std/collections/hash/
map.rs

1#[cfg(test)]
2mod tests;
3
4use hashbrown::hash_map as base;
5
6use self::Entry::*;
7use crate::borrow::Borrow;
8use crate::collections::{TryReserveError, TryReserveErrorKind};
9use crate::error::Error;
10use crate::fmt::{self, Debug};
11use crate::hash::{BuildHasher, Hash, RandomState};
12use crate::iter::FusedIterator;
13use crate::ops::Index;
14
15/// A [hash map] implemented with quadratic probing and SIMD lookup.
16///
17/// By default, `HashMap` uses a hashing algorithm selected to provide
18/// resistance against HashDoS attacks. The algorithm is randomly seeded, and a
19/// reasonable best-effort is made to generate this seed from a high quality,
20/// secure source of randomness provided by the host without blocking the
21/// program. Because of this, the randomness of the seed depends on the output
22/// quality of the system's random number coroutine when the seed is created.
23/// In particular, seeds generated when the system's entropy pool is abnormally
24/// low such as during system boot may be of a lower quality.
25///
26/// The default hashing algorithm is currently SipHash 1-3, though this is
27/// subject to change at any point in the future. While its performance is very
28/// competitive for medium sized keys, other hashing algorithms will outperform
29/// it for small keys such as integers as well as large keys such as long
30/// strings, though those algorithms will typically *not* protect against
31/// attacks such as HashDoS.
32///
33/// The hashing algorithm can be replaced on a per-`HashMap` basis using the
34/// [`default`], [`with_hasher`], and [`with_capacity_and_hasher`] methods.
35/// There are many alternative [hashing algorithms available on crates.io].
36///
37/// It is required that the keys implement the [`Eq`] and [`Hash`] traits, although
38/// this can frequently be achieved by using `#[derive(PartialEq, Eq, Hash)]`.
39/// If you implement these yourself, it is important that the following
40/// property holds:
41///
42/// ```text
43/// k1 == k2 -> hash(k1) == hash(k2)
44/// ```
45///
46/// In other words, if two keys are equal, their hashes must be equal.
47/// Violating this property is a logic error.
48///
49/// It is also a logic error for a key to be modified in such a way that the key's
50/// hash, as determined by the [`Hash`] trait, or its equality, as determined by
51/// the [`Eq`] trait, changes while it is in the map. This is normally only
52/// possible through [`Cell`], [`RefCell`], global state, I/O, or unsafe code.
53///
54/// The behavior resulting from either logic error is not specified, but will
55/// be encapsulated to the `HashMap` that observed the logic error and not
56/// result in undefined behavior. This could include panics, incorrect results,
57/// aborts, memory leaks, and non-termination.
58///
59/// The hash table implementation is a Rust port of Google's [SwissTable].
60/// The original C++ version of SwissTable can be found [here], and this
61/// [CppCon talk] gives an overview of how the algorithm works.
62///
63/// [hash map]: crate::collections#use-a-hashmap-when
64/// [hashing algorithms available on crates.io]: https://crates.io/keywords/hasher
65/// [SwissTable]: https://abseil.io/blog/20180927-swisstables
66/// [here]: https://github.com/abseil/abseil-cpp/blob/master/absl/container/internal/raw_hash_set.h
67/// [CppCon talk]: https://www.youtube.com/watch?v=ncHmEUmJZf4
68///
69/// # Examples
70///
71/// ```
72/// use std::collections::HashMap;
73///
74/// // Type inference lets us omit an explicit type signature (which
75/// // would be `HashMap<String, String>` in this example).
76/// let mut book_reviews = HashMap::new();
77///
78/// // Review some books.
79/// book_reviews.insert(
80///     "Adventures of Huckleberry Finn".to_string(),
81///     "My favorite book.".to_string(),
82/// );
83/// book_reviews.insert(
84///     "Grimms' Fairy Tales".to_string(),
85///     "Masterpiece.".to_string(),
86/// );
87/// book_reviews.insert(
88///     "Pride and Prejudice".to_string(),
89///     "Very enjoyable.".to_string(),
90/// );
91/// book_reviews.insert(
92///     "The Adventures of Sherlock Holmes".to_string(),
93///     "Eye lyked it alot.".to_string(),
94/// );
95///
96/// // Check for a specific one.
97/// // When collections store owned values (String), they can still be
98/// // queried using references (&str).
99/// if !book_reviews.contains_key("Les Misérables") {
100///     println!("We've got {} reviews, but Les Misérables ain't one.",
101///              book_reviews.len());
102/// }
103///
104/// // oops, this review has a lot of spelling mistakes, let's delete it.
105/// book_reviews.remove("The Adventures of Sherlock Holmes");
106///
107/// // Look up the values associated with some keys.
108/// let to_find = ["Pride and Prejudice", "Alice's Adventure in Wonderland"];
109/// for &book in &to_find {
110///     match book_reviews.get(book) {
111///         Some(review) => println!("{book}: {review}"),
112///         None => println!("{book} is unreviewed.")
113///     }
114/// }
115///
116/// // Look up the value for a key (will panic if the key is not found).
117/// println!("Review for Jane: {}", book_reviews["Pride and Prejudice"]);
118///
119/// // Iterate over everything.
120/// for (book, review) in &book_reviews {
121///     println!("{book}: \"{review}\"");
122/// }
123/// ```
124///
125/// A `HashMap` with a known list of items can be initialized from an array:
126///
127/// ```
128/// use std::collections::HashMap;
129///
130/// let solar_distance = HashMap::from([
131///     ("Mercury", 0.4),
132///     ("Venus", 0.7),
133///     ("Earth", 1.0),
134///     ("Mars", 1.5),
135/// ]);
136/// ```
137///
138/// `HashMap` implements an [`Entry` API](#method.entry), which allows
139/// for complex methods of getting, setting, updating and removing keys and
140/// their values:
141///
142/// ```
143/// use std::collections::HashMap;
144///
145/// // type inference lets us omit an explicit type signature (which
146/// // would be `HashMap<&str, u8>` in this example).
147/// let mut player_stats = HashMap::new();
148///
149/// fn random_stat_buff() -> u8 {
150///     // could actually return some random value here - let's just return
151///     // some fixed value for now
152///     42
153/// }
154///
155/// // insert a key only if it doesn't already exist
156/// player_stats.entry("health").or_insert(100);
157///
158/// // insert a key using a function that provides a new value only if it
159/// // doesn't already exist
160/// player_stats.entry("defence").or_insert_with(random_stat_buff);
161///
162/// // update a key, guarding against the key possibly not being set
163/// let stat = player_stats.entry("attack").or_insert(100);
164/// *stat += random_stat_buff();
165///
166/// // modify an entry before an insert with in-place mutation
167/// player_stats.entry("mana").and_modify(|mana| *mana += 200).or_insert(100);
168/// ```
169///
170/// The easiest way to use `HashMap` with a custom key type is to derive [`Eq`] and [`Hash`].
171/// We must also derive [`PartialEq`].
172///
173/// [`RefCell`]: crate::cell::RefCell
174/// [`Cell`]: crate::cell::Cell
175/// [`default`]: Default::default
176/// [`with_hasher`]: Self::with_hasher
177/// [`with_capacity_and_hasher`]: Self::with_capacity_and_hasher
178///
179/// ```
180/// use std::collections::HashMap;
181///
182/// #[derive(Hash, Eq, PartialEq, Debug)]
183/// struct Viking {
184///     name: String,
185///     country: String,
186/// }
187///
188/// impl Viking {
189///     /// Creates a new Viking.
190///     fn new(name: &str, country: &str) -> Viking {
191///         Viking { name: name.to_string(), country: country.to_string() }
192///     }
193/// }
194///
195/// // Use a HashMap to store the vikings' health points.
196/// let vikings = HashMap::from([
197///     (Viking::new("Einar", "Norway"), 25),
198///     (Viking::new("Olaf", "Denmark"), 24),
199///     (Viking::new("Harald", "Iceland"), 12),
200/// ]);
201///
202/// // Use derived implementation to print the status of the vikings.
203/// for (viking, health) in &vikings {
204///     println!("{viking:?} has {health} hp");
205/// }
206/// ```
207///
208/// # Usage in `const` and `static`
209///
210/// As explained above, `HashMap` is randomly seeded: each `HashMap` instance uses a different seed,
211/// which means that `HashMap::new` cannot be used in const context. To construct a `HashMap` in the
212/// initializer of a `const` or `static` item, you will have to use a different hasher that does not
213/// involve a random seed, as demonstrated in the following example. **A `HashMap` constructed this
214/// way is not resistant against HashDoS!**
215///
216/// ```rust
217/// use std::collections::HashMap;
218/// use std::hash::{BuildHasherDefault, DefaultHasher};
219/// use std::sync::Mutex;
220///
221/// const EMPTY_MAP: HashMap<String, Vec<i32>, BuildHasherDefault<DefaultHasher>> =
222///     HashMap::with_hasher(BuildHasherDefault::new());
223/// static MAP: Mutex<HashMap<String, Vec<i32>, BuildHasherDefault<DefaultHasher>>> =
224///     Mutex::new(HashMap::with_hasher(BuildHasherDefault::new()));
225/// ```
226
227#[cfg_attr(not(test), rustc_diagnostic_item = "HashMap")]
228#[stable(feature = "rust1", since = "1.0.0")]
229#[rustc_insignificant_dtor]
230pub struct HashMap<K, V, S = RandomState> {
231    base: base::HashMap<K, V, S>,
232}
233
234impl<K, V> HashMap<K, V, RandomState> {
235    /// Creates an empty `HashMap`.
236    ///
237    /// The hash map is initially created with a capacity of 0, so it will not allocate until it
238    /// is first inserted into.
239    ///
240    /// # Examples
241    ///
242    /// ```
243    /// use std::collections::HashMap;
244    /// let mut map: HashMap<&str, i32> = HashMap::new();
245    /// ```
246    #[inline]
247    #[must_use]
248    #[stable(feature = "rust1", since = "1.0.0")]
249    pub fn new() -> HashMap<K, V, RandomState> {
250        Default::default()
251    }
252
253    /// Creates an empty `HashMap` with at least the specified capacity.
254    ///
255    /// The hash map will be able to hold at least `capacity` elements without
256    /// reallocating. This method is allowed to allocate for more elements than
257    /// `capacity`. If `capacity` is zero, the hash map will not allocate.
258    ///
259    /// # Examples
260    ///
261    /// ```
262    /// use std::collections::HashMap;
263    /// let mut map: HashMap<&str, i32> = HashMap::with_capacity(10);
264    /// ```
265    #[inline]
266    #[must_use]
267    #[stable(feature = "rust1", since = "1.0.0")]
268    pub fn with_capacity(capacity: usize) -> HashMap<K, V, RandomState> {
269        HashMap::with_capacity_and_hasher(capacity, Default::default())
270    }
271}
272
273impl<K, V, S> HashMap<K, V, S> {
274    /// Creates an empty `HashMap` which will use the given hash builder to hash
275    /// keys.
276    ///
277    /// The created map has the default initial capacity.
278    ///
279    /// Warning: `hash_builder` is normally randomly generated, and
280    /// is designed to allow HashMaps to be resistant to attacks that
281    /// cause many collisions and very poor performance. Setting it
282    /// manually using this function can expose a DoS attack vector.
283    ///
284    /// The `hash_builder` passed should implement the [`BuildHasher`] trait for
285    /// the `HashMap` to be useful, see its documentation for details.
286    ///
287    /// # Examples
288    ///
289    /// ```
290    /// use std::collections::HashMap;
291    /// use std::hash::RandomState;
292    ///
293    /// let s = RandomState::new();
294    /// let mut map = HashMap::with_hasher(s);
295    /// map.insert(1, 2);
296    /// ```
297    #[inline]
298    #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
299    #[rustc_const_stable(feature = "const_collections_with_hasher", since = "1.85.0")]
300    pub const fn with_hasher(hash_builder: S) -> HashMap<K, V, S> {
301        HashMap { base: base::HashMap::with_hasher(hash_builder) }
302    }
303
304    /// Creates an empty `HashMap` with at least the specified capacity, using
305    /// `hasher` to hash the keys.
306    ///
307    /// The hash map will be able to hold at least `capacity` elements without
308    /// reallocating. This method is allowed to allocate for more elements than
309    /// `capacity`. If `capacity` is zero, the hash map will not allocate.
310    ///
311    /// Warning: `hasher` is normally randomly generated, and
312    /// is designed to allow HashMaps to be resistant to attacks that
313    /// cause many collisions and very poor performance. Setting it
314    /// manually using this function can expose a DoS attack vector.
315    ///
316    /// The `hasher` passed should implement the [`BuildHasher`] trait for
317    /// the `HashMap` to be useful, see its documentation for details.
318    ///
319    /// # Examples
320    ///
321    /// ```
322    /// use std::collections::HashMap;
323    /// use std::hash::RandomState;
324    ///
325    /// let s = RandomState::new();
326    /// let mut map = HashMap::with_capacity_and_hasher(10, s);
327    /// map.insert(1, 2);
328    /// ```
329    #[inline]
330    #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
331    pub fn with_capacity_and_hasher(capacity: usize, hasher: S) -> HashMap<K, V, S> {
332        HashMap { base: base::HashMap::with_capacity_and_hasher(capacity, hasher) }
333    }
334
335    /// Returns the number of elements the map can hold without reallocating.
336    ///
337    /// This number is a lower bound; the `HashMap<K, V>` might be able to hold
338    /// more, but is guaranteed to be able to hold at least this many.
339    ///
340    /// # Examples
341    ///
342    /// ```
343    /// use std::collections::HashMap;
344    /// let map: HashMap<i32, i32> = HashMap::with_capacity(100);
345    /// assert!(map.capacity() >= 100);
346    /// ```
347    #[inline]
348    #[stable(feature = "rust1", since = "1.0.0")]
349    pub fn capacity(&self) -> usize {
350        self.base.capacity()
351    }
352
353    /// An iterator visiting all keys in arbitrary order.
354    /// The iterator element type is `&'a K`.
355    ///
356    /// # Examples
357    ///
358    /// ```
359    /// use std::collections::HashMap;
360    ///
361    /// let map = HashMap::from([
362    ///     ("a", 1),
363    ///     ("b", 2),
364    ///     ("c", 3),
365    /// ]);
366    ///
367    /// for key in map.keys() {
368    ///     println!("{key}");
369    /// }
370    /// ```
371    ///
372    /// # Performance
373    ///
374    /// In the current implementation, iterating over keys takes O(capacity) time
375    /// instead of O(len) because it internally visits empty buckets too.
376    #[rustc_lint_query_instability]
377    #[stable(feature = "rust1", since = "1.0.0")]
378    pub fn keys(&self) -> Keys<'_, K, V> {
379        Keys { inner: self.iter() }
380    }
381
382    /// Creates a consuming iterator visiting all the keys in arbitrary order.
383    /// The map cannot be used after calling this.
384    /// The iterator element type is `K`.
385    ///
386    /// # Examples
387    ///
388    /// ```
389    /// use std::collections::HashMap;
390    ///
391    /// let map = HashMap::from([
392    ///     ("a", 1),
393    ///     ("b", 2),
394    ///     ("c", 3),
395    /// ]);
396    ///
397    /// let mut vec: Vec<&str> = map.into_keys().collect();
398    /// // The `IntoKeys` iterator produces keys in arbitrary order, so the
399    /// // keys must be sorted to test them against a sorted array.
400    /// vec.sort_unstable();
401    /// assert_eq!(vec, ["a", "b", "c"]);
402    /// ```
403    ///
404    /// # Performance
405    ///
406    /// In the current implementation, iterating over keys takes O(capacity) time
407    /// instead of O(len) because it internally visits empty buckets too.
