6 use hashbrown::hash_map as base;
8 use crate::borrow::Borrow;
10 use crate::collections::TryReserveError;
11 use crate::collections::TryReserveErrorKind;
12 use crate::fmt::{self, Debug};
14 use crate::hash::{BuildHasher, Hash, Hasher, SipHasher13};
15 use crate::iter::{FromIterator, FusedIterator};
16 use crate::ops::Index;
19 /// A [hash map] implemented with quadratic probing and SIMD lookup.
21 /// By default, `HashMap` uses a hashing algorithm selected to provide
22 /// resistance against HashDoS attacks. The algorithm is randomly seeded, and a
23 /// reasonable best-effort is made to generate this seed from a high quality,
24 /// secure source of randomness provided by the host without blocking the
25 /// program. Because of this, the randomness of the seed depends on the output
26 /// quality of the system's random number generator when the seed is created.
27 /// In particular, seeds generated when the system's entropy pool is abnormally
28 /// low such as during system boot may be of a lower quality.
30 /// The default hashing algorithm is currently SipHash 1-3, though this is
31 /// subject to change at any point in the future. While its performance is very
32 /// competitive for medium sized keys, other hashing algorithms will outperform
33 /// it for small keys such as integers as well as large keys such as long
34 /// strings, though those algorithms will typically *not* protect against
35 /// attacks such as HashDoS.
37 /// The hashing algorithm can be replaced on a per-`HashMap` basis using the
38 /// [`default`], [`with_hasher`], and [`with_capacity_and_hasher`] methods.
39 /// There are many alternative [hashing algorithms available on crates.io].
41 /// It is required that the keys implement the [`Eq`] and [`Hash`] traits, although
42 /// this can frequently be achieved by using `#[derive(PartialEq, Eq, Hash)]`.
43 /// If you implement these yourself, it is important that the following
47 /// k1 == k2 -> hash(k1) == hash(k2)
50 /// In other words, if two keys are equal, their hashes must be equal.
52 /// It is a logic error for a key to be modified in such a way that the key's
53 /// hash, as determined by the [`Hash`] trait, or its equality, as determined by
54 /// the [`Eq`] trait, changes while it is in the map. This is normally only
55 /// possible through [`Cell`], [`RefCell`], global state, I/O, or unsafe code.
56 /// The behavior resulting from such a logic error is not specified, but will
57 /// not result in undefined behavior. This could include panics, incorrect results,
58 /// aborts, memory leaks, and non-termination.
60 /// The hash table implementation is a Rust port of Google's [SwissTable].
61 /// The original C++ version of SwissTable can be found [here], and this
62 /// [CppCon talk] gives an overview of how the algorithm works.
64 /// [hash map]: crate::collections#use-a-hashmap-when
65 /// [hashing algorithms available on crates.io]: https://crates.io/keywords/hasher
66 /// [SwissTable]: https://abseil.io/blog/20180927-swisstables
67 /// [here]: https://github.com/abseil/abseil-cpp/blob/master/absl/container/internal/raw_hash_set.h
68 /// [CppCon talk]: https://www.youtube.com/watch?v=ncHmEUmJZf4
73 /// use std::collections::HashMap;
75 /// // Type inference lets us omit an explicit type signature (which
76 /// // would be `HashMap<String, String>` in this example).
77 /// let mut book_reviews = HashMap::new();
79 /// // Review some books.
80 /// book_reviews.insert(
81 /// "Adventures of Huckleberry Finn".to_string(),
82 /// "My favorite book.".to_string(),
84 /// book_reviews.insert(
85 /// "Grimms' Fairy Tales".to_string(),
86 /// "Masterpiece.".to_string(),
88 /// book_reviews.insert(
89 /// "Pride and Prejudice".to_string(),
90 /// "Very enjoyable.".to_string(),
92 /// book_reviews.insert(
93 /// "The Adventures of Sherlock Holmes".to_string(),
94 /// "Eye lyked it alot.".to_string(),
97 /// // Check for a specific one.
98 /// // When collections store owned values (String), they can still be
99 /// // queried using references (&str).
100 /// if !book_reviews.contains_key("Les Misérables") {
101 /// println!("We've got {} reviews, but Les Misérables ain't one.",
102 /// book_reviews.len());
105 /// // oops, this review has a lot of spelling mistakes, let's delete it.
106 /// book_reviews.remove("The Adventures of Sherlock Holmes");
108 /// // Look up the values associated with some keys.
109 /// let to_find = ["Pride and Prejudice", "Alice's Adventure in Wonderland"];
110 /// for &book in &to_find {
111 /// match book_reviews.get(book) {
112 /// Some(review) => println!("{}: {}", book, review),
113 /// None => println!("{} is unreviewed.", book)
117 /// // Look up the value for a key (will panic if the key is not found).
118 /// println!("Review for Jane: {}", book_reviews["Pride and Prejudice"]);
120 /// // Iterate over everything.
121 /// for (book, review) in &book_reviews {
122 /// println!("{}: \"{}\"", book, review);
126 /// A `HashMap` with a known list of items can be initialized from an array:
129 /// use std::collections::HashMap;
131 /// let solar_distance = HashMap::from([
132 /// ("Mercury", 0.4),
139 /// `HashMap` implements an [`Entry API`](#method.entry), which allows
140 /// for complex methods of getting, setting, updating and removing keys and
144 /// use std::collections::HashMap;
146 /// // type inference lets us omit an explicit type signature (which
147 /// // would be `HashMap<&str, u8>` in this example).
148 /// let mut player_stats = HashMap::new();
150 /// fn random_stat_buff() -> u8 {
151 /// // could actually return some random value here - let's just return
152 /// // some fixed value for now
156 /// // insert a key only if it doesn't already exist
157 /// player_stats.entry("health").or_insert(100);
159 /// // insert a key using a function that provides a new value only if it
160 /// // doesn't already exist
161 /// player_stats.entry("defence").or_insert_with(random_stat_buff);
163 /// // update a key, guarding against the key possibly not being set
164 /// let stat = player_stats.entry("attack").or_insert(100);
165 /// *stat += random_stat_buff();
168 /// The easiest way to use `HashMap` with a custom key type is to derive [`Eq`] and [`Hash`].
169 /// We must also derive [`PartialEq`].
171 /// [`RefCell`]: crate::cell::RefCell
172 /// [`Cell`]: crate::cell::Cell
173 /// [`default`]: Default::default
174 /// [`with_hasher`]: Self::with_hasher
175 /// [`with_capacity_and_hasher`]: Self::with_capacity_and_hasher
178 /// use std::collections::HashMap;
180 /// #[derive(Hash, Eq, PartialEq, Debug)]
187 /// /// Creates a new Viking.
188 /// fn new(name: &str, country: &str) -> Viking {
189 /// Viking { name: name.to_string(), country: country.to_string() }
193 /// // Use a HashMap to store the vikings' health points.
194 /// let vikings = HashMap::from([
195 /// (Viking::new("Einar", "Norway"), 25),
196 /// (Viking::new("Olaf", "Denmark"), 24),
197 /// (Viking::new("Harald", "Iceland"), 12),
200 /// // Use derived implementation to print the status of the vikings.
201 /// for (viking, health) in &vikings {
202 /// println!("{:?} has {} hp", viking, health);
206 #[cfg_attr(not(test), rustc_diagnostic_item = "HashMap")]
207 #[stable(feature = "rust1", since = "1.0.0")]
208 #[rustc_insignificant_dtor]
209 pub struct HashMap<K, V, S = RandomState> {
210 base: base::HashMap<K, V, S>,
213 impl<K, V> HashMap<K, V, RandomState> {
214 /// Creates an empty `HashMap`.
216 /// The hash map is initially created with a capacity of 0, so it will not allocate until it
217 /// is first inserted into.
222 /// use std::collections::HashMap;
223 /// let mut map: HashMap<&str, i32> = HashMap::new();
227 #[stable(feature = "rust1", since = "1.0.0")]
228 pub fn new() -> HashMap<K, V, RandomState> {
232 /// Creates an empty `HashMap` with the specified capacity.
234 /// The hash map will be able to hold at least `capacity` elements without
235 /// reallocating. If `capacity` is 0, the hash map will not allocate.
240 /// use std::collections::HashMap;
241 /// let mut map: HashMap<&str, i32> = HashMap::with_capacity(10);
245 #[stable(feature = "rust1", since = "1.0.0")]
246 pub fn with_capacity(capacity: usize) -> HashMap<K, V, RandomState> {
247 HashMap::with_capacity_and_hasher(capacity, Default::default())
251 impl<K, V, S> HashMap<K, V, S> {
252 /// Creates an empty `HashMap` which will use the given hash builder to hash
255 /// The created map has the default initial capacity.
257 /// Warning: `hash_builder` is normally randomly generated, and
258 /// is designed to allow HashMaps to be resistant to attacks that
259 /// cause many collisions and very poor performance. Setting it
260 /// manually using this function can expose a DoS attack vector.
262 /// The `hash_builder` passed should implement the [`BuildHasher`] trait for
263 /// the HashMap to be useful, see its documentation for details.
268 /// use std::collections::HashMap;
269 /// use std::collections::hash_map::RandomState;
271 /// let s = RandomState::new();
272 /// let mut map = HashMap::with_hasher(s);
273 /// map.insert(1, 2);
276 #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
277 pub fn with_hasher(hash_builder: S) -> HashMap<K, V, S> {
278 HashMap { base: base::HashMap::with_hasher(hash_builder) }
281 /// Creates an empty `HashMap` with the specified capacity, using `hash_builder`
282 /// to hash the keys.
284 /// The hash map will be able to hold at least `capacity` elements without
285 /// reallocating. If `capacity` is 0, the hash map will not allocate.
287 /// Warning: `hash_builder` is normally randomly generated, and
288 /// is designed to allow HashMaps to be resistant to attacks that
289 /// cause many collisions and very poor performance. Setting it
290 /// manually using this function can expose a DoS attack vector.
292 /// The `hash_builder` passed should implement the [`BuildHasher`] trait for
293 /// the HashMap to be useful, see its documentation for details.
298 /// use std::collections::HashMap;
299 /// use std::collections::hash_map::RandomState;
301 /// let s = RandomState::new();
302 /// let mut map = HashMap::with_capacity_and_hasher(10, s);
303 /// map.insert(1, 2);
306 #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
307 pub fn with_capacity_and_hasher(capacity: usize, hash_builder: S) -> HashMap<K, V, S> {
308 HashMap { base: base::HashMap::with_capacity_and_hasher(capacity, hash_builder) }
311 /// Returns the number of elements the map can hold without reallocating.
313 /// This number is a lower bound; the `HashMap<K, V>` might be able to hold
314 /// more, but is guaranteed to be able to hold at least this many.
319 /// use std::collections::HashMap;
320 /// let map: HashMap<i32, i32> = HashMap::with_capacity(100);
321 /// assert!(map.capacity() >= 100);
324 #[stable(feature = "rust1", since = "1.0.0")]
325 pub fn capacity(&self) -> usize {
329 /// An iterator visiting all keys in arbitrary order.
330 /// The iterator element type is `&'a K`.
