
// The created HashMap also doesn't allocate memory
assert_eq!(map.capacity(), 0);
// Now we insert element inside created HashMap
map.insert("One", 1);
// We can see that the HashMap holds 1 element
assert_eq!(map.len(), 1);
// And it also allocates some capacity
assert!(map.capacity() > 1);
Creates an empty HashMap with the specified capacity using the given allocator.
The hash map will be able to hold at least capacity elements without
reallocating. If capacity is 0, the hash map will not allocate.
§HashDoS resistance
The hash_builder normally use a fixed key by default and that does
not allow the HashMap to be protected against attacks such as HashDoS.
Users who require HashDoS resistance should explicitly use
std::collections::hash_map::RandomState
as the hasher when creating a HashMap, for example with
with_capacity_and_hasher_in method.
§Examples
use hashbrown::HashMap;
use bumpalo::Bump;
let bump = Bump::new();
let mut map = HashMap::with_capacity_in(5, &bump);
// The created HashMap holds none elements
assert_eq!(map.len(), 0);
// But it can hold at least 5 elements without reallocating
let empty_map_capacity = map.capacity();
assert!(empty_map_capacity >= 5);
// Now we insert some 5 elements inside created HashMap
map.insert("One", 1);
map.insert("Two", 2);
map.insert("Three", 3);
map.insert("Four", 4);
map.insert("Five", 5);
// We can see that the HashMap holds 5 elements
assert_eq!(map.len(), 5);
// But its capacity isn't changed
assert_eq!(map.capacity(), empty_map_capacity)
Creates an empty HashMap which will use the given hash builder to hash
keys.
The hash map is initially created with a capacity of 0, so it will not
allocate until it is first inserted into.
§HashDoS resistance
The hash_builder normally use a fixed key by default and that does
not allow the HashMap to be protected against attacks such as HashDoS.
Users who require HashDoS resistance should explicitly use
std::collections::hash_map::RandomState
as the hasher when creating a HashMap.
The hash_builder passed should implement the BuildHasher trait for
the HashMap to be useful, see its documentation for details.
§Examples
use hashbrown::HashMap;
use hashbrown::DefaultHashBuilder;
let s = DefaultHashBuilder::default();
let mut map = HashMap::with_hasher(s);
assert_eq!(map.len(), 0);
assert_eq!(map.capacity(), 0);
map.insert(1, 2);
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.
§HashDoS resistance
The hash_builder normally use a fixed key by default and that does
not allow the HashMap to be protected against attacks such as HashDoS.
Users who require HashDoS resistance should explicitly use
std::collections::hash_map::RandomState
as the hasher when creating a HashMap.
The hash_builder passed should implement the BuildHasher trait for
the HashMap to be useful, see its documentation for details.
§Examples
use hashbrown::HashMap;
use hashbrown::DefaultHashBuilder;
let s = DefaultHashBuilder::default();
let mut map = HashMap::with_capacity_and_hasher(10, s);
assert_eq!(map.len(), 0);
assert!(map.capacity() >= 10);
map.insert(1, 2);
Returns a reference to the underlying allocator.
Creates an empty HashMap which will use the given hash builder to hash
keys. It will be allocated with the given allocator.
The hash map is initially created with a capacity of 0, so it will not allocate until it
is first inserted into.
§HashDoS resistance
The hash_builder normally use a fixed key by default and that does
not allow the HashMap to be protected against attacks such as HashDoS.
Users who require HashDoS resistance should explicitly use
std::collections::hash_map::RandomState
as the hasher when creating a HashMap.
§Examples
use hashbrown::HashMap;
use hashbrown::DefaultHashBuilder;
let s = DefaultHashBuilder::default();
let mut map = HashMap::with_hasher(s);
map.insert(1, 2);
Creates an empty HashMap with the specified capacity, using hash_builder
to hash the keys. It will be allocated with the given allocator.
The hash map will be able to hold at least capacity elements without
reallocating. If capacity is 0, the hash map will not allocate.
§HashDoS resistance
The hash_builder normally use a fixed key by default and that does
not allow the HashMap to be protected against attacks such as HashDoS.
Users who require HashDoS resistance should explicitly use
std::collections::hash_map::RandomState
as the hasher when creating a HashMap.
§Examples
use hashbrown::HashMap;
use hashbrown::DefaultHashBuilder;
let s = DefaultHashBuilder::default();
let mut map = HashMap::with_capacity_and_hasher(10, s);
map.insert(1, 2);
Returns a reference to the map’s BuildHasher.