408    #[inline]
409    #[rustc_lint_query_instability]
410    #[stable(feature = "map_into_keys_values", since = "1.54.0")]
411    pub fn into_keys(self) -> IntoKeys<K, V> {
412        IntoKeys { inner: self.into_iter() }
413    }
414
415    /// An iterator visiting all values in arbitrary order.
416    /// The iterator element type is `&'a V`.
417    ///
418    /// # Examples
419    ///
420    /// ```
421    /// use std::collections::HashMap;
422    ///
423    /// let map = HashMap::from([
424    ///     ("a", 1),
425    ///     ("b", 2),
426    ///     ("c", 3),
427    /// ]);
428    ///
429    /// for val in map.values() {
430    ///     println!("{val}");
431    /// }
432    /// ```
433    ///
434    /// # Performance
435    ///
436    /// In the current implementation, iterating over values takes O(capacity) time
437    /// instead of O(len) because it internally visits empty buckets too.
438    #[rustc_lint_query_instability]
439    #[stable(feature = "rust1", since = "1.0.0")]
440    pub fn values(&self) -> Values<'_, K, V> {
441        Values { inner: self.iter() }
442    }
443
444    /// An iterator visiting all values mutably in arbitrary order.
445    /// The iterator element type is `&'a mut V`.
446    ///
447    /// # Examples
448    ///
449    /// ```
450    /// use std::collections::HashMap;
451    ///
452    /// let mut map = HashMap::from([
453    ///     ("a", 1),
454    ///     ("b", 2),
455    ///     ("c", 3),
456    /// ]);
457    ///
458    /// for val in map.values_mut() {
459    ///     *val = *val + 10;
460    /// }
461    ///
462    /// for val in map.values() {
463    ///     println!("{val}");
464    /// }
465    /// ```
466    ///
467    /// # Performance
468    ///
469    /// In the current implementation, iterating over values takes O(capacity) time
470    /// instead of O(len) because it internally visits empty buckets too.
471    #[rustc_lint_query_instability]
472    #[stable(feature = "map_values_mut", since = "1.10.0")]
473    pub fn values_mut(&mut self) -> ValuesMut<'_, K, V> {
474        ValuesMut { inner: self.iter_mut() }
475    }
476
477    /// Creates a consuming iterator visiting all the values in arbitrary order.
478    /// The map cannot be used after calling this.
479    /// The iterator element type is `V`.
480    ///
481    /// # Examples
482    ///
483    /// ```
484    /// use std::collections::HashMap;
485    ///
486    /// let map = HashMap::from([
487    ///     ("a", 1),
488    ///     ("b", 2),
489    ///     ("c", 3),
490    /// ]);
491    ///
492    /// let mut vec: Vec<i32> = map.into_values().collect();
493    /// // The `IntoValues` iterator produces values in arbitrary order, so
494    /// // the values must be sorted to test them against a sorted array.
495    /// vec.sort_unstable();
496    /// assert_eq!(vec, [1, 2, 3]);
497    /// ```
498    ///
499    /// # Performance
500    ///
501    /// In the current implementation, iterating over values takes O(capacity) time
502    /// instead of O(len) because it internally visits empty buckets too.
503    #[inline]
504    #[rustc_lint_query_instability]
505    #[stable(feature = "map_into_keys_values", since = "1.54.0")]
506    pub fn into_values(self) -> IntoValues<K, V> {
507        IntoValues { inner: self.into_iter() }
508    }
509
510    /// An iterator visiting all key-value pairs in arbitrary order.
511    /// The iterator element type is `(&'a K, &'a V)`.
512    ///
513    /// # Examples
514    ///
515    /// ```
516    /// use std::collections::HashMap;
517    ///
518    /// let map = HashMap::from([
519    ///     ("a", 1),
520    ///     ("b", 2),
521    ///     ("c", 3),
522    /// ]);
523    ///
524    /// for (key, val) in map.iter() {
525    ///     println!("key: {key} val: {val}");
526    /// }
527    /// ```
528    ///
529    /// # Performance
530    ///
531    /// In the current implementation, iterating over map takes O(capacity) time
532    /// instead of O(len) because it internally visits empty buckets too.
533    #[rustc_lint_query_instability]
534    #[stable(feature = "rust1", since = "1.0.0")]
535    pub fn iter(&self) -> Iter<'_, K, V> {
536        Iter { base: self.base.iter() }
537    }
538
539    /// An iterator visiting all key-value pairs in arbitrary order,
540    /// with mutable references to the values.
541    /// The iterator element type is `(&'a K, &'a mut V)`.
542    ///
543    /// # Examples
544    ///
545    /// ```
546    /// use std::collections::HashMap;
547    ///
548    /// let mut map = HashMap::from([
549    ///     ("a", 1),
550    ///     ("b", 2),
551    ///     ("c", 3),
552    /// ]);
553    ///
554    /// // Update all values
555    /// for (_, val) in map.iter_mut() {
556    ///     *val *= 2;
557    /// }
558    ///
559    /// for (key, val) in &map {
560    ///     println!("key: {key} val: {val}");
561    /// }
562    /// ```
563    ///
564    /// # Performance
565    ///
566    /// In the current implementation, iterating over map takes O(capacity) time
567    /// instead of O(len) because it internally visits empty buckets too.
568    #[rustc_lint_query_instability]
569    #[stable(feature = "rust1", since = "1.0.0")]
570    pub fn iter_mut(&mut self) -> IterMut<'_, K, V> {
571        IterMut { base: self.base.iter_mut() }
572    }
573
574    /// Returns the number of elements in the map.
575    ///
576    /// # Examples
577    ///
578    /// ```
579    /// use std::collections::HashMap;
580    ///
581    /// let mut a = HashMap::new();
582    /// assert_eq!(a.len(), 0);
583    /// a.insert(1, "a");
584    /// assert_eq!(a.len(), 1);
585    /// ```
586    #[stable(feature = "rust1", since = "1.0.0")]
587    pub fn len(&self) -> usize {
588        self.base.len()
589    }
590
591    /// Returns `true` if the map contains no elements.
592    ///
593    /// # Examples
594    ///
595    /// ```
596    /// use std::collections::HashMap;
597    ///
598    /// let mut a = HashMap::new();
599    /// assert!(a.is_empty());
600    /// a.insert(1, "a");
601    /// assert!(!a.is_empty());
602    /// ```
603    #[inline]
604    #[stable(feature = "rust1", since = "1.0.0")]
605    pub fn is_empty(&self) -> bool {
606        self.base.is_empty()
607    }
608
609    /// Clears the map, returning all key-value pairs as an iterator. Keeps the
610    /// allocated memory for reuse.
611    ///
612    /// If the returned iterator is dropped before being fully consumed, it
613    /// drops the remaining key-value pairs. The returned iterator keeps a
614    /// mutable borrow on the map to optimize its implementation.
615    ///
616    /// # Examples
617    ///
618    /// ```
619    /// use std::collections::HashMap;
620    ///
621    /// let mut a = HashMap::new();
622    /// a.insert(1, "a");
623    /// a.insert(2, "b");
624    ///
625    /// for (k, v) in a.drain().take(1) {
626    ///     assert!(k == 1 || k == 2);
627    ///     assert!(v == "a" || v == "b");
628    /// }
629    ///
630    /// assert!(a.is_empty());
631    /// ```
632    #[inline]
633    #[rustc_lint_query_instability]
634    #[stable(feature = "drain", since = "1.6.0")]
635    pub fn drain(&mut self) -> Drain<'_, K, V> {
636        Drain { base: self.base.drain() }
637    }
638
639    /// Creates an iterator which uses a closure to determine if an element should be removed.
640    ///
641    /// If the closure returns true, the element is removed from the map and yielded.
642    /// If the closure returns false, or panics, the element remains in the map and will not be
643    /// yielded.
644    ///
645    /// Note that `extract_if` lets you mutate every value in the filter closure, regardless of
646    /// whether you choose to keep or remove it.
647    ///
648    /// If the returned `ExtractIf` is not exhausted, e.g. because it is dropped without iterating
649    /// or the iteration short-circuits, then the remaining elements will be retained.
650    /// Use [`retain`] with a negated predicate if you do not need the returned iterator.
651    ///
652    /// [`retain`]: HashMap::retain
653    ///
654    /// # Examples
655    ///
656    /// Splitting a map into even and odd keys, reusing the original map:
657    ///
658    /// ```
659    /// use std::collections::HashMap;
660    ///
661    /// let mut map: HashMap<i32, i32> = (0..8).map(|x| (x, x)).collect();
662    /// let extracted: HashMap<i32, i32> = map.extract_if(|k, _v| k % 2 == 0).collect();
663    ///
664    /// let mut evens = extracted.keys().copied().collect::<Vec<_>>();
665    /// let mut odds = map.keys().copied().collect::<Vec<_>>();
666    /// evens.sort();
667    /// odds.sort();
668    ///
669    /// assert_eq!(evens, vec![0, 2, 4, 6]);
670    /// assert_eq!(odds, vec![1, 3, 5, 7]);
671    /// ```
672    #[inline]
673    #[rustc_lint_query_instability]
674    #[stable(feature = "hash_extract_if", since = "CURRENT_RUSTC_VERSION")]
675    pub fn extract_if<F>(&mut self, pred: F) -> ExtractIf<'_, K, V, F>
676    where
677        F: FnMut(&K, &mut V) -> bool,
678    {
679        ExtractIf { base: self.base.extract_if(pred) }
680    }
681
682    /// Retains only the elements specified by the predicate.
683    ///
684    /// In other words, remove all pairs `(k, v)` for which `f(&k, &mut v)` returns `false`.
685    /// The elements are visited in unsorted (and unspecified) order.
686    ///
687    /// # Examples
688    ///
689    /// ```
690    /// use std::collections::HashMap;
691    ///
692    /// let mut map: HashMap<i32, i32> = (0..8).map(|x| (x, x*10)).collect();
693    /// map.retain(|&k, _| k % 2 == 0);
694    /// assert_eq!(map.len(), 4);
695    /// ```
696    ///
697    /// # Performance
698    ///
699    /// In the current implementation, this operation takes O(capacity) time
700    /// instead of O(len) because it internally visits empty buckets too.
701    #[inline]
702    #[rustc_lint_query_instability]
703    #[stable(feature = "retain_hash_collection", since = "1.18.0")]
704    pub fn retain<F>(&mut self, f: F)
705    where
706        F: FnMut(&K, &mut V) -> bool,
707    {
708        self.base.retain(f)
709    }
710
711    /// Clears the map, removing all key-value pairs. Keeps the allocated memory
712    /// for reuse.
713    ///
714    /// # Examples
715    ///
716    /// ```
717    /// use std::collections::HashMap;
718    ///
719    /// let mut a = HashMap::new();
720    /// a.insert(1, "a");
721    /// a.clear();
722    /// assert!(a.is_empty());
723    /// ```
724    #[inline]
725    #[stable(feature = "rust1", since = "1.0.0")]
726    pub fn clear(&mut self) {
727        self.base.clear();
728    }
729
730    /// Returns a reference to the map's [`BuildHasher`].
731    ///
732    /// # Examples
733    ///
734    /// ```
735    /// use std::collections::HashMap;
736    /// use std::hash::RandomState;
737    ///
738    /// let hasher = RandomState::new();
739    /// let map: HashMap<i32, i32> = HashMap::with_hasher(hasher);
740    /// let hasher: &RandomState = map.hasher();
741    /// ```
742    #[inline]
743    #[stable(feature = "hashmap_public_hasher", since = "1.9.0")]
744    pub fn hasher(&self) -> &S {
745        self.base.hasher()
746    }
747}
748
749impl<K, V, S> HashMap<K, V, S>
750where
751    K: Eq + Hash,
752    S: BuildHasher,
753{
754    /// Reserves capacity for at least `additional` more elements to be inserted
755    /// in the `HashMap`. The collection may reserve more space to speculatively
756    /// avoid frequent reallocations. After calling `reserve`,
757    /// capacity will be greater than or equal to `self.len() + additional`.
758    /// Does nothing if capacity is already sufficient.
759    ///
760    /// # Panics
761    ///
762    /// Panics if the new allocation size overflows [`usize`].
763    ///
764    /// # Examples
765    ///
766    /// ```
767    /// use std::collections::HashMap;
768    /// let mut map: HashMap<&str, i32> = HashMap::new();
769    /// map.reserve(10);
770    /// ```
771    #[inline]
772    #[stable(feature = "rust1", since = "1.0.0")]
773    pub fn reserve(&mut self, additional: usize) {
774        self.base.reserve(additional)
775    }
776
777    /// Tries to reserve capacity for at least `additional` more elements to be inserted
778    /// in the `HashMap`. The collection may reserve more space to speculatively
779    /// avoid frequent reallocations. After calling `try_reserve`,
780    /// capacity will be greater than or equal to `self.len() + additional` if
781    /// it returns `Ok(())`.
782    /// Does nothing if capacity is already sufficient.
783    ///
784    /// # Errors
785    ///
786    /// If the capacity overflows, or the allocator reports a failure, then an error
787    /// is returned.
788    ///
789    /// # Examples
790    ///
791    /// ```
792    /// use std::collections::HashMap;
793    ///
794    /// let mut map: HashMap<&str, isize> = HashMap::new();
795    /// map.try_reserve(10).expect("why is the test harness OOMing on a handful of bytes?");
796    /// ```
797    #[inline]
798    #[stable(feature = "try_reserve", since = "1.57.0")]
799    pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
800        self.base.try_reserve(additional).map_err(map_try_reserve_error)
801    }
802
803    /// Shrinks the capacity of the map as much as possible. It will drop
804    /// down as much as possible while maintaining the internal rules
805    /// and possibly leaving some space in accordance with the resize policy.
806    ///
807    /// # Examples
808    ///
809    /// ```
810    /// use std::collections::HashMap;
811    ///
812    /// let mut map: HashMap<i32, i32> = HashMap::with_capacity(100);
813    /// map.insert(1, 2);
814    /// map.insert(3, 4);
815    /// assert!(map.capacity() >= 100);
816    /// map.shrink_to_fit();
817    /// assert!(map.capacity() >= 2);
818    /// ```
819    #[inline]
820    #[stable(feature = "rust1", since = "1.0.0")]
821    pub fn shrink_to_fit(&mut self) {
822        self.base.shrink_to_fit();
823    }
824
825    /// Shrinks the capacity of the map with a lower limit. It will drop
826    /// down no lower than the supplied limit while maintaining the internal rules
827    /// and possibly leaving some space in accordance with the resize policy.
828    ///
829    /// If the current capacity is less than the lower limit, this is a no-op.
830    ///
831    /// # Examples
832    ///
833    /// ```
834    /// use std::collections::HashMap;
835    ///
836    /// let mut map: HashMap<i32, i32> = HashMap::with_capacity(100);
837    /// map.insert(1, 2);
838    /// map.insert(3, 4);
839    /// assert!(map.capacity() >= 100);
840    /// map.shrink_to(10);
841    /// assert!(map.capacity() >= 10);
842    /// map.shrink_to(0);
843    /// assert!(map.capacity() >= 2);
844    /// ```
845    #[inline]
846    #[stable(feature = "shrink_to", since = "1.56.0")]
847    pub fn shrink_to(&mut self, min_capacity: usize) {
848        self.base.shrink_to(min_capacity);
849    }
850
851    /// Gets the given key's corresponding entry in the map for in-place manipulation.