335 /// use std::collections::HashMap;
337 /// let mut map = HashMap::new();
338 /// map.insert("a", 1);
339 /// map.insert("b", 2);
340 /// map.insert("c", 3);
342 /// for key in map.keys() {
343 /// println!("{}", key);
346 #[stable(feature = "rust1", since = "1.0.0")]
347 pub fn keys(&self) -> Keys<'_, K, V> {
348 Keys { inner: self.iter() }
351 /// An iterator visiting all values in arbitrary order.
352 /// The iterator element type is `&'a V`.
357 /// use std::collections::HashMap;
359 /// let mut map = HashMap::new();
360 /// map.insert("a", 1);
361 /// map.insert("b", 2);
362 /// map.insert("c", 3);
364 /// for val in map.values() {
365 /// println!("{}", val);
368 #[stable(feature = "rust1", since = "1.0.0")]
369 pub fn values(&self) -> Values<'_, K, V> {
370 Values { inner: self.iter() }
373 /// An iterator visiting all values mutably in arbitrary order.
374 /// The iterator element type is `&'a mut V`.
379 /// use std::collections::HashMap;
381 /// let mut map = HashMap::new();
383 /// map.insert("a", 1);
384 /// map.insert("b", 2);
385 /// map.insert("c", 3);
387 /// for val in map.values_mut() {
388 /// *val = *val + 10;
391 /// for val in map.values() {
392 /// println!("{}", val);
395 #[stable(feature = "map_values_mut", since = "1.10.0")]
396 pub fn values_mut(&mut self) -> ValuesMut<'_, K, V> {
397 ValuesMut { inner: self.iter_mut() }
400 /// An iterator visiting all key-value pairs in arbitrary order.
401 /// The iterator element type is `(&'a K, &'a V)`.
406 /// use std::collections::HashMap;
408 /// let mut map = HashMap::new();
409 /// map.insert("a", 1);
410 /// map.insert("b", 2);
411 /// map.insert("c", 3);
413 /// for (key, val) in map.iter() {
414 /// println!("key: {} val: {}", key, val);
417 #[cfg_attr(not(bootstrap), rustc_lint_query_instability)]
418 #[stable(feature = "rust1", since = "1.0.0")]
419 pub fn iter(&self) -> Iter<'_, K, V> {
420 Iter { base: self.base.iter() }
423 /// An iterator visiting all key-value pairs in arbitrary order,
424 /// with mutable references to the values.
425 /// The iterator element type is `(&'a K, &'a mut V)`.
430 /// use std::collections::HashMap;
432 /// let mut map = HashMap::new();
433 /// map.insert("a", 1);
434 /// map.insert("b", 2);
435 /// map.insert("c", 3);
437 /// // Update all values
438 /// for (_, val) in map.iter_mut() {
442 /// for (key, val) in &map {
443 /// println!("key: {} val: {}", key, val);
446 #[cfg_attr(not(bootstrap), rustc_lint_query_instability)]
447 #[stable(feature = "rust1", since = "1.0.0")]
448 pub fn iter_mut(&mut self) -> IterMut<'_, K, V> {
449 IterMut { base: self.base.iter_mut() }
452 /// Returns the number of elements in the map.
457 /// use std::collections::HashMap;
459 /// let mut a = HashMap::new();
460 /// assert_eq!(a.len(), 0);
461 /// a.insert(1, "a");
462 /// assert_eq!(a.len(), 1);
464 #[stable(feature = "rust1", since = "1.0.0")]
465 pub fn len(&self) -> usize {
469 /// Returns `true` if the map contains no elements.
474 /// use std::collections::HashMap;
476 /// let mut a = HashMap::new();
477 /// assert!(a.is_empty());
478 /// a.insert(1, "a");
479 /// assert!(!a.is_empty());
482 #[stable(feature = "rust1", since = "1.0.0")]
483 pub fn is_empty(&self) -> bool {
487 /// Clears the map, returning all key-value pairs as an iterator. Keeps the
488 /// allocated memory for reuse.
493 /// use std::collections::HashMap;
495 /// let mut a = HashMap::new();
496 /// a.insert(1, "a");
497 /// a.insert(2, "b");
499 /// for (k, v) in a.drain().take(1) {
500 /// assert!(k == 1 || k == 2);
501 /// assert!(v == "a" || v == "b");
504 /// assert!(a.is_empty());
507 #[cfg_attr(not(bootstrap), rustc_lint_query_instability)]
508 #[stable(feature = "drain", since = "1.6.0")]
509 pub fn drain(&mut self) -> Drain<'_, K, V> {
510 Drain { base: self.base.drain() }
513 /// Creates an iterator which uses a closure to determine if an element should be removed.
515 /// If the closure returns true, the element is removed from the map and yielded.
516 /// If the closure returns false, or panics, the element remains in the map and will not be
519 /// Note that `drain_filter` lets you mutate every value in the filter closure, regardless of
520 /// whether you choose to keep or remove it.
522 /// If the iterator is only partially consumed or not consumed at all, each of the remaining
523 /// elements will still be subjected to the closure and removed and dropped if it returns true.
525 /// It is unspecified how many more elements will be subjected to the closure
526 /// if a panic occurs in the closure, or a panic occurs while dropping an element,
527 /// or if the `DrainFilter` value is leaked.
531 /// Splitting a map into even and odd keys, reusing the original map:
534 /// #![feature(hash_drain_filter)]
535 /// use std::collections::HashMap;
537 /// let mut map: HashMap<i32, i32> = (0..8).map(|x| (x, x)).collect();
538 /// let drained: HashMap<i32, i32> = map.drain_filter(|k, _v| k % 2 == 0).collect();
540 /// let mut evens = drained.keys().copied().collect::<Vec<_>>();
541 /// let mut odds = map.keys().copied().collect::<Vec<_>>();
545 /// assert_eq!(evens, vec![0, 2, 4, 6]);
546 /// assert_eq!(odds, vec![1, 3, 5, 7]);
549 #[cfg_attr(not(bootstrap), rustc_lint_query_instability)]
550 #[unstable(feature = "hash_drain_filter", issue = "59618")]
551 pub fn drain_filter<F>(&mut self, pred: F) -> DrainFilter<'_, K, V, F>
553 F: FnMut(&K, &mut V) -> bool,
555 DrainFilter { base: self.base.drain_filter(pred) }
558 /// Clears the map, removing all key-value pairs. Keeps the allocated memory
564 /// use std::collections::HashMap;
566 /// let mut a = HashMap::new();
567 /// a.insert(1, "a");
569 /// assert!(a.is_empty());
572 #[stable(feature = "rust1", since = "1.0.0")]
573 pub fn clear(&mut self) {
577 /// Returns a reference to the map's [`BuildHasher`].
582 /// use std::collections::HashMap;
583 /// use std::collections::hash_map::RandomState;
585 /// let hasher = RandomState::new();
586 /// let map: HashMap<i32, i32> = HashMap::with_hasher(hasher);
587 /// let hasher: &RandomState = map.hasher();
590 #[stable(feature = "hashmap_public_hasher", since = "1.9.0")]
591 pub fn hasher(&self) -> &S {
596 impl<K, V, S> HashMap<K, V, S>
601 /// Reserves capacity for at least `additional` more elements to be inserted
602 /// in the `HashMap`. The collection may reserve more space to avoid
603 /// frequent reallocations.
607 /// Panics if the new allocation size overflows [`usize`].
612 /// use std::collections::HashMap;
613 /// let mut map: HashMap<&str, i32> = HashMap::new();
617 #[stable(feature = "rust1", since = "1.0.0")]
618 pub fn reserve(&mut self, additional: usize) {
619 self.base.reserve(additional)
622 /// Tries to reserve capacity for at least `additional` more elements to be inserted
623 /// in the given `HashMap<K, V>`. The collection may reserve more space to avoid
624 /// frequent reallocations.
628 /// If the capacity overflows, or the allocator reports a failure, then an error
634 /// use std::collections::HashMap;
636 /// let mut map: HashMap<&str, isize> = HashMap::new();
637 /// map.try_reserve(10).expect("why is the test harness OOMing on 10 bytes?");
640 #[stable(feature = "try_reserve", since = "1.57.0")]
641 pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
642 self.base.try_reserve(additional).map_err(map_try_reserve_error)
645 /// Shrinks the capacity of the map as much as possible. It will drop
646 /// down as much as possible while maintaining the internal rules
647 /// and possibly leaving some space in accordance with the resize policy.
652 /// use std::collections::HashMap;
654 /// let mut map: HashMap<i32, i32> = HashMap::with_capacity(100);
655 /// map.insert(1, 2);
656 /// map.insert(3, 4);
657 /// assert!(map.capacity() >= 100);
658 /// map.shrink_to_fit();
659 /// assert!(map.capacity() >= 2);
662 #[stable(feature = "rust1", since = "1.0.0")]
663 pub fn shrink_to_fit(&mut self) {
664 self.base.shrink_to_fit();
667 /// Shrinks the capacity of the map with a lower limit. It will drop
668 /// down no lower than the supplied limit while maintaining the internal rules
669 /// and possibly leaving some space in accordance with the resize policy.
671 /// If the current capacity is less than the lower limit, this is a no-op.
676 /// use std::collections::HashMap;
678 /// let mut map: HashMap<i32, i32> = HashMap::with_capacity(100);
679 /// map.insert(1, 2);
680 /// map.insert(3, 4);
681 /// assert!(map.capacity() >= 100);
682 /// map.shrink_to(10);
683 /// assert!(map.capacity() >= 10);
684 /// map.shrink_to(0);
685 /// assert!(map.capacity() >= 2);
688 #[stable(feature = "shrink_to", since = "1.56.0")]
689 pub fn shrink_to(&mut self, min_capacity: usize) {
690 self.base.shrink_to(min_capacity);
693 /// Gets the given key's corresponding entry in the map for in-place manipulation.
698 /// use std::collections::HashMap;
700 /// let mut letters = HashMap::new();
702 /// for ch in "a short treatise on fungi".chars() {
703 /// let counter = letters.entry(ch).or_insert(0);
707 /// assert_eq!(letters[&'s'], 2);
708 /// assert_eq!(letters[&'t'], 3);
709 /// assert_eq!(letters[&'u'], 1);
710 /// assert_eq!(letters.get(&'y'), None);
713 #[stable(feature = "rust1", since = "1.0.0")]
714 pub fn entry(&mut self, key: K) -> Entry<'_, K, V> {
715 map_entry(self.base.rustc_entry(key))
718 /// Returns a reference to the value corresponding to the key.
720 /// The key may be any borrowed form of the map's key type, but
721 /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
727 /// use std::collections::HashMap;
729 /// let mut map = HashMap::new();
730 /// map.insert(1, "a");
731 /// assert_eq!(map.get(&1), Some(&"a"));
732 /// assert_eq!(map.get(&2), None);
734 #[stable(feature = "rust1", since = "1.0.0")]
736 pub fn get<Q: ?Sized>(&self, k: &Q) -> Option<&V>
744 /// Returns the key-value pair corresponding to the supplied key.
746 /// The supplied key may be any borrowed form of the map's key type, but
747 /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
753 /// use std::collections::HashMap;
755 /// let mut map = HashMap::new();
756 /// map.insert(1, "a");
757 /// assert_eq!(map.get_key_value(&1), Some((&1, &"a")));
758 /// assert_eq!(map.get_key_value(&2), None);
761 #[stable(feature = "map_get_key_value", since = "1.40.0")]
762 pub fn get_key_value<Q: ?Sized>(&self, k: &Q) -> Option<(&K, &V)>
767 self.base.get_key_value(k)
770 /// Returns `true` if the map contains a value for the specified key.
