1 // Copyright 2014-2015 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
12 use self::VacantEntryState::*;
16 use fmt::{self, Debug};
17 use hash::{Hash, SipHasher, BuildHasher};
18 use iter::{self, Map, FromIterator};
19 use mem::{self, replace};
20 use ops::{Deref, Index};
21 use rand::{self, Rng};
32 use super::table::BucketState::{
37 const INITIAL_LOG2_CAP: usize = 5;
38 const INITIAL_CAPACITY: usize = 1 << INITIAL_LOG2_CAP; // 2^5
40 /// The default behavior of HashMap implements a load factor of 90.9%.
41 /// This behavior is characterized by the following condition:
43 /// - if size > 0.909 * capacity: grow the map
45 struct DefaultResizePolicy;
47 impl DefaultResizePolicy {
48 fn new() -> DefaultResizePolicy {
53 fn min_capacity(&self, usable_size: usize) -> usize {
54 // Here, we are rephrasing the logic by specifying the lower limit
57 // - if `cap < size * 1.1`: grow the map
61 /// An inverse of `min_capacity`, approximately.
63 fn usable_capacity(&self, cap: usize) -> usize {
64 // As the number of entries approaches usable capacity,
65 // min_capacity(size) must be smaller than the internal capacity,
66 // so that the map is not resized:
67 // `min_capacity(usable_capacity(x)) <= x`.
68 // The left-hand side can only be smaller due to flooring by integer
71 // This doesn't have to be checked for overflow since allocation size
72 // in bytes will overflow earlier than multiplication by 10.
74 // As per https://github.com/rust-lang/rust/pull/30991 this is updated
75 // to be: (cap * den + den - 1) / num
76 (cap * 10 + 10 - 1) / 11
81 fn test_resize_policy() {
82 let rp = DefaultResizePolicy;
84 assert!(rp.min_capacity(rp.usable_capacity(n)) <= n);
85 assert!(rp.usable_capacity(rp.min_capacity(n)) <= n);
89 // The main performance trick in this hashmap is called Robin Hood Hashing.
90 // It gains its excellent performance from one essential operation:
92 // If an insertion collides with an existing element, and that element's
93 // "probe distance" (how far away the element is from its ideal location)
94 // is higher than how far we've already probed, swap the elements.
96 // This massively lowers variance in probe distance, and allows us to get very
97 // high load factors with good performance. The 90% load factor I use is rather
100 // > Why a load factor of approximately 90%?
102 // In general, all the distances to initial buckets will converge on the mean.
103 // At a load factor of α, the odds of finding the target bucket after k
104 // probes is approximately 1-α^k. If we set this equal to 50% (since we converge
105 // on the mean) and set k=8 (64-byte cache line / 8-byte hash), α=0.92. I round
106 // this down to make the math easier on the CPU and avoid its FPU.
107 // Since on average we start the probing in the middle of a cache line, this
108 // strategy pulls in two cache lines of hashes on every lookup. I think that's
109 // pretty good, but if you want to trade off some space, it could go down to one
110 // cache line on average with an α of 0.84.
112 // > Wait, what? Where did you get 1-α^k from?
114 // On the first probe, your odds of a collision with an existing element is α.
115 // The odds of doing this twice in a row is approximately α^2. For three times,
116 // α^3, etc. Therefore, the odds of colliding k times is α^k. The odds of NOT
117 // colliding after k tries is 1-α^k.
119 // The paper from 1986 cited below mentions an implementation which keeps track
120 // of the distance-to-initial-bucket histogram. This approach is not suitable
121 // for modern architectures because it requires maintaining an internal data
122 // structure. This allows very good first guesses, but we are most concerned
123 // with guessing entire cache lines, not individual indexes. Furthermore, array
124 // accesses are no longer linear and in one direction, as we have now. There
125 // is also memory and cache pressure that this would entail that would be very
126 // difficult to properly see in a microbenchmark.
128 // ## Future Improvements (FIXME!)
130 // Allow the load factor to be changed dynamically and/or at initialization.
132 // Also, would it be possible for us to reuse storage when growing the
133 // underlying table? This is exactly the use case for 'realloc', and may
134 // be worth exploring.
136 // ## Future Optimizations (FIXME!)
138 // Another possible design choice that I made without any real reason is
139 // parameterizing the raw table over keys and values. Technically, all we need
140 // is the size and alignment of keys and values, and the code should be just as
141 // efficient (well, we might need one for power-of-two size and one for not...).
142 // This has the potential to reduce code bloat in rust executables, without
143 // really losing anything except 4 words (key size, key alignment, val size,
144 // val alignment) which can be passed in to every call of a `RawTable` function.
145 // This would definitely be an avenue worth exploring if people start complaining
146 // about the size of rust executables.
148 // Annotate exceedingly likely branches in `table::make_hash`
149 // and `search_hashed` to reduce instruction cache pressure
150 // and mispredictions once it becomes possible (blocked on issue #11092).
152 // Shrinking the table could simply reallocate in place after moving buckets
153 // to the first half.
155 // The growth algorithm (fragment of the Proof of Correctness)
156 // --------------------
158 // The growth algorithm is basically a fast path of the naive reinsertion-
159 // during-resize algorithm. Other paths should never be taken.
161 // Consider growing a robin hood hashtable of capacity n. Normally, we do this
162 // by allocating a new table of capacity `2n`, and then individually reinsert
163 // each element in the old table into the new one. This guarantees that the
164 // new table is a valid robin hood hashtable with all the desired statistical
165 // properties. Remark that the order we reinsert the elements in should not
166 // matter. For simplicity and efficiency, we will consider only linear
167 // reinsertions, which consist of reinserting all elements in the old table
168 // into the new one by increasing order of index. However we will not be
169 // starting our reinsertions from index 0 in general. If we start from index
170 // i, for the purpose of reinsertion we will consider all elements with real
171 // index j < i to have virtual index n + j.
173 // Our hash generation scheme consists of generating a 64-bit hash and
174 // truncating the most significant bits. When moving to the new table, we
175 // simply introduce a new bit to the front of the hash. Therefore, if an
176 // elements has ideal index i in the old table, it can have one of two ideal
177 // locations in the new table. If the new bit is 0, then the new ideal index
178 // is i. If the new bit is 1, then the new ideal index is n + i. Intuitively,
179 // we are producing two independent tables of size n, and for each element we
180 // independently choose which table to insert it into with equal probability.
181 // However the rather than wrapping around themselves on overflowing their
182 // indexes, the first table overflows into the first, and the first into the
183 // second. Visually, our new table will look something like:
185 // [yy_xxx_xxxx_xxx|xx_yyy_yyyy_yyy]
187 // Where x's are elements inserted into the first table, y's are elements
188 // inserted into the second, and _'s are empty sections. We now define a few
189 // key concepts that we will use later. Note that this is a very abstract
190 // perspective of the table. A real resized table would be at least half
193 // Theorem: A linear robin hood reinsertion from the first ideal element
194 // produces identical results to a linear naive reinsertion from the same
197 // FIXME(Gankro, pczarn): review the proof and put it all in a separate README.md
199 /// A hash map implementation which uses linear probing with Robin
200 /// Hood bucket stealing.
202 /// The hashes are all keyed by the thread-local random number generator
203 /// on creation by default. This means that the ordering of the keys is
204 /// randomized, but makes the tables more resistant to
205 /// denial-of-service attacks (Hash DoS). This behavior can be
206 /// overridden with one of the constructors.
208 /// It is required that the keys implement the `Eq` and `Hash` traits, although
209 /// this can frequently be achieved by using `#[derive(PartialEq, Eq, Hash)]`.
210 /// If you implement these yourself, it is important that the following
214 /// k1 == k2 -> hash(k1) == hash(k2)
217 /// In other words, if two keys are equal, their hashes must be equal.
219 /// It is a logic error for a key to be modified in such a way that the key's
220 /// hash, as determined by the `Hash` trait, or its equality, as determined by
221 /// the `Eq` trait, changes while it is in the map. This is normally only
222 /// possible through `Cell`, `RefCell`, global state, I/O, or unsafe code.
224 /// Relevant papers/articles:
226 /// 1. Pedro Celis. ["Robin Hood Hashing"](https://cs.uwaterloo.ca/research/tr/1986/CS-86-14.pdf)
227 /// 2. Emmanuel Goossaert. ["Robin Hood
228 /// hashing"](http://codecapsule.com/2013/11/11/robin-hood-hashing/)
229 /// 3. Emmanuel Goossaert. ["Robin Hood hashing: backward shift
230 /// deletion"](http://codecapsule.com/2013/11/17/robin-hood-hashing-backward-shift-deletion/)
235 /// use std::collections::HashMap;
237 /// // type inference lets us omit an explicit type signature (which
238 /// // would be `HashMap<&str, &str>` in this example).