§Examples
use hashbrown::HashMap;
use hashbrown::DefaultHashBuilder;
let hasher = DefaultHashBuilder::default();
let map: HashMap<i32, i32> = HashMap::with_hasher(hasher);
let hasher: &DefaultHashBuilder = map.hasher();
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 hashbrown::HashMap;
let map: HashMap<i32, i32> = HashMap::with_capacity(100);
assert_eq!(map.len(), 0);
assert!(map.capacity() >= 100);
An iterator visiting all keys in arbitrary order.
The iterator element type is &'a K.
§Examples
use hashbrown::HashMap;
let mut map = HashMap::new();
map.insert("a", 1);
map.insert("b", 2);
map.insert("c", 3);
assert_eq!(map.len(), 3);
let mut vec: Vec<&str> = Vec::new();
for key in map.keys() {
println!("{}", key);
vec.push(*key);
}
// The `Keys` iterator produces keys in arbitrary order, so the
// keys must be sorted to test them against a sorted array.
vec.sort_unstable();
assert_eq!(vec, ["a", "b", "c"]);
assert_eq!(map.len(), 3);
An iterator visiting all values in arbitrary order.
The iterator element type is &'a V.
§Examples
use hashbrown::HashMap;
let mut map = HashMap::new();
map.insert("a", 1);
map.insert("b", 2);
map.insert("c", 3);
assert_eq!(map.len(), 3);
let mut vec: Vec<i32> = Vec::new();
for val in map.values() {
println!("{}", val);
vec.push(*val);
}
// The `Values` iterator produces values in arbitrary order, so the
// values must be sorted to test them against a sorted array.
vec.sort_unstable();
assert_eq!(vec, [1, 2, 3]);
assert_eq!(map.len(), 3);
An iterator visiting all values mutably in arbitrary order.
The iterator element type is &'a mut V.
§Examples
use hashbrown::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;
}
assert_eq!(map.len(), 3);
let mut vec: Vec<i32> = Vec::new();
for val in map.values() {
println!("{}", val);
vec.push(*val);
}
// The `Values` iterator produces values in arbitrary order, so the
// values must be sorted to test them against a sorted array.
vec.sort_unstable();
assert_eq!(vec, [11, 12, 13]);
assert_eq!(map.len(), 3);
An iterator visiting all key-value pairs in arbitrary order.
The iterator element type is (&'a K, &'a V).
§Examples
use hashbrown::HashMap;
let mut map = HashMap::new();
map.insert("a", 1);
map.insert("b", 2);
map.insert("c", 3);
assert_eq!(map.len(), 3);
let mut vec: Vec<(&str, i32)> = Vec::new();
for (key, val) in map.iter() {
println!("key: {} val: {}", key, val);
vec.push((*key, *val));
}
// The `Iter` iterator produces items in arbitrary order, so the
// items must be sorted to test them against a sorted array.
vec.sort_unstable();
assert_eq!(vec, [("a", 1), ("b", 2), ("c", 3)]);
assert_eq!(map.len(), 3);
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 hashbrown::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;
}
assert_eq!(map.len(), 3);
let mut vec: Vec<(&str, i32)> = Vec::new();
for (key, val) in &map {
println!("key: {} val: {}", key, val);
vec.push((*key, *val));
}
// The `Iter` iterator produces items in arbitrary order, so the
// items must be sorted to test them against a sorted array.
vec.sort_unstable();
assert_eq!(vec, [("a", 2), ("b", 4), ("c", 6)]);
assert_eq!(map.len(), 3);
Returns the number of elements in the map.
§Examples
use hashbrown::HashMap;
let mut a = HashMap::new();
assert_eq!(a.len(), 0);
a.insert(1, "a");
assert_eq!(a.len(), 1);
Returns true if the map contains no elements.
§Examples
use hashbrown::HashMap;
let mut a = HashMap::new();
assert!(a.is_empty());
a.insert(1, "a");
assert!(!a.is_empty());
Clears the map, returning all key-value pairs as an iterator. Keeps the
allocated memory for reuse.
If the returned iterator is dropped before being fully consumed, it
drops the remaining key-value pairs. The returned iterator keeps a
mutable borrow on the vector to optimize its implementation.
§Examples
use hashbrown::HashMap;
let mut a = HashMap::new();
a.insert(1, "a");
a.insert(2, "b");
let capacity_before_drain = a.capacity();
for (k, v) in a.drain().take(1) {
assert!(k == 1 || k == 2);
assert!(v == "a" || v == "b");
}
// As we can see, the map is empty and contains no element.
assert!(a.is_empty() && a.len() == 0);
// But map capacity is equal to old one.
assert_eq!(a.capacity(), capacity_before_drain);
let mut a = HashMap::new();
a.insert(1, "a");
a.insert(2, "b");
{ // Iterator is dropped without being consumed.
let d = a.drain();
}
// But the map is empty even if we do not use Drain iterator.
assert!(a.is_empty());
Retains only the elements specified by the predicate. Keeps the
allocated memory for reuse.