852    ///
853    /// # Examples
854    ///
855    /// ```
856    /// use std::collections::HashMap;
857    ///
858    /// let mut letters = HashMap::new();
859    ///
860    /// for ch in "a short treatise on fungi".chars() {
861    ///     letters.entry(ch).and_modify(|counter| *counter += 1).or_insert(1);
862    /// }
863    ///
864    /// assert_eq!(letters[&'s'], 2);
865    /// assert_eq!(letters[&'t'], 3);
866    /// assert_eq!(letters[&'u'], 1);
867    /// assert_eq!(letters.get(&'y'), None);
868    /// ```
869    #[inline]
870    #[stable(feature = "rust1", since = "1.0.0")]
871    pub fn entry(&mut self, key: K) -> Entry<'_, K, V> {
872        map_entry(self.base.rustc_entry(key))
873    }
874
875    /// Returns a reference to the value corresponding to the key.
876    ///
877    /// The key may be any borrowed form of the map's key type, but
878    /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
879    /// the key type.
880    ///
881    /// # Examples
882    ///
883    /// ```
884    /// use std::collections::HashMap;
885    ///
886    /// let mut map = HashMap::new();
887    /// map.insert(1, "a");
888    /// assert_eq!(map.get(&1), Some(&"a"));
889    /// assert_eq!(map.get(&2), None);
890    /// ```
891    #[stable(feature = "rust1", since = "1.0.0")]
892    #[inline]
893    pub fn get<Q: ?Sized>(&self, k: &Q) -> Option<&V>
894    where
895        K: Borrow<Q>,
896        Q: Hash + Eq,
897    {
898        self.base.get(k)
899    }
900
901    /// Returns the key-value pair corresponding to the supplied key. This is
902    /// potentially useful:
903    /// - for key types where non-identical keys can be considered equal;
904    /// - for getting the `&K` stored key value from a borrowed `&Q` lookup key; or
905    /// - for getting a reference to a key with the same lifetime as the collection.
906    ///
907    /// The supplied key may be any borrowed form of the map's key type, but
908    /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
909    /// the key type.
910    ///
911    /// # Examples
912    ///
913    /// ```
914    /// use std::collections::HashMap;
915    /// use std::hash::{Hash, Hasher};
916    ///
917    /// #[derive(Clone, Copy, Debug)]
918    /// struct S {
919    ///     id: u32,
920    /// #   #[allow(unused)] // prevents a "field `name` is never read" error
921    ///     name: &'static str, // ignored by equality and hashing operations
922    /// }
923    ///
924    /// impl PartialEq for S {
925    ///     fn eq(&self, other: &S) -> bool {
926    ///         self.id == other.id
927    ///     }
928    /// }
929    ///
930    /// impl Eq for S {}
931    ///
932    /// impl Hash for S {
933    ///     fn hash<H: Hasher>(&self, state: &mut H) {
934    ///         self.id.hash(state);
935    ///     }
936    /// }
937    ///
938    /// let j_a = S { id: 1, name: "Jessica" };
939    /// let j_b = S { id: 1, name: "Jess" };
940    /// let p = S { id: 2, name: "Paul" };
941    /// assert_eq!(j_a, j_b);
942    ///
943    /// let mut map = HashMap::new();
944    /// map.insert(j_a, "Paris");
945    /// assert_eq!(map.get_key_value(&j_a), Some((&j_a, &"Paris")));
946    /// assert_eq!(map.get_key_value(&j_b), Some((&j_a, &"Paris"))); // the notable case
947    /// assert_eq!(map.get_key_value(&p), None);
948    /// ```
949    #[inline]
950    #[stable(feature = "map_get_key_value", since = "1.40.0")]
951    pub fn get_key_value<Q: ?Sized>(&self, k: &Q) -> Option<(&K, &V)>
952    where
953        K: Borrow<Q>,
954        Q: Hash + Eq,
955    {
956        self.base.get_key_value(k)
957    }
958
959    /// Attempts to get mutable references to `N` values in the map at once.
960    ///
961    /// Returns an array of length `N` with the results of each query. For soundness, at most one
962    /// mutable reference will be returned to any value. `None` will be used if the key is missing.
963    ///
964    /// # Panics
965    ///
966    /// Panics if any keys are overlapping.
967    ///
968    /// # Examples
969    ///
970    /// ```
971    /// use std::collections::HashMap;
972    ///
973    /// let mut libraries = HashMap::new();
974    /// libraries.insert("Bodleian Library".to_string(), 1602);
975    /// libraries.insert("Athenæum".to_string(), 1807);
976    /// libraries.insert("Herzogin-Anna-Amalia-Bibliothek".to_string(), 1691);
977    /// libraries.insert("Library of Congress".to_string(), 1800);
978    ///
979    /// // Get Athenæum and Bodleian Library
980    /// let [Some(a), Some(b)] = libraries.get_disjoint_mut([
981    ///     "Athenæum",
982    ///     "Bodleian Library",
983    /// ]) else { panic!() };
984    ///
985    /// // Assert values of Athenæum and Library of Congress
986    /// let got = libraries.get_disjoint_mut([
987    ///     "Athenæum",
988    ///     "Library of Congress",
989    /// ]);
990    /// assert_eq!(
991    ///     got,
992    ///     [
993    ///         Some(&mut 1807),
994    ///         Some(&mut 1800),
995    ///     ],
996    /// );
997    ///
998    /// // Missing keys result in None
999    /// let got = libraries.get_disjoint_mut([
1000    ///     "Athenæum",
1001    ///     "New York Public Library",
1002    /// ]);
1003    /// assert_eq!(
1004    ///     got,
1005    ///     [
1006    ///         Some(&mut 1807),
1007    ///         None
1008    ///     ]
1009    /// );
1010    /// ```
1011    ///
1012    /// ```should_panic
1013    /// use std::collections::HashMap;
1014    ///
1015    /// let mut libraries = HashMap::new();
1016    /// libraries.insert("Athenæum".to_string(), 1807);
1017    ///
1018    /// // Duplicate keys panic!
1019    /// let got = libraries.get_disjoint_mut([
1020    ///     "Athenæum",
1021    ///     "Athenæum",
1022    /// ]);
1023    /// ```
1024    #[inline]
1025    #[doc(alias = "get_many_mut")]
1026    #[stable(feature = "map_many_mut", since = "1.86.0")]
1027    pub fn get_disjoint_mut<Q: ?Sized, const N: usize>(
1028        &mut self,
1029        ks: [&Q; N],
1030    ) -> [Option<&'_ mut V>; N]
1031    where
1032        K: Borrow<Q>,
1033        Q: Hash + Eq,
1034    {
1035        self.base.get_many_mut(ks)
1036    }
1037
1038    /// Attempts to get mutable references to `N` values in the map at once, without validating that
1039    /// the values are unique.
1040    ///
1041    /// Returns an array of length `N` with the results of each query. `None` will be used if
1042    /// the key is missing.
1043    ///
1044    /// For a safe alternative see [`get_disjoint_mut`](`HashMap::get_disjoint_mut`).
1045    ///
1046    /// # Safety
1047    ///
1048    /// Calling this method with overlapping keys is *[undefined behavior]* even if the resulting
1049    /// references are not used.
1050    ///
1051    /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
1052    ///
1053    /// # Examples
1054    ///
1055    /// ```
1056    /// use std::collections::HashMap;
1057    ///
1058    /// let mut libraries = HashMap::new();
1059    /// libraries.insert("Bodleian Library".to_string(), 1602);
1060    /// libraries.insert("Athenæum".to_string(), 1807);
1061    /// libraries.insert("Herzogin-Anna-Amalia-Bibliothek".to_string(), 1691);
1062    /// libraries.insert("Library of Congress".to_string(), 1800);
1063    ///
1064    /// // SAFETY: The keys do not overlap.
1065    /// let [Some(a), Some(b)] = (unsafe { libraries.get_disjoint_unchecked_mut([
1066    ///     "Athenæum",
1067    ///     "Bodleian Library",
1068    /// ]) }) else { panic!() };
1069    ///
1070    /// // SAFETY: The keys do not overlap.
1071    /// let got = unsafe { libraries.get_disjoint_unchecked_mut([
1072    ///     "Athenæum",
1073    ///     "Library of Congress",
1074    /// ]) };
1075    /// assert_eq!(
1076    ///     got,
1077    ///     [
1078    ///         Some(&mut 1807),
1079    ///         Some(&mut 1800),
1080    ///     ],
1081    /// );
1082    ///
1083    /// // SAFETY: The keys do not overlap.
1084    /// let got = unsafe { libraries.get_disjoint_unchecked_mut([
1085    ///     "Athenæum",
1086    ///     "New York Public Library",
1087    /// ]) };
1088    /// // Missing keys result in None
1089    /// assert_eq!(got, [Some(&mut 1807), None]);
1090    /// ```
1091    #[inline]
1092    #[doc(alias = "get_many_unchecked_mut")]
1093    #[stable(feature = "map_many_mut", since = "1.86.0")]
1094    pub unsafe fn get_disjoint_unchecked_mut<Q: ?Sized, const N: usize>(
1095        &mut self,
1096        ks: [&Q; N],
1097    ) -> [Option<&'_ mut V>; N]
1098    where
1099        K: Borrow<Q>,
1100        Q: Hash + Eq,
1101    {
1102        unsafe { self.base.get_many_unchecked_mut(ks) }
1103    }
1104
1105    /// Returns `true` if the map contains a value for the specified key.
1106    ///
1107    /// The key may be any borrowed form of the map's key type, but
1108    /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
1109    /// the key type.
1110    ///
1111    /// # Examples
1112    ///
1113    /// ```
1114    /// use std::collections::HashMap;
1115    ///
1116    /// let mut map = HashMap::new();
1117    /// map.insert(1, "a");
1118    /// assert_eq!(map.contains_key(&1), true);
1119    /// assert_eq!(map.contains_key(&2), false);
1120    /// ```
1121    #[inline]
1122    #[stable(feature = "rust1", since = "1.0.0")]
1123    #[cfg_attr(not(test), rustc_diagnostic_item = "hashmap_contains_key")]
1124    pub fn contains_key<Q: ?Sized>(&self, k: &Q) -> bool
1125    where
1126        K: Borrow<Q>,
1127        Q: Hash + Eq,
1128    {
1129        self.base.contains_key(k)
1130    }
1131
1132    /// Returns a mutable reference to the value corresponding to the key.
1133    ///
1134    /// The key may be any borrowed form of the map's key type, but
1135    /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
1136    /// the key type.
1137    ///
1138    /// # Examples
1139    ///
1140    /// ```
1141    /// use std::collections::HashMap;
1142    ///
1143    /// let mut map = HashMap::new();
1144    /// map.insert(1, "a");
1145    /// if let Some(x) = map.get_mut(&1) {
1146    ///     *x = "b";
1147    /// }
1148    /// assert_eq!(map[&1], "b");
1149    /// ```
1150    #[inline]
1151    #[stable(feature = "rust1", since = "1.0.0")]
1152    pub fn get_mut<Q: ?Sized>(&mut self, k: &Q) -> Option<&mut V>
1153    where
1154        K: Borrow<Q>,
1155        Q: Hash + Eq,
1156    {
1157        self.base.get_mut(k)
1158    }
1159
1160    /// Inserts a key-value pair into the map.
1161    ///
1162    /// If the map did not have this key present, [`None`] is returned.
1163    ///
1164    /// If the map did have this key present, the value is updated, and the old
1165    /// value is returned. The key is not updated, though; this matters for
1166    /// types that can be `==` without being identical. See the [module-level
1167    /// documentation] for more.
1168    ///
1169    /// [module-level documentation]: crate::collections#insert-and-complex-keys
1170    ///
1171    /// # Examples
1172    ///
1173    /// ```
1174    /// use std::collections::HashMap;
1175    ///
1176    /// let mut map = HashMap::new();
1177    /// assert_eq!(map.insert(37, "a"), None);
1178    /// assert_eq!(map.is_empty(), false);
1179    ///
1180    /// map.insert(37, "b");
1181    /// assert_eq!(map.insert(37, "c"), Some("b"));
1182    /// assert_eq!(map[&37], "c");
1183    /// ```
1184    #[inline]
1185    #[stable(feature = "rust1", since = "1.0.0")]
1186    #[rustc_confusables("push", "append", "put")]
1187    #[cfg_attr(not(test), rustc_diagnostic_item = "hashmap_insert")]
1188    pub fn insert(&mut self, k: K, v: V) -> Option<V> {
1189        self.base.insert(k, v)
1190    }
1191
1192    /// Tries to insert a key-value pair into the map, and returns
1193    /// a mutable reference to the value in the entry.
1194    ///
1195    /// If the map already had this key present, nothing is updated, and
1196    /// an error containing the occupied entry and the value is returned.
1197    ///
1198    /// # Examples
1199    ///
1200    /// Basic usage:
1201    ///
1202    /// ```
1203    /// #![feature(map_try_insert)]
1204    ///
1205    /// use std::collections::HashMap;
1206    ///
1207    /// let mut map = HashMap::new();
1208    /// assert_eq!(map.try_insert(37, "a").unwrap(), &"a");
1209    ///
1210    /// let err = map.try_insert(37, "b").unwrap_err();
1211    /// assert_eq!(err.entry.key(), &37);
1212    /// assert_eq!(err.entry.get(), &"a");
1213    /// assert_eq!(err.value, "b");
1214    /// ```
1215    #[unstable(feature = "map_try_insert", issue = "82766")]
1216    pub fn try_insert(&mut self, key: K, value: V) -> Result<&mut V, OccupiedError<'_, K, V>> {
1217        match self.entry(key) {
1218            Occupied(entry) => Err(OccupiedError { entry, value }),
1219            Vacant(entry) => Ok(entry.insert(value)),
1220        }
1221    }
1222
1223    /// Removes a key from the map, returning the value at the key if the key
1224    /// was previously in the map.
1225    ///
1226    /// The key may be any borrowed form of the map's key type, but
1227    /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
1228    /// the key type.
1229    ///
1230    /// # Examples
1231    ///
1232    /// ```
1233    /// use std::collections::HashMap;
1234    ///
1235    /// let mut map = HashMap::new();
1236    /// map.insert(1, "a");
1237    /// assert_eq!(map.remove(&1), Some("a"));
1238    /// assert_eq!(map.remove(&1), None);
1239    /// ```
1240    #[inline]
1241    #[stable(feature = "rust1", since = "1.0.0")]
1242    #[rustc_confusables("delete", "take")]
1243    pub fn remove<Q: ?Sized>(&mut self, k: &Q) -> Option<V>
1244    where
1245        K: Borrow<Q>,
1246        Q: Hash + Eq,
1247    {
1248        self.base.remove(k)
1249    }
1250
1251    /// Removes a key from the map, returning the stored key and value if the
1252    /// key was previously in the map.
1253    ///
1254    /// The key may be any borrowed form of the map's key type, but
1255    /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
1256    /// the key type.
1257    ///
1258    /// # Examples
1259    ///
1260    /// ```
1261    /// use std::collections::HashMap;
1262    ///
1263    /// # fn main() {
1264    /// let mut map = HashMap::new();
1265    /// map.insert(1, "a");
1266    /// assert_eq!(map.remove_entry(&1), Some((1, "a")));
1267    /// assert_eq!(map.remove(&1), None);
1268    /// # }
1269    /// ```
1270    #[inline]
1271    #[stable(feature = "hash_map_remove_entry", since = "1.27.0")]
1272    pub fn remove_entry<Q: ?Sized>(&mut self, k: &Q) -> Option<(K, V)>
1273    where
1274        K: Borrow<Q>,
1275        Q: Hash + Eq,
1276    {
1277        self.base.remove_entry(k)
1278    }
1279}
1280
1281impl<K, V, S> HashMap<K, V, S>
1282where
1283    S: BuildHasher,
1284{
1285    /// Creates a raw entry builder for the `HashMap`.