772 /// The key may be any borrowed form of the map's key type, but
773 /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
779 /// use std::collections::HashMap;
781 /// let mut map = HashMap::new();
782 /// map.insert(1, "a");
783 /// assert_eq!(map.contains_key(&1), true);
784 /// assert_eq!(map.contains_key(&2), false);
787 #[stable(feature = "rust1", since = "1.0.0")]
788 pub fn contains_key<Q: ?Sized>(&self, k: &Q) -> bool
793 self.base.contains_key(k)
796 /// Returns a mutable reference to the value corresponding to the key.
798 /// The key may be any borrowed form of the map's key type, but
799 /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
805 /// use std::collections::HashMap;
807 /// let mut map = HashMap::new();
808 /// map.insert(1, "a");
809 /// if let Some(x) = map.get_mut(&1) {
812 /// assert_eq!(map[&1], "b");
815 #[stable(feature = "rust1", since = "1.0.0")]
816 pub fn get_mut<Q: ?Sized>(&mut self, k: &Q) -> Option<&mut V>
824 /// Inserts a key-value pair into the map.
826 /// If the map did not have this key present, [`None`] is returned.
828 /// If the map did have this key present, the value is updated, and the old
829 /// value is returned. The key is not updated, though; this matters for
830 /// types that can be `==` without being identical. See the [module-level
831 /// documentation] for more.
833 /// [module-level documentation]: crate::collections#insert-and-complex-keys
838 /// use std::collections::HashMap;
840 /// let mut map = HashMap::new();
841 /// assert_eq!(map.insert(37, "a"), None);
842 /// assert_eq!(map.is_empty(), false);
844 /// map.insert(37, "b");
845 /// assert_eq!(map.insert(37, "c"), Some("b"));
846 /// assert_eq!(map[&37], "c");
849 #[stable(feature = "rust1", since = "1.0.0")]
850 pub fn insert(&mut self, k: K, v: V) -> Option<V> {
851 self.base.insert(k, v)
854 /// Tries to insert a key-value pair into the map, and returns
855 /// a mutable reference to the value in the entry.
857 /// If the map already had this key present, nothing is updated, and
858 /// an error containing the occupied entry and the value is returned.
865 /// #![feature(map_try_insert)]
867 /// use std::collections::HashMap;
869 /// let mut map = HashMap::new();
870 /// assert_eq!(map.try_insert(37, "a").unwrap(), &"a");
872 /// let err = map.try_insert(37, "b").unwrap_err();
873 /// assert_eq!(err.entry.key(), &37);
874 /// assert_eq!(err.entry.get(), &"a");
875 /// assert_eq!(err.value, "b");
877 #[unstable(feature = "map_try_insert", issue = "82766")]
878 pub fn try_insert(&mut self, key: K, value: V) -> Result<&mut V, OccupiedError<'_, K, V>> {
879 match self.entry(key) {
880 Occupied(entry) => Err(OccupiedError { entry, value }),
881 Vacant(entry) => Ok(entry.insert(value)),
885 /// Removes a key from the map, returning the value at the key if the key
886 /// was previously in the map.
888 /// The key may be any borrowed form of the map's key type, but
889 /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
895 /// use std::collections::HashMap;
897 /// let mut map = HashMap::new();
898 /// map.insert(1, "a");
899 /// assert_eq!(map.remove(&1), Some("a"));
900 /// assert_eq!(map.remove(&1), None);
903 #[stable(feature = "rust1", since = "1.0.0")]
904 pub fn remove<Q: ?Sized>(&mut self, k: &Q) -> Option<V>
912 /// Removes a key from the map, returning the stored key and value if the
913 /// key was previously in the map.
915 /// The key may be any borrowed form of the map's key type, but
916 /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
922 /// use std::collections::HashMap;
925 /// let mut map = HashMap::new();
926 /// map.insert(1, "a");
927 /// assert_eq!(map.remove_entry(&1), Some((1, "a")));
928 /// assert_eq!(map.remove(&1), None);
932 #[stable(feature = "hash_map_remove_entry", since = "1.27.0")]
933 pub fn remove_entry<Q: ?Sized>(&mut self, k: &Q) -> Option<(K, V)>
938 self.base.remove_entry(k)
941 /// Retains only the elements specified by the predicate.
943 /// In other words, remove all pairs `(k, v)` such that `f(&k, &mut v)` returns `false`.
944 /// The elements are visited in unsorted (and unspecified) order.
949 /// use std::collections::HashMap;
951 /// let mut map: HashMap<i32, i32> = (0..8).map(|x| (x, x*10)).collect();
952 /// map.retain(|&k, _| k % 2 == 0);
953 /// assert_eq!(map.len(), 4);
956 #[cfg_attr(not(bootstrap), rustc_lint_query_instability)]
957 #[stable(feature = "retain_hash_collection", since = "1.18.0")]
958 pub fn retain<F>(&mut self, f: F)
960 F: FnMut(&K, &mut V) -> bool,
965 /// Creates a consuming iterator visiting all the keys in arbitrary order.
966 /// The map cannot be used after calling this.
967 /// The iterator element type is `K`.
972 /// use std::collections::HashMap;
974 /// let mut map = HashMap::new();
975 /// map.insert("a", 1);
976 /// map.insert("b", 2);
977 /// map.insert("c", 3);
979 /// let mut vec: Vec<&str> = map.into_keys().collect();
980 /// // The `IntoKeys` iterator produces keys in arbitrary order, so the
981 /// // keys must be sorted to test them against a sorted array.
982 /// vec.sort_unstable();
983 /// assert_eq!(vec, ["a", "b", "c"]);
986 #[cfg_attr(not(bootstrap), rustc_lint_query_instability)]
987 #[stable(feature = "map_into_keys_values", since = "1.54.0")]
988 pub fn into_keys(self) -> IntoKeys<K, V> {
989 IntoKeys { inner: self.into_iter() }
992 /// Creates a consuming iterator visiting all the values in arbitrary order.
993 /// The map cannot be used after calling this.
994 /// The iterator element type is `V`.
999 /// use std::collections::HashMap;
1001 /// let mut map = HashMap::new();
1002 /// map.insert("a", 1);
1003 /// map.insert("b", 2);
1004 /// map.insert("c", 3);
1006 /// let mut vec: Vec<i32> = map.into_values().collect();
1007 /// // The `IntoValues` iterator produces values in arbitrary order, so
1008 /// // the values must be sorted to test them against a sorted array.
1009 /// vec.sort_unstable();
1010 /// assert_eq!(vec, [1, 2, 3]);
1013 #[cfg_attr(not(bootstrap), rustc_lint_query_instability)]
1014 #[stable(feature = "map_into_keys_values", since = "1.54.0")]
1015 pub fn into_values(self) -> IntoValues<K, V> {
1016 IntoValues { inner: self.into_iter() }
1020 impl<K, V, S> HashMap<K, V, S>
1024 /// Creates a raw entry builder for the HashMap.
1026 /// Raw entries provide the lowest level of control for searching and
1027 /// manipulating a map. They must be manually initialized with a hash and
1028 /// then manually searched. After this, insertions into a vacant entry
1029 /// still require an owned key to be provided.
1031 /// Raw entries are useful for such exotic situations as:
1033 /// * Hash memoization
1034 /// * Deferring the creation of an owned key until it is known to be required
1035 /// * Using a search key that doesn't work with the Borrow trait
1036 /// * Using custom comparison logic without newtype wrappers
1038 /// Because raw entries provide much more low-level control, it's much easier
1039 /// to put the HashMap into an inconsistent state which, while memory-safe,
1040 /// will cause the map to produce seemingly random results. Higher-level and
1041 /// more foolproof APIs like `entry` should be preferred when possible.
1043 /// In particular, the hash used to initialized the raw entry must still be
1044 /// consistent with the hash of the key that is ultimately stored in the entry.
1045 /// This is because implementations of HashMap may need to recompute hashes
1046 /// when resizing, at which point only the keys are available.
1048 /// Raw entries give mutable access to the keys. This must not be used
1049 /// to modify how the key would compare or hash, as the map will not re-evaluate
1050 /// where the key should go, meaning the keys may become "lost" if their
1051 /// location does not reflect their state. For instance, if you change a key
1052 /// so that the map now contains keys which compare equal, search may start
1053 /// acting erratically, with two keys randomly masking each other. Implementations
1054 /// are free to assume this doesn't happen (within the limits of memory-safety).
1056 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1057 pub fn raw_entry_mut(&mut self) -> RawEntryBuilderMut<'_, K, V, S> {
1058 RawEntryBuilderMut { map: self }
1061 /// Creates a raw immutable entry builder for the HashMap.
1063 /// Raw entries provide the lowest level of control for searching and
1064 /// manipulating a map. They must be manually initialized with a hash and
1065 /// then manually searched.
1067 /// This is useful for
1068 /// * Hash memoization
1069 /// * Using a search key that doesn't work with the Borrow trait
1070 /// * Using custom comparison logic without newtype wrappers
1072 /// Unless you are in such a situation, higher-level and more foolproof APIs like
1073 /// `get` should be preferred.
1075 /// Immutable raw entries have very limited use; you might instead want `raw_entry_mut`.
1077 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1078 pub fn raw_entry(&self) -> RawEntryBuilder<'_, K, V, S> {
1079 RawEntryBuilder { map: self }
1083 #[stable(feature = "rust1", since = "1.0.0")]
1084 impl<K, V, S> Clone for HashMap<K, V, S>
1091 fn clone(&self) -> Self {
1092 Self { base: self.base.clone() }
1096 fn clone_from(&mut self, other: &Self) {
1097 self.base.clone_from(&other.base);
1101 #[stable(feature = "rust1", since = "1.0.0")]
1102 impl<K, V, S> PartialEq for HashMap<K, V, S>
1108 fn eq(&self, other: &HashMap<K, V, S>) -> bool {
1109 if self.len() != other.len() {
1113 self.iter().all(|(key, value)| other.get(key).map_or(false, |v| *value == *v))
1117 #[stable(feature = "rust1", since = "1.0.0")]
1118 impl<K, V, S> Eq for HashMap<K, V, S>
1126 #[stable(feature = "rust1", since = "1.0.0")]
1127 impl<K, V, S> Debug for HashMap<K, V, S>
1132 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1133 f.debug_map().entries(self.iter()).finish()
1137 #[stable(feature = "rust1", since = "1.0.0")]
1138 impl<K, V, S> Default for HashMap<K, V, S>
1142 /// Creates an empty `HashMap<K, V, S>`, with the `Default` value for the hasher.
1144 fn default() -> HashMap<K, V, S> {
1145 HashMap::with_hasher(Default::default())
1149 #[stable(feature = "rust1", since = "1.0.0")]
1150 impl<K, Q: ?Sized, V, S> Index<&Q> for HashMap<K, V, S>
1152 K: Eq + Hash + Borrow<Q>,
1158 /// Returns a reference to the value corresponding to the supplied key.
1162 /// Panics if the key is not present in the `HashMap`.