239 /// let mut book_reviews = HashMap::new();
241 /// // review some books.
242 /// book_reviews.insert("Adventures of Huckleberry Finn", "My favorite book.");
243 /// book_reviews.insert("Grimms' Fairy Tales", "Masterpiece.");
244 /// book_reviews.insert("Pride and Prejudice", "Very enjoyable.");
245 /// book_reviews.insert("The Adventures of Sherlock Holmes", "Eye lyked it alot.");
247 /// // check for a specific one.
248 /// if !book_reviews.contains_key("Les Misérables") {
249 /// println!("We've got {} reviews, but Les Misérables ain't one.",
250 /// book_reviews.len());
253 /// // oops, this review has a lot of spelling mistakes, let's delete it.
254 /// book_reviews.remove("The Adventures of Sherlock Holmes");
256 /// // look up the values associated with some keys.
257 /// let to_find = ["Pride and Prejudice", "Alice's Adventure in Wonderland"];
258 /// for book in &to_find {
259 /// match book_reviews.get(book) {
260 /// Some(review) => println!("{}: {}", book, review),
261 /// None => println!("{} is unreviewed.", book)
265 /// // iterate over everything.
266 /// for (book, review) in &book_reviews {
267 /// println!("{}: \"{}\"", book, review);
271 /// `HashMap` also implements an [`Entry API`](#method.entry), which allows
272 /// for more complex methods of getting, setting, updating and removing keys and
276 /// use std::collections::HashMap;
278 /// // type inference lets us omit an explicit type signature (which
279 /// // would be `HashMap<&str, u8>` in this example).
280 /// let mut player_stats = HashMap::new();
282 /// fn random_stat_buff() -> u8 {
283 /// // could actually return some random value here - let's just return
284 /// // some fixed value for now
288 /// // insert a key only if it doesn't already exist
289 /// player_stats.entry("health").or_insert(100);
291 /// // insert a key using a function that provides a new value only if it
292 /// // doesn't already exist
293 /// player_stats.entry("defence").or_insert_with(random_stat_buff);
295 /// // update a key, guarding against the key possibly not being set
296 /// let stat = player_stats.entry("attack").or_insert(100);
297 /// *stat += random_stat_buff();
300 /// The easiest way to use `HashMap` with a custom type as key is to derive `Eq` and `Hash`.
301 /// We must also derive `PartialEq`.
304 /// use std::collections::HashMap;
306 /// #[derive(Hash, Eq, PartialEq, Debug)]
313 /// /// Create a new Viking.
314 /// fn new(name: &str, country: &str) -> Viking {
315 /// Viking { name: name.to_string(), country: country.to_string() }
319 /// // Use a HashMap to store the vikings' health points.
320 /// let mut vikings = HashMap::new();
322 /// vikings.insert(Viking::new("Einar", "Norway"), 25);
323 /// vikings.insert(Viking::new("Olaf", "Denmark"), 24);
324 /// vikings.insert(Viking::new("Harald", "Iceland"), 12);
326 /// // Use derived implementation to print the status of the vikings.
327 /// for (viking, health) in &vikings {
328 /// println!("{:?} has {} hp", viking, health);
332 #[stable(feature = "rust1", since = "1.0.0")]
333 pub struct HashMap<K, V, S = RandomState> {
334 // All hashes are keyed on these values, to prevent hash collision attacks.
337 table: RawTable<K, V>,
339 resize_policy: DefaultResizePolicy,
342 /// Search for a pre-hashed key.
344 fn search_hashed<K, V, M, F>(table: M,
347 -> InternalEntry<K, V, M> where
348 M: Deref<Target=RawTable<K, V>>,
349 F: FnMut(&K) -> bool,
351 // This is the only function where capacity can be zero. To avoid
352 // undefined behavior when Bucket::new gets the raw bucket in this
353 // case, immediately return the appropriate search result.
354 if table.capacity() == 0 {
355 return InternalEntry::TableIsEmpty;
358 let size = table.size() as isize;
359 let mut probe = Bucket::new(table, hash);
360 let ib = probe.index() as isize;
363 let full = match probe.peek() {
366 return InternalEntry::Vacant {
368 elem: NoElem(bucket),
371 Full(bucket) => bucket
374 let robin_ib = full.index() as isize - full.displacement() as isize;
377 // Found a luckier bucket than me.
378 // We can finish the search early if we hit any bucket
379 // with a lower distance to initial bucket than we've probed.
380 return InternalEntry::Vacant {
382 elem: NeqElem(full, robin_ib as usize),
386 // If the hash doesn't match, it can't be this one..
387 if hash == full.hash() {
388 // If the key doesn't match, it can't be this one..
389 if is_match(full.read().0) {
390 return InternalEntry::Occupied {
397 debug_assert!(probe.index() as isize != ib + size + 1);
401 fn pop_internal<K, V>(starting_bucket: FullBucketMut<K, V>) -> (K, V) {
402 let (empty, retkey, retval) = starting_bucket.take();
403 let mut gap = match empty.gap_peek() {
405 None => return (retkey, retval)
408 while gap.full().displacement() != 0 {
409 gap = match gap.shift() {
415 // Now we've done all our shifting. Return the value we grabbed earlier.
419 /// Perform robin hood bucket stealing at the given `bucket`. You must
420 /// also pass the position of that bucket's initial bucket so we don't have
421 /// to recalculate it.
423 /// `hash`, `k`, and `v` are the elements to "robin hood" into the hashtable.
424 fn robin_hood<'a, K: 'a, V: 'a>(bucket: FullBucketMut<'a, K, V>,
430 let starting_index = bucket.index();
432 let table = bucket.table(); // FIXME "lifetime too short".
435 // Save the *starting point*.
436 let mut bucket = bucket.stash();
437 // There can be at most `size - dib` buckets to displace, because
438 // in the worst case, there are `size` elements and we already are
439 // `displacement` buckets away from the initial one.
440 let idx_end = starting_index + size - bucket.displacement();
443 let (old_hash, old_key, old_val) = bucket.replace(hash, key, val);
449 let probe = bucket.next();
450 debug_assert!(probe.index() != idx_end);
452 let full_bucket = match probe.peek() {
455 let bucket = bucket.put(hash, key, val);
456 // Now that it's stolen, just read the value's pointer
457 // right out of the table! Go back to the *starting point*.
459 // This use of `into_table` is misleading. It turns the
460 // bucket, which is a FullBucket on top of a
461 // FullBucketMut, into just one FullBucketMut. The "table"
462 // refers to the inner FullBucketMut in this context.
463 return bucket.into_table().into_mut_refs().1;
465 Full(bucket) => bucket
468 let probe_ib = full_bucket.index() - full_bucket.displacement();
470 bucket = full_bucket;
472 // Robin hood! Steal the spot.
481 impl<K, V, S> HashMap<K, V, S>
482 where K: Eq + Hash, S: BuildHasher
484 fn make_hash<X: ?Sized>(&self, x: &X) -> SafeHash where X: Hash {
485 table::make_hash(&self.hash_builder, x)
488 /// Search for a key, yielding the index if it's found in the hashtable.
489 /// If you already have the hash for the key lying around, use
492 fn search<'a, Q: ?Sized>(&'a self, q: &Q) -> InternalEntry<K, V, &'a RawTable<K, V>>
493 where K: Borrow<Q>, Q: Eq + Hash
495 let hash = self.make_hash(q);
496 search_hashed(&self.table, hash, |k| q.eq(k.borrow()))
500 fn search_mut<'a, Q: ?Sized>(&'a mut self, q: &Q) -> InternalEntry<K, V, &'a mut RawTable<K, V>>
501 where K: Borrow<Q>, Q: Eq + Hash
503 let hash = self.make_hash(q);
504 search_hashed(&mut self.table, hash, |k| q.eq(k.borrow()))
507 // The caller should ensure that invariants by Robin Hood Hashing hold.
508 fn insert_hashed_ordered(&mut self, hash: SafeHash, k: K, v: V) {
509 let cap = self.table.capacity();
510 let mut buckets = Bucket::new(&mut self.table, hash);
511 let ib = buckets.index();
513 while buckets.index() != ib + cap {
514 // We don't need to compare hashes for value swap.
515 // Not even DIBs for Robin Hood.
516 buckets = match buckets.peek() {
518 empty.put(hash, k, v);
521 Full(b) => b.into_bucket()
525 panic!("Internal HashMap error: Out of space.");
529 impl<K: Hash + Eq, V> HashMap<K, V, RandomState> {
530 /// Creates an empty HashMap.
535 /// use std::collections::HashMap;
536 /// let mut map: HashMap<&str, isize> = HashMap::new();
539 #[stable(feature = "rust1", since = "1.0.0")]
540 pub fn new() -> HashMap<K, V, RandomState> {
544 /// Creates an empty hash map with the given initial capacity.