1286    ///
1287    /// Raw entries provide the lowest level of control for searching and
1288    /// manipulating a map. They must be manually initialized with a hash and
1289    /// then manually searched. After this, insertions into a vacant entry
1290    /// still require an owned key to be provided.
1291    ///
1292    /// Raw entries are useful for such exotic situations as:
1293    ///
1294    /// * Hash memoization
1295    /// * Deferring the creation of an owned key until it is known to be required
1296    /// * Using a search key that doesn't work with the Borrow trait
1297    /// * Using custom comparison logic without newtype wrappers
1298    ///
1299    /// Because raw entries provide much more low-level control, it's much easier
1300    /// to put the `HashMap` into an inconsistent state which, while memory-safe,
1301    /// will cause the map to produce seemingly random results. Higher-level and
1302    /// more foolproof APIs like `entry` should be preferred when possible.
1303    ///
1304    /// In particular, the hash used to initialize the raw entry must still be
1305    /// consistent with the hash of the key that is ultimately stored in the entry.
1306    /// This is because implementations of `HashMap` may need to recompute hashes
1307    /// when resizing, at which point only the keys are available.
1308    ///
1309    /// Raw entries give mutable access to the keys. This must not be used
1310    /// to modify how the key would compare or hash, as the map will not re-evaluate
1311    /// where the key should go, meaning the keys may become "lost" if their
1312    /// location does not reflect their state. For instance, if you change a key
1313    /// so that the map now contains keys which compare equal, search may start
1314    /// acting erratically, with two keys randomly masking each other. Implementations
1315    /// are free to assume this doesn't happen (within the limits of memory-safety).
1316    #[inline]
1317    #[unstable(feature = "hash_raw_entry", issue = "56167")]
1318    pub fn raw_entry_mut(&mut self) -> RawEntryBuilderMut<'_, K, V, S> {
1319        RawEntryBuilderMut { map: self }
1320    }
1321
1322    /// Creates a raw immutable entry builder for the `HashMap`.
1323    ///
1324    /// Raw entries provide the lowest level of control for searching and
1325    /// manipulating a map. They must be manually initialized with a hash and
1326    /// then manually searched.
1327    ///
1328    /// This is useful for
1329    /// * Hash memoization
1330    /// * Using a search key that doesn't work with the Borrow trait
1331    /// * Using custom comparison logic without newtype wrappers
1332    ///
1333    /// Unless you are in such a situation, higher-level and more foolproof APIs like
1334    /// `get` should be preferred.
1335    ///
1336    /// Immutable raw entries have very limited use; you might instead want `raw_entry_mut`.
1337    #[inline]
1338    #[unstable(feature = "hash_raw_entry", issue = "56167")]
1339    pub fn raw_entry(&self) -> RawEntryBuilder<'_, K, V, S> {
1340        RawEntryBuilder { map: self }
1341    }
1342}
1343
1344#[stable(feature = "rust1", since = "1.0.0")]
1345impl<K, V, S> Clone for HashMap<K, V, S>
1346where
1347    K: Clone,
1348    V: Clone,
1349    S: Clone,
1350{
1351    #[inline]
1352    fn clone(&self) -> Self {
1353        Self { base: self.base.clone() }
1354    }
1355
1356    #[inline]
1357    fn clone_from(&mut self, source: &Self) {
1358        self.base.clone_from(&source.base);
1359    }
1360}
1361
1362#[stable(feature = "rust1", since = "1.0.0")]
1363impl<K, V, S> PartialEq for HashMap<K, V, S>
1364where
1365    K: Eq + Hash,
1366    V: PartialEq,
1367    S: BuildHasher,
1368{
1369    fn eq(&self, other: &HashMap<K, V, S>) -> bool {
1370        if self.len() != other.len() {
1371            return false;
1372        }
1373
1374        self.iter().all(|(key, value)| other.get(key).map_or(false, |v| *value == *v))
1375    }
1376}
1377
1378#[stable(feature = "rust1", since = "1.0.0")]
1379impl<K, V, S> Eq for HashMap<K, V, S>
1380where
1381    K: Eq + Hash,
1382    V: Eq,
1383    S: BuildHasher,
1384{
1385}
1386
1387#[stable(feature = "rust1", since = "1.0.0")]
1388impl<K, V, S> Debug for HashMap<K, V, S>
1389where
1390    K: Debug,
1391    V: Debug,
1392{
1393    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1394        f.debug_map().entries(self.iter()).finish()
1395    }
1396}
1397
1398#[stable(feature = "rust1", since = "1.0.0")]
1399impl<K, V, S> Default for HashMap<K, V, S>
1400where
1401    S: Default,
1402{
1403    /// Creates an empty `HashMap<K, V, S>`, with the `Default` value for the hasher.
1404    #[inline]
1405    fn default() -> HashMap<K, V, S> {
1406        HashMap::with_hasher(Default::default())
1407    }
1408}
1409
1410#[stable(feature = "rust1", since = "1.0.0")]
1411impl<K, Q: ?Sized, V, S> Index<&Q> for HashMap<K, V, S>
1412where
1413    K: Eq + Hash + Borrow<Q>,
1414    Q: Eq + Hash,
1415    S: BuildHasher,
1416{
1417    type Output = V;
1418
1419    /// Returns a reference to the value corresponding to the supplied key.
1420    ///
1421    /// # Panics
1422    ///
1423    /// Panics if the key is not present in the `HashMap`.
1424    #[inline]
1425    fn index(&self, key: &Q) -> &V {
1426        self.get(key).expect("no entry found for key")
1427    }
1428}
1429
1430#[stable(feature = "std_collections_from_array", since = "1.56.0")]
1431// Note: as what is currently the most convenient built-in way to construct
1432// a HashMap, a simple usage of this function must not *require* the user
1433// to provide a type annotation in order to infer the third type parameter
1434// (the hasher parameter, conventionally "S").
1435// To that end, this impl is defined using RandomState as the concrete
1436// type of S, rather than being generic over `S: BuildHasher + Default`.
1437// It is expected that users who want to specify a hasher will manually use
1438// `with_capacity_and_hasher`.
1439// If type parameter defaults worked on impls, and if type parameter
1440// defaults could be mixed with const generics, then perhaps
1441// this could be generalized.
1442// See also the equivalent impl on HashSet.
1443impl<K, V, const N: usize> From<[(K, V); N]> for HashMap<K, V, RandomState>
1444where
1445    K: Eq + Hash,
1446{
1447    /// Converts a `[(K, V); N]` into a `HashMap<K, V>`.
1448    ///
1449    /// If any entries in the array have equal keys,
1450    /// all but one of the corresponding values will be dropped.
1451    ///
1452    /// # Examples
1453    ///
1454    /// ```
1455    /// use std::collections::HashMap;
1456    ///
1457    /// let map1 = HashMap::from([(1, 2), (3, 4)]);
1458    /// let map2: HashMap<_, _> = [(1, 2), (3, 4)].into();
1459    /// assert_eq!(map1, map2);
1460    /// ```
1461    fn from(arr: [(K, V); N]) -> Self {
1462        Self::from_iter(arr)
1463    }
1464}
1465
1466/// An iterator over the entries of a `HashMap`.
1467///
1468/// This `struct` is created by the [`iter`] method on [`HashMap`]. See its
1469/// documentation for more.
1470///
1471/// [`iter`]: HashMap::iter
1472///
1473/// # Example
1474///
1475/// ```
1476/// use std::collections::HashMap;
1477///
1478/// let map = HashMap::from([
1479///     ("a", 1),
1480/// ]);
1481/// let iter = map.iter();
1482/// ```
1483#[stable(feature = "rust1", since = "1.0.0")]
1484#[cfg_attr(not(test), rustc_diagnostic_item = "hashmap_iter_ty")]
1485pub struct Iter<'a, K: 'a, V: 'a> {
1486    base: base::Iter<'a, K, V>,
1487}
1488
1489// FIXME(#26925) Remove in favor of `#[derive(Clone)]`
1490#[stable(feature = "rust1", since = "1.0.0")]
1491impl<K, V> Clone for Iter<'_, K, V> {
1492    #[inline]
1493    fn clone(&self) -> Self {
1494        Iter { base: self.base.clone() }
1495    }
1496}
1497
1498#[stable(feature = "default_iters_hash", since = "1.83.0")]
1499impl<K, V> Default for Iter<'_, K, V> {
1500    #[inline]
1501    fn default() -> Self {
1502        Iter { base: Default::default() }
1503    }
1504}
1505
1506#[stable(feature = "std_debug", since = "1.16.0")]
1507impl<K: Debug, V: Debug> fmt::Debug for Iter<'_, K, V> {
1508    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1509        f.debug_list().entries(self.clone()).finish()
1510    }
1511}
1512
1513/// A mutable iterator over the entries of a `HashMap`.
1514///
1515/// This `struct` is created by the [`iter_mut`] method on [`HashMap`]. See its
1516/// documentation for more.
1517///
1518/// [`iter_mut`]: HashMap::iter_mut
1519///
1520/// # Example
1521///
1522/// ```
1523/// use std::collections::HashMap;
1524///
1525/// let mut map = HashMap::from([
1526///     ("a", 1),
1527/// ]);
1528/// let iter = map.iter_mut();
1529/// ```
1530#[stable(feature = "rust1", since = "1.0.0")]
1531#[cfg_attr(not(test), rustc_diagnostic_item = "hashmap_iter_mut_ty")]
1532pub struct IterMut<'a, K: 'a, V: 'a> {
1533    base: base::IterMut<'a, K, V>,
1534}
1535
1536impl<'a, K, V> IterMut<'a, K, V> {
1537    /// Returns an iterator of references over the remaining items.
1538    #[inline]
1539    pub(super) fn iter(&self) -> Iter<'_, K, V> {
1540        Iter { base: self.base.rustc_iter() }
1541    }
1542}
1543
1544#[stable(feature = "default_iters_hash", since = "1.83.0")]
1545impl<K, V> Default for IterMut<'_, K, V> {
1546    #[inline]
1547    fn default() -> Self {
1548        IterMut { base: Default::default() }
1549    }
1550}
1551
1552/// An owning iterator over the entries of a `HashMap`.
1553///
1554/// This `struct` is created by the [`into_iter`] method on [`HashMap`]
1555/// (provided by the [`IntoIterator`] trait). See its documentation for more.
1556///
1557/// [`into_iter`]: IntoIterator::into_iter
1558///
1559/// # Example
1560///
1561/// ```
1562/// use std::collections::HashMap;
1563///
1564/// let map = HashMap::from([
1565///     ("a", 1),
1566/// ]);
1567/// let iter = map.into_iter();
1568/// ```
1569#[stable(feature = "rust1", since = "1.0.0")]
1570pub struct IntoIter<K, V> {
1571    base: base::IntoIter<K, V>,
1572}
1573
1574impl<K, V> IntoIter<K, V> {
1575    /// Returns an iterator of references over the remaining items.
1576    #[inline]
1577    pub(super) fn iter(&self) -> Iter<'_, K, V> {
1578        Iter { base: self.base.rustc_iter() }
1579    }
1580}
1581
1582#[stable(feature = "default_iters_hash", since = "1.83.0")]
1583impl<K, V> Default for IntoIter<K, V> {
1584    #[inline]
1585    fn default() -> Self {
1586        IntoIter { base: Default::default() }
1587    }
1588}
1589
1590/// An iterator over the keys of a `HashMap`.
1591///
1592/// This `struct` is created by the [`keys`] method on [`HashMap`]. See its
1593/// documentation for more.
1594///
1595/// [`keys`]: HashMap::keys
1596///
1597/// # Example
1598///
1599/// ```
1600/// use std::collections::HashMap;
1601///
1602/// let map = HashMap::from([
1603///     ("a", 1),
1604/// ]);
1605/// let iter_keys = map.keys();
1606/// ```
1607#[stable(feature = "rust1", since = "1.0.0")]
1608#[cfg_attr(not(test), rustc_diagnostic_item = "hashmap_keys_ty")]
1609pub struct Keys<'a, K: 'a, V: 'a> {
1610    inner: Iter<'a, K, V>,
1611}
1612
1613// FIXME(#26925) Remove in favor of `#[derive(Clone)]`
1614#[stable(feature = "rust1", since = "1.0.0")]
1615impl<K, V> Clone for Keys<'_, K, V> {
1616    #[inline]
1617    fn clone(&self) -> Self {
1618        Keys { inner: self.inner.clone() }
1619    }
1620}
1621
1622#[stable(feature = "default_iters_hash", since = "1.83.0")]
1623impl<K, V> Default for Keys<'_, K, V> {
1624    #[inline]
1625    fn default() -> Self {
1626        Keys { inner: Default::default() }
1627    }
1628}
1629
1630#[stable(feature = "std_debug", since = "1.16.0")]
1631impl<K: Debug, V> fmt::Debug for Keys<'_, K, V> {
1632    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1633        f.debug_list().entries(self.clone()).finish()
1634    }
1635}
1636
1637/// An iterator over the values of a `HashMap`.
1638///
1639/// This `struct` is created by the [`values`] method on [`HashMap`]. See its
1640/// documentation for more.
1641///
1642/// [`values`]: HashMap::values
1643///
1644/// # Example
1645///
1646/// ```
1647/// use std::collections::HashMap;
1648///
1649/// let map = HashMap::from([
1650///     ("a", 1),
1651/// ]);
1652/// let iter_values = map.values();
1653/// ```
1654#[stable(feature = "rust1", since = "1.0.0")]
1655#[cfg_attr(not(test), rustc_diagnostic_item = "hashmap_values_ty")]
1656pub struct Values<'a, K: 'a, V: 'a> {
1657    inner: Iter<'a, K, V>,
1658}
1659
1660// FIXME(#26925) Remove in favor of `#[derive(Clone)]`
1661#[stable(feature = "rust1", since = "1.0.0")]
1662impl<K, V> Clone for Values<'_, K, V> {
1663    #[inline]
1664    fn clone(&self) -> Self {
1665        Values { inner: self.inner.clone() }
1666    }
1667}
1668
1669#[stable(feature = "default_iters_hash", since = "1.83.0")]
1670impl<K, V> Default for Values<'_, K, V> {
1671    #[inline]
1672    fn default() -> Self {
1673        Values { inner: Default::default() }
1674    }
1675}
1676
1677#[stable(feature = "std_debug", since = "1.16.0")]
1678impl<K, V: Debug> fmt::Debug for Values<'_, K, V> {
1679    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1680        f.debug_list().entries(self.clone()).finish()
1681    }
1682}
1683
1684/// A draining iterator over the entries of a `HashMap`.
1685///
1686/// This `struct` is created by the [`drain`] method on [`HashMap`]. See its
1687/// documentation for more.
1688///
1689/// [`drain`]: HashMap::drain
1690///
1691/// # Example
1692///
1693/// ```
1694/// use std::collections::HashMap;
1695///
1696/// let mut map = HashMap::from([
1697///     ("a", 1),
1698/// ]);
1699/// let iter = map.drain();
1700/// ```
1701#[stable(feature = "drain", since = "1.6.0")]
1702#[cfg_attr(not(test), rustc_diagnostic_item = "hashmap_drain_ty")]
1703pub struct Drain<'a, K: 'a, V: 'a> {
1704    base: base::Drain<'a, K, V>,
1705}
1706
1707impl<'a, K, V> Drain<'a, K, V> {
1708    /// Returns an iterator of references over the remaining items.