1164 fn index(&self, key: &Q) -> &V {
1165 self.get(key).expect("no entry found for key")
1169 #[stable(feature = "std_collections_from_array", since = "1.56.0")]
1170 // Note: as what is currently the most convenient built-in way to construct
1171 // a HashMap, a simple usage of this function must not *require* the user
1172 // to provide a type annotation in order to infer the third type parameter
1173 // (the hasher parameter, conventionally "S").
1174 // To that end, this impl is defined using RandomState as the concrete
1175 // type of S, rather than being generic over `S: BuildHasher + Default`.
1176 // It is expected that users who want to specify a hasher will manually use
1177 // `with_capacity_and_hasher`.
1178 // If type parameter defaults worked on impls, and if type parameter
1179 // defaults could be mixed with const generics, then perhaps
1180 // this could be generalized.
1181 // See also the equivalent impl on HashSet.
1182 impl<K, V, const N: usize> From<[(K, V); N]> for HashMap<K, V, RandomState>
1189 /// use std::collections::HashMap;
1191 /// let map1 = HashMap::from([(1, 2), (3, 4)]);
1192 /// let map2: HashMap<_, _> = [(1, 2), (3, 4)].into();
1193 /// assert_eq!(map1, map2);
1195 fn from(arr: [(K, V); N]) -> Self {
1196 crate::array::IntoIter::new(arr).collect()
1200 /// An iterator over the entries of a `HashMap`.
1202 /// This `struct` is created by the [`iter`] method on [`HashMap`]. See its
1203 /// documentation for more.
1205 /// [`iter`]: HashMap::iter
1210 /// use std::collections::HashMap;
1212 /// let mut map = HashMap::new();
1213 /// map.insert("a", 1);
1214 /// let iter = map.iter();
1216 #[stable(feature = "rust1", since = "1.0.0")]
1217 pub struct Iter<'a, K: 'a, V: 'a> {
1218 base: base::Iter<'a, K, V>,
1221 // FIXME(#26925) Remove in favor of `#[derive(Clone)]`
1222 #[stable(feature = "rust1", since = "1.0.0")]
1223 impl<K, V> Clone for Iter<'_, K, V> {
1225 fn clone(&self) -> Self {
1226 Iter { base: self.base.clone() }
1230 #[stable(feature = "std_debug", since = "1.16.0")]
1231 impl<K: Debug, V: Debug> fmt::Debug for Iter<'_, K, V> {
1232 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1233 f.debug_list().entries(self.clone()).finish()
1237 /// A mutable iterator over the entries of a `HashMap`.
1239 /// This `struct` is created by the [`iter_mut`] method on [`HashMap`]. See its
1240 /// documentation for more.
1242 /// [`iter_mut`]: HashMap::iter_mut
1247 /// use std::collections::HashMap;
1249 /// let mut map = HashMap::new();
1250 /// map.insert("a", 1);
1251 /// let iter = map.iter_mut();
1253 #[stable(feature = "rust1", since = "1.0.0")]
1254 pub struct IterMut<'a, K: 'a, V: 'a> {
1255 base: base::IterMut<'a, K, V>,
1258 impl<'a, K, V> IterMut<'a, K, V> {
1259 /// Returns an iterator of references over the remaining items.
1261 pub(super) fn iter(&self) -> Iter<'_, K, V> {
1262 Iter { base: self.base.rustc_iter() }
1266 /// An owning iterator over the entries of a `HashMap`.
1268 /// This `struct` is created by the [`into_iter`] method on [`HashMap`]
1269 /// (provided by the [`IntoIterator`] trait). See its documentation for more.
1271 /// [`into_iter`]: IntoIterator::into_iter
1272 /// [`IntoIterator`]: crate::iter::IntoIterator
1277 /// use std::collections::HashMap;
1279 /// let mut map = HashMap::new();
1280 /// map.insert("a", 1);
1281 /// let iter = map.into_iter();
1283 #[stable(feature = "rust1", since = "1.0.0")]
1284 pub struct IntoIter<K, V> {
1285 base: base::IntoIter<K, V>,
1288 impl<K, V> IntoIter<K, V> {
1289 /// Returns an iterator of references over the remaining items.
1291 pub(super) fn iter(&self) -> Iter<'_, K, V> {
1292 Iter { base: self.base.rustc_iter() }
1296 /// An iterator over the keys of a `HashMap`.
1298 /// This `struct` is created by the [`keys`] method on [`HashMap`]. See its
1299 /// documentation for more.
1301 /// [`keys`]: HashMap::keys
1306 /// use std::collections::HashMap;
1308 /// let mut map = HashMap::new();
1309 /// map.insert("a", 1);
1310 /// let iter_keys = map.keys();
1312 #[stable(feature = "rust1", since = "1.0.0")]
1313 pub struct Keys<'a, K: 'a, V: 'a> {
1314 inner: Iter<'a, K, V>,
1317 // FIXME(#26925) Remove in favor of `#[derive(Clone)]`
1318 #[stable(feature = "rust1", since = "1.0.0")]
1319 impl<K, V> Clone for Keys<'_, K, V> {
1321 fn clone(&self) -> Self {
1322 Keys { inner: self.inner.clone() }
1326 #[stable(feature = "std_debug", since = "1.16.0")]
1327 impl<K: Debug, V> fmt::Debug for Keys<'_, K, V> {
1328 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1329 f.debug_list().entries(self.clone()).finish()
1333 /// An iterator over the values of a `HashMap`.
1335 /// This `struct` is created by the [`values`] method on [`HashMap`]. See its
1336 /// documentation for more.
1338 /// [`values`]: HashMap::values
1343 /// use std::collections::HashMap;
1345 /// let mut map = HashMap::new();
1346 /// map.insert("a", 1);
1347 /// let iter_values = map.values();
1349 #[stable(feature = "rust1", since = "1.0.0")]
1350 pub struct Values<'a, K: 'a, V: 'a> {
1351 inner: Iter<'a, K, V>,
1354 // FIXME(#26925) Remove in favor of `#[derive(Clone)]`
1355 #[stable(feature = "rust1", since = "1.0.0")]
1356 impl<K, V> Clone for Values<'_, K, V> {
1358 fn clone(&self) -> Self {
1359 Values { inner: self.inner.clone() }
1363 #[stable(feature = "std_debug", since = "1.16.0")]
1364 impl<K, V: Debug> fmt::Debug for Values<'_, K, V> {
1365 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1366 f.debug_list().entries(self.clone()).finish()
1370 /// A draining iterator over the entries of a `HashMap`.
1372 /// This `struct` is created by the [`drain`] method on [`HashMap`]. See its
1373 /// documentation for more.
1375 /// [`drain`]: HashMap::drain
1380 /// use std::collections::HashMap;
1382 /// let mut map = HashMap::new();
1383 /// map.insert("a", 1);
1384 /// let iter = map.drain();
1386 #[stable(feature = "drain", since = "1.6.0")]
1387 pub struct Drain<'a, K: 'a, V: 'a> {
1388 base: base::Drain<'a, K, V>,
1391 impl<'a, K, V> Drain<'a, K, V> {
1392 /// Returns an iterator of references over the remaining items.
1394 pub(super) fn iter(&self) -> Iter<'_, K, V> {
1395 Iter { base: self.base.rustc_iter() }
1399 /// A draining, filtering iterator over the entries of a `HashMap`.
1401 /// This `struct` is created by the [`drain_filter`] method on [`HashMap`].
1403 /// [`drain_filter`]: HashMap::drain_filter
1408 /// #![feature(hash_drain_filter)]
1410 /// use std::collections::HashMap;
1412 /// let mut map = HashMap::new();
1413 /// map.insert("a", 1);
1414 /// let iter = map.drain_filter(|_k, v| *v % 2 == 0);
1416 #[unstable(feature = "hash_drain_filter", issue = "59618")]
1417 pub struct DrainFilter<'a, K, V, F>
1419 F: FnMut(&K, &mut V) -> bool,
1421 base: base::DrainFilter<'a, K, V, F>,
1424 /// A mutable iterator over the values of a `HashMap`.
1426 /// This `struct` is created by the [`values_mut`] method on [`HashMap`]. See its
1427 /// documentation for more.
1429 /// [`values_mut`]: HashMap::values_mut
1434 /// use std::collections::HashMap;
1436 /// let mut map = HashMap::new();
1437 /// map.insert("a", 1);
1438 /// let iter_values = map.values_mut();
1440 #[stable(feature = "map_values_mut", since = "1.10.0")]
1441 pub struct ValuesMut<'a, K: 'a, V: 'a> {
1442 inner: IterMut<'a, K, V>,
1445 /// An owning iterator over the keys of a `HashMap`.
1447 /// This `struct` is created by the [`into_keys`] method on [`HashMap`].
1448 /// See its documentation for more.
1450 /// [`into_keys`]: HashMap::into_keys
1455 /// use std::collections::HashMap;
1457 /// let mut map = HashMap::new();
1458 /// map.insert("a", 1);
1459 /// let iter_keys = map.into_keys();
1461 #[stable(feature = "map_into_keys_values", since = "1.54.0")]
1462 pub struct IntoKeys<K, V> {
1463 inner: IntoIter<K, V>,
1466 /// An owning iterator over the values of a `HashMap`.
1468 /// This `struct` is created by the [`into_values`] method on [`HashMap`].
1469 /// See its documentation for more.
1471 /// [`into_values`]: HashMap::into_values
1476 /// use std::collections::HashMap;
1478 /// let mut map = HashMap::new();
1479 /// map.insert("a", 1);
1480 /// let iter_keys = map.into_values();
1482 #[stable(feature = "map_into_keys_values", since = "1.54.0")]
1483 pub struct IntoValues<K, V> {
1484 inner: IntoIter<K, V>,
1487 /// A builder for computing where in a HashMap a key-value pair would be stored.
1489 /// See the [`HashMap::raw_entry_mut`] docs for usage examples.
1490 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1491 pub struct RawEntryBuilderMut<'a, K: 'a, V: 'a, S: 'a> {
1492 map: &'a mut HashMap<K, V, S>,
1495 /// A view into a single entry in a map, which may either be vacant or occupied.
1497 /// This is a lower-level version of [`Entry`].
1499 /// This `enum` is constructed through the [`raw_entry_mut`] method on [`HashMap`],
1500 /// then calling one of the methods of that [`RawEntryBuilderMut`].
1502 /// [`raw_entry_mut`]: HashMap::raw_entry_mut
1503 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1504 pub enum RawEntryMut<'a, K: 'a, V: 'a, S: 'a> {
1505 /// An occupied entry.
1506 Occupied(RawOccupiedEntryMut<'a, K, V, S>),
1508 Vacant(RawVacantEntryMut<'a, K, V, S>),
1511 /// A view into an occupied entry in a `HashMap`.
1512 /// It is part of the [`RawEntryMut`] enum.
1513 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1514 pub struct RawOccupiedEntryMut<'a, K: 'a, V: 'a, S: 'a> {
1515 base: base::RawOccupiedEntryMut<'a, K, V, S>,
1518 /// A view into a vacant entry in a `HashMap`.
1519 /// It is part of the [`RawEntryMut`] enum.
1520 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1521 pub struct RawVacantEntryMut<'a, K: 'a, V: 'a, S: 'a> {
1522 base: base::RawVacantEntryMut<'a, K, V, S>,
1525 /// A builder for computing where in a HashMap a key-value pair would be stored.
1527 /// See the [`HashMap::raw_entry`] docs for usage examples.