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 hashbrown::HashMap;
let mut map: HashMap<i32, i32> = (0..8).map(|x|(x, x*10)).collect();
assert_eq!(map.len(), 8);
map.retain(|&k, _| k % 2 == 0);
// We can see, that the number of elements inside map is changed.
assert_eq!(map.len(), 4);
let mut vec: Vec<(i32, i32)> = map.iter().map(|(&k, &v)| (k, v)).collect();
vec.sort_unstable();
assert_eq!(vec, [(0, 0), (2, 20), (4, 40), (6, 60)]);
Drains elements which are true under the given predicate,
and returns an iterator over the removed items.
In other words, move all pairs (k, v) such that f(&k, &mut v) returns true out
into another iterator.
Note that extract_if lets you mutate every value in the filter closure, regardless of
whether you choose to keep or remove it.
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.
Keeps the allocated memory for reuse.
§Examples
use hashbrown::HashMap;
let mut map: HashMap<i32, i32> = (0..8).map(|x| (x, x)).collect();
let drained: HashMap<i32, i32> = map.extract_if(|k, _v| k % 2 == 0).collect();
let mut evens = drained.keys().cloned().collect::<Vec<_>>();
let mut odds = map.keys().cloned().collect::<Vec<_>>();
evens.sort();
odds.sort();
assert_eq!(evens, vec![0, 2, 4, 6]);
assert_eq!(odds, vec![1, 3, 5, 7]);
let mut map: HashMap<i32, i32> = (0..8).map(|x| (x, x)).collect();
{ // Iterator is dropped without being consumed.
let d = map.extract_if(|k, _v| k % 2 != 0);
}
// ExtractIf was not exhausted, therefore no elements were drained.
assert_eq!(map.len(), 8);
Clears the map, removing all key-value pairs. Keeps the allocated memory
for reuse.
§Examples
use hashbrown::HashMap;
let mut a = HashMap::new();
a.insert(1, "a");
let capacity_before_clear = a.capacity();
a.clear();
// Map is empty.
assert!(a.is_empty());
// But map capacity is equal to old one.
assert_eq!(a.capacity(), capacity_before_clear);
Creates a consuming iterator visiting all the keys in arbitrary order.
The map cannot be used after calling this.
The iterator element type is K.
§Examples
use hashbrown::HashMap;
let mut map = HashMap::new();
map.insert("a", 1);
map.insert("b", 2);
map.insert("c", 3);
let mut vec: Vec<&str> = map.into_keys().collect();
// The `IntoKeys` iterator produces keys in arbitrary order, so the
// keys must be sorted to test them against a sorted array.
vec.sort_unstable();
assert_eq!(vec, ["a", "b", "c"]);
Creates a consuming iterator visiting all the values in arbitrary order.
The map cannot be used after calling this.
The iterator element type is V.
§Examples
use hashbrown::HashMap;
let mut map = HashMap::new();
map.insert("a", 1);
map.insert("b", 2);
map.insert("c", 3);
let mut vec: Vec<i32> = map.into_values().collect();
// The `IntoValues` iterator produces values in arbitrary order, so
// the values must be sorted to test them against a sorted array.
vec.sort_unstable();
assert_eq!(vec, [1, 2, 3]);
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 capacity exceeds isize::MAX bytes and abort the program
in case of allocation error. Use try_reserve instead
if you want to handle memory allocation failure.
§Examples
use hashbrown::HashMap;
let mut map: HashMap<&str, i32> = HashMap::new();
// Map is empty and doesn't allocate memory
assert_eq!(map.capacity(), 0);
map.reserve(10);
// And now map can hold at least 10 elements
assert!(map.capacity() >= 10);
Tries to reserve capacity for at least additional more elements to be inserted
in the given HashMap<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::HashMap;
let mut map: HashMap<&str, isize> = HashMap::new();
// Map is empty and doesn't allocate memory
assert_eq!(map.capacity(), 0);
map.try_reserve(10).expect("why is the test harness OOMing on 10 bytes?");
// And now map can hold at least 10 elements
assert!(map.capacity() >= 10);
If the capacity overflows, or the allocator reports a failure, then an error
is returned:
use hashbrown::HashMap;
use hashbrown::TryReserveError;
let mut map: HashMap<i32, i32> = HashMap::new();
match map.try_reserve(usize::MAX) {
Err(error) => match error {
TryReserveError::CapacityOverflow => {}
_ => panic!("TryReserveError::AllocError ?"),
},
_ => panic!(),
}
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 hashbrown::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);
Shrinks the capacity of the map 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.