1709    #[inline]
1710    pub(super) fn iter(&self) -> Iter<'_, K, V> {
1711        Iter { base: self.base.rustc_iter() }
1712    }
1713}
1714
1715/// A draining, filtering iterator over the entries of a `HashMap`.
1716///
1717/// This `struct` is created by the [`extract_if`] method on [`HashMap`].
1718///
1719/// [`extract_if`]: HashMap::extract_if
1720///
1721/// # Example
1722///
1723/// ```
1724/// use std::collections::HashMap;
1725///
1726/// let mut map = HashMap::from([
1727///     ("a", 1),
1728/// ]);
1729/// let iter = map.extract_if(|_k, v| *v % 2 == 0);
1730/// ```
1731#[stable(feature = "hash_extract_if", since = "CURRENT_RUSTC_VERSION")]
1732#[must_use = "iterators are lazy and do nothing unless consumed"]
1733pub struct ExtractIf<'a, K, V, F>
1734where
1735    F: FnMut(&K, &mut V) -> bool,
1736{
1737    base: base::ExtractIf<'a, K, V, F>,
1738}
1739
1740/// A mutable iterator over the values of a `HashMap`.
1741///
1742/// This `struct` is created by the [`values_mut`] method on [`HashMap`]. See its
1743/// documentation for more.
1744///
1745/// [`values_mut`]: HashMap::values_mut
1746///
1747/// # Example
1748///
1749/// ```
1750/// use std::collections::HashMap;
1751///
1752/// let mut map = HashMap::from([
1753///     ("a", 1),
1754/// ]);
1755/// let iter_values = map.values_mut();
1756/// ```
1757#[stable(feature = "map_values_mut", since = "1.10.0")]
1758#[cfg_attr(not(test), rustc_diagnostic_item = "hashmap_values_mut_ty")]
1759pub struct ValuesMut<'a, K: 'a, V: 'a> {
1760    inner: IterMut<'a, K, V>,
1761}
1762
1763#[stable(feature = "default_iters_hash", since = "1.83.0")]
1764impl<K, V> Default for ValuesMut<'_, K, V> {
1765    #[inline]
1766    fn default() -> Self {
1767        ValuesMut { inner: Default::default() }
1768    }
1769}
1770
1771/// An owning iterator over the keys of a `HashMap`.
1772///
1773/// This `struct` is created by the [`into_keys`] method on [`HashMap`].
1774/// See its documentation for more.
1775///
1776/// [`into_keys`]: HashMap::into_keys
1777///
1778/// # Example
1779///
1780/// ```
1781/// use std::collections::HashMap;
1782///
1783/// let map = HashMap::from([
1784///     ("a", 1),
1785/// ]);
1786/// let iter_keys = map.into_keys();
1787/// ```
1788#[stable(feature = "map_into_keys_values", since = "1.54.0")]
1789pub struct IntoKeys<K, V> {
1790    inner: IntoIter<K, V>,
1791}
1792
1793#[stable(feature = "default_iters_hash", since = "1.83.0")]
1794impl<K, V> Default for IntoKeys<K, V> {
1795    #[inline]
1796    fn default() -> Self {
1797        IntoKeys { inner: Default::default() }
1798    }
1799}
1800
1801/// An owning iterator over the values of a `HashMap`.
1802///
1803/// This `struct` is created by the [`into_values`] method on [`HashMap`].
1804/// See its documentation for more.
1805///
1806/// [`into_values`]: HashMap::into_values
1807///
1808/// # Example
1809///
1810/// ```
1811/// use std::collections::HashMap;
1812///
1813/// let map = HashMap::from([
1814///     ("a", 1),
1815/// ]);
1816/// let iter_keys = map.into_values();
1817/// ```
1818#[stable(feature = "map_into_keys_values", since = "1.54.0")]
1819pub struct IntoValues<K, V> {
1820    inner: IntoIter<K, V>,
1821}
1822
1823#[stable(feature = "default_iters_hash", since = "1.83.0")]
1824impl<K, V> Default for IntoValues<K, V> {
1825    #[inline]
1826    fn default() -> Self {
1827        IntoValues { inner: Default::default() }
1828    }
1829}
1830
1831/// A builder for computing where in a HashMap a key-value pair would be stored.
1832///
1833/// See the [`HashMap::raw_entry_mut`] docs for usage examples.
1834#[unstable(feature = "hash_raw_entry", issue = "56167")]
1835pub struct RawEntryBuilderMut<'a, K: 'a, V: 'a, S: 'a> {
1836    map: &'a mut HashMap<K, V, S>,
1837}
1838
1839/// A view into a single entry in a map, which may either be vacant or occupied.
1840///
1841/// This is a lower-level version of [`Entry`].
1842///
1843/// This `enum` is constructed through the [`raw_entry_mut`] method on [`HashMap`],
1844/// then calling one of the methods of that [`RawEntryBuilderMut`].
1845///
1846/// [`raw_entry_mut`]: HashMap::raw_entry_mut
1847#[unstable(feature = "hash_raw_entry", issue = "56167")]
1848pub enum RawEntryMut<'a, K: 'a, V: 'a, S: 'a> {
1849    /// An occupied entry.
1850    Occupied(RawOccupiedEntryMut<'a, K, V, S>),
1851    /// A vacant entry.
1852    Vacant(RawVacantEntryMut<'a, K, V, S>),
1853}
1854
1855/// A view into an occupied entry in a `HashMap`.
1856/// It is part of the [`RawEntryMut`] enum.
1857#[unstable(feature = "hash_raw_entry", issue = "56167")]
1858pub struct RawOccupiedEntryMut<'a, K: 'a, V: 'a, S: 'a> {
1859    base: base::RawOccupiedEntryMut<'a, K, V, S>,
1860}
1861
1862/// A view into a vacant entry in a `HashMap`.
1863/// It is part of the [`RawEntryMut`] enum.
1864#[unstable(feature = "hash_raw_entry", issue = "56167")]
1865pub struct RawVacantEntryMut<'a, K: 'a, V: 'a, S: 'a> {
1866    base: base::RawVacantEntryMut<'a, K, V, S>,
1867}
1868
1869/// A builder for computing where in a HashMap a key-value pair would be stored.
1870///
1871/// See the [`HashMap::raw_entry`] docs for usage examples.
1872#[unstable(feature = "hash_raw_entry", issue = "56167")]
1873pub struct RawEntryBuilder<'a, K: 'a, V: 'a, S: 'a> {
1874    map: &'a HashMap<K, V, S>,
1875}
1876
1877impl<'a, K, V, S> RawEntryBuilderMut<'a, K, V, S>
1878where
1879    S: BuildHasher,
1880{
1881    /// Creates a `RawEntryMut` from the given key.
1882    #[inline]
1883    #[unstable(feature = "hash_raw_entry", issue = "56167")]
1884    pub fn from_key<Q: ?Sized>(self, k: &Q) -> RawEntryMut<'a, K, V, S>
1885    where
1886        K: Borrow<Q>,
1887        Q: Hash + Eq,
1888    {
1889        map_raw_entry(self.map.base.raw_entry_mut().from_key(k))
1890    }
1891
1892    /// Creates a `RawEntryMut` from the given key and its hash.
1893    #[inline]
1894    #[unstable(feature = "hash_raw_entry", issue = "56167")]
1895    pub fn from_key_hashed_nocheck<Q: ?Sized>(self, hash: u64, k: &Q) -> RawEntryMut<'a, K, V, S>
1896    where
1897        K: Borrow<Q>,
1898        Q: Eq,
1899    {
1900        map_raw_entry(self.map.base.raw_entry_mut().from_key_hashed_nocheck(hash, k))
1901    }
1902
1903    /// Creates a `RawEntryMut` from the given hash.
1904    #[inline]
1905    #[unstable(feature = "hash_raw_entry", issue = "56167")]
1906    pub fn from_hash<F>(self, hash: u64, is_match: F) -> RawEntryMut<'a, K, V, S>
1907    where
1908        for<'b> F: FnMut(&'b K) -> bool,
1909    {
1910        map_raw_entry(self.map.base.raw_entry_mut().from_hash(hash, is_match))
1911    }
1912}
1913
1914impl<'a, K, V, S> RawEntryBuilder<'a, K, V, S>
1915where
1916    S: BuildHasher,
1917{
1918    /// Access an entry by key.
1919    #[inline]
1920    #[unstable(feature = "hash_raw_entry", issue = "56167")]
1921    pub fn from_key<Q: ?Sized>(self, k: &Q) -> Option<(&'a K, &'a V)>
1922    where
1923        K: Borrow<Q>,
1924        Q: Hash + Eq,
1925    {
1926        self.map.base.raw_entry().from_key(k)
1927    }
1928
1929    /// Access an entry by a key and its hash.
1930    #[inline]
1931    #[unstable(feature = "hash_raw_entry", issue = "56167")]
1932    pub fn from_key_hashed_nocheck<Q: ?Sized>(self, hash: u64, k: &Q) -> Option<(&'a K, &'a V)>
1933    where
1934        K: Borrow<Q>,
1935        Q: Hash + Eq,
1936    {
1937        self.map.base.raw_entry().from_key_hashed_nocheck(hash, k)
1938    }
1939
1940    /// Access an entry by hash.
1941    #[inline]
1942    #[unstable(feature = "hash_raw_entry", issue = "56167")]
1943    pub fn from_hash<F>(self, hash: u64, is_match: F) -> Option<(&'a K, &'a V)>
1944    where
1945        F: FnMut(&K) -> bool,
1946    {
1947        self.map.base.raw_entry().from_hash(hash, is_match)
1948    }
1949}
1950
1951impl<'a, K, V, S> RawEntryMut<'a, K, V, S> {
1952    /// Ensures a value is in the entry by inserting the default if empty, and returns
1953    /// mutable references to the key and value in the entry.
1954    ///
1955    /// # Examples
1956    ///
1957    /// ```
1958    /// #![feature(hash_raw_entry)]
1959    /// use std::collections::HashMap;
1960    ///
1961    /// let mut map: HashMap<&str, u32> = HashMap::new();
1962    ///
1963    /// map.raw_entry_mut().from_key("poneyland").or_insert("poneyland", 3);
1964    /// assert_eq!(map["poneyland"], 3);
1965    ///
1966    /// *map.raw_entry_mut().from_key("poneyland").or_insert("poneyland", 10).1 *= 2;
1967    /// assert_eq!(map["poneyland"], 6);
1968    /// ```
1969    #[inline]
1970    #[unstable(feature = "hash_raw_entry", issue = "56167")]
1971    pub fn or_insert(self, default_key: K, default_val: V) -> (&'a mut K, &'a mut V)
1972    where
1973        K: Hash,
1974        S: BuildHasher,
1975    {
1976        match self {
1977            RawEntryMut::Occupied(entry) => entry.into_key_value(),
1978            RawEntryMut::Vacant(entry) => entry.insert(default_key, default_val),
1979        }
1980    }
1981
1982    /// Ensures a value is in the entry by inserting the result of the default function if empty,
1983    /// and returns mutable references to the key and value in the entry.
1984    ///
1985    /// # Examples
1986    ///
1987    /// ```
1988    /// #![feature(hash_raw_entry)]
1989    /// use std::collections::HashMap;
1990    ///
1991    /// let mut map: HashMap<&str, String> = HashMap::new();
1992    ///
1993    /// map.raw_entry_mut().from_key("poneyland").or_insert_with(|| {
1994    ///     ("poneyland", "hoho".to_string())
1995    /// });
1996    ///
1997    /// assert_eq!(map["poneyland"], "hoho".to_string());
1998    /// ```
1999    #[inline]
2000    #[unstable(feature = "hash_raw_entry", issue = "56167")]
2001    pub fn or_insert_with<F>(self, default: F) -> (&'a mut K, &'a mut V)
2002    where
2003        F: FnOnce() -> (K, V),
2004        K: Hash,
2005        S: BuildHasher,
2006    {
2007        match self {
2008            RawEntryMut::Occupied(entry) => entry.into_key_value(),
2009            RawEntryMut::Vacant(entry) => {
2010                let (k, v) = default();
2011                entry.insert(k, v)
2012            }
2013        }
2014    }
2015
2016    /// Provides in-place mutable access to an occupied entry before any
2017    /// potential inserts into the map.
2018    ///
2019    /// # Examples
2020    ///
2021    /// ```
2022    /// #![feature(hash_raw_entry)]
2023    /// use std::collections::HashMap;
2024    ///
2025    /// let mut map: HashMap<&str, u32> = HashMap::new();
2026    ///
2027    /// map.raw_entry_mut()
2028    ///    .from_key("poneyland")
2029    ///    .and_modify(|_k, v| { *v += 1 })
2030    ///    .or_insert("poneyland", 42);
2031    /// assert_eq!(map["poneyland"], 42);
2032    ///
2033    /// map.raw_entry_mut()
2034    ///    .from_key("poneyland")
2035    ///    .and_modify(|_k, v| { *v += 1 })
2036    ///    .or_insert("poneyland", 0);
2037    /// assert_eq!(map["poneyland"], 43);
2038    /// ```
2039    #[inline]
2040    #[unstable(feature = "hash_raw_entry", issue = "56167")]
2041    pub fn and_modify<F>(self, f: F) -> Self
2042    where
2043        F: FnOnce(&mut K, &mut V),
2044    {
2045        match self {
2046            RawEntryMut::Occupied(mut entry) => {
2047                {
2048                    let (k, v) = entry.get_key_value_mut();
2049                    f(k, v);
2050                }
2051                RawEntryMut::Occupied(entry)
2052            }
2053            RawEntryMut::Vacant(entry) => RawEntryMut::Vacant(entry),
2054        }
2055    }
2056}
2057
2058impl<'a, K, V, S> RawOccupiedEntryMut<'a, K, V, S> {
2059    /// Gets a reference to the key in the entry.
2060    #[inline]
2061    #[must_use]
2062    #[unstable(feature = "hash_raw_entry", issue = "56167")]
2063    pub fn key(&self) -> &K {
2064        self.base.key()
2065    }
2066
2067    /// Gets a mutable reference to the key in the entry.
2068    #[inline]
2069    #[must_use]
2070    #[unstable(feature = "hash_raw_entry", issue = "56167")]
2071    pub fn key_mut(&mut self) -> &mut K {
2072        self.base.key_mut()
2073    }
2074
2075    /// Converts the entry into a mutable reference to the key in the entry
2076    /// with a lifetime bound to the map itself.
2077    #[inline]
2078    #[must_use = "`self` will be dropped if the result is not used"]
2079    #[unstable(feature = "hash_raw_entry", issue = "56167")]
2080    pub fn into_key(self) -> &'a mut K {
2081        self.base.into_key()
2082    }
2083
2084    /// Gets a reference to the value in the entry.
2085    #[inline]
2086    #[must_use]
2087    #[unstable(feature = "hash_raw_entry", issue = "56167")]
2088    pub fn get(&self) -> &V {
2089        self.base.get()
2090    }
2091
2092    /// Converts the `OccupiedEntry` into a mutable reference to the value in the entry
2093    /// with a lifetime bound to the map itself.
2094    #[inline]
2095    #[must_use = "`self` will be dropped if the result is not used"]
2096    #[unstable(feature = "hash_raw_entry", issue = "56167")]
2097    pub fn into_mut(self) -> &'a mut V {
2098        self.base.into_mut()
2099    }
2100
2101    /// Gets a mutable reference to the value in the entry.