549 /// use std::collections::HashMap;
550 /// let mut map: HashMap<&str, isize> = HashMap::with_capacity(10);
553 #[stable(feature = "rust1", since = "1.0.0")]
554 pub fn with_capacity(capacity: usize) -> HashMap<K, V, RandomState> {
555 HashMap::with_capacity_and_hasher(capacity, Default::default())
559 impl<K, V, S> HashMap<K, V, S>
560 where K: Eq + Hash, S: BuildHasher
562 /// Creates an empty hashmap which will use the given hash builder to hash
565 /// The created map has the default initial capacity.
567 /// Warning: `hash_builder` is normally randomly generated, and
568 /// is designed to allow HashMaps to be resistant to attacks that
569 /// cause many collisions and very poor performance. Setting it
570 /// manually using this function can expose a DoS attack vector.
575 /// use std::collections::HashMap;
576 /// use std::collections::hash_map::RandomState;
578 /// let s = RandomState::new();
579 /// let mut map = HashMap::with_hasher(s);
580 /// map.insert(1, 2);
583 #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
584 pub fn with_hasher(hash_builder: S) -> HashMap<K, V, S> {
586 hash_builder: hash_builder,
587 resize_policy: DefaultResizePolicy::new(),
588 table: RawTable::new(0),
592 /// Creates an empty HashMap with space for at least `capacity`
593 /// elements, using `hasher` to hash the keys.
595 /// Warning: `hasher` is normally randomly generated, and
596 /// is designed to allow HashMaps to be resistant to attacks that
597 /// cause many collisions and very poor performance. Setting it
598 /// manually using this function can expose a DoS attack vector.
603 /// use std::collections::HashMap;
604 /// use std::collections::hash_map::RandomState;
606 /// let s = RandomState::new();
607 /// let mut map = HashMap::with_capacity_and_hasher(10, s);
608 /// map.insert(1, 2);
611 #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
612 pub fn with_capacity_and_hasher(capacity: usize, hash_builder: S)
613 -> HashMap<K, V, S> {
614 let resize_policy = DefaultResizePolicy::new();
615 let min_cap = max(INITIAL_CAPACITY, resize_policy.min_capacity(capacity));
616 let internal_cap = min_cap.checked_next_power_of_two().expect("capacity overflow");
617 assert!(internal_cap >= capacity, "capacity overflow");
619 hash_builder: hash_builder,
620 resize_policy: resize_policy,
621 table: RawTable::new(internal_cap),
625 /// Returns a reference to the map's hasher.
626 #[unstable(feature = "hashmap_public_hasher", reason = "don't want to make insta-stable",
628 pub fn hasher(&self) -> &S {
632 /// Returns the number of elements the map can hold without reallocating.
634 /// This number is a lower bound; the `HashMap<K, V>` might be able to hold
635 /// more, but is guaranteed to be able to hold at least this many.
640 /// use std::collections::HashMap;
641 /// let map: HashMap<isize, isize> = HashMap::with_capacity(100);
642 /// assert!(map.capacity() >= 100);
645 #[stable(feature = "rust1", since = "1.0.0")]
646 pub fn capacity(&self) -> usize {
647 self.resize_policy.usable_capacity(self.table.capacity())
650 /// Reserves capacity for at least `additional` more elements to be inserted
651 /// in the `HashMap`. The collection may reserve more space to avoid
652 /// frequent reallocations.
656 /// Panics if the new allocation size overflows `usize`.
661 /// use std::collections::HashMap;
662 /// let mut map: HashMap<&str, isize> = HashMap::new();
665 #[stable(feature = "rust1", since = "1.0.0")]
666 pub fn reserve(&mut self, additional: usize) {
667 let new_size = self.len().checked_add(additional).expect("capacity overflow");
668 let min_cap = self.resize_policy.min_capacity(new_size);
670 // An invalid value shouldn't make us run out of space. This includes
671 // an overflow check.
672 assert!(new_size <= min_cap);
674 if self.table.capacity() < min_cap {
675 let new_capacity = max(min_cap.next_power_of_two(), INITIAL_CAPACITY);
676 self.resize(new_capacity);
680 /// Resizes the internal vectors to a new capacity. It's your responsibility to:
681 /// 1) Make sure the new capacity is enough for all the elements, accounting
682 /// for the load factor.
683 /// 2) Ensure new_capacity is a power of two or zero.
684 fn resize(&mut self, new_capacity: usize) {
685 assert!(self.table.size() <= new_capacity);
686 assert!(new_capacity.is_power_of_two() || new_capacity == 0);
688 let mut old_table = replace(&mut self.table, RawTable::new(new_capacity));
689 let old_size = old_table.size();
691 if old_table.capacity() == 0 || old_table.size() == 0 {
696 // Specialization of the other branch.
697 let mut bucket = Bucket::first(&mut old_table);
699 // "So a few of the first shall be last: for many be called,
702 // We'll most likely encounter a few buckets at the beginning that
703 // have their initial buckets near the end of the table. They were
704 // placed at the beginning as the probe wrapped around the table
705 // during insertion. We must skip forward to a bucket that won't
706 // get reinserted too early and won't unfairly steal others spot.
707 // This eliminates the need for robin hood.
709 bucket = match bucket.peek() {
711 if full.displacement() == 0 {
712 // This bucket occupies its ideal spot.
713 // It indicates the start of another "cluster".
714 bucket = full.into_bucket();
717 // Leaving this bucket in the last cluster for later.
721 // Encountered a hole between clusters.
728 // This is how the buckets might be laid out in memory:
729 // ($ marks an initialized bucket)
731 // |$$$_$$$$$$_$$$$$|
733 // But we've skipped the entire initial cluster of buckets
734 // and will continue iteration in this order:
737 // ^ wrap around once end is reached
740 // ^ exit once table.size == 0
742 bucket = match bucket.peek() {
744 let h = bucket.hash();
745 let (b, k, v) = bucket.take();
746 self.insert_hashed_ordered(h, k, v);
748 let t = b.table(); // FIXME "lifetime too short".
749 if t.size() == 0 { break }
753 Empty(b) => b.into_bucket()
758 assert_eq!(self.table.size(), old_size);
761 /// Shrinks the capacity of the map as much as possible. It will drop
762 /// down as much as possible while maintaining the internal rules
763 /// and possibly leaving some space in accordance with the resize policy.
768 /// use std::collections::HashMap;
770 /// let mut map: HashMap<isize, isize> = HashMap::with_capacity(100);
771 /// map.insert(1, 2);
772 /// map.insert(3, 4);
773 /// assert!(map.capacity() >= 100);
774 /// map.shrink_to_fit();
775 /// assert!(map.capacity() >= 2);
777 #[stable(feature = "rust1", since = "1.0.0")]
778 pub fn shrink_to_fit(&mut self) {
779 let min_capacity = self.resize_policy.min_capacity(self.len());
780 let min_capacity = max(min_capacity.next_power_of_two(), INITIAL_CAPACITY);
782 // An invalid value shouldn't make us run out of space.
783 debug_assert!(self.len() <= min_capacity);
785 if self.table.capacity() != min_capacity {
786 let old_table = replace(&mut self.table, RawTable::new(min_capacity));
787 let old_size = old_table.size();
789 // Shrink the table. Naive algorithm for resizing:
790 for (h, k, v) in old_table.into_iter() {
791 self.insert_hashed_nocheck(h, k, v);
794 debug_assert_eq!(self.table.size(), old_size);
798 /// Insert a pre-hashed key-value pair, without first checking
799 /// that there's enough room in the buckets. Returns a reference to the
800 /// newly insert value.
802 /// If the key already exists, the hashtable will be returned untouched
803 /// and a reference to the existing element will be returned.
804 fn insert_hashed_nocheck(&mut self, hash: SafeHash, k: K, v: V) -> Option<V> {
805 let entry = search_hashed(&mut self.table, hash, |key| *key == k).into_entry(k);
807 Some(Occupied(mut elem)) => {
810 Some(Vacant(elem)) => {
820 /// An iterator visiting all keys in arbitrary order.
821 /// Iterator element type is `&'a K`.
826 /// use std::collections::HashMap;
828 /// let mut map = HashMap::new();
829 /// map.insert("a", 1);
830 /// map.insert("b", 2);
831 /// map.insert("c", 3);
833 /// for key in map.keys() {
834 /// println!("{}", key);
837 #[stable(feature = "rust1", since = "1.0.0")]
838 pub fn keys<'a>(&'a self) -> Keys<'a, K, V> {
839 fn first<A, B>((a, _): (A, B)) -> A { a }
840 let first: fn((&'a K,&'a V)) -> &'a K = first; // coerce to fn ptr
842 Keys { inner: self.iter().map(first) }
845 /// An iterator visiting all values in arbitrary order.
846 /// Iterator element type is `&'a V`.