This function does nothing if the current capacity is smaller than the
supplied minimum capacity.
§Examples
use hashbrown::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(10);
assert!(map.capacity() >= 10);
map.shrink_to(0);
assert!(map.capacity() >= 2);
map.shrink_to(10);
assert!(map.capacity() >= 2);
Gets the given key’s corresponding entry in the map for in-place manipulation.
§Examples
use hashbrown::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 entry_ref<'a, 'b, Q>(
&'a mut self,
key: &'b Q,
) -> EntryRef<'a, 'b, K, Q, V, S, A>Gets the given key’s corresponding entry by reference in the map for in-place manipulation.
§Examples
use hashbrown::HashMap;
let mut words: HashMap<String, usize> = HashMap::new();
let source = ["poneyland", "horseyland", "poneyland", "poneyland"];
for (i, &s) in source.iter().enumerate() {
let counter = words.entry_ref(s).or_insert(0);
*counter += 1;
}
assert_eq!(words["poneyland"], 3);
assert_eq!(words["horseyland"], 1);
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 hashbrown::HashMap;
let mut map = HashMap::new();
map.insert(1, "a");
assert_eq!(map.get(&1), Some(&"a"));
assert_eq!(map.get(&2), None);
Returns the key-value pair corresponding to the supplied key.
The supplied 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 hashbrown::HashMap;
let mut map = HashMap::new();
map.insert(1, "a");
assert_eq!(map.get_key_value(&1), Some((&1, &"a")));
assert_eq!(map.get_key_value(&2), None);
Returns the key-value pair corresponding to the supplied key, with a mutable reference to value.
The supplied 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 hashbrown::HashMap;
let mut map = HashMap::new();
map.insert(1, "a");
let (k, v) = map.get_key_value_mut(&1).unwrap();
assert_eq!(k, &1);
assert_eq!(v, &mut "a");
*v = "b";
assert_eq!(map.get_key_value_mut(&1), Some((&1, &mut "b")));
assert_eq!(map.get_key_value_mut(&2), None);
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 hashbrown::HashMap;
let mut map = HashMap::new();
map.insert(1, "a");
assert_eq!(map.contains_key(&1), true);
assert_eq!(map.contains_key(&2), false);
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 hashbrown::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");
assert_eq!(map.get_mut(&2), None);
Attempts to get mutable references to N values in the map at once.
Returns an array of length N with the results of each query. For soundness, at most one
mutable reference will be returned to any value. None will be used if the key is missing.
§Panics
Panics if any keys are overlapping.
§Examples
use hashbrown::HashMap;
let mut libraries = HashMap::new();
libraries.insert("Bodleian Library".to_string(), 1602);
libraries.insert("Athenæum".to_string(), 1807);
libraries.insert("Herzogin-Anna-Amalia-Bibliothek".to_string(), 1691);
libraries.insert("Library of Congress".to_string(), 1800);
// Get Athenæum and Bodleian Library
let [Some(a), Some(b)] = libraries.get_many_mut([
"Athenæum",
"Bodleian Library",
]) else { panic!() };
// Assert values of Athenæum and Library of Congress
let got = libraries.get_many_mut([
"Athenæum",
"Library of Congress",
]);
assert_eq!(
got,
[
Some(&mut 1807),
Some(&mut 1800),
],
);
// Missing keys result in None
let got = libraries.get_many_mut([
"Athenæum",
"New York Public Library",
]);
assert_eq!(
got,
[
Some(&mut 1807),
None
]
);
ⓘuse hashbrown::HashMap;
let mut libraries = HashMap::new();
libraries.insert("Athenæum".to_string(), 1807);
// Duplicate keys panic!
let got = libraries.get_many_mut([
"Athenæum",
"Athenæum",
]);
Attempts to get mutable references to N values in the map at once, without validating that
the values are unique.
Returns an array of length N with the results of each query. None will be used if
the key is missing.
For a safe alternative see get_many_mut.
§Safety
Calling this method with overlapping keys is undefined behavior even if the resulting
references are not used.