2102    #[inline]
2103    #[must_use]
2104    #[unstable(feature = "hash_raw_entry", issue = "56167")]
2105    pub fn get_mut(&mut self) -> &mut V {
2106        self.base.get_mut()
2107    }
2108
2109    /// Gets a reference to the key and value in the entry.
2110    #[inline]
2111    #[must_use]
2112    #[unstable(feature = "hash_raw_entry", issue = "56167")]
2113    pub fn get_key_value(&mut self) -> (&K, &V) {
2114        self.base.get_key_value()
2115    }
2116
2117    /// Gets a mutable reference to the key and value in the entry.
2118    #[inline]
2119    #[unstable(feature = "hash_raw_entry", issue = "56167")]
2120    pub fn get_key_value_mut(&mut self) -> (&mut K, &mut V) {
2121        self.base.get_key_value_mut()
2122    }
2123
2124    /// Converts the `OccupiedEntry` into a mutable reference to the key and value in the entry
2125    /// with a lifetime bound to the map itself.
2126    #[inline]
2127    #[must_use = "`self` will be dropped if the result is not used"]
2128    #[unstable(feature = "hash_raw_entry", issue = "56167")]
2129    pub fn into_key_value(self) -> (&'a mut K, &'a mut V) {
2130        self.base.into_key_value()
2131    }
2132
2133    /// Sets the value of the entry, and returns the entry's old value.
2134    #[inline]
2135    #[unstable(feature = "hash_raw_entry", issue = "56167")]
2136    pub fn insert(&mut self, value: V) -> V {
2137        self.base.insert(value)
2138    }
2139
2140    /// Sets the value of the entry, and returns the entry's old value.
2141    #[inline]
2142    #[unstable(feature = "hash_raw_entry", issue = "56167")]
2143    pub fn insert_key(&mut self, key: K) -> K {
2144        self.base.insert_key(key)
2145    }
2146
2147    /// Takes the value out of the entry, and returns it.
2148    #[inline]
2149    #[unstable(feature = "hash_raw_entry", issue = "56167")]
2150    pub fn remove(self) -> V {
2151        self.base.remove()
2152    }
2153
2154    /// Take the ownership of the key and value from the map.
2155    #[inline]
2156    #[unstable(feature = "hash_raw_entry", issue = "56167")]
2157    pub fn remove_entry(self) -> (K, V) {
2158        self.base.remove_entry()
2159    }
2160}
2161
2162impl<'a, K, V, S> RawVacantEntryMut<'a, K, V, S> {
2163    /// Sets the value of the entry with the `VacantEntry`'s key,
2164    /// and returns a mutable reference to it.
2165    #[inline]
2166    #[unstable(feature = "hash_raw_entry", issue = "56167")]
2167    pub fn insert(self, key: K, value: V) -> (&'a mut K, &'a mut V)
2168    where
2169        K: Hash,
2170        S: BuildHasher,
2171    {
2172        self.base.insert(key, value)
2173    }
2174
2175    /// Sets the value of the entry with the VacantEntry's key,
2176    /// and returns a mutable reference to it.
2177    #[inline]
2178    #[unstable(feature = "hash_raw_entry", issue = "56167")]
2179    pub fn insert_hashed_nocheck(self, hash: u64, key: K, value: V) -> (&'a mut K, &'a mut V)
2180    where
2181        K: Hash,
2182        S: BuildHasher,
2183    {
2184        self.base.insert_hashed_nocheck(hash, key, value)
2185    }
2186}
2187
2188#[unstable(feature = "hash_raw_entry", issue = "56167")]
2189impl<K, V, S> Debug for RawEntryBuilderMut<'_, K, V, S> {
2190    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2191        f.debug_struct("RawEntryBuilder").finish_non_exhaustive()
2192    }
2193}
2194
2195#[unstable(feature = "hash_raw_entry", issue = "56167")]
2196impl<K: Debug, V: Debug, S> Debug for RawEntryMut<'_, K, V, S> {
2197    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2198        match *self {
2199            RawEntryMut::Vacant(ref v) => f.debug_tuple("RawEntry").field(v).finish(),
2200            RawEntryMut::Occupied(ref o) => f.debug_tuple("RawEntry").field(o).finish(),
2201        }
2202    }
2203}
2204
2205#[unstable(feature = "hash_raw_entry", issue = "56167")]
2206impl<K: Debug, V: Debug, S> Debug for RawOccupiedEntryMut<'_, K, V, S> {
2207    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2208        f.debug_struct("RawOccupiedEntryMut")
2209            .field("key", self.key())
2210            .field("value", self.get())
2211            .finish_non_exhaustive()
2212    }
2213}
2214
2215#[unstable(feature = "hash_raw_entry", issue = "56167")]
2216impl<K, V, S> Debug for RawVacantEntryMut<'_, K, V, S> {
2217    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2218        f.debug_struct("RawVacantEntryMut").finish_non_exhaustive()
2219    }
2220}
2221
2222#[unstable(feature = "hash_raw_entry", issue = "56167")]
2223impl<K, V, S> Debug for RawEntryBuilder<'_, K, V, S> {
2224    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2225        f.debug_struct("RawEntryBuilder").finish_non_exhaustive()
2226    }
2227}
2228
2229/// A view into a single entry in a map, which may either be vacant or occupied.
2230///
2231/// This `enum` is constructed from the [`entry`] method on [`HashMap`].
2232///
2233/// [`entry`]: HashMap::entry
2234#[stable(feature = "rust1", since = "1.0.0")]
2235#[cfg_attr(not(test), rustc_diagnostic_item = "HashMapEntry")]
2236pub enum Entry<'a, K: 'a, V: 'a> {
2237    /// An occupied entry.
2238    #[stable(feature = "rust1", since = "1.0.0")]
2239    Occupied(#[stable(feature = "rust1", since = "1.0.0")] OccupiedEntry<'a, K, V>),
2240
2241    /// A vacant entry.
2242    #[stable(feature = "rust1", since = "1.0.0")]
2243    Vacant(#[stable(feature = "rust1", since = "1.0.0")] VacantEntry<'a, K, V>),
2244}
2245
2246#[stable(feature = "debug_hash_map", since = "1.12.0")]
2247impl<K: Debug, V: Debug> Debug for Entry<'_, K, V> {
2248    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2249        match *self {
2250            Vacant(ref v) => f.debug_tuple("Entry").field(v).finish(),
2251            Occupied(ref o) => f.debug_tuple("Entry").field(o).finish(),
2252        }
2253    }
2254}
2255
2256/// A view into an occupied entry in a `HashMap`.
2257/// It is part of the [`Entry`] enum.
2258#[stable(feature = "rust1", since = "1.0.0")]
2259pub struct OccupiedEntry<'a, K: 'a, V: 'a> {
2260    base: base::RustcOccupiedEntry<'a, K, V>,
2261}
2262
2263#[stable(feature = "debug_hash_map", since = "1.12.0")]
2264impl<K: Debug, V: Debug> Debug for OccupiedEntry<'_, K, V> {
2265    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2266        f.debug_struct("OccupiedEntry")
2267            .field("key", self.key())
2268            .field("value", self.get())
2269            .finish_non_exhaustive()
2270    }
2271}
2272
2273/// A view into a vacant entry in a `HashMap`.
2274/// It is part of the [`Entry`] enum.
2275#[stable(feature = "rust1", since = "1.0.0")]
2276pub struct VacantEntry<'a, K: 'a, V: 'a> {
2277    base: base::RustcVacantEntry<'a, K, V>,
2278}
2279
2280#[stable(feature = "debug_hash_map", since = "1.12.0")]
2281impl<K: Debug, V> Debug for VacantEntry<'_, K, V> {
2282    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2283        f.debug_tuple("VacantEntry").field(self.key()).finish()
2284    }
2285}
2286
2287/// The error returned by [`try_insert`](HashMap::try_insert) when the key already exists.
2288///
2289/// Contains the occupied entry, and the value that was not inserted.
2290#[unstable(feature = "map_try_insert", issue = "82766")]
2291pub struct OccupiedError<'a, K: 'a, V: 'a> {
2292    /// The entry in the map that was already occupied.
2293    pub entry: OccupiedEntry<'a, K, V>,
2294    /// The value which was not inserted, because the entry was already occupied.
2295    pub value: V,
2296}
2297
2298#[unstable(feature = "map_try_insert", issue = "82766")]
2299impl<K: Debug, V: Debug> Debug for OccupiedError<'_, K, V> {
2300    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2301        f.debug_struct("OccupiedError")
2302            .field("key", self.entry.key())
2303            .field("old_value", self.entry.get())
2304            .field("new_value", &self.value)
2305            .finish_non_exhaustive()
2306    }
2307}
2308
2309#[unstable(feature = "map_try_insert", issue = "82766")]
2310impl<'a, K: Debug, V: Debug> fmt::Display for OccupiedError<'a, K, V> {
2311    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2312        write!(
2313            f,
2314            "failed to insert {:?}, key {:?} already exists with value {:?}",
2315            self.value,
2316            self.entry.key(),
2317            self.entry.get(),
2318        )
2319    }
2320}
2321
2322#[unstable(feature = "map_try_insert", issue = "82766")]
2323impl<'a, K: fmt::Debug, V: fmt::Debug> Error for OccupiedError<'a, K, V> {
2324    #[allow(deprecated)]
2325    fn description(&self) -> &str {
2326        "key already exists"
2327    }
2328}
2329
2330#[stable(feature = "rust1", since = "1.0.0")]
2331impl<'a, K, V, S> IntoIterator for &'a HashMap<K, V, S> {
2332    type Item = (&'a K, &'a V);
2333    type IntoIter = Iter<'a, K, V>;
2334
2335    #[inline]
2336    #[rustc_lint_query_instability]
2337    fn into_iter(self) -> Iter<'a, K, V> {
2338        self.iter()
2339    }
2340}
2341
2342#[stable(feature = "rust1", since = "1.0.0")]
2343impl<'a, K, V, S> IntoIterator for &'a mut HashMap<K, V, S> {
2344    type Item = (&'a K, &'a mut V);
2345    type IntoIter = IterMut<'a, K, V>;
2346
2347    #[inline]
2348    #[rustc_lint_query_instability]
2349    fn into_iter(self) -> IterMut<'a, K, V> {
2350        self.iter_mut()
2351    }
2352}
2353
2354#[stable(feature = "rust1", since = "1.0.0")]
2355impl<K, V, S> IntoIterator for HashMap<K, V, S> {
2356    type Item = (K, V);
2357    type IntoIter = IntoIter<K, V>;
2358
2359    /// Creates a consuming iterator, that is, one that moves each key-value
2360    /// pair out of the map in arbitrary order. The map cannot be used after
2361    /// calling this.
2362    ///
2363    /// # Examples
2364    ///
2365    /// ```
2366    /// use std::collections::HashMap;
2367    ///
2368    /// let map = HashMap::from([
2369    ///     ("a", 1),
2370    ///     ("b", 2),
2371    ///     ("c", 3),
2372    /// ]);
2373    ///
2374    /// // Not possible with .iter()
2375    /// let vec: Vec<(&str, i32)> = map.into_iter().collect();
2376    /// ```
2377    #[inline]
2378    #[rustc_lint_query_instability]
2379    fn into_iter(self) -> IntoIter<K, V> {
2380        IntoIter { base: self.base.into_iter() }
2381    }
2382}
2383
2384#[stable(feature = "rust1", since = "1.0.0")]
2385impl<'a, K, V> Iterator for Iter<'a, K, V> {
2386    type Item = (&'a K, &'a V);
2387
2388    #[inline]
2389    fn next(&mut self) -> Option<(&'a K, &'a V)> {
2390        self.base.next()
2391    }
2392    #[inline]
2393    fn size_hint(&self) -> (usize, Option<usize>) {
2394        self.base.size_hint()
2395    }
2396    #[inline]
2397    fn count(self) -> usize {
2398        self.base.len()
2399    }
2400    #[inline]
2401    fn fold<B, F>(self, init: B, f: F) -> B
2402    where
2403        Self: Sized,
2404        F: FnMut(B, Self::Item) -> B,
2405    {
2406        self.base.fold(init, f)
2407    }
2408}
2409#[stable(feature = "rust1", since = "1.0.0")]
2410impl<K, V> ExactSizeIterator for Iter<'_, K, V> {
2411    #[inline]
2412    fn len(&self) -> usize {
2413        self.base.len()
2414    }
2415}
2416
2417#[stable(feature = "fused", since = "1.26.0")]
2418impl<K, V> FusedIterator for Iter<'_, K, V> {}
2419
2420#[stable(feature = "rust1", since = "1.0.0")]
2421impl<'a, K, V> Iterator for IterMut<'a, K, V> {
2422    type Item = (&'a K, &'a mut V);
2423
2424    #[inline]
2425    fn next(&mut self) -> Option<(&'a K, &'a mut V)> {
2426        self.base.next()
2427    }
2428    #[inline]
2429    fn size_hint(&self) -> (usize, Option<usize>) {
2430        self.base.size_hint()
2431    }
2432    #[inline]
2433    fn count(self) -> usize {
2434        self.base.len()
2435    }
2436    #[inline]
2437    fn fold<B, F>(self, init: B, f: F) -> B
2438    where
2439        Self: Sized,
2440        F: FnMut(B, Self::Item) -> B,
2441    {
2442        self.base.fold(init, f)
2443    }
2444}
2445#[stable(feature = "rust1", since = "1.0.0")]
2446impl<K, V> ExactSizeIterator for IterMut<'_, K, V> {
2447    #[inline]
2448    fn len(&self) -> usize {
2449        self.base.len()
2450    }
2451}
2452#[stable(feature = "fused", since = "1.26.0")]
2453impl<K, V> FusedIterator for IterMut<'_, K, V> {}
2454
2455#[stable(feature = "std_debug", since = "1.16.0")]
2456impl<K, V> fmt::Debug for IterMut<'_, K, V>
2457where
2458    K: fmt::Debug,
2459    V: fmt::Debug,
2460{
2461    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2462        f.debug_list().entries(self.iter()).finish()
2463    }
2464}
2465
2466#[stable(feature = "rust1", since = "1.0.0")]
2467impl<K, V> Iterator for IntoIter<K, V> {
2468    type Item = (K, V);
2469
2470    #[inline]
2471    fn next(&mut self) -> Option<(K, V)> {
2472        self.base.next()
2473    }
2474    #[inline]
2475    fn size_hint(&self) -> (usize, Option<usize>) {
2476        self.base.size_hint()
2477    }
2478    #[inline]
2479    fn count(self) -> usize {
2480        self.base.len()
2481    }
2482    #[inline]
2483    fn fold<B, F>(self, init: B, f: F) -> B
2484    where
2485        Self: Sized,
2486        F: FnMut(B, Self::Item) -> B,
2487    {
2488        self.base.fold(init, f)
2489    }
2490}
2491#[stable(feature = "rust1", since = "1.0.0")]
2492impl<K, V> ExactSizeIterator for IntoIter<K, V> {
2493    #[inline]
2494    fn len(&self) -> usize {
2495        self.base.len()
2496    }
2497}
2498#[stable(feature = "fused", since = "1.26.0")]
2499impl<K, V> FusedIterator for IntoIter<K, V> {}
2500
2501#[stable(feature = "std_debug", since = "1.16.0")]
2502impl<K: Debug, V: Debug> fmt::Debug for IntoIter<K, V> {
2503    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2504        f.debug_list().entries(self.iter()).finish()
2505    }
2506}