851 /// use std::collections::HashMap;
853 /// let mut map = HashMap::new();
854 /// map.insert("a", 1);
855 /// map.insert("b", 2);
856 /// map.insert("c", 3);
858 /// for val in map.values() {
859 /// println!("{}", val);
862 #[stable(feature = "rust1", since = "1.0.0")]
863 pub fn values<'a>(&'a self) -> Values<'a, K, V> {
864 fn second<A, B>((_, b): (A, B)) -> B { b }
865 let second: fn((&'a K,&'a V)) -> &'a V = second; // coerce to fn ptr
867 Values { inner: self.iter().map(second) }
870 /// An iterator visiting all key-value pairs in arbitrary order.
871 /// Iterator element type is `(&'a K, &'a V)`.
876 /// use std::collections::HashMap;
878 /// let mut map = HashMap::new();
879 /// map.insert("a", 1);
880 /// map.insert("b", 2);
881 /// map.insert("c", 3);
883 /// for (key, val) in map.iter() {
884 /// println!("key: {} val: {}", key, val);
887 #[stable(feature = "rust1", since = "1.0.0")]
888 pub fn iter(&self) -> Iter<K, V> {
889 Iter { inner: self.table.iter() }
892 /// An iterator visiting all key-value pairs in arbitrary order,
893 /// with mutable references to the values.
894 /// Iterator element type is `(&'a K, &'a mut V)`.
899 /// use std::collections::HashMap;
901 /// let mut map = HashMap::new();
902 /// map.insert("a", 1);
903 /// map.insert("b", 2);
904 /// map.insert("c", 3);
906 /// // Update all values
907 /// for (_, val) in map.iter_mut() {
911 /// for (key, val) in &map {
912 /// println!("key: {} val: {}", key, val);
915 #[stable(feature = "rust1", since = "1.0.0")]
916 pub fn iter_mut(&mut self) -> IterMut<K, V> {
917 IterMut { inner: self.table.iter_mut() }
920 /// Gets the given key's corresponding entry in the map for in-place manipulation.
925 /// use std::collections::HashMap;
927 /// let mut letters = HashMap::new();
929 /// for ch in "a short treatise on fungi".chars() {
930 /// let counter = letters.entry(ch).or_insert(0);
934 /// assert_eq!(letters[&'s'], 2);
935 /// assert_eq!(letters[&'t'], 3);
936 /// assert_eq!(letters[&'u'], 1);
937 /// assert_eq!(letters.get(&'y'), None);
939 #[stable(feature = "rust1", since = "1.0.0")]
940 pub fn entry(&mut self, key: K) -> Entry<K, V> {
943 self.search_mut(&key).into_entry(key).expect("unreachable")
946 /// Returns the number of elements in the map.
951 /// use std::collections::HashMap;
953 /// let mut a = HashMap::new();
954 /// assert_eq!(a.len(), 0);
955 /// a.insert(1, "a");
956 /// assert_eq!(a.len(), 1);
958 #[stable(feature = "rust1", since = "1.0.0")]
959 pub fn len(&self) -> usize { self.table.size() }
961 /// Returns true if the map contains no elements.
966 /// use std::collections::HashMap;
968 /// let mut a = HashMap::new();
969 /// assert!(a.is_empty());
970 /// a.insert(1, "a");
971 /// assert!(!a.is_empty());
974 #[stable(feature = "rust1", since = "1.0.0")]
975 pub fn is_empty(&self) -> bool { self.len() == 0 }
977 /// Clears the map, returning all key-value pairs as an iterator. Keeps the
978 /// allocated memory for reuse.
983 /// use std::collections::HashMap;
985 /// let mut a = HashMap::new();
986 /// a.insert(1, "a");
987 /// a.insert(2, "b");
989 /// for (k, v) in a.drain().take(1) {
990 /// assert!(k == 1 || k == 2);
991 /// assert!(v == "a" || v == "b");
994 /// assert!(a.is_empty());
997 #[stable(feature = "drain", since = "1.6.0")]
998 pub fn drain(&mut self) -> Drain<K, V> {
999 fn last_two<A, B, C>((_, b, c): (A, B, C)) -> (B, C) { (b, c) }
1000 let last_two: fn((SafeHash, K, V)) -> (K, V) = last_two; // coerce to fn pointer
1003 inner: self.table.drain().map(last_two),
1007 /// Clears the map, removing all key-value pairs. Keeps the allocated memory
1013 /// use std::collections::HashMap;
1015 /// let mut a = HashMap::new();
1016 /// a.insert(1, "a");
1018 /// assert!(a.is_empty());
1020 #[stable(feature = "rust1", since = "1.0.0")]
1022 pub fn clear(&mut self) {
1026 /// Returns a reference to the value corresponding to the key.
1028 /// The key may be any borrowed form of the map's key type, but
1029 /// `Hash` and `Eq` on the borrowed form *must* match those for
1035 /// use std::collections::HashMap;
1037 /// let mut map = HashMap::new();
1038 /// map.insert(1, "a");
1039 /// assert_eq!(map.get(&1), Some(&"a"));
1040 /// assert_eq!(map.get(&2), None);
1042 #[stable(feature = "rust1", since = "1.0.0")]
1043 pub fn get<Q: ?Sized>(&self, k: &Q) -> Option<&V>
1044 where K: Borrow<Q>, Q: Hash + Eq
1046 self.search(k).into_occupied_bucket().map(|bucket| bucket.into_refs().1)
1049 /// Returns true if the map contains a value for the specified key.
1051 /// The key may be any borrowed form of the map's key type, but
1052 /// `Hash` and `Eq` on the borrowed form *must* match those for
1058 /// use std::collections::HashMap;
1060 /// let mut map = HashMap::new();
1061 /// map.insert(1, "a");
1062 /// assert_eq!(map.contains_key(&1), true);
1063 /// assert_eq!(map.contains_key(&2), false);
1065 #[stable(feature = "rust1", since = "1.0.0")]
1066 pub fn contains_key<Q: ?Sized>(&self, k: &Q) -> bool
1067 where K: Borrow<Q>, Q: Hash + Eq
1069 self.search(k).into_occupied_bucket().is_some()
1072 /// Returns a mutable reference to the value corresponding to the key.
1074 /// The key may be any borrowed form of the map's key type, but
1075 /// `Hash` and `Eq` on the borrowed form *must* match those for
1081 /// use std::collections::HashMap;
1083 /// let mut map = HashMap::new();
1084 /// map.insert(1, "a");
1085 /// if let Some(x) = map.get_mut(&1) {
1088 /// assert_eq!(map[&1], "b");
1090 #[stable(feature = "rust1", since = "1.0.0")]
1091 pub fn get_mut<Q: ?Sized>(&mut self, k: &Q) -> Option<&mut V>
1092 where K: Borrow<Q>, Q: Hash + Eq
1094 self.search_mut(k).into_occupied_bucket().map(|bucket| bucket.into_mut_refs().1)
1097 /// Inserts a key-value pair into the map.
1099 /// If the map did not have this key present, `None` is returned.
1101 /// If the map did have this key present, the value is updated, and the old
1102 /// value is returned. The key is not updated, though; this matters for
1103 /// types that can be `==` without being identical. See the [module-level
1104 /// documentation] for more.
1106 /// [module-level documentation]: index.html#insert-and-complex-keys
1111 /// use std::collections::HashMap;
1113 /// let mut map = HashMap::new();
1114 /// assert_eq!(map.insert(37, "a"), None);
1115 /// assert_eq!(map.is_empty(), false);
1117 /// map.insert(37, "b");
1118 /// assert_eq!(map.insert(37, "c"), Some("b"));
1119 /// assert_eq!(map[&37], "c");
1121 #[stable(feature = "rust1", since = "1.0.0")]
1122 pub fn insert(&mut self, k: K, v: V) -> Option<V> {
1123 let hash = self.make_hash(&k);
1125 self.insert_hashed_nocheck(hash, k, v)
1128 /// Removes a key from the map, returning the value at the key if the key
1129 /// was previously in the map.