§Examples
use hashbrown::HashMap;
let mut libraries = HashMap::new();
libraries.insert("Bodleian Library".to_string(), 1602);
libraries.insert("Athenæum".to_string(), 1807);
libraries.insert("Herzogin-Anna-Amalia-Bibliothek".to_string(), 1691);
libraries.insert("Library of Congress".to_string(), 1800);
// SAFETY: The keys do not overlap.
let [Some(a), Some(b)] = (unsafe { libraries.get_many_unchecked_mut([
"Athenæum",
"Bodleian Library",
]) }) else { panic!() };
// SAFETY: The keys do not overlap.
let got = unsafe { libraries.get_many_unchecked_mut([
"Athenæum",
"Library of Congress",
]) };
assert_eq!(
got,
[
Some(&mut 1807),
Some(&mut 1800),
],
);
// SAFETY: The keys do not overlap.
let got = unsafe { libraries.get_many_unchecked_mut([
"Athenæum",
"New York Public Library",
]) };
// Missing keys result in None
assert_eq!(got, [Some(&mut 1807), None]);
Attempts to get mutable references to N values in the map at once, with immutable
references to the corresponding keys.
Returns an array of length N with the results of each query. For soundness, at most one
mutable reference will be returned to any value. None will be used if the key is missing.
§Panics
Panics if any keys are overlapping.
§Examples
use hashbrown::HashMap;
let mut libraries = HashMap::new();
libraries.insert("Bodleian Library".to_string(), 1602);
libraries.insert("Athenæum".to_string(), 1807);
libraries.insert("Herzogin-Anna-Amalia-Bibliothek".to_string(), 1691);
libraries.insert("Library of Congress".to_string(), 1800);
let got = libraries.get_many_key_value_mut([
"Bodleian Library",
"Herzogin-Anna-Amalia-Bibliothek",
]);
assert_eq!(
got,
[
Some((&"Bodleian Library".to_string(), &mut 1602)),
Some((&"Herzogin-Anna-Amalia-Bibliothek".to_string(), &mut 1691)),
],
);
// Missing keys result in None
let got = libraries.get_many_key_value_mut([
"Bodleian Library",
"Gewandhaus",
]);
assert_eq!(got, [Some((&"Bodleian Library".to_string(), &mut 1602)), None]);
ⓘuse hashbrown::HashMap;
let mut libraries = HashMap::new();
libraries.insert("Bodleian Library".to_string(), 1602);
libraries.insert("Herzogin-Anna-Amalia-Bibliothek".to_string(), 1691);
// Duplicate keys result in panic!
let got = libraries.get_many_key_value_mut([
"Bodleian Library",
"Herzogin-Anna-Amalia-Bibliothek",
"Herzogin-Anna-Amalia-Bibliothek",
]);
Attempts to get mutable references to N values in the map at once, with immutable
references to the corresponding keys, without validating that the values are unique.
Returns an array of length N with the results of each query. None will be returned if
any of the keys are missing.
For a safe alternative see get_many_key_value_mut.
§Safety
Calling this method with overlapping keys is undefined behavior even if the resulting
references are not used.
§Examples
use hashbrown::HashMap;
let mut libraries = HashMap::new();
libraries.insert("Bodleian Library".to_string(), 1602);
libraries.insert("Athenæum".to_string(), 1807);
libraries.insert("Herzogin-Anna-Amalia-Bibliothek".to_string(), 1691);
libraries.insert("Library of Congress".to_string(), 1800);
let got = libraries.get_many_key_value_mut([
"Bodleian Library",
"Herzogin-Anna-Amalia-Bibliothek",
]);
assert_eq!(
got,
[
Some((&"Bodleian Library".to_string(), &mut 1602)),
Some((&"Herzogin-Anna-Amalia-Bibliothek".to_string(), &mut 1691)),
],
);
// Missing keys result in None
let got = libraries.get_many_key_value_mut([
"Bodleian Library",
"Gewandhaus",
]);
assert_eq!(
got,
[
Some((&"Bodleian Library".to_string(), &mut 1602)),
None,
],
);
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 std::collections
module-level documentation for more.
§Examples
use hashbrown::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");
Insert a key-value pair into the map without checking
if the key already exists in the map.
This operation is faster than regular insert, because it does not perform
lookup before insertion.
This operation is useful during initial population of the map.
For example, when constructing a map from another map, we know
that keys are unique.
Returns a reference to the key and value just inserted.
§Safety
This operation is safe if a key does not exist in the map.
However, if a key exists in the map already, the behavior is unspecified:
this operation may panic, loop forever, or any following operation with the map
may panic, loop forever or return arbitrary result.
That said, this operation (and following operations) are guaranteed to
not violate memory safety.
However this operation is still unsafe because the resulting HashMap
may be passed to unsafe code which does expect the map to behave
correctly, and would cause unsoundness as a result.