2507
2508#[stable(feature = "rust1", since = "1.0.0")]
2509impl<'a, K, V> Iterator for Keys<'a, K, V> {
2510    type Item = &'a K;
2511
2512    #[inline]
2513    fn next(&mut self) -> Option<&'a K> {
2514        self.inner.next().map(|(k, _)| k)
2515    }
2516    #[inline]
2517    fn size_hint(&self) -> (usize, Option<usize>) {
2518        self.inner.size_hint()
2519    }
2520    #[inline]
2521    fn count(self) -> usize {
2522        self.inner.len()
2523    }
2524    #[inline]
2525    fn fold<B, F>(self, init: B, mut f: F) -> B
2526    where
2527        Self: Sized,
2528        F: FnMut(B, Self::Item) -> B,
2529    {
2530        self.inner.fold(init, |acc, (k, _)| f(acc, k))
2531    }
2532}
2533#[stable(feature = "rust1", since = "1.0.0")]
2534impl<K, V> ExactSizeIterator for Keys<'_, K, V> {
2535    #[inline]
2536    fn len(&self) -> usize {
2537        self.inner.len()
2538    }
2539}
2540#[stable(feature = "fused", since = "1.26.0")]
2541impl<K, V> FusedIterator for Keys<'_, K, V> {}
2542
2543#[stable(feature = "rust1", since = "1.0.0")]
2544impl<'a, K, V> Iterator for Values<'a, K, V> {
2545    type Item = &'a V;
2546
2547    #[inline]
2548    fn next(&mut self) -> Option<&'a V> {
2549        self.inner.next().map(|(_, v)| v)
2550    }
2551    #[inline]
2552    fn size_hint(&self) -> (usize, Option<usize>) {
2553        self.inner.size_hint()
2554    }
2555    #[inline]
2556    fn count(self) -> usize {
2557        self.inner.len()
2558    }
2559    #[inline]
2560    fn fold<B, F>(self, init: B, mut f: F) -> B
2561    where
2562        Self: Sized,
2563        F: FnMut(B, Self::Item) -> B,
2564    {
2565        self.inner.fold(init, |acc, (_, v)| f(acc, v))
2566    }
2567}
2568#[stable(feature = "rust1", since = "1.0.0")]
2569impl<K, V> ExactSizeIterator for Values<'_, K, V> {
2570    #[inline]
2571    fn len(&self) -> usize {
2572        self.inner.len()
2573    }
2574}
2575#[stable(feature = "fused", since = "1.26.0")]
2576impl<K, V> FusedIterator for Values<'_, K, V> {}
2577
2578#[stable(feature = "map_values_mut", since = "1.10.0")]
2579impl<'a, K, V> Iterator for ValuesMut<'a, K, V> {
2580    type Item = &'a mut V;
2581
2582    #[inline]
2583    fn next(&mut self) -> Option<&'a mut V> {
2584        self.inner.next().map(|(_, v)| v)
2585    }
2586    #[inline]
2587    fn size_hint(&self) -> (usize, Option<usize>) {
2588        self.inner.size_hint()
2589    }
2590    #[inline]
2591    fn count(self) -> usize {
2592        self.inner.len()
2593    }
2594    #[inline]
2595    fn fold<B, F>(self, init: B, mut f: F) -> B
2596    where
2597        Self: Sized,
2598        F: FnMut(B, Self::Item) -> B,
2599    {
2600        self.inner.fold(init, |acc, (_, v)| f(acc, v))
2601    }
2602}
2603#[stable(feature = "map_values_mut", since = "1.10.0")]
2604impl<K, V> ExactSizeIterator for ValuesMut<'_, K, V> {
2605    #[inline]
2606    fn len(&self) -> usize {
2607        self.inner.len()
2608    }
2609}
2610#[stable(feature = "fused", since = "1.26.0")]
2611impl<K, V> FusedIterator for ValuesMut<'_, K, V> {}
2612
2613#[stable(feature = "std_debug", since = "1.16.0")]
2614impl<K, V: fmt::Debug> fmt::Debug for ValuesMut<'_, K, V> {
2615    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2616        f.debug_list().entries(self.inner.iter().map(|(_, val)| val)).finish()
2617    }
2618}
2619
2620#[stable(feature = "map_into_keys_values", since = "1.54.0")]
2621impl<K, V> Iterator for IntoKeys<K, V> {
2622    type Item = K;
2623
2624    #[inline]
2625    fn next(&mut self) -> Option<K> {
2626        self.inner.next().map(|(k, _)| k)
2627    }
2628    #[inline]
2629    fn size_hint(&self) -> (usize, Option<usize>) {
2630        self.inner.size_hint()
2631    }
2632    #[inline]
2633    fn count(self) -> usize {
2634        self.inner.len()
2635    }
2636    #[inline]
2637    fn fold<B, F>(self, init: B, mut f: F) -> B
2638    where
2639        Self: Sized,
2640        F: FnMut(B, Self::Item) -> B,
2641    {
2642        self.inner.fold(init, |acc, (k, _)| f(acc, k))
2643    }
2644}
2645#[stable(feature = "map_into_keys_values", since = "1.54.0")]
2646impl<K, V> ExactSizeIterator for IntoKeys<K, V> {
2647    #[inline]
2648    fn len(&self) -> usize {
2649        self.inner.len()
2650    }
2651}
2652#[stable(feature = "map_into_keys_values", since = "1.54.0")]
2653impl<K, V> FusedIterator for IntoKeys<K, V> {}
2654
2655#[stable(feature = "map_into_keys_values", since = "1.54.0")]
2656impl<K: Debug, V> fmt::Debug for IntoKeys<K, V> {
2657    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2658        f.debug_list().entries(self.inner.iter().map(|(k, _)| k)).finish()
2659    }
2660}
2661
2662#[stable(feature = "map_into_keys_values", since = "1.54.0")]
2663impl<K, V> Iterator for IntoValues<K, V> {
2664    type Item = V;
2665
2666    #[inline]
2667    fn next(&mut self) -> Option<V> {
2668        self.inner.next().map(|(_, v)| v)
2669    }
2670    #[inline]
2671    fn size_hint(&self) -> (usize, Option<usize>) {
2672        self.inner.size_hint()
2673    }
2674    #[inline]
2675    fn count(self) -> usize {
2676        self.inner.len()
2677    }
2678    #[inline]
2679    fn fold<B, F>(self, init: B, mut f: F) -> B
2680    where
2681        Self: Sized,
2682        F: FnMut(B, Self::Item) -> B,
2683    {
2684        self.inner.fold(init, |acc, (_, v)| f(acc, v))
2685    }
2686}
2687#[stable(feature = "map_into_keys_values", since = "1.54.0")]
2688impl<K, V> ExactSizeIterator for IntoValues<K, V> {
2689    #[inline]
2690    fn len(&self) -> usize {
2691        self.inner.len()
2692    }
2693}
2694#[stable(feature = "map_into_keys_values", since = "1.54.0")]
2695impl<K, V> FusedIterator for IntoValues<K, V> {}
2696
2697#[stable(feature = "map_into_keys_values", since = "1.54.0")]
2698impl<K, V: Debug> fmt::Debug for IntoValues<K, V> {
2699    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2700        f.debug_list().entries(self.inner.iter().map(|(_, v)| v)).finish()
2701    }
2702}
2703
2704#[stable(feature = "drain", since = "1.6.0")]
2705impl<'a, K, V> Iterator for Drain<'a, K, V> {
2706    type Item = (K, V);
2707
2708    #[inline]
2709    fn next(&mut self) -> Option<(K, V)> {
2710        self.base.next()
2711    }
2712    #[inline]
2713    fn size_hint(&self) -> (usize, Option<usize>) {
2714        self.base.size_hint()
2715    }
2716    #[inline]
2717    fn fold<B, F>(self, init: B, f: F) -> B
2718    where
2719        Self: Sized,
2720        F: FnMut(B, Self::Item) -> B,
2721    {
2722        self.base.fold(init, f)
2723    }
2724}
2725#[stable(feature = "drain", since = "1.6.0")]
2726impl<K, V> ExactSizeIterator for Drain<'_, K, V> {
2727    #[inline]
2728    fn len(&self) -> usize {
2729        self.base.len()
2730    }
2731}
2732#[stable(feature = "fused", since = "1.26.0")]
2733impl<K, V> FusedIterator for Drain<'_, K, V> {}
2734
2735#[stable(feature = "std_debug", since = "1.16.0")]
2736impl<K, V> fmt::Debug for Drain<'_, K, V>
2737where
2738    K: fmt::Debug,
2739    V: fmt::Debug,
2740{
2741    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2742        f.debug_list().entries(self.iter()).finish()
2743    }
2744}
2745
2746#[stable(feature = "hash_extract_if", since = "CURRENT_RUSTC_VERSION")]
2747impl<K, V, F> Iterator for ExtractIf<'_, K, V, F>
2748where
2749    F: FnMut(&K, &mut V) -> bool,
2750{
2751    type Item = (K, V);
2752
2753    #[inline]
2754    fn next(&mut self) -> Option<(K, V)> {
2755        self.base.next()
2756    }
2757    #[inline]
2758    fn size_hint(&self) -> (usize, Option<usize>) {
2759        self.base.size_hint()
2760    }
2761}
2762
2763#[stable(feature = "hash_extract_if", since = "CURRENT_RUSTC_VERSION")]
2764impl<K, V, F> FusedIterator for ExtractIf<'_, K, V, F> where F: FnMut(&K, &mut V) -> bool {}
2765
2766#[stable(feature = "hash_extract_if", since = "CURRENT_RUSTC_VERSION")]
2767impl<'a, K, V, F> fmt::Debug for ExtractIf<'a, K, V, F>
2768where
2769    F: FnMut(&K, &mut V) -> bool,
2770{
2771    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
2772        f.debug_struct("ExtractIf").finish_non_exhaustive()
2773    }
2774}
2775
2776impl<'a, K, V> Entry<'a, K, V> {
2777    /// Ensures a value is in the entry by inserting the default if empty, and returns
2778    /// a mutable reference to the value in the entry.
2779    ///
2780    /// # Examples
2781    ///
2782    /// ```
2783    /// use std::collections::HashMap;
2784    ///
2785    /// let mut map: HashMap<&str, u32> = HashMap::new();
2786    ///
2787    /// map.entry("poneyland").or_insert(3);
2788    /// assert_eq!(map["poneyland"], 3);
2789    ///
2790    /// *map.entry("poneyland").or_insert(10) *= 2;
2791    /// assert_eq!(map["poneyland"], 6);
2792    /// ```
2793    #[inline]
2794    #[stable(feature = "rust1", since = "1.0.0")]
2795    pub fn or_insert(self, default: V) -> &'a mut V {
2796        match self {
2797            Occupied(entry) => entry.into_mut(),
2798            Vacant(entry) => entry.insert(default),
2799        }
2800    }
2801
2802    /// Ensures a value is in the entry by inserting the result of the default function if empty,
2803    /// and returns a mutable reference to the value in the entry.
2804    ///
2805    /// # Examples
2806    ///
2807    /// ```
2808    /// use std::collections::HashMap;
2809    ///
2810    /// let mut map = HashMap::new();
2811    /// let value = "hoho";
2812    ///
2813    /// map.entry("poneyland").or_insert_with(|| value);
2814    ///
2815    /// assert_eq!(map["poneyland"], "hoho");
2816    /// ```
2817    #[inline]
2818    #[stable(feature = "rust1", since = "1.0.0")]
2819    pub fn or_insert_with<F: FnOnce() -> V>(self, default: F) -> &'a mut V {
2820        match self {
2821            Occupied(entry) => entry.into_mut(),
2822            Vacant(entry) => entry.insert(default()),
2823        }
2824    }
2825
2826    /// Ensures a value is in the entry by inserting, if empty, the result of the default function.
2827    /// This method allows for generating key-derived values for insertion by providing the default
2828    /// function a reference to the key that was moved during the `.entry(key)` method call.
2829    ///
2830    /// The reference to the moved key is provided so that cloning or copying the key is
2831    /// unnecessary, unlike with `.or_insert_with(|| ... )`.
2832    ///
2833    /// # Examples
2834    ///
2835    /// ```
2836    /// use std::collections::HashMap;
2837    ///
2838    /// let mut map: HashMap<&str, usize> = HashMap::new();
2839    ///
2840    /// map.entry("poneyland").or_insert_with_key(|key| key.chars().count());
2841    ///
2842    /// assert_eq!(map["poneyland"], 9);
2843    /// ```
2844    #[inline]
2845    #[stable(feature = "or_insert_with_key", since = "1.50.0")]
2846    pub fn or_insert_with_key<F: FnOnce(&K) -> V>(self, default: F) -> &'a mut V {
2847        match self {
2848            Occupied(entry) => entry.into_mut(),
2849            Vacant(entry) => {
2850                let value = default(entry.key());
2851                entry.insert(value)
2852            }
2853        }
2854    }
2855
2856    /// Returns a reference to this entry's key.
2857    ///
2858    /// # Examples
2859    ///
2860    /// ```
2861    /// use std::collections::HashMap;
2862    ///
2863    /// let mut map: HashMap<&str, u32> = HashMap::new();
2864    /// assert_eq!(map.entry("poneyland").key(), &"poneyland");
2865    /// ```
2866    #[inline]
2867    #[stable(feature = "map_entry_keys", since = "1.10.0")]
2868    pub fn key(&self) -> &K {
2869        match *self {
2870            Occupied(ref entry) => entry.key(),
2871            Vacant(ref entry) => entry.key(),
2872        }
2873    }
2874
2875    /// Provides in-place mutable access to an occupied entry before any
2876    /// potential inserts into the map.
2877    ///
2878    /// # Examples
2879    ///
2880    /// ```
2881    /// use std::collections::HashMap;
2882    ///
2883    /// let mut map: HashMap<&str, u32> = HashMap::new();
2884    ///
2885    /// map.entry("poneyland")
2886    ///    .and_modify(|e| { *e += 1 })
2887    ///    .or_insert(42);
2888    /// assert_eq!(map["poneyland"], 42);
2889    ///
2890    /// map.entry("poneyland")
2891    ///    .and_modify(|e| { *e += 1 })
2892    ///    .or_insert(42);
2893    /// assert_eq!(map["poneyland"], 43);
2894    /// ```
2895    #[inline]
2896    #[stable(feature = "entry_and_modify", since = "1.26.0")]
2897    pub fn and_modify<F>(self, f: F) -> Self
2898    where
2899        F: FnOnce(&mut V),
2900    {
2901        match self {
2902            Occupied(mut entry) => {
2903                f(entry.get_mut());
2904                Occupied(entry)
2905            }
2906            Vacant(entry) => Vacant(entry),
2907        }
2908    }
2909
2910    /// Sets the value of the entry, and returns an `OccupiedEntry`.
2911    ///
2912    /// # Examples
2913    ///
2914    /// ```
2915    /// use std::collections::HashMap;
2916    ///
2917    /// let mut map: HashMap<&str, String> = HashMap::new();
2918    /// let entry = map.entry("poneyland").insert_entry("hoho".to_string());
2919    ///
2920    /// assert_eq!(entry.key(), &"poneyland");
2921    /// ```
2922    #[inline]
2923    #[stable(feature = "entry_insert", since = "1.83.0")]
2924    pub fn insert_entry(self, value: V) -> OccupiedEntry<'a, K, V> {
2925        match self {
2926            Occupied(mut entry) => {
2927                entry.insert(value);
2928                entry
2929            }
2930            Vacant(entry) => entry.insert_entry(value),
2931        }
2932    }
2933}
2934
2935impl<'a, K, V: Default> Entry<'a, K, V> {
2936    /// Ensures a value is in the entry by inserting the default value if empty,
2937    /// and returns a mutable reference to the value in the entry.