1131 /// The key may be any borrowed form of the map's key type, but
1132 /// `Hash` and `Eq` on the borrowed form *must* match those for
1138 /// use std::collections::HashMap;
1140 /// let mut map = HashMap::new();
1141 /// map.insert(1, "a");
1142 /// assert_eq!(map.remove(&1), Some("a"));
1143 /// assert_eq!(map.remove(&1), None);
1145 #[stable(feature = "rust1", since = "1.0.0")]
1146 pub fn remove<Q: ?Sized>(&mut self, k: &Q) -> Option<V>
1147 where K: Borrow<Q>, Q: Hash + Eq
1149 if self.table.size() == 0 {
1153 self.search_mut(k).into_occupied_bucket().map(|bucket| pop_internal(bucket).1)
1157 #[stable(feature = "rust1", since = "1.0.0")]
1158 impl<K, V, S> PartialEq for HashMap<K, V, S>
1159 where K: Eq + Hash, V: PartialEq, S: BuildHasher
1161 fn eq(&self, other: &HashMap<K, V, S>) -> bool {
1162 if self.len() != other.len() { return false; }
1164 self.iter().all(|(key, value)|
1165 other.get(key).map_or(false, |v| *value == *v)
1170 #[stable(feature = "rust1", since = "1.0.0")]
1171 impl<K, V, S> Eq for HashMap<K, V, S>
1172 where K: Eq + Hash, V: Eq, S: BuildHasher
1175 #[stable(feature = "rust1", since = "1.0.0")]
1176 impl<K, V, S> Debug for HashMap<K, V, S>
1177 where K: Eq + Hash + Debug, V: Debug, S: BuildHasher
1179 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1180 f.debug_map().entries(self.iter()).finish()
1184 #[stable(feature = "rust1", since = "1.0.0")]
1185 impl<K, V, S> Default for HashMap<K, V, S>
1187 S: BuildHasher + Default,
1189 fn default() -> HashMap<K, V, S> {
1190 HashMap::with_hasher(Default::default())
1194 #[stable(feature = "rust1", since = "1.0.0")]
1195 impl<'a, K, Q: ?Sized, V, S> Index<&'a Q> for HashMap<K, V, S>
1196 where K: Eq + Hash + Borrow<Q>,
1203 fn index(&self, index: &Q) -> &V {
1204 self.get(index).expect("no entry found for key")
1208 /// HashMap iterator.
1209 #[stable(feature = "rust1", since = "1.0.0")]
1210 pub struct Iter<'a, K: 'a, V: 'a> {
1211 inner: table::Iter<'a, K, V>
1214 // FIXME(#19839) Remove in favor of `#[derive(Clone)]`
1215 #[stable(feature = "rust1", since = "1.0.0")]
1216 impl<'a, K, V> Clone for Iter<'a, K, V> {
1217 fn clone(&self) -> Iter<'a, K, V> {
1219 inner: self.inner.clone()
1224 /// HashMap mutable values iterator.
1225 #[stable(feature = "rust1", since = "1.0.0")]
1226 pub struct IterMut<'a, K: 'a, V: 'a> {
1227 inner: table::IterMut<'a, K, V>
1230 /// HashMap move iterator.
1231 #[stable(feature = "rust1", since = "1.0.0")]
1232 pub struct IntoIter<K, V> {
1233 inner: iter::Map<table::IntoIter<K, V>, fn((SafeHash, K, V)) -> (K, V)>
1236 /// HashMap keys iterator.
1237 #[stable(feature = "rust1", since = "1.0.0")]
1238 pub struct Keys<'a, K: 'a, V: 'a> {
1239 inner: Map<Iter<'a, K, V>, fn((&'a K, &'a V)) -> &'a K>
1242 // FIXME(#19839) Remove in favor of `#[derive(Clone)]`
1243 #[stable(feature = "rust1", since = "1.0.0")]
1244 impl<'a, K, V> Clone for Keys<'a, K, V> {
1245 fn clone(&self) -> Keys<'a, K, V> {
1247 inner: self.inner.clone()
1252 /// HashMap values iterator.
1253 #[stable(feature = "rust1", since = "1.0.0")]
1254 pub struct Values<'a, K: 'a, V: 'a> {
1255 inner: Map<Iter<'a, K, V>, fn((&'a K, &'a V)) -> &'a V>
1258 // FIXME(#19839) Remove in favor of `#[derive(Clone)]`
1259 #[stable(feature = "rust1", since = "1.0.0")]
1260 impl<'a, K, V> Clone for Values<'a, K, V> {
1261 fn clone(&self) -> Values<'a, K, V> {
1263 inner: self.inner.clone()
1268 /// HashMap drain iterator.
1269 #[stable(feature = "drain", since = "1.6.0")]
1270 pub struct Drain<'a, K: 'a, V: 'a> {
1271 inner: iter::Map<table::Drain<'a, K, V>, fn((SafeHash, K, V)) -> (K, V)>
1274 enum InternalEntry<K, V, M> {
1276 elem: FullBucket<K, V, M>,
1280 elem: VacantEntryState<K, V, M>,
1285 impl<K, V, M> InternalEntry<K, V, M> {
1287 fn into_occupied_bucket(self) -> Option<FullBucket<K, V, M>> {
1289 InternalEntry::Occupied { elem } => Some(elem),
1295 impl<'a, K, V> InternalEntry<K, V, &'a mut RawTable<K, V>> {
1297 fn into_entry(self, key: K) -> Option<Entry<'a, K, V>> {
1299 InternalEntry::Occupied { elem } => {
1300 Some(Occupied(OccupiedEntry {
1305 InternalEntry::Vacant { hash, elem } => {
1306 Some(Vacant(VacantEntry {
1312 InternalEntry::TableIsEmpty => None
1317 /// A view into a single location in a map, which may be vacant or occupied.
1318 #[stable(feature = "rust1", since = "1.0.0")]
1319 pub enum Entry<'a, K: 'a, V: 'a> {
1320 /// An occupied Entry.
1321 #[stable(feature = "rust1", since = "1.0.0")]
1323 #[stable(feature = "rust1", since = "1.0.0")] OccupiedEntry<'a, K, V>
1327 #[stable(feature = "rust1", since = "1.0.0")]
1329 #[stable(feature = "rust1", since = "1.0.0")] VacantEntry<'a, K, V>
1333 /// A view into a single occupied location in a HashMap.
1334 #[stable(feature = "rust1", since = "1.0.0")]
1335 pub struct OccupiedEntry<'a, K: 'a, V: 'a> {
1337 elem: FullBucket<K, V, &'a mut RawTable<K, V>>,
1340 /// A view into a single empty location in a HashMap.
1341 #[stable(feature = "rust1", since = "1.0.0")]
1342 pub struct VacantEntry<'a, K: 'a, V: 'a> {
1345 elem: VacantEntryState<K, V, &'a mut RawTable<K, V>>,
1348 /// Possible states of a VacantEntry.
1349 enum VacantEntryState<K, V, M> {
1350 /// The index is occupied, but the key to insert has precedence,
1351 /// and will kick the current one out on insertion.
1352 NeqElem(FullBucket<K, V, M>, usize),
1353 /// The index is genuinely vacant.