1528 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1529 pub struct RawEntryBuilder<'a, K: 'a, V: 'a, S: 'a> {
1530 map: &'a HashMap<K, V, S>,
1533 impl<'a, K, V, S> RawEntryBuilderMut<'a, K, V, S>
1537 /// Creates a `RawEntryMut` from the given key.
1539 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1540 pub fn from_key<Q: ?Sized>(self, k: &Q) -> RawEntryMut<'a, K, V, S>
1545 map_raw_entry(self.map.base.raw_entry_mut().from_key(k))
1548 /// Creates a `RawEntryMut` from the given key and its hash.
1550 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1551 pub fn from_key_hashed_nocheck<Q: ?Sized>(self, hash: u64, k: &Q) -> RawEntryMut<'a, K, V, S>
1556 map_raw_entry(self.map.base.raw_entry_mut().from_key_hashed_nocheck(hash, k))
1559 /// Creates a `RawEntryMut` from the given hash.
1561 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1562 pub fn from_hash<F>(self, hash: u64, is_match: F) -> RawEntryMut<'a, K, V, S>
1564 for<'b> F: FnMut(&'b K) -> bool,
1566 map_raw_entry(self.map.base.raw_entry_mut().from_hash(hash, is_match))
1570 impl<'a, K, V, S> RawEntryBuilder<'a, K, V, S>
1574 /// Access an entry by key.
1576 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1577 pub fn from_key<Q: ?Sized>(self, k: &Q) -> Option<(&'a K, &'a V)>
1582 self.map.base.raw_entry().from_key(k)
1585 /// Access an entry by a key and its hash.
1587 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1588 pub fn from_key_hashed_nocheck<Q: ?Sized>(self, hash: u64, k: &Q) -> Option<(&'a K, &'a V)>
1593 self.map.base.raw_entry().from_key_hashed_nocheck(hash, k)
1596 /// Access an entry by hash.
1598 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1599 pub fn from_hash<F>(self, hash: u64, is_match: F) -> Option<(&'a K, &'a V)>
1601 F: FnMut(&K) -> bool,
1603 self.map.base.raw_entry().from_hash(hash, is_match)
1607 impl<'a, K, V, S> RawEntryMut<'a, K, V, S> {
1608 /// Ensures a value is in the entry by inserting the default if empty, and returns
1609 /// mutable references to the key and value in the entry.
1614 /// #![feature(hash_raw_entry)]
1615 /// use std::collections::HashMap;
1617 /// let mut map: HashMap<&str, u32> = HashMap::new();
1619 /// map.raw_entry_mut().from_key("poneyland").or_insert("poneyland", 3);
1620 /// assert_eq!(map["poneyland"], 3);
1622 /// *map.raw_entry_mut().from_key("poneyland").or_insert("poneyland", 10).1 *= 2;
1623 /// assert_eq!(map["poneyland"], 6);
1626 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1627 pub fn or_insert(self, default_key: K, default_val: V) -> (&'a mut K, &'a mut V)
1633 RawEntryMut::Occupied(entry) => entry.into_key_value(),
1634 RawEntryMut::Vacant(entry) => entry.insert(default_key, default_val),
1638 /// Ensures a value is in the entry by inserting the result of the default function if empty,
1639 /// and returns mutable references to the key and value in the entry.
1644 /// #![feature(hash_raw_entry)]
1645 /// use std::collections::HashMap;
1647 /// let mut map: HashMap<&str, String> = HashMap::new();
1649 /// map.raw_entry_mut().from_key("poneyland").or_insert_with(|| {
1650 /// ("poneyland", "hoho".to_string())
1653 /// assert_eq!(map["poneyland"], "hoho".to_string());
1656 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1657 pub fn or_insert_with<F>(self, default: F) -> (&'a mut K, &'a mut V)
1659 F: FnOnce() -> (K, V),
1664 RawEntryMut::Occupied(entry) => entry.into_key_value(),
1665 RawEntryMut::Vacant(entry) => {
1666 let (k, v) = default();
1672 /// Provides in-place mutable access to an occupied entry before any
1673 /// potential inserts into the map.
1678 /// #![feature(hash_raw_entry)]
1679 /// use std::collections::HashMap;
1681 /// let mut map: HashMap<&str, u32> = HashMap::new();
1683 /// map.raw_entry_mut()
1684 /// .from_key("poneyland")
1685 /// .and_modify(|_k, v| { *v += 1 })
1686 /// .or_insert("poneyland", 42);
1687 /// assert_eq!(map["poneyland"], 42);
1689 /// map.raw_entry_mut()
1690 /// .from_key("poneyland")
1691 /// .and_modify(|_k, v| { *v += 1 })
1692 /// .or_insert("poneyland", 0);
1693 /// assert_eq!(map["poneyland"], 43);
1696 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1697 pub fn and_modify<F>(self, f: F) -> Self
1699 F: FnOnce(&mut K, &mut V),
1702 RawEntryMut::Occupied(mut entry) => {
1704 let (k, v) = entry.get_key_value_mut();
1707 RawEntryMut::Occupied(entry)
1709 RawEntryMut::Vacant(entry) => RawEntryMut::Vacant(entry),
1714 impl<'a, K, V, S> RawOccupiedEntryMut<'a, K, V, S> {
1715 /// Gets a reference to the key in the entry.
1717 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1718 pub fn key(&self) -> &K {
1722 /// Gets a mutable reference to the key in the entry.
1724 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1725 pub fn key_mut(&mut self) -> &mut K {
1729 /// Converts the entry into a mutable reference to the key in the entry
1730 /// with a lifetime bound to the map itself.
1732 #[must_use = "`self` will be dropped if the result is not used"]
1733 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1734 pub fn into_key(self) -> &'a mut K {
1735 self.base.into_key()
1738 /// Gets a reference to the value in the entry.
1740 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1741 pub fn get(&self) -> &V {
1745 /// Converts the `OccupiedEntry` into a mutable reference to the value in the entry
1746 /// with a lifetime bound to the map itself.
1748 #[must_use = "`self` will be dropped if the result is not used"]
1749 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1750 pub fn into_mut(self) -> &'a mut V {
1751 self.base.into_mut()
1754 /// Gets a mutable reference to the value in the entry.
1756 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1757 pub fn get_mut(&mut self) -> &mut V {
1761 /// Gets a reference to the key and value in the entry.
1763 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1764 pub fn get_key_value(&mut self) -> (&K, &V) {
1765 self.base.get_key_value()
1768 /// Gets a mutable reference to the key and value in the entry.
1770 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1771 pub fn get_key_value_mut(&mut self) -> (&mut K, &mut V) {
1772 self.base.get_key_value_mut()
1775 /// Converts the `OccupiedEntry` into a mutable reference to the key and value in the entry
1776 /// with a lifetime bound to the map itself.
1778 #[must_use = "`self` will be dropped if the result is not used"]
1779 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1780 pub fn into_key_value(self) -> (&'a mut K, &'a mut V) {
1781 self.base.into_key_value()
1784 /// Sets the value of the entry, and returns the entry's old value.
1786 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1787 pub fn insert(&mut self, value: V) -> V {
1788 self.base.insert(value)
1791 /// Sets the value of the entry, and returns the entry's old value.
1793 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1794 pub fn insert_key(&mut self, key: K) -> K {
1795 self.base.insert_key(key)
1798 /// Takes the value out of the entry, and returns it.
1800 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1801 pub fn remove(self) -> V {
1805 /// Take the ownership of the key and value from the map.
1807 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1808 pub fn remove_entry(self) -> (K, V) {
1809 self.base.remove_entry()
1813 impl<'a, K, V, S> RawVacantEntryMut<'a, K, V, S> {
1814 /// Sets the value of the entry with the `VacantEntry`'s key,
1815 /// and returns a mutable reference to it.
1817 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1818 pub fn insert(self, key: K, value: V) -> (&'a mut K, &'a mut V)
1823 self.base.insert(key, value)
1826 /// Sets the value of the entry with the VacantEntry's key,
1827 /// and returns a mutable reference to it.
1829 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1830 pub fn insert_hashed_nocheck(self, hash: u64, key: K, value: V) -> (&'a mut K, &'a mut V)
1835 self.base.insert_hashed_nocheck(hash, key, value)
1839 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1840 impl<K, V, S> Debug for RawEntryBuilderMut<'_, K, V, S> {
1841 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1842 f.debug_struct("RawEntryBuilder").finish_non_exhaustive()
1846 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1847 impl<K: Debug, V: Debug, S> Debug for RawEntryMut<'_, K, V, S> {
1848 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1850 RawEntryMut::Vacant(ref v) => f.debug_tuple("RawEntry").field(v).finish(),
1851 RawEntryMut::Occupied(ref o) => f.debug_tuple("RawEntry").field(o).finish(),
1856 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1857 impl<K: Debug, V: Debug, S> Debug for RawOccupiedEntryMut<'_, K, V, S> {
1858 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1859 f.debug_struct("RawOccupiedEntryMut")
1860 .field("key", self.key())
1861 .field("value", self.get())
1862 .finish_non_exhaustive()
1866 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1867 impl<K, V, S> Debug for RawVacantEntryMut<'_, K, V, S> {
1868 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1869 f.debug_struct("RawVacantEntryMut").finish_non_exhaustive()
1873 #[unstable(feature = "hash_raw_entry", issue = "56167")]
1874 impl<K, V, S> Debug for RawEntryBuilder<'_, K, V, S> {
1875 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1876 f.debug_struct("RawEntryBuilder").finish_non_exhaustive()
1880 /// A view into a single entry in a map, which may either be vacant or occupied.
1882 /// This `enum` is constructed from the [`entry`] method on [`HashMap`].
1884 /// [`entry`]: HashMap::entry
1885 #[stable(feature = "rust1", since = "1.0.0")]
1886 #[cfg_attr(not(test), rustc_diagnostic_item = "HashMapEntry")]
1887 pub enum Entry<'a, K: 'a, V: 'a> {
1888 /// An occupied entry.
1889 #[stable(feature = "rust1", since = "1.0.0")]
1890 Occupied(#[stable(feature = "rust1", since = "1.0.0")] OccupiedEntry<'a, K, V>),
1893 #[stable(feature = "rust1", since = "1.0.0")]
1894 Vacant(#[stable(feature = "rust1", since = "1.0.0")] VacantEntry<'a, K, V>),
1897 #[stable(feature = "debug_hash_map", since = "1.12.0")]
1898 impl<K: Debug, V: Debug> Debug for Entry<'_, K, V> {
1899 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1901 Vacant(ref v) => f.debug_tuple("Entry").field(v).finish(),
1902 Occupied(ref o) => f.debug_tuple("Entry").field(o).finish(),
1907 /// A view into an occupied entry in a `HashMap`.
1908 /// It is part of the [`Entry`] enum.
1909 #[stable(feature = "rust1", since = "1.0.0")]
1910 pub struct OccupiedEntry<'a, K: 'a, V: 'a> {
1911 base: base::RustcOccupiedEntry<'a, K, V>,
1914 #[stable(feature = "debug_hash_map", since = "1.12.0")]
1915 impl<K: Debug, V: Debug> Debug for OccupiedEntry<'_, K, V> {
1916 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1917 f.debug_struct("OccupiedEntry")
1918 .field("key", self.key())
1919 .field("value", self.get())
1920 .finish_non_exhaustive()
1924 /// A view into a vacant entry in a `HashMap`.