§Examples
use hashbrown::HashMap;
let mut map1 = HashMap::new();
assert_eq!(map1.insert(1, "a"), None);
assert_eq!(map1.insert(2, "b"), None);
assert_eq!(map1.insert(3, "c"), None);
assert_eq!(map1.len(), 3);
let mut map2 = HashMap::new();
for (key, value) in map1.into_iter() {
unsafe {
map2.insert_unique_unchecked(key, value);
}
}
let (key, value) = unsafe { map2.insert_unique_unchecked(4, "d") };
assert_eq!(key, &4);
assert_eq!(value, &mut "d");
*value = "e";
assert_eq!(map2[&1], "a");
assert_eq!(map2[&2], "b");
assert_eq!(map2[&3], "c");
assert_eq!(map2[&4], "e");
assert_eq!(map2.len(), 4);
Tries to insert a key-value pair into the map, and returns
a mutable reference to the value in the entry.
§Errors
If the map already had this key present, nothing is updated, and
an error containing the occupied entry and the value is returned.
§Examples
Basic usage:
use hashbrown::HashMap;
use hashbrown::hash_map::OccupiedError;
let mut map = HashMap::new();
assert_eq!(map.try_insert(37, "a").unwrap(), &"a");
match map.try_insert(37, "b") {
Err(OccupiedError { entry, value }) => {
assert_eq!(entry.key(), &37);
assert_eq!(entry.get(), &"a");
assert_eq!(value, "b");
}
_ => panic!()
}
Removes a key from the map, returning the value at the key if the key
was previously in the map. Keeps the allocated memory for reuse.
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 hashbrown::HashMap;
let mut map = HashMap::new();
// The map is empty
assert!(map.is_empty() && map.capacity() == 0);
map.insert(1, "a");
assert_eq!(map.remove(&1), Some("a"));
assert_eq!(map.remove(&1), None);
// Now map holds none elements
assert!(map.is_empty());
Removes a key from the map, returning the stored key and value if the
key was previously in the map. Keeps the allocated memory for reuse.
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 hashbrown::HashMap;
let mut map = HashMap::new();
// The map is empty
assert!(map.is_empty() && map.capacity() == 0);
map.insert(1, "a");
assert_eq!(map.remove_entry(&1), Some((1, "a")));
assert_eq!(map.remove(&1), None);
// Now map hold none elements
assert!(map.is_empty());
Returns the total amount of memory allocated internally by the hash
set, in bytes.
The returned number is informational only. It is intended to be
primarily used for memory profiling.
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).
§Examples
use core::hash::{BuildHasher, Hash};
use hashbrown::hash_map::{HashMap, RawEntryMut};
let mut map = HashMap::new();
map.extend([("a", 100), ("b", 200), ("c", 300)]);
fn compute_hash<K: Hash + ?Sized, S: BuildHasher>(hash_builder: &S, key: &K) -> u64 {
use core::hash::Hasher;
let mut state = hash_builder.build_hasher();
key.hash(&mut state);
state.finish()
}
// Existing key (insert and update)
match map.raw_entry_mut().from_key(&"a") {
RawEntryMut::Vacant(_) => unreachable!(),
RawEntryMut::Occupied(mut view) => {
assert_eq!(view.get(), &100);
let v = view.get_mut();
let new_v = (*v) * 10;
*v = new_v;
assert_eq!(view.insert(1111), 1000);
}
}
assert_eq!(map[&"a"], 1111);
assert_eq!(map.len(), 3);
// Existing key (take)
let hash = compute_hash(map.hasher(), &"c");
match map.raw_entry_mut().from_key_hashed_nocheck(hash, &"c") {
RawEntryMut::Vacant(_) => unreachable!(),
RawEntryMut::Occupied(view) => {
assert_eq!(view.remove_entry(), ("c", 300));
}
}
assert_eq!(map.raw_entry().from_key(&"c"), None);
assert_eq!(map.len(), 2);
// Nonexistent key (insert and update)
let key = "d";
let hash = compute_hash(map.hasher(), &key);
match map.raw_entry_mut().from_hash(hash, |q| *q == key) {
RawEntryMut::Occupied(_) => unreachable!(),
RawEntryMut::Vacant(view) => {
let (k, value) = view.insert("d", 4000);
assert_eq!((*k, *value), ("d", 4000));
*value = 40000;
}
}
assert_eq!(map[&"d"], 40000);
assert_eq!(map.len(), 3);
match map.raw_entry_mut().from_hash(hash, |q| *q == key) {
RawEntryMut::Vacant(_) => unreachable!(),
RawEntryMut::Occupied(view) => {
assert_eq!(view.remove_entry(), ("d", 40000));
}
}
assert_eq!(map.get(&"d"), None);
assert_eq!(map.len(), 2);
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.