2938    ///
2939    /// # Examples
2940    ///
2941    /// ```
2942    /// # fn main() {
2943    /// use std::collections::HashMap;
2944    ///
2945    /// let mut map: HashMap<&str, Option<u32>> = HashMap::new();
2946    /// map.entry("poneyland").or_default();
2947    ///
2948    /// assert_eq!(map["poneyland"], None);
2949    /// # }
2950    /// ```
2951    #[inline]
2952    #[stable(feature = "entry_or_default", since = "1.28.0")]
2953    pub fn or_default(self) -> &'a mut V {
2954        match self {
2955            Occupied(entry) => entry.into_mut(),
2956            Vacant(entry) => entry.insert(Default::default()),
2957        }
2958    }
2959}
2960
2961impl<'a, K, V> OccupiedEntry<'a, K, V> {
2962    /// Gets a reference to the key in the entry.
2963    ///
2964    /// # Examples
2965    ///
2966    /// ```
2967    /// use std::collections::HashMap;
2968    ///
2969    /// let mut map: HashMap<&str, u32> = HashMap::new();
2970    /// map.entry("poneyland").or_insert(12);
2971    /// assert_eq!(map.entry("poneyland").key(), &"poneyland");
2972    /// ```
2973    #[inline]
2974    #[stable(feature = "map_entry_keys", since = "1.10.0")]
2975    pub fn key(&self) -> &K {
2976        self.base.key()
2977    }
2978
2979    /// Take the ownership of the key and value from the map.
2980    ///
2981    /// # Examples
2982    ///
2983    /// ```
2984    /// use std::collections::HashMap;
2985    /// use std::collections::hash_map::Entry;
2986    ///
2987    /// let mut map: HashMap<&str, u32> = HashMap::new();
2988    /// map.entry("poneyland").or_insert(12);
2989    ///
2990    /// if let Entry::Occupied(o) = map.entry("poneyland") {
2991    ///     // We delete the entry from the map.
2992    ///     o.remove_entry();
2993    /// }
2994    ///
2995    /// assert_eq!(map.contains_key("poneyland"), false);
2996    /// ```
2997    #[inline]
2998    #[stable(feature = "map_entry_recover_keys2", since = "1.12.0")]
2999    pub fn remove_entry(self) -> (K, V) {
3000        self.base.remove_entry()
3001    }
3002
3003    /// Gets a reference to the value in the entry.
3004    ///
3005    /// # Examples
3006    ///
3007    /// ```
3008    /// use std::collections::HashMap;
3009    /// use std::collections::hash_map::Entry;
3010    ///
3011    /// let mut map: HashMap<&str, u32> = HashMap::new();
3012    /// map.entry("poneyland").or_insert(12);
3013    ///
3014    /// if let Entry::Occupied(o) = map.entry("poneyland") {
3015    ///     assert_eq!(o.get(), &12);
3016    /// }
3017    /// ```
3018    #[inline]
3019    #[stable(feature = "rust1", since = "1.0.0")]
3020    pub fn get(&self) -> &V {
3021        self.base.get()
3022    }
3023
3024    /// Gets a mutable reference to the value in the entry.
3025    ///
3026    /// If you need a reference to the `OccupiedEntry` which may outlive the
3027    /// destruction of the `Entry` value, see [`into_mut`].
3028    ///
3029    /// [`into_mut`]: Self::into_mut
3030    ///
3031    /// # Examples
3032    ///
3033    /// ```
3034    /// use std::collections::HashMap;
3035    /// use std::collections::hash_map::Entry;
3036    ///
3037    /// let mut map: HashMap<&str, u32> = HashMap::new();
3038    /// map.entry("poneyland").or_insert(12);
3039    ///
3040    /// assert_eq!(map["poneyland"], 12);
3041    /// if let Entry::Occupied(mut o) = map.entry("poneyland") {
3042    ///     *o.get_mut() += 10;
3043    ///     assert_eq!(*o.get(), 22);
3044    ///
3045    ///     // We can use the same Entry multiple times.
3046    ///     *o.get_mut() += 2;
3047    /// }
3048    ///
3049    /// assert_eq!(map["poneyland"], 24);
3050    /// ```
3051    #[inline]
3052    #[stable(feature = "rust1", since = "1.0.0")]
3053    pub fn get_mut(&mut self) -> &mut V {
3054        self.base.get_mut()
3055    }
3056
3057    /// Converts the `OccupiedEntry` into a mutable reference to the value in the entry
3058    /// with a lifetime bound to the map itself.
3059    ///
3060    /// If you need multiple references to the `OccupiedEntry`, see [`get_mut`].
3061    ///
3062    /// [`get_mut`]: Self::get_mut
3063    ///
3064    /// # Examples
3065    ///
3066    /// ```
3067    /// use std::collections::HashMap;
3068    /// use std::collections::hash_map::Entry;
3069    ///
3070    /// let mut map: HashMap<&str, u32> = HashMap::new();
3071    /// map.entry("poneyland").or_insert(12);
3072    ///
3073    /// assert_eq!(map["poneyland"], 12);
3074    /// if let Entry::Occupied(o) = map.entry("poneyland") {
3075    ///     *o.into_mut() += 10;
3076    /// }
3077    ///
3078    /// assert_eq!(map["poneyland"], 22);
3079    /// ```
3080    #[inline]
3081    #[stable(feature = "rust1", since = "1.0.0")]
3082    pub fn into_mut(self) -> &'a mut V {
3083        self.base.into_mut()
3084    }
3085
3086    /// Sets the value of the entry, and returns the entry's old value.
3087    ///
3088    /// # Examples
3089    ///
3090    /// ```
3091    /// use std::collections::HashMap;
3092    /// use std::collections::hash_map::Entry;
3093    ///
3094    /// let mut map: HashMap<&str, u32> = HashMap::new();
3095    /// map.entry("poneyland").or_insert(12);
3096    ///
3097    /// if let Entry::Occupied(mut o) = map.entry("poneyland") {
3098    ///     assert_eq!(o.insert(15), 12);
3099    /// }
3100    ///
3101    /// assert_eq!(map["poneyland"], 15);
3102    /// ```
3103    #[inline]
3104    #[stable(feature = "rust1", since = "1.0.0")]
3105    pub fn insert(&mut self, value: V) -> V {
3106        self.base.insert(value)
3107    }
3108
3109    /// Takes the value out of the entry, and returns it.
3110    ///
3111    /// # Examples
3112    ///
3113    /// ```
3114    /// use std::collections::HashMap;
3115    /// use std::collections::hash_map::Entry;
3116    ///
3117    /// let mut map: HashMap<&str, u32> = HashMap::new();
3118    /// map.entry("poneyland").or_insert(12);
3119    ///
3120    /// if let Entry::Occupied(o) = map.entry("poneyland") {
3121    ///     assert_eq!(o.remove(), 12);
3122    /// }
3123    ///
3124    /// assert_eq!(map.contains_key("poneyland"), false);
3125    /// ```
3126    #[inline]
3127    #[stable(feature = "rust1", since = "1.0.0")]
3128    pub fn remove(self) -> V {
3129        self.base.remove()
3130    }
3131}
3132
3133impl<'a, K: 'a, V: 'a> VacantEntry<'a, K, V> {
3134    /// Gets a reference to the key that would be used when inserting a value
3135    /// through the `VacantEntry`.
3136    ///
3137    /// # Examples
3138    ///
3139    /// ```
3140    /// use std::collections::HashMap;
3141    ///
3142    /// let mut map: HashMap<&str, u32> = HashMap::new();
3143    /// assert_eq!(map.entry("poneyland").key(), &"poneyland");
3144    /// ```
3145    #[inline]
3146    #[stable(feature = "map_entry_keys", since = "1.10.0")]
3147    pub fn key(&self) -> &K {
3148        self.base.key()
3149    }
3150
3151    /// Take ownership of the key.
3152    ///
3153    /// # Examples
3154    ///
3155    /// ```
3156    /// use std::collections::HashMap;
3157    /// use std::collections::hash_map::Entry;
3158    ///
3159    /// let mut map: HashMap<&str, u32> = HashMap::new();
3160    ///
3161    /// if let Entry::Vacant(v) = map.entry("poneyland") {
3162    ///     v.into_key();
3163    /// }
3164    /// ```
3165    #[inline]
3166    #[stable(feature = "map_entry_recover_keys2", since = "1.12.0")]
3167    pub fn into_key(self) -> K {
3168        self.base.into_key()
3169    }
3170
3171    /// Sets the value of the entry with the `VacantEntry`'s key,
3172    /// and returns a mutable reference to it.
3173    ///
3174    /// # Examples
3175    ///
3176    /// ```
3177    /// use std::collections::HashMap;
3178    /// use std::collections::hash_map::Entry;
3179    ///
3180    /// let mut map: HashMap<&str, u32> = HashMap::new();
3181    ///
3182    /// if let Entry::Vacant(o) = map.entry("poneyland") {
3183    ///     o.insert(37);
3184    /// }
3185    /// assert_eq!(map["poneyland"], 37);
3186    /// ```
3187    #[inline]
3188    #[stable(feature = "rust1", since = "1.0.0")]
3189    pub fn insert(self, value: V) -> &'a mut V {
3190        self.base.insert(value)
3191    }
3192
3193    /// Sets the value of the entry with the `VacantEntry`'s key,
3194    /// and returns an `OccupiedEntry`.
3195    ///
3196    /// # Examples
3197    ///
3198    /// ```
3199    /// use std::collections::HashMap;
3200    /// use std::collections::hash_map::Entry;
3201    ///
3202    /// let mut map: HashMap<&str, u32> = HashMap::new();
3203    ///
3204    /// if let Entry::Vacant(o) = map.entry("poneyland") {
3205    ///     o.insert_entry(37);
3206    /// }
3207    /// assert_eq!(map["poneyland"], 37);
3208    /// ```
3209    #[inline]
3210    #[stable(feature = "entry_insert", since = "1.83.0")]
3211    pub fn insert_entry(self, value: V) -> OccupiedEntry<'a, K, V> {
3212        let base = self.base.insert_entry(value);
3213        OccupiedEntry { base }
3214    }
3215}
3216
3217#[stable(feature = "rust1", since = "1.0.0")]
3218impl<K, V, S> FromIterator<(K, V)> for HashMap<K, V, S>
3219where
3220    K: Eq + Hash,
3221    S: BuildHasher + Default,
3222{
3223    /// Constructs a `HashMap<K, V>` from an iterator of key-value pairs.
3224    ///
3225    /// If the iterator produces any pairs with equal keys,
3226    /// all but one of the corresponding values will be dropped.
3227    fn from_iter<T: IntoIterator<Item = (K, V)>>(iter: T) -> HashMap<K, V, S> {
3228        let mut map = HashMap::with_hasher(Default::default());
3229        map.extend(iter);
3230        map
3231    }
3232}
3233
3234/// Inserts all new key-values from the iterator and replaces values with existing
3235/// keys with new values returned from the iterator.
3236#[stable(feature = "rust1", since = "1.0.0")]
3237impl<K, V, S> Extend<(K, V)> for HashMap<K, V, S>
3238where
3239    K: Eq + Hash,
3240    S: BuildHasher,
3241{
3242    #[inline]
3243    fn extend<T: IntoIterator<Item = (K, V)>>(&mut self, iter: T) {
3244        self.base.extend(iter)
3245    }
3246
3247    #[inline]
3248    fn extend_one(&mut self, (k, v): (K, V)) {
3249        self.base.insert(k, v);
3250    }
3251
3252    #[inline]
3253    fn extend_reserve(&mut self, additional: usize) {
3254        self.base.extend_reserve(additional);
3255    }
3256}
3257
3258#[stable(feature = "hash_extend_copy", since = "1.4.0")]
3259impl<'a, K, V, S> Extend<(&'a K, &'a V)> for HashMap<K, V, S>
3260where
3261    K: Eq + Hash + Copy,
3262    V: Copy,
3263    S: BuildHasher,
3264{
3265    #[inline]
3266    fn extend<T: IntoIterator<Item = (&'a K, &'a V)>>(&mut self, iter: T) {
3267        self.base.extend(iter)
3268    }
3269
3270    #[inline]
3271    fn extend_one(&mut self, (&k, &v): (&'a K, &'a V)) {
3272        self.base.insert(k, v);
3273    }
3274
3275    #[inline]
3276    fn extend_reserve(&mut self, additional: usize) {
3277        Extend::<(K, V)>::extend_reserve(self, additional)
3278    }
3279}
3280
3281#[inline]
3282fn map_entry<'a, K: 'a, V: 'a>(raw: base::RustcEntry<'a, K, V>) -> Entry<'a, K, V> {
3283    match raw {
3284        base::RustcEntry::Occupied(base) => Entry::Occupied(OccupiedEntry { base }),
3285        base::RustcEntry::Vacant(base) => Entry::Vacant(VacantEntry { base }),
3286    }
3287}
3288
3289#[inline]
3290pub(super) fn map_try_reserve_error(err: hashbrown::TryReserveError) -> TryReserveError {
3291    match err {
3292        hashbrown::TryReserveError::CapacityOverflow => {
3293            TryReserveErrorKind::CapacityOverflow.into()
3294        }
3295        hashbrown::TryReserveError::AllocError { layout } => {
3296            TryReserveErrorKind::AllocError { layout, non_exhaustive: () }.into()
3297        }
3298    }
3299}
3300
3301#[inline]
3302fn map_raw_entry<'a, K: 'a, V: 'a, S: 'a>(
3303    raw: base::RawEntryMut<'a, K, V, S>,
3304) -> RawEntryMut<'a, K, V, S> {
3305    match raw {
3306        base::RawEntryMut::Occupied(base) => RawEntryMut::Occupied(RawOccupiedEntryMut { base }),
3307        base::RawEntryMut::Vacant(base) => RawEntryMut::Vacant(RawVacantEntryMut { base }),
3308    }
3309}
3310
3311#[allow(dead_code)]
3312fn assert_covariance() {
3313    fn map_key<'new>(v: HashMap<&'static str, u8>) -> HashMap<&'new str, u8> {
3314        v
3315    }
3316    fn map_val<'new>(v: HashMap<u8, &'static str>) -> HashMap<u8, &'new str> {
3317        v
3318    }
3319    fn iter_key<'a, 'new>(v: Iter<'a, &'static str, u8>) -> Iter<'a, &'new str, u8> {
3320        v
3321    }
3322    fn iter_val<'a, 'new>(v: Iter<'a, u8, &'static str>) -> Iter<'a, u8, &'new str> {
3323        v
3324    }
3325    fn into_iter_key<'new>(v: IntoIter<&'static str, u8>) -> IntoIter<&'new str, u8> {
3326        v
3327    }
3328    fn into_iter_val<'new>(v: IntoIter<u8, &'static str>) -> IntoIter<u8, &'new str> {
3329        v
3330    }
3331    fn keys_key<'a, 'new>(v: Keys<'a, &'static str, u8>) -> Keys<'a, &'new str, u8> {
3332        v
3333    }
3334    fn keys_val<'a, 'new>(v: Keys<'a, u8, &'static str>) -> Keys<'a, u8, &'new str> {
3335        v
3336    }
3337    fn values_key<'a, 'new>(v: Values<'a, &'static str, u8>) -> Values<'a, &'new str, u8> {
3338        v
3339    }
3340    fn values_val<'a, 'new>(v: Values<'a, u8, &'static str>) -> Values<'a, u8, &'new str> {
3341        v
3342    }
3343    fn drain<'new>(
3344        d: Drain<'static, &'static str, &'static str>,
3345    ) -> Drain<'new, &'new str, &'new str> {
3346        d
3347    }
3348}