1925 /// It is part of the [`Entry`] enum.
1926 #[stable(feature = "rust1", since = "1.0.0")]
1927 pub struct VacantEntry<'a, K: 'a, V: 'a> {
1928 base: base::RustcVacantEntry<'a, K, V>,
1931 #[stable(feature = "debug_hash_map", since = "1.12.0")]
1932 impl<K: Debug, V> Debug for VacantEntry<'_, K, V> {
1933 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1934 f.debug_tuple("VacantEntry").field(self.key()).finish()
1938 /// The error returned by [`try_insert`](HashMap::try_insert) when the key already exists.
1940 /// Contains the occupied entry, and the value that was not inserted.
1941 #[unstable(feature = "map_try_insert", issue = "82766")]
1942 pub struct OccupiedError<'a, K: 'a, V: 'a> {
1943 /// The entry in the map that was already occupied.
1944 pub entry: OccupiedEntry<'a, K, V>,
1945 /// The value which was not inserted, because the entry was already occupied.
1949 #[unstable(feature = "map_try_insert", issue = "82766")]
1950 impl<K: Debug, V: Debug> Debug for OccupiedError<'_, K, V> {
1951 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1952 f.debug_struct("OccupiedError")
1953 .field("key", self.entry.key())
1954 .field("old_value", self.entry.get())
1955 .field("new_value", &self.value)
1956 .finish_non_exhaustive()
1960 #[unstable(feature = "map_try_insert", issue = "82766")]
1961 impl<'a, K: Debug, V: Debug> fmt::Display for OccupiedError<'a, K, V> {
1962 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1965 "failed to insert {:?}, key {:?} already exists with value {:?}",
1973 #[stable(feature = "rust1", since = "1.0.0")]
1974 impl<'a, K, V, S> IntoIterator for &'a HashMap<K, V, S> {
1975 type Item = (&'a K, &'a V);
1976 type IntoIter = Iter<'a, K, V>;
1979 #[cfg_attr(not(bootstrap), rustc_lint_query_instability)]
1980 fn into_iter(self) -> Iter<'a, K, V> {
1985 #[stable(feature = "rust1", since = "1.0.0")]
1986 impl<'a, K, V, S> IntoIterator for &'a mut HashMap<K, V, S> {
1987 type Item = (&'a K, &'a mut V);
1988 type IntoIter = IterMut<'a, K, V>;
1991 #[cfg_attr(not(bootstrap), rustc_lint_query_instability)]
1992 fn into_iter(self) -> IterMut<'a, K, V> {
1997 #[stable(feature = "rust1", since = "1.0.0")]
1998 impl<K, V, S> IntoIterator for HashMap<K, V, S> {
2000 type IntoIter = IntoIter<K, V>;
2002 /// Creates a consuming iterator, that is, one that moves each key-value
2003 /// pair out of the map in arbitrary order. The map cannot be used after
2009 /// use std::collections::HashMap;
2011 /// let mut map = HashMap::new();
2012 /// map.insert("a", 1);
2013 /// map.insert("b", 2);
2014 /// map.insert("c", 3);
2016 /// // Not possible with .iter()
2017 /// let vec: Vec<(&str, i32)> = map.into_iter().collect();
2020 #[cfg_attr(not(bootstrap), rustc_lint_query_instability)]
2021 fn into_iter(self) -> IntoIter<K, V> {
2022 IntoIter { base: self.base.into_iter() }
2026 #[stable(feature = "rust1", since = "1.0.0")]
2027 impl<'a, K, V> Iterator for Iter<'a, K, V> {
2028 type Item = (&'a K, &'a V);
2031 fn next(&mut self) -> Option<(&'a K, &'a V)> {
2035 fn size_hint(&self) -> (usize, Option<usize>) {
2036 self.base.size_hint()
2039 #[stable(feature = "rust1", since = "1.0.0")]
2040 impl<K, V> ExactSizeIterator for Iter<'_, K, V> {
2042 fn len(&self) -> usize {
2047 #[stable(feature = "fused", since = "1.26.0")]
2048 impl<K, V> FusedIterator for Iter<'_, K, V> {}
2050 #[stable(feature = "rust1", since = "1.0.0")]
2051 impl<'a, K, V> Iterator for IterMut<'a, K, V> {
2052 type Item = (&'a K, &'a mut V);
2055 fn next(&mut self) -> Option<(&'a K, &'a mut V)> {
2059 fn size_hint(&self) -> (usize, Option<usize>) {
2060 self.base.size_hint()
2063 #[stable(feature = "rust1", since = "1.0.0")]
2064 impl<K, V> ExactSizeIterator for IterMut<'_, K, V> {
2066 fn len(&self) -> usize {
2070 #[stable(feature = "fused", since = "1.26.0")]
2071 impl<K, V> FusedIterator for IterMut<'_, K, V> {}
2073 #[stable(feature = "std_debug", since = "1.16.0")]
2074 impl<K, V> fmt::Debug for IterMut<'_, K, V>
2079 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2080 f.debug_list().entries(self.iter()).finish()
2084 #[stable(feature = "rust1", since = "1.0.0")]
2085 impl<K, V> Iterator for IntoIter<K, V> {
2089 fn next(&mut self) -> Option<(K, V)> {
2093 fn size_hint(&self) -> (usize, Option<usize>) {
2094 self.base.size_hint()
2097 #[stable(feature = "rust1", since = "1.0.0")]
2098 impl<K, V> ExactSizeIterator for IntoIter<K, V> {
2100 fn len(&self) -> usize {
2104 #[stable(feature = "fused", since = "1.26.0")]
2105 impl<K, V> FusedIterator for IntoIter<K, V> {}
2107 #[stable(feature = "std_debug", since = "1.16.0")]
2108 impl<K: Debug, V: Debug> fmt::Debug for IntoIter<K, V> {
2109 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2110 f.debug_list().entries(self.iter()).finish()
2114 #[stable(feature = "rust1", since = "1.0.0")]
2115 impl<'a, K, V> Iterator for Keys<'a, K, V> {
2119 fn next(&mut self) -> Option<&'a K> {
2120 self.inner.next().map(|(k, _)| k)
2123 fn size_hint(&self) -> (usize, Option<usize>) {
2124 self.inner.size_hint()
2127 #[stable(feature = "rust1", since = "1.0.0")]
2128 impl<K, V> ExactSizeIterator for Keys<'_, K, V> {
2130 fn len(&self) -> usize {
2134 #[stable(feature = "fused", since = "1.26.0")]
2135 impl<K, V> FusedIterator for Keys<'_, K, V> {}
2137 #[stable(feature = "rust1", since = "1.0.0")]
2138 impl<'a, K, V> Iterator for Values<'a, K, V> {
2142 fn next(&mut self) -> Option<&'a V> {
2143 self.inner.next().map(|(_, v)| v)
2146 fn size_hint(&self) -> (usize, Option<usize>) {
2147 self.inner.size_hint()
2150 #[stable(feature = "rust1", since = "1.0.0")]
2151 impl<K, V> ExactSizeIterator for Values<'_, K, V> {
2153 fn len(&self) -> usize {
2157 #[stable(feature = "fused", since = "1.26.0")]
2158 impl<K, V> FusedIterator for Values<'_, K, V> {}
2160 #[stable(feature = "map_values_mut", since = "1.10.0")]
2161 impl<'a, K, V> Iterator for ValuesMut<'a, K, V> {
2162 type Item = &'a mut V;
2165 fn next(&mut self) -> Option<&'a mut V> {
2166 self.inner.next().map(|(_, v)| v)
2169 fn size_hint(&self) -> (usize, Option<usize>) {
2170 self.inner.size_hint()
2173 #[stable(feature = "map_values_mut", since = "1.10.0")]
2174 impl<K, V> ExactSizeIterator for ValuesMut<'_, K, V> {
2176 fn len(&self) -> usize {
2180 #[stable(feature = "fused", since = "1.26.0")]
2181 impl<K, V> FusedIterator for ValuesMut<'_, K, V> {}
2183 #[stable(feature = "std_debug", since = "1.16.0")]
2184 impl<K, V: fmt::Debug> fmt::Debug for ValuesMut<'_, K, V> {
2185 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2186 f.debug_list().entries(self.inner.iter().map(|(_, val)| val)).finish()
2190 #[stable(feature = "map_into_keys_values", since = "1.54.0")]
2191 impl<K, V> Iterator for IntoKeys<K, V> {
2195 fn next(&mut self) -> Option<K> {
2196 self.inner.next().map(|(k, _)| k)
2199 fn size_hint(&self) -> (usize, Option<usize>) {
2200 self.inner.size_hint()
2203 #[stable(feature = "map_into_keys_values", since = "1.54.0")]
2204 impl<K, V> ExactSizeIterator for IntoKeys<K, V> {
2206 fn len(&self) -> usize {
2210 #[stable(feature = "map_into_keys_values", since = "1.54.0")]
2211 impl<K, V> FusedIterator for IntoKeys<K, V> {}
2213 #[stable(feature = "map_into_keys_values", since = "1.54.0")]
2214 impl<K: Debug, V> fmt::Debug for IntoKeys<K, V> {
2215 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2216 f.debug_list().entries(self.inner.iter().map(|(k, _)| k)).finish()
2220 #[stable(feature = "map_into_keys_values", since = "1.54.0")]
2221 impl<K, V> Iterator for IntoValues<K, V> {
2225 fn next(&mut self) -> Option<V> {
2226 self.inner.next().map(|(_, v)| v)
2229 fn size_hint(&self) -> (usize, Option<usize>) {
2230 self.inner.size_hint()
2233 #[stable(feature = "map_into_keys_values", since = "1.54.0")]
2234 impl<K, V> ExactSizeIterator for IntoValues<K, V> {
2236 fn len(&self) -> usize {
2240 #[stable(feature = "map_into_keys_values", since = "1.54.0")]
2241 impl<K, V> FusedIterator for IntoValues<K, V> {}
2243 #[stable(feature = "map_into_keys_values", since = "1.54.0")]
2244 impl<K, V: Debug> fmt::Debug for IntoValues<K, V> {
2245 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2246 f.debug_list().entries(self.inner.iter().map(|(_, v)| v)).finish()
2250 #[stable(feature = "drain", since = "1.6.0")]
2251 impl<'a, K, V> Iterator for Drain<'a, K, V> {
2255 fn next(&mut self) -> Option<(K, V)> {
2259 fn size_hint(&self) -> (usize, Option<usize>) {
2260 self.base.size_hint()
2263 #[stable(feature = "drain", since = "1.6.0")]
2264 impl<K, V> ExactSizeIterator for Drain<'_, K, V> {
2266 fn len(&self) -> usize {
2270 #[stable(feature = "fused", since = "1.26.0")]
2271 impl<K, V> FusedIterator for Drain<'_, K, V> {}
2273 #[stable(feature = "std_debug", since = "1.16.0")]
2274 impl<K, V> fmt::Debug for Drain<'_, K, V>
2279 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2280 f.debug_list().entries(self.iter()).finish()
2284 #[unstable(feature = "hash_drain_filter", issue = "59618")]
2285 impl<K, V, F> Iterator for DrainFilter<'_, K, V, F>
2287 F: FnMut(&K, &mut V) -> bool,
2292 fn next(&mut self) -> Option<(K, V)> {
2296 fn size_hint(&self) -> (usize, Option<usize>) {
2297 self.base.size_hint()
2301 #[unstable(feature = "hash_drain_filter", issue = "59618")]
2302 impl<K, V, F> FusedIterator for DrainFilter<'_, K, V, F> where F: FnMut(&K, &mut V) -> bool {}
2304 #[unstable(feature = "hash_drain_filter", issue = "59618")]
2305 impl<'a, K, V, F> fmt::Debug for DrainFilter<'a, K, V, F>
2307 F: FnMut(&K, &mut V) -> bool,
2309 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2310 f.debug_struct("DrainFilter").finish_non_exhaustive()
2314 impl<'a, K, V> Entry<'a, K, V> {
2315 /// Ensures a value is in the entry by inserting the default if empty, and returns
2316 /// a mutable reference to the value in the entry.