§Examples
use core::hash::{BuildHasher, Hash};
use hashbrown::HashMap;
let mut map = HashMap::new();
map.extend([("a", 100), ("b", 200), ("c", 300)]);
fn compute_hash<K: Hash + ?Sized, S: BuildHasher>(hash_builder: &S, key: &K) -> u64 {
use core::hash::Hasher;
let mut state = hash_builder.build_hasher();
key.hash(&mut state);
state.finish()
}
for k in ["a", "b", "c", "d", "e", "f"] {
let hash = compute_hash(map.hasher(), k);
let v = map.get(&k).cloned();
let kv = v.as_ref().map(|v| (&k, v));
println!("Key: {} and value: {:?}", k, v);
assert_eq!(map.raw_entry().from_key(&k), kv);
assert_eq!(map.raw_entry().from_hash(hash, |q| *q == k), kv);
assert_eq!(map.raw_entry().from_key_hashed_nocheck(hash, &k), kv);
}
Trait Implementations§
Performs copy-assignment from source. Read more
Formats the value using the given formatter. Read more
Creates an empty HashMap<K, V, S, A>, with the Default value for the hasher and allocator.
§Examples
use hashbrown::HashMap;
use std::collections::hash_map::RandomState;
// You can specify all types of HashMap, including hasher and allocator.
// Created map is empty and don't allocate memory
let map: HashMap<u32, String> = Default::default();
assert_eq!(map.capacity(), 0);
let map: HashMap<u32, String, RandomState> = HashMap::default();
assert_eq!(map.capacity(), 0);
Source§Inserts all new key-values from the iterator and replaces values with existing
keys with new values returned from the iterator.
Inserts all new key-values from the iterator to existing HashMap<K, V, S, A>.
Replace values with existing keys with new values returned from the iterator.
The keys and values must implement Copy trait.
§Examples
use hashbrown::hash_map::HashMap;
let mut map = HashMap::new();
map.insert(1, 100);
let arr = [(1, 1), (2, 2)];
let some_iter = arr.iter();
map.extend(some_iter);
// Replace values with existing keys with new values returned from the iterator.
// So that the map.get(&1) doesn't return Some(&100).
assert_eq!(map.get(&1), Some(&1));
let some_vec: Vec<_> = vec![(3, 3), (4, 4)];
map.extend(&some_vec);
let some_arr = [(5, 5), (6, 6)];
map.extend(&some_arr);
let mut vec: Vec<_> = map.into_iter().collect();
// The `IntoIter` iterator produces items in arbitrary order, so the
// items must be sorted to test them against a sorted array.
vec.sort_unstable();
assert_eq!(vec, [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)]);
🔬This is a nightly-only experimental API. (extend_one) Extends a collection with exactly one element.
🔬This is a nightly-only experimental API. (extend_one) Reserves capacity in a collection for the given number of additional elements. Read moreSource§Inserts all new key-values from the iterator and replaces values with existing
keys with new values returned from the iterator.
Inserts all new key-values from the iterator to existing HashMap<K, V, S, A>.
Replace values with existing keys with new values returned from the iterator.
The keys and values must implement Copy trait.
§Examples
use hashbrown::hash_map::HashMap;
let mut map = HashMap::new();
map.insert(1, 100);
let arr = [(1, 1), (2, 2)];
let some_iter = arr.iter().map(|(k, v)| (k, v));
map.extend(some_iter);
// Replace values with existing keys with new values returned from the iterator.
// So that the map.get(&1) doesn't return Some(&100).
assert_eq!(map.get(&1), Some(&1));
let some_vec: Vec<_> = vec![(3, 3), (4, 4)];
map.extend(some_vec.iter().map(|(k, v)| (k, v)));
let some_arr = [(5, 5), (6, 6)];
map.extend(some_arr.iter().map(|(k, v)| (k, v)));
// You can also extend from another HashMap
let mut new_map = HashMap::new();
new_map.extend(&map);
assert_eq!(new_map, map);
let mut vec: Vec<_> = new_map.into_iter().collect();
// The `IntoIter` iterator produces items in arbitrary order, so the
// items must be sorted to test them against a sorted array.
vec.sort_unstable();
assert_eq!(vec, [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)]);
🔬This is a nightly-only experimental API. (extend_one) Extends a collection with exactly one element.
🔬This is a nightly-only experimental API. (extend_one) Reserves capacity in a collection for the given number of additional elements. Read moreSource§Inserts all new key-values from the iterator and replaces values with existing
keys with new values returned from the iterator.
Inserts all new key-values from the iterator to existing HashMap<K, V, S, A>.
Replace values with existing keys with new values returned from the iterator.