1354 NoElem(EmptyBucket<K, V, M>),
1357 #[stable(feature = "rust1", since = "1.0.0")]
1358 impl<'a, K, V, S> IntoIterator for &'a HashMap<K, V, S>
1359 where K: Eq + Hash, S: BuildHasher
1361 type Item = (&'a K, &'a V);
1362 type IntoIter = Iter<'a, K, V>;
1364 fn into_iter(self) -> Iter<'a, K, V> {
1369 #[stable(feature = "rust1", since = "1.0.0")]
1370 impl<'a, K, V, S> IntoIterator for &'a mut HashMap<K, V, S>
1371 where K: Eq + Hash, S: BuildHasher
1373 type Item = (&'a K, &'a mut V);
1374 type IntoIter = IterMut<'a, K, V>;
1376 fn into_iter(mut self) -> IterMut<'a, K, V> {
1381 #[stable(feature = "rust1", since = "1.0.0")]
1382 impl<K, V, S> IntoIterator for HashMap<K, V, S>
1383 where K: Eq + Hash, S: BuildHasher
1386 type IntoIter = IntoIter<K, V>;
1388 /// Creates a consuming iterator, that is, one that moves each key-value
1389 /// pair out of the map in arbitrary order. The map cannot be used after
1395 /// use std::collections::HashMap;
1397 /// let mut map = HashMap::new();
1398 /// map.insert("a", 1);
1399 /// map.insert("b", 2);
1400 /// map.insert("c", 3);
1402 /// // Not possible with .iter()
1403 /// let vec: Vec<(&str, isize)> = map.into_iter().collect();
1405 fn into_iter(self) -> IntoIter<K, V> {
1406 fn last_two<A, B, C>((_, b, c): (A, B, C)) -> (B, C) { (b, c) }
1407 let last_two: fn((SafeHash, K, V)) -> (K, V) = last_two;
1410 inner: self.table.into_iter().map(last_two)
1415 #[stable(feature = "rust1", since = "1.0.0")]
1416 impl<'a, K, V> Iterator for Iter<'a, K, V> {
1417 type Item = (&'a K, &'a V);
1419 #[inline] fn next(&mut self) -> Option<(&'a K, &'a V)> { self.inner.next() }
1420 #[inline] fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
1422 #[stable(feature = "rust1", since = "1.0.0")]
1423 impl<'a, K, V> ExactSizeIterator for Iter<'a, K, V> {
1424 #[inline] fn len(&self) -> usize { self.inner.len() }
1427 #[stable(feature = "rust1", since = "1.0.0")]
1428 impl<'a, K, V> Iterator for IterMut<'a, K, V> {
1429 type Item = (&'a K, &'a mut V);
1431 #[inline] fn next(&mut self) -> Option<(&'a K, &'a mut V)> { self.inner.next() }
1432 #[inline] fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
1434 #[stable(feature = "rust1", since = "1.0.0")]
1435 impl<'a, K, V> ExactSizeIterator for IterMut<'a, K, V> {
1436 #[inline] fn len(&self) -> usize { self.inner.len() }
1439 #[stable(feature = "rust1", since = "1.0.0")]
1440 impl<K, V> Iterator for IntoIter<K, V> {
1443 #[inline] fn next(&mut self) -> Option<(K, V)> { self.inner.next() }
1444 #[inline] fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
1446 #[stable(feature = "rust1", since = "1.0.0")]
1447 impl<K, V> ExactSizeIterator for IntoIter<K, V> {
1448 #[inline] fn len(&self) -> usize { self.inner.len() }
1451 #[stable(feature = "rust1", since = "1.0.0")]
1452 impl<'a, K, V> Iterator for Keys<'a, K, V> {
1455 #[inline] fn next(&mut self) -> Option<(&'a K)> { self.inner.next() }
1456 #[inline] fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
1458 #[stable(feature = "rust1", since = "1.0.0")]
1459 impl<'a, K, V> ExactSizeIterator for Keys<'a, K, V> {
1460 #[inline] fn len(&self) -> usize { self.inner.len() }
1463 #[stable(feature = "rust1", since = "1.0.0")]
1464 impl<'a, K, V> Iterator for Values<'a, K, V> {
1467 #[inline] fn next(&mut self) -> Option<(&'a V)> { self.inner.next() }
1468 #[inline] fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
1470 #[stable(feature = "rust1", since = "1.0.0")]
1471 impl<'a, K, V> ExactSizeIterator for Values<'a, K, V> {
1472 #[inline] fn len(&self) -> usize { self.inner.len() }
1475 #[stable(feature = "rust1", since = "1.0.0")]
1476 impl<'a, K, V> Iterator for Drain<'a, K, V> {
1479 #[inline] fn next(&mut self) -> Option<(K, V)> { self.inner.next() }
1480 #[inline] fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
1482 #[stable(feature = "rust1", since = "1.0.0")]
1483 impl<'a, K, V> ExactSizeIterator for Drain<'a, K, V> {
1484 #[inline] fn len(&self) -> usize { self.inner.len() }
1487 impl<'a, K, V> Entry<'a, K, V> {
1488 #[stable(feature = "rust1", since = "1.0.0")]
1489 /// Ensures a value is in the entry by inserting the default if empty, and returns
1490 /// a mutable reference to the value in the entry.
1491 pub fn or_insert(self, default: V) -> &'a mut V {
1493 Occupied(entry) => entry.into_mut(),
1494 Vacant(entry) => entry.insert(default),
1498 #[stable(feature = "rust1", since = "1.0.0")]
1499 /// Ensures a value is in the entry by inserting the result of the default function if empty,
1500 /// and returns a mutable reference to the value in the entry.
1501 pub fn or_insert_with<F: FnOnce() -> V>(self, default: F) -> &'a mut V {
1503 Occupied(entry) => entry.into_mut(),
1504 Vacant(entry) => entry.insert(default()),
1509 impl<'a, K, V> OccupiedEntry<'a, K, V> {
1510 /// Gets a reference to the key in the entry.
1511 #[unstable(feature = "map_entry_keys", issue = "32281")]
1512 pub fn key(&self) -> &K {
1516 /// Gets a reference to the value in the entry.
1517 #[stable(feature = "rust1", since = "1.0.0")]
1518 pub fn get(&self) -> &V {
1522 /// Gets a mutable reference to the value in the entry.
1523 #[stable(feature = "rust1", since = "1.0.0")]
1524 pub fn get_mut(&mut self) -> &mut V {
1525 self.elem.read_mut().1
1528 /// Converts the OccupiedEntry into a mutable reference to the value in the entry
1529 /// with a lifetime bound to the map itself
1530 #[stable(feature = "rust1", since = "1.0.0")]
1531 pub fn into_mut(self) -> &'a mut V {
1532 self.elem.into_mut_refs().1
1535 /// Sets the value of the entry, and returns the entry's old value
1536 #[stable(feature = "rust1", since = "1.0.0")]
1537 pub fn insert(&mut self, mut value: V) -> V {
1538 let old_value = self.get_mut();
1539 mem::swap(&mut value, old_value);
1543 /// Takes the value out of the entry, and returns it
1544 #[stable(feature = "rust1", since = "1.0.0")]
1545 pub fn remove(self) -> V {
1546 pop_internal(self.elem).1
1548 /// Returns a key that was used for search.
1550 /// The key was retained for further use.
1551 fn take_key(&mut self) -> Option<K> {
1556 impl<'a, K: 'a, V: 'a> VacantEntry<'a, K, V> {
1557 /// Gets a reference to the key that would be used when inserting a value
1558 /// through the VacantEntry.
1559 #[unstable(feature = "map_entry_keys", issue = "32281")]
1560 pub fn key(&self) -> &K {
1564 /// Sets the value of the entry with the VacantEntry's key,
1565 /// and returns a mutable reference to it
1566 #[stable(feature = "rust1", since = "1.0.0")]
1567 pub fn insert(self, value: V) -> &'a mut V {
1569 NeqElem(bucket, ib) => {
1570 robin_hood(bucket, ib, self.hash, self.key, value)
1573 bucket.put(self.hash, self.key, value).into_mut_refs().1
1579 #[stable(feature = "rust1", since = "1.0.0")]
1580 impl<K, V, S> FromIterator<(K, V)> for HashMap<K, V, S>
1581 where K: Eq + Hash, S: BuildHasher + Default
1583 fn from_iter<T: IntoIterator<Item=(K, V)>>(iterable: T) -> HashMap<K, V, S> {
1584 let iter = iterable.into_iter();
1585 let lower = iter.size_hint().0;
1586 let mut map = HashMap::with_capacity_and_hasher(lower, Default::default());
1592 #[stable(feature = "rust1", since = "1.0.0")]
1593 impl<K, V, S> Extend<(K, V)> for HashMap<K, V, S>
1594 where K: Eq + Hash, S: BuildHasher
1596 fn extend<T: IntoIterator<Item=(K, V)>>(&mut self, iter: T) {
1597 for (k, v) in iter {
1603 #[stable(feature = "hash_extend_copy", since = "1.4.0")]
1604 impl<'a, K, V, S> Extend<(&'a K, &'a V)> for HashMap<K, V, S>
1605 where K: Eq + Hash + Copy, V: Copy, S: BuildHasher
1607 fn extend<T: IntoIterator<Item=(&'a K, &'a V)>>(&mut self, iter: T) {
1608 self.extend(iter.into_iter().map(|(&key, &value)| (key, value)));
1612 /// `RandomState` is the default state for `HashMap` types.
1614 /// A particular instance `RandomState` will create the same instances of
1615 /// `Hasher`, but the hashers created by two different `RandomState`
1616 /// instances are unlikely to produce the same result for the same values.
1618 #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
1619 pub struct RandomState {
1625 /// Constructs a new `RandomState` that is initialized with random keys.