2321 /// use std::collections::HashMap;
2323 /// let mut map: HashMap<&str, u32> = HashMap::new();
2325 /// map.entry("poneyland").or_insert(3);
2326 /// assert_eq!(map["poneyland"], 3);
2328 /// *map.entry("poneyland").or_insert(10) *= 2;
2329 /// assert_eq!(map["poneyland"], 6);
2332 #[stable(feature = "rust1", since = "1.0.0")]
2333 pub fn or_insert(self, default: V) -> &'a mut V {
2335 Occupied(entry) => entry.into_mut(),
2336 Vacant(entry) => entry.insert(default),
2340 /// Ensures a value is in the entry by inserting the result of the default function if empty,
2341 /// and returns a mutable reference to the value in the entry.
2346 /// use std::collections::HashMap;
2348 /// let mut map: HashMap<&str, String> = HashMap::new();
2349 /// let s = "hoho".to_string();
2351 /// map.entry("poneyland").or_insert_with(|| s);
2353 /// assert_eq!(map["poneyland"], "hoho".to_string());
2356 #[stable(feature = "rust1", since = "1.0.0")]
2357 pub fn or_insert_with<F: FnOnce() -> V>(self, default: F) -> &'a mut V {
2359 Occupied(entry) => entry.into_mut(),
2360 Vacant(entry) => entry.insert(default()),
2364 /// Ensures a value is in the entry by inserting, if empty, the result of the default function.
2365 /// This method allows for generating key-derived values for insertion by providing the default
2366 /// function a reference to the key that was moved during the `.entry(key)` method call.
2368 /// The reference to the moved key is provided so that cloning or copying the key is
2369 /// unnecessary, unlike with `.or_insert_with(|| ... )`.
2374 /// use std::collections::HashMap;
2376 /// let mut map: HashMap<&str, usize> = HashMap::new();
2378 /// map.entry("poneyland").or_insert_with_key(|key| key.chars().count());
2380 /// assert_eq!(map["poneyland"], 9);
2383 #[stable(feature = "or_insert_with_key", since = "1.50.0")]
2384 pub fn or_insert_with_key<F: FnOnce(&K) -> V>(self, default: F) -> &'a mut V {
2386 Occupied(entry) => entry.into_mut(),
2388 let value = default(entry.key());
2394 /// Returns a reference to this entry's key.
2399 /// use std::collections::HashMap;
2401 /// let mut map: HashMap<&str, u32> = HashMap::new();
2402 /// assert_eq!(map.entry("poneyland").key(), &"poneyland");
2405 #[stable(feature = "map_entry_keys", since = "1.10.0")]
2406 pub fn key(&self) -> &K {
2408 Occupied(ref entry) => entry.key(),
2409 Vacant(ref entry) => entry.key(),
2413 /// Provides in-place mutable access to an occupied entry before any
2414 /// potential inserts into the map.
2419 /// use std::collections::HashMap;
2421 /// let mut map: HashMap<&str, u32> = HashMap::new();
2423 /// map.entry("poneyland")
2424 /// .and_modify(|e| { *e += 1 })
2426 /// assert_eq!(map["poneyland"], 42);
2428 /// map.entry("poneyland")
2429 /// .and_modify(|e| { *e += 1 })
2431 /// assert_eq!(map["poneyland"], 43);
2434 #[stable(feature = "entry_and_modify", since = "1.26.0")]
2435 pub fn and_modify<F>(self, f: F) -> Self
2440 Occupied(mut entry) => {
2444 Vacant(entry) => Vacant(entry),
2448 /// Sets the value of the entry, and returns an `OccupiedEntry`.
2453 /// #![feature(entry_insert)]
2454 /// use std::collections::HashMap;
2456 /// let mut map: HashMap<&str, String> = HashMap::new();
2457 /// let entry = map.entry("poneyland").insert("hoho".to_string());
2459 /// assert_eq!(entry.key(), &"poneyland");
2462 #[unstable(feature = "entry_insert", issue = "65225")]
2463 pub fn insert(self, value: V) -> OccupiedEntry<'a, K, V> {
2465 Occupied(mut entry) => {
2466 entry.insert(value);
2469 Vacant(entry) => entry.insert_entry(value),
2474 impl<'a, K, V: Default> Entry<'a, K, V> {
2475 /// Ensures a value is in the entry by inserting the default value if empty,
2476 /// and returns a mutable reference to the value in the entry.
2482 /// use std::collections::HashMap;
2484 /// let mut map: HashMap<&str, Option<u32>> = HashMap::new();
2485 /// map.entry("poneyland").or_default();
2487 /// assert_eq!(map["poneyland"], None);
2491 #[stable(feature = "entry_or_default", since = "1.28.0")]
2492 pub fn or_default(self) -> &'a mut V {
2494 Occupied(entry) => entry.into_mut(),
2495 Vacant(entry) => entry.insert(Default::default()),
2500 impl<'a, K, V> OccupiedEntry<'a, K, V> {
2501 /// Gets a reference to the key in the entry.
2506 /// use std::collections::HashMap;
2508 /// let mut map: HashMap<&str, u32> = HashMap::new();
2509 /// map.entry("poneyland").or_insert(12);
2510 /// assert_eq!(map.entry("poneyland").key(), &"poneyland");
2513 #[stable(feature = "map_entry_keys", since = "1.10.0")]
2514 pub fn key(&self) -> &K {
2518 /// Take the ownership of the key and value from the map.
2523 /// use std::collections::HashMap;
2524 /// use std::collections::hash_map::Entry;
2526 /// let mut map: HashMap<&str, u32> = HashMap::new();
2527 /// map.entry("poneyland").or_insert(12);
2529 /// if let Entry::Occupied(o) = map.entry("poneyland") {
2530 /// // We delete the entry from the map.
2531 /// o.remove_entry();
2534 /// assert_eq!(map.contains_key("poneyland"), false);
2537 #[stable(feature = "map_entry_recover_keys2", since = "1.12.0")]
2538 pub fn remove_entry(self) -> (K, V) {
2539 self.base.remove_entry()
2542 /// Gets a reference to the value in the entry.
2547 /// use std::collections::HashMap;
2548 /// use std::collections::hash_map::Entry;
2550 /// let mut map: HashMap<&str, u32> = HashMap::new();
2551 /// map.entry("poneyland").or_insert(12);
2553 /// if let Entry::Occupied(o) = map.entry("poneyland") {
2554 /// assert_eq!(o.get(), &12);
2558 #[stable(feature = "rust1", since = "1.0.0")]
2559 pub fn get(&self) -> &V {
2563 /// Gets a mutable reference to the value in the entry.
2565 /// If you need a reference to the `OccupiedEntry` which may outlive the
2566 /// destruction of the `Entry` value, see [`into_mut`].
2568 /// [`into_mut`]: Self::into_mut
2573 /// use std::collections::HashMap;
2574 /// use std::collections::hash_map::Entry;
2576 /// let mut map: HashMap<&str, u32> = HashMap::new();
2577 /// map.entry("poneyland").or_insert(12);
2579 /// assert_eq!(map["poneyland"], 12);
2580 /// if let Entry::Occupied(mut o) = map.entry("poneyland") {
2581 /// *o.get_mut() += 10;
2582 /// assert_eq!(*o.get(), 22);
2584 /// // We can use the same Entry multiple times.
2585 /// *o.get_mut() += 2;
2588 /// assert_eq!(map["poneyland"], 24);
2591 #[stable(feature = "rust1", since = "1.0.0")]
2592 pub fn get_mut(&mut self) -> &mut V {
2596 /// Converts the `OccupiedEntry` into a mutable reference to the value in the entry
2597 /// with a lifetime bound to the map itself.
2599 /// If you need multiple references to the `OccupiedEntry`, see [`get_mut`].
2601 /// [`get_mut`]: Self::get_mut
2606 /// use std::collections::HashMap;
2607 /// use std::collections::hash_map::Entry;
2609 /// let mut map: HashMap<&str, u32> = HashMap::new();
2610 /// map.entry("poneyland").or_insert(12);
2612 /// assert_eq!(map["poneyland"], 12);
2613 /// if let Entry::Occupied(o) = map.entry("poneyland") {
2614 /// *o.into_mut() += 10;
2617 /// assert_eq!(map["poneyland"], 22);
2620 #[stable(feature = "rust1", since = "1.0.0")]
2621 pub fn into_mut(self) -> &'a mut V {
2622 self.base.into_mut()
2625 /// Sets the value of the entry, and returns the entry's old value.
2630 /// use std::collections::HashMap;
2631 /// use std::collections::hash_map::Entry;
2633 /// let mut map: HashMap<&str, u32> = HashMap::new();
2634 /// map.entry("poneyland").or_insert(12);
2636 /// if let Entry::Occupied(mut o) = map.entry("poneyland") {
2637 /// assert_eq!(o.insert(15), 12);
2640 /// assert_eq!(map["poneyland"], 15);
2643 #[stable(feature = "rust1", since = "1.0.0")]
2644 pub fn insert(&mut self, value: V) -> V {
2645 self.base.insert(value)
2648 /// Takes the value out of the entry, and returns it.
2653 /// use std::collections::HashMap;
2654 /// use std::collections::hash_map::Entry;
2656 /// let mut map: HashMap<&str, u32> = HashMap::new();
2657 /// map.entry("poneyland").or_insert(12);
2659 /// if let Entry::Occupied(o) = map.entry("poneyland") {
2660 /// assert_eq!(o.remove(), 12);
2663 /// assert_eq!(map.contains_key("poneyland"), false);
2666 #[stable(feature = "rust1", since = "1.0.0")]
2667 pub fn remove(self) -> V {
2671 /// Replaces the entry, returning the old key and value. The new key in the hash map will be
2672 /// the key used to create this entry.
2677 /// #![feature(map_entry_replace)]
2678 /// use std::collections::hash_map::{Entry, HashMap};
2679 /// use std::rc::Rc;
2681 /// let mut map: HashMap<Rc<String>, u32> = HashMap::new();
2682 /// map.insert(Rc::new("Stringthing".to_string()), 15);
2684 /// let my_key = Rc::new("Stringthing".to_string());
2686 /// if let Entry::Occupied(entry) = map.entry(my_key) {
2687 /// // Also replace the key with a handle to our other key.
2688 /// let (old_key, old_value): (Rc<String>, u32) = entry.replace_entry(16);
2693 #[unstable(feature = "map_entry_replace", issue = "44286")]
2694 pub fn replace_entry(self, value: V) -> (K, V) {
2695 self.base.replace_entry(value)
2698 /// Replaces the key in the hash map with the key used to create this entry.