§Examples
use hashbrown::hash_map::HashMap;
let mut map = HashMap::new();
map.insert(1, 100);
let some_iter = [(1, 1), (2, 2)].into_iter();
map.extend(some_iter);
// Replace values with existing keys with new values returned from the iterator.
// So that the map.get(&1) doesn't return Some(&100).
assert_eq!(map.get(&1), Some(&1));
let some_vec: Vec<_> = vec![(3, 3), (4, 4)];
map.extend(some_vec);
let some_arr = [(5, 5), (6, 6)];
map.extend(some_arr);
let old_map_len = map.len();
// You can also extend from another HashMap
let mut new_map = HashMap::new();
new_map.extend(map);
assert_eq!(new_map.len(), old_map_len);
let mut vec: Vec<_> = new_map.into_iter().collect();
// The `IntoIter` iterator produces items in arbitrary order, so the
// items must be sorted to test them against a sorted array.
vec.sort_unstable();
assert_eq!(vec, [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)]);
🔬This is a nightly-only experimental API. (extend_one) Extends a collection with exactly one element.
🔬This is a nightly-only experimental API. (extend_one) Reserves capacity in a collection for the given number of additional elements. Read more
Converts to this type from the input type. Source§Available on crate feature default-hasher only.
§Examples
use hashbrown::HashMap;
let map1 = HashMap::from([(1, 2), (3, 4)]);
let map2: HashMap<_, _> = [(1, 2), (3, 4)].into();
assert_eq!(map1, map2);
Returns a reference to the value corresponding to the supplied key.
§Panics
Panics if the key is not present in the HashMap.
§Examples
use hashbrown::HashMap;
let map: HashMap<_, _> = [("a", "One"), ("b", "Two")].into();
assert_eq!(map[&"a"], "One");
assert_eq!(map[&"b"], "Two");
The returned type after indexing.
Creates an iterator over the entries of a HashMap in arbitrary order.
The iterator element type is (&'a K, &'a V).
Return the same Iter struct as by the iter method on HashMap.
§Examples
use hashbrown::HashMap;
let map_one: HashMap<_, _> = [(1, "a"), (2, "b"), (3, "c")].into();
let mut map_two = HashMap::new();
for (key, value) in &map_one {
println!("Key: {}, Value: {}", key, value);
map_two.insert(*key, *value);
}
assert_eq!(map_one, map_two);
The type of the elements being iterated over.
Which kind of iterator are we turning this into?
Creates an iterator over the entries of a HashMap in arbitrary order
with mutable references to the values. The iterator element type is
(&'a K, &'a mut V).
Return the same IterMut struct as by the iter_mut method on
HashMap.
§Examples
use hashbrown::HashMap;
let mut map: HashMap<_, _> = [("a", 1), ("b", 2), ("c", 3)].into();
for (key, value) in &mut map {
println!("Key: {}, Value: {}", key, value);
*value *= 2;
}
let mut vec = map.iter().collect::<Vec<_>>();
// The `Iter` iterator produces items in arbitrary order, so the
// items must be sorted to test them against a sorted array.
vec.sort_unstable();
assert_eq!(vec, [(&"a", &2), (&"b", &4), (&"c", &6)]);
The type of the elements being iterated over.
Which kind of iterator are we turning this into?
Creates a consuming iterator, that is, one that moves each key-value
pair out of the map in arbitrary order. The map cannot be used after
calling this.
§Examples
use hashbrown::HashMap;
let map: HashMap<_, _> = [("a", 1), ("b", 2), ("c", 3)].into();
// Not possible with .iter()
let mut vec: Vec<(&str, i32)> = map.into_iter().collect();
// The `IntoIter` iterator produces items in arbitrary order, so
// the items must be sorted to test them against a sorted array.
vec.sort_unstable();
assert_eq!(vec, [("a", 1), ("b", 2), ("c", 3)]);
The type of the elements being iterated over.
Which kind of iterator are we turning this into?
Auto Trait Implementations§Blanket Implementations§
Immutably borrows from an owned value. Read more
Mutably borrows from an owned value. Read more
🔬This is a nightly-only experimental API. (clone_to_uninit) Performs copy-assignment from self to dest. Read more
Compare self to key and return true if they are equal.
Returns the argument unchanged.
Calls U::from(self).
That is, this conversion is whatever the implementation of
From<T> for U chooses to do.
The resulting type after obtaining ownership.
Creates owned data from borrowed data, usually by cloning. Read more
Uses borrowed data to replace owned data, usually by cloning. Read more
The type returned in the event of a conversion error.
Performs the conversion.
The type returned in the event of a conversion error.
Performs the conversion. |