1627 #[allow(deprecated)] // rand
1628 #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
1629 pub fn new() -> RandomState {
1630 let mut r = rand::thread_rng();
1631 RandomState { k0: r.gen(), k1: r.gen() }
1635 #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
1636 impl BuildHasher for RandomState {
1637 type Hasher = SipHasher;
1639 fn build_hasher(&self) -> SipHasher {
1640 SipHasher::new_with_keys(self.k0, self.k1)
1644 #[stable(feature = "rust1", since = "1.0.0")]
1645 impl Default for RandomState {
1647 fn default() -> RandomState {
1652 impl<K, S, Q: ?Sized> super::Recover<Q> for HashMap<K, (), S>
1653 where K: Eq + Hash + Borrow<Q>, S: BuildHasher, Q: Eq + Hash
1657 fn get(&self, key: &Q) -> Option<&K> {
1658 self.search(key).into_occupied_bucket().map(|bucket| bucket.into_refs().0)
1661 fn take(&mut self, key: &Q) -> Option<K> {
1662 if self.table.size() == 0 {
1666 self.search_mut(key).into_occupied_bucket().map(|bucket| pop_internal(bucket).0)
1669 fn replace(&mut self, key: K) -> Option<K> {
1672 match self.entry(key) {
1673 Occupied(mut occupied) => {
1674 let key = occupied.take_key().unwrap();
1675 Some(mem::replace(occupied.elem.read_mut().0, key))
1690 use super::Entry::{Occupied, Vacant};
1692 use rand::{thread_rng, Rng};
1695 fn test_create_capacity_zero() {
1696 let mut m = HashMap::with_capacity(0);
1698 assert!(m.insert(1, 1).is_none());
1700 assert!(m.contains_key(&1));
1701 assert!(!m.contains_key(&0));
1706 let mut m = HashMap::new();
1707 assert_eq!(m.len(), 0);
1708 assert!(m.insert(1, 2).is_none());
1709 assert_eq!(m.len(), 1);
1710 assert!(m.insert(2, 4).is_none());
1711 assert_eq!(m.len(), 2);
1712 assert_eq!(*m.get(&1).unwrap(), 2);
1713 assert_eq!(*m.get(&2).unwrap(), 4);
1718 let mut m = HashMap::new();
1719 assert_eq!(m.len(), 0);
1720 assert!(m.insert(1, 2).is_none());
1721 assert_eq!(m.len(), 1);
1722 assert!(m.insert(2, 4).is_none());
1723 assert_eq!(m.len(), 2);
1725 assert_eq!(*m2.get(&1).unwrap(), 2);
1726 assert_eq!(*m2.get(&2).unwrap(), 4);
1727 assert_eq!(m2.len(), 2);
1730 thread_local! { static DROP_VECTOR: RefCell<Vec<isize>> = RefCell::new(Vec::new()) }
1732 #[derive(Hash, PartialEq, Eq)]
1738 fn new(k: usize) -> Dropable {
1739 DROP_VECTOR.with(|slot| {
1740 slot.borrow_mut()[k] += 1;
1747 impl Drop for Dropable {
1748 fn drop(&mut self) {
1749 DROP_VECTOR.with(|slot| {
1750 slot.borrow_mut()[self.k] -= 1;
1755 impl Clone for Dropable {
1756 fn clone(&self) -> Dropable {
1757 Dropable::new(self.k)
1763 DROP_VECTOR.with(|slot| {
1764 *slot.borrow_mut() = vec![0; 200];
1768 let mut m = HashMap::new();
1770 DROP_VECTOR.with(|v| {
1772 assert_eq!(v.borrow()[i], 0);
1777 let d1 = Dropable::new(i);
1778 let d2 = Dropable::new(i+100);
1782 DROP_VECTOR.with(|v| {
1784 assert_eq!(v.borrow()[i], 1);
1789 let k = Dropable::new(i);
1790 let v = m.remove(&k);
1792 assert!(v.is_some());
1794 DROP_VECTOR.with(|v| {
1795 assert_eq!(v.borrow()[i], 1);
1796 assert_eq!(v.borrow()[i+100], 1);
1800 DROP_VECTOR.with(|v| {
1802 assert_eq!(v.borrow()[i], 0);
1803 assert_eq!(v.borrow()[i+100], 0);
1807 assert_eq!(v.borrow()[i], 1);
1808 assert_eq!(v.borrow()[i+100], 1);
1813 DROP_VECTOR.with(|v| {
1815 assert_eq!(v.borrow()[i], 0);
1821 fn test_into_iter_drops() {
1822 DROP_VECTOR.with(|v| {
1823 *v.borrow_mut() = vec![0; 200];
1827 let mut hm = HashMap::new();
1829 DROP_VECTOR.with(|v| {
1831 assert_eq!(v.borrow()[i], 0);
1836 let d1 = Dropable::new(i);
1837 let d2 = Dropable::new(i+100);
1841 DROP_VECTOR.with(|v| {
1843 assert_eq!(v.borrow()[i], 1);
1850 // By the way, ensure that cloning doesn't screw up the dropping.
1854 let mut half = hm.into_iter().take(50);
1856 DROP_VECTOR.with(|v| {
1858 assert_eq!(v.borrow()[i], 1);
1862 for _ in half.by_ref() {}
1864 DROP_VECTOR.with(|v| {
1865 let nk = (0..100).filter(|&i| {
1869 let nv = (0..100).filter(|&i| {
1870 v.borrow()[i+100] == 1
1878 DROP_VECTOR.with(|v| {
1880 assert_eq!(v.borrow()[i], 0);
1886 fn test_empty_remove() {
1887 let mut m: HashMap<isize, bool> = HashMap::new();
1888 assert_eq!(m.remove(&0), None);
1892 fn test_empty_entry() {
1893 let mut m: HashMap<isize, bool> = HashMap::new();
1895 Occupied(_) => panic!(),
1898 assert!(*m.entry(0).or_insert(true));
1899 assert_eq!(m.len(), 1);
1903 fn test_empty_iter() {
1904 let mut m: HashMap<isize, bool> = HashMap::new();
1905 assert_eq!(m.drain().next(), None);
1906 assert_eq!(m.keys().next(), None);
1907 assert_eq!(m.values().next(), None);
1908 assert_eq!(m.iter().next(), None);
1909 assert_eq!(m.iter_mut().next(), None);
1910 assert_eq!(m.len(), 0);
1911 assert!(m.is_empty());
1912 assert_eq!(m.into_iter().next(), None);
1916 fn test_lots_of_insertions() {
1917 let mut m = HashMap::new();
1919 // Try this a few times to make sure we never screw up the hashmap's
1922 assert!(m.is_empty());
1925 assert!(m.insert(i, i).is_none());
1929 assert_eq!(r, Some(&j));
1932 for j in i+1..1001 {
1934 assert_eq!(r, None);
1938 for i in 1001..2001 {
1939 assert!(!m.contains_key(&i));
1944 assert!(m.remove(&i).is_some());
1947 assert!(!m.contains_key(&j));
1950 for j in i+1..1001 {
1951 assert!(m.contains_key(&j));
1956 assert!(!m.contains_key(&i));
1960 assert!(m.insert(i, i).is_none());
1964 for i in (1..1001).rev() {
1965 assert!(m.remove(&i).is_some());
1968 assert!(!m.contains_key(&j));
1972 assert!(m.contains_key(&j));
1979 fn test_find_mut() {
1980 let mut m = HashMap::new();
1981 assert!(m.insert(1, 12).is_none());
1982 assert!(m.insert(2, 8).is_none());
1983 assert!(m.insert(5, 14).is_none());
1985 match m.get_mut(&5) {
1986 None => panic!(), Some(x) => *x = new
1988 assert_eq!(m.get(&5), Some(&new));
1992 fn test_insert_overwrite() {
1993 let mut m = HashMap::new();
1994 assert!(m.insert(1, 2).is_none());
1995 assert_eq!(*m.get(&1).unwrap(), 2);
1996 assert!(!m.insert(1, 3).is_none());
1997 assert_eq!(*m.get(&1).unwrap(), 3);
2001 fn test_insert_conflicts() {
2002 let mut m = HashMap::with_capacity(4);
2003 assert!(m.insert(1, 2).is_none());
2004 assert!(m.insert(5, 3).is_none());
2005 assert!(m.insert(9, 4).is_none());
2006 assert_eq!(*m.get(&9).unwrap(), 4);
2007 assert_eq!(*m.get(&5).unwrap(), 3);
2008 assert_eq!(*m.get(&1).unwrap(), 2);
2012 fn test_conflict_remove() {
2013 let mut m = HashMap::with_capacity(4);
2014 assert!(m.insert(1, 2).is_none());
2015 assert_eq!(*m.get(&1).unwrap(), 2);
2016 assert!(m.insert(5, 3).is_none());
2017 assert_eq!(*m.get(&1).unwrap(), 2);
2018 assert_eq!(*m.get(&5).unwrap(), 3);
2019 assert!(m.insert(9, 4).is_none());
2020 assert_eq!(*m.get(&1).unwrap(), 2);
2021 assert_eq!(*m.get(&5).unwrap(), 3);
2022 assert_eq!(*m.get(&9).unwrap(), 4);
2023 assert!(m.remove(&1).is_some());
2024 assert_eq!(*m.get(&9).unwrap(), 4);
2025 assert_eq!(*m.get(&5).unwrap(), 3);
2029 fn test_is_empty() {
2030 let mut m = HashMap::with_capacity(4);
2031 assert!(m.insert(1, 2).is_none());
2032 assert!(!m.is_empty());
2033 assert!(m.remove(&1).is_some());
2034 assert!(m.is_empty());
2039 let mut m = HashMap::new();
2041 assert_eq!(m.remove(&1), Some(2));
2042 assert_eq!(m.remove(&1), None);
2047 let mut m = HashMap::with_capacity(4);
2049 assert!(m.insert(i, i*2).is_none());
2051 assert_eq!(m.len(), 32);
2053 let mut observed: u32 = 0;
2056 assert_eq!(*v, *k * 2);
2057 observed |= 1 << *k;
2059 assert_eq!(observed, 0xFFFF_FFFF);
2064 let vec = vec![(1, 'a'), (2, 'b'), (3, 'c')];
2065 let map: HashMap<_, _> = vec.into_iter().collect();
2066 let keys: Vec<_> = map.keys().cloned().collect();
2067 assert_eq!(keys.len(), 3);
2068 assert!(keys.contains(&1));
2069 assert!(keys.contains(&2));
2070 assert!(keys.contains(&3));
2075 let vec = vec![(1, 'a'), (2, 'b'), (3, 'c')];
2076 let map: HashMap<_, _> = vec.into_iter().collect();
2077 let values: Vec<_> = map.values().cloned().collect();
2078 assert_eq!(values.len(), 3);
2079 assert!(values.contains(&'a'));
2080 assert!(values.contains(&'b'));
2081 assert!(values.contains(&'c'));
2086 let mut m = HashMap::new();
2087 assert!(m.get(&1).is_none());
2091 Some(v) => assert_eq!(*v, 2)
2097 let mut m1 = HashMap::new();
2102 let mut m2 = HashMap::new();
2115 let mut map = HashMap::new();
2116 let empty: HashMap<i32, i32> = HashMap::new();
2121 let map_str = format!("{:?}", map);
2123 assert!(map_str == "{1: 2, 3: 4}" ||
2124 map_str == "{3: 4, 1: 2}");
2125 assert_eq!(format!("{:?}", empty), "{}");
2130 let mut m = HashMap::new();
2132 assert_eq!(m.len(), 0);
2133 assert!(m.is_empty());
2136 let old_cap = m.table.capacity();
2137 while old_cap == m.table.capacity() {
2142 assert_eq!(m.len(), i);
2143 assert!(!m.is_empty());
2147 fn test_behavior_resize_policy() {
2148 let mut m = HashMap::new();
2150 assert_eq!(m.len(), 0);
2151 assert_eq!(m.table.capacity(), 0);
2152 assert!(m.is_empty());
2156 assert!(m.is_empty());
2157 let initial_cap = m.table.capacity();
2158 m.reserve(initial_cap);
2159 let cap = m.table.capacity();
2161 assert_eq!(cap, initial_cap * 2);
2164 for _ in 0..cap * 3 / 4 {
2168 // three quarters full
2170 assert_eq!(m.len(), i);
2171 assert_eq!(m.table.capacity(), cap);
2173 for _ in 0..cap / 4 {
2179 let new_cap = m.table.capacity();
2180 assert_eq!(new_cap, cap * 2);
2182 for _ in 0..cap / 2 - 1 {
2185 assert_eq!(m.table.capacity(), new_cap);
2187 // A little more than one quarter full.