2703 /// #![feature(map_entry_replace)]
2704 /// use std::collections::hash_map::{Entry, HashMap};
2705 /// use std::rc::Rc;
2707 /// let mut map: HashMap<Rc<String>, u32> = HashMap::new();
2708 /// let known_strings: Vec<Rc<String>> = Vec::new();
2710 /// // Initialise known strings, run program, etc.
2712 /// reclaim_memory(&mut map, &known_strings);
2714 /// fn reclaim_memory(map: &mut HashMap<Rc<String>, u32>, known_strings: &[Rc<String>] ) {
2715 /// for s in known_strings {
2716 /// if let Entry::Occupied(entry) = map.entry(Rc::clone(s)) {
2717 /// // Replaces the entry's key with our version of it in `known_strings`.
2718 /// entry.replace_key();
2724 #[unstable(feature = "map_entry_replace", issue = "44286")]
2725 pub fn replace_key(self) -> K {
2726 self.base.replace_key()
2730 impl<'a, K: 'a, V: 'a> VacantEntry<'a, K, V> {
2731 /// Gets a reference to the key that would be used when inserting a value
2732 /// through the `VacantEntry`.
2737 /// use std::collections::HashMap;
2739 /// let mut map: HashMap<&str, u32> = HashMap::new();
2740 /// assert_eq!(map.entry("poneyland").key(), &"poneyland");
2743 #[stable(feature = "map_entry_keys", since = "1.10.0")]
2744 pub fn key(&self) -> &K {
2748 /// Take ownership of the key.
2753 /// use std::collections::HashMap;
2754 /// use std::collections::hash_map::Entry;
2756 /// let mut map: HashMap<&str, u32> = HashMap::new();
2758 /// if let Entry::Vacant(v) = map.entry("poneyland") {
2763 #[stable(feature = "map_entry_recover_keys2", since = "1.12.0")]
2764 pub fn into_key(self) -> K {
2765 self.base.into_key()
2768 /// Sets the value of the entry with the `VacantEntry`'s key,
2769 /// and returns a mutable reference to it.
2774 /// use std::collections::HashMap;
2775 /// use std::collections::hash_map::Entry;
2777 /// let mut map: HashMap<&str, u32> = HashMap::new();
2779 /// if let Entry::Vacant(o) = map.entry("poneyland") {
2782 /// assert_eq!(map["poneyland"], 37);
2785 #[stable(feature = "rust1", since = "1.0.0")]
2786 pub fn insert(self, value: V) -> &'a mut V {
2787 self.base.insert(value)
2790 /// Sets the value of the entry with the `VacantEntry`'s key,
2791 /// and returns an `OccupiedEntry`.
2796 /// use std::collections::HashMap;
2797 /// use std::collections::hash_map::Entry;
2799 /// let mut map: HashMap<&str, u32> = HashMap::new();
2801 /// if let Entry::Vacant(o) = map.entry("poneyland") {
2804 /// assert_eq!(map["poneyland"], 37);
2807 fn insert_entry(self, value: V) -> OccupiedEntry<'a, K, V> {
2808 let base = self.base.insert_entry(value);
2809 OccupiedEntry { base }
2813 #[stable(feature = "rust1", since = "1.0.0")]
2814 impl<K, V, S> FromIterator<(K, V)> for HashMap<K, V, S>
2817 S: BuildHasher + Default,
2819 fn from_iter<T: IntoIterator<Item = (K, V)>>(iter: T) -> HashMap<K, V, S> {
2820 let mut map = HashMap::with_hasher(Default::default());
2826 /// Inserts all new key-values from the iterator and replaces values with existing
2827 /// keys with new values returned from the iterator.
2828 #[stable(feature = "rust1", since = "1.0.0")]
2829 impl<K, V, S> Extend<(K, V)> for HashMap<K, V, S>
2835 fn extend<T: IntoIterator<Item = (K, V)>>(&mut self, iter: T) {
2836 self.base.extend(iter)
2840 fn extend_one(&mut self, (k, v): (K, V)) {
2841 self.base.insert(k, v);
2845 fn extend_reserve(&mut self, additional: usize) {
2846 self.base.extend_reserve(additional);
2850 #[stable(feature = "hash_extend_copy", since = "1.4.0")]
2851 impl<'a, K, V, S> Extend<(&'a K, &'a V)> for HashMap<K, V, S>
2853 K: Eq + Hash + Copy,
2858 fn extend<T: IntoIterator<Item = (&'a K, &'a V)>>(&mut self, iter: T) {
2859 self.base.extend(iter)
2863 fn extend_one(&mut self, (&k, &v): (&'a K, &'a V)) {
2864 self.base.insert(k, v);
2868 fn extend_reserve(&mut self, additional: usize) {
2869 Extend::<(K, V)>::extend_reserve(self, additional)
2873 /// `RandomState` is the default state for [`HashMap`] types.
2875 /// A particular instance `RandomState` will create the same instances of
2876 /// [`Hasher`], but the hashers created by two different `RandomState`
2877 /// instances are unlikely to produce the same result for the same values.
2882 /// use std::collections::HashMap;
2883 /// use std::collections::hash_map::RandomState;
2885 /// let s = RandomState::new();
2886 /// let mut map = HashMap::with_hasher(s);
2887 /// map.insert(1, 2);
2890 #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
2891 pub struct RandomState {
2897 /// Constructs a new `RandomState` that is initialized with random keys.
2902 /// use std::collections::hash_map::RandomState;
2904 /// let s = RandomState::new();
2907 #[allow(deprecated)]
2910 #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
2911 pub fn new() -> RandomState {
2912 // Historically this function did not cache keys from the OS and instead
2913 // simply always called `rand::thread_rng().gen()` twice. In #31356 it
2914 // was discovered, however, that because we re-seed the thread-local RNG
2915 // from the OS periodically that this can cause excessive slowdown when
2916 // many hash maps are created on a thread. To solve this performance
2917 // trap we cache the first set of randomly generated keys per-thread.
2919 // Later in #36481 it was discovered that exposing a deterministic
2920 // iteration order allows a form of DOS attack. To counter that we
2921 // increment one of the seeds on every RandomState creation, giving
2922 // every corresponding HashMap a different iteration order.
2923 thread_local!(static KEYS: Cell<(u64, u64)> = {
2924 Cell::new(sys::hashmap_random_keys())
2928 let (k0, k1) = keys.get();
2929 keys.set((k0.wrapping_add(1), k1));
2930 RandomState { k0, k1 }
2935 #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
2936 impl BuildHasher for RandomState {
2937 type Hasher = DefaultHasher;
2939 #[allow(deprecated)]
2940 fn build_hasher(&self) -> DefaultHasher {
2941 DefaultHasher(SipHasher13::new_with_keys(self.k0, self.k1))
2945 /// The default [`Hasher`] used by [`RandomState`].
2947 /// The internal algorithm is not specified, and so it and its hashes should
2948 /// not be relied upon over releases.
2949 #[stable(feature = "hashmap_default_hasher", since = "1.13.0")]
2950 #[allow(deprecated)]
2951 #[derive(Clone, Debug)]
2952 pub struct DefaultHasher(SipHasher13);
2954 impl DefaultHasher {
2955 /// Creates a new `DefaultHasher`.
2957 /// This hasher is not guaranteed to be the same as all other
2958 /// `DefaultHasher` instances, but is the same as all other `DefaultHasher`
2959 /// instances created through `new` or `default`.
2960 #[stable(feature = "hashmap_default_hasher", since = "1.13.0")]
2961 #[allow(deprecated)]
2963 pub fn new() -> DefaultHasher {
2964 DefaultHasher(SipHasher13::new_with_keys(0, 0))
2968 #[stable(feature = "hashmap_default_hasher", since = "1.13.0")]
2969 impl Default for DefaultHasher {
2970 /// Creates a new `DefaultHasher` using [`new`].
2971 /// See its documentation for more.
2973 /// [`new`]: DefaultHasher::new
2974 fn default() -> DefaultHasher {
2975 DefaultHasher::new()
2979 #[stable(feature = "hashmap_default_hasher", since = "1.13.0")]
2980 impl Hasher for DefaultHasher {
2982 fn write(&mut self, msg: &[u8]) {
2987 fn finish(&self) -> u64 {
2992 #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
2993 impl Default for RandomState {
2994 /// Constructs a new `RandomState`.
2996 fn default() -> RandomState {
3001 #[stable(feature = "std_debug", since = "1.16.0")]
3002 impl fmt::Debug for RandomState {
3003 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
3004 f.debug_struct("RandomState").finish_non_exhaustive()
3009 fn map_entry<'a, K: 'a, V: 'a>(raw: base::RustcEntry<'a, K, V>) -> Entry<'a, K, V> {
3011 base::RustcEntry::Occupied(base) => Entry::Occupied(OccupiedEntry { base }),
3012 base::RustcEntry::Vacant(base) => Entry::Vacant(VacantEntry { base }),
3017 pub(super) fn map_try_reserve_error(err: hashbrown::TryReserveError) -> TryReserveError {
3019 hashbrown::TryReserveError::CapacityOverflow => {
3020 TryReserveErrorKind::CapacityOverflow.into()
3022 hashbrown::TryReserveError::AllocError { layout } => {
3023 TryReserveErrorKind::AllocError { layout, non_exhaustive: () }.into()
3029 fn map_raw_entry<'a, K: 'a, V: 'a, S: 'a>(
3030 raw: base::RawEntryMut<'a, K, V, S>,
3031 ) -> RawEntryMut<'a, K, V, S> {
3033 base::RawEntryMut::Occupied(base) => RawEntryMut::Occupied(RawOccupiedEntryMut { base }),
3034 base::RawEntryMut::Vacant(base) => RawEntryMut::Vacant(RawVacantEntryMut { base }),
3039 fn assert_covariance() {
3040 fn map_key<'new>(v: HashMap<&'static str, u8>) -> HashMap<&'new str, u8> {
3043 fn map_val<'new>(v: HashMap<u8, &'static str>) -> HashMap<u8, &'new str> {
3046 fn iter_key<'a, 'new>(v: Iter<'a, &'static str, u8>) -> Iter<'a, &'new str, u8> {
3049 fn iter_val<'a, 'new>(v: Iter<'a, u8, &'static str>) -> Iter<'a, u8, &'new str> {
3052 fn into_iter_key<'new>(v: IntoIter<&'static str, u8>) -> IntoIter<&'new str, u8> {
3055 fn into_iter_val<'new>(v: IntoIter<u8, &'static str>) -> IntoIter<u8, &'new str> {
3058 fn keys_key<'a, 'new>(v: Keys<'a, &'static str, u8>) -> Keys<'a, &'new str, u8> {
3061 fn keys_val<'a, 'new>(v: Keys<'a, u8, &'static str>) -> Keys<'a, u8, &'new str> {
3064 fn values_key<'a, 'new>(v: Values<'a, &'static str, u8>) -> Values<'a, &'new str, u8> {
3067 fn values_val<'a, 'new>(v: Values<'a, u8, &'static str>) -> Values<'a, u8, &'new str> {
3071 d: Drain<'static, &'static str, &'static str>,
3072 ) -> Drain<'new, &'new str, &'new str> {