2189 assert_eq!(m.table.capacity(), cap);
2190 // again, a little more than half full
2191 for _ in 0..cap / 2 - 1 {
2197 assert_eq!(m.len(), i);
2198 assert!(!m.is_empty());
2199 assert_eq!(m.table.capacity(), initial_cap);
2203 fn test_reserve_shrink_to_fit() {
2204 let mut m = HashMap::new();
2207 assert!(m.capacity() >= m.len());
2213 let usable_cap = m.capacity();
2214 for i in 128..(128 + 256) {
2216 assert_eq!(m.capacity(), usable_cap);
2219 for i in 100..(128 + 256) {
2220 assert_eq!(m.remove(&i), Some(i));
2224 assert_eq!(m.len(), 100);
2225 assert!(!m.is_empty());
2226 assert!(m.capacity() >= m.len());
2229 assert_eq!(m.remove(&i), Some(i));
2234 assert_eq!(m.len(), 1);
2235 assert!(m.capacity() >= m.len());
2236 assert_eq!(m.remove(&0), Some(0));
2240 fn test_from_iter() {
2241 let xs = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
2243 let map: HashMap<_, _> = xs.iter().cloned().collect();
2245 for &(k, v) in &xs {
2246 assert_eq!(map.get(&k), Some(&v));
2251 fn test_size_hint() {
2252 let xs = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
2254 let map: HashMap<_, _> = xs.iter().cloned().collect();
2256 let mut iter = map.iter();
2258 for _ in iter.by_ref().take(3) {}
2260 assert_eq!(iter.size_hint(), (3, Some(3)));
2264 fn test_iter_len() {
2265 let xs = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
2267 let map: HashMap<_, _> = xs.iter().cloned().collect();
2269 let mut iter = map.iter();
2271 for _ in iter.by_ref().take(3) {}
2273 assert_eq!(iter.len(), 3);
2277 fn test_mut_size_hint() {
2278 let xs = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
2280 let mut map: HashMap<_, _> = xs.iter().cloned().collect();
2282 let mut iter = map.iter_mut();
2284 for _ in iter.by_ref().take(3) {}
2286 assert_eq!(iter.size_hint(), (3, Some(3)));
2290 fn test_iter_mut_len() {
2291 let xs = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
2293 let mut map: HashMap<_, _> = xs.iter().cloned().collect();
2295 let mut iter = map.iter_mut();
2297 for _ in iter.by_ref().take(3) {}
2299 assert_eq!(iter.len(), 3);
2304 let mut map = HashMap::new();
2310 assert_eq!(map[&2], 1);
2315 fn test_index_nonexistent() {
2316 let mut map = HashMap::new();
2327 let xs = [(1, 10), (2, 20), (3, 30), (4, 40), (5, 50), (6, 60)];
2329 let mut map: HashMap<_, _> = xs.iter().cloned().collect();
2331 // Existing key (insert)
2332 match map.entry(1) {
2333 Vacant(_) => unreachable!(),
2334 Occupied(mut view) => {
2335 assert_eq!(view.get(), &10);
2336 assert_eq!(view.insert(100), 10);
2339 assert_eq!(map.get(&1).unwrap(), &100);
2340 assert_eq!(map.len(), 6);
2343 // Existing key (update)
2344 match map.entry(2) {
2345 Vacant(_) => unreachable!(),
2346 Occupied(mut view) => {
2347 let v = view.get_mut();
2348 let new_v = (*v) * 10;
2352 assert_eq!(map.get(&2).unwrap(), &200);
2353 assert_eq!(map.len(), 6);
2355 // Existing key (take)
2356 match map.entry(3) {
2357 Vacant(_) => unreachable!(),
2359 assert_eq!(view.remove(), 30);
2362 assert_eq!(map.get(&3), None);
2363 assert_eq!(map.len(), 5);
2366 // Inexistent key (insert)
2367 match map.entry(10) {
2368 Occupied(_) => unreachable!(),
2370 assert_eq!(*view.insert(1000), 1000);
2373 assert_eq!(map.get(&10).unwrap(), &1000);
2374 assert_eq!(map.len(), 6);
2378 fn test_entry_take_doesnt_corrupt() {
2379 #![allow(deprecated)] //rand
2381 fn check(m: &HashMap<isize, ()>) {
2383 assert!(m.contains_key(k),
2384 "{} is in keys() but not in the map?", k);
2388 let mut m = HashMap::new();
2389 let mut rng = thread_rng();
2391 // Populate the map with some items.
2393 let x = rng.gen_range(-10, 10);
2398 let x = rng.gen_range(-10, 10);
2402 println!("{}: remove {}", i, x);
2412 fn test_extend_ref() {
2413 let mut a = HashMap::new();
2415 let mut b = HashMap::new();
2417 b.insert(3, "three");
2421 assert_eq!(a.len(), 3);
2422 assert_eq!(a[&1], "one");
2423 assert_eq!(a[&2], "two");
2424 assert_eq!(a[&3], "three");
2428 fn test_capacity_not_less_than_len() {
2429 let mut a = HashMap::new();
2437 assert!(a.capacity() > a.len());
2439 let free = a.capacity() - a.len();
2445 assert_eq!(a.len(), a.capacity());
2447 // Insert at capacity should cause allocation.
2449 assert!(a.capacity() > a.len());
2453 fn test_occupied_entry_key() {
2454 let mut a = HashMap::new();
2455 let key = "hello there";
2456 let value = "value goes here";
2457 assert!(a.is_empty());
2458 a.insert(key.clone(), value.clone());
2459 assert_eq!(a.len(), 1);
2460 assert_eq!(a[key], value);
2462 match a.entry(key.clone()) {
2463 Vacant(_) => panic!(),
2464 Occupied(e) => assert_eq!(key, *e.key()),
2466 assert_eq!(a.len(), 1);
2467 assert_eq!(a[key], value);
2471 fn test_vacant_entry_key() {
2472 let mut a = HashMap::new();
2473 let key = "hello there";
2474 let value = "value goes here";
2476 assert!(a.is_empty());
2477 match a.entry(key.clone()) {
2478 Occupied(_) => panic!(),
2480 assert_eq!(key, *e.key());
2481 e.insert(value.clone());
2484 assert_eq!(a.len(), 1);
2485 assert_eq!(a[key], value);