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::*;
17 use fmt::{self, Debug};
19 use hash::{Hash, Hasher, BuildHasher, SipHasher13};
20 use iter::{FromIterator, FusedIterator};
21 use mem::{self, replace};
22 use ops::{Deref, Index, InPlace, Place, Placer};
26 use super::table::{self, Bucket, EmptyBucket, FullBucket, FullBucketMut, RawTable, SafeHash};
27 use super::table::BucketState::{Empty, Full};
29 const MIN_NONZERO_RAW_CAPACITY: usize = 32; // must be a power of two
31 /// The default behavior of HashMap implements a maximum load factor of 90.9%.
33 struct DefaultResizePolicy;
35 impl DefaultResizePolicy {
36 fn new() -> DefaultResizePolicy {
40 /// A hash map's "capacity" is the number of elements it can hold without
41 /// being resized. Its "raw capacity" is the number of slots required to
42 /// provide that capacity, accounting for maximum loading. The raw capacity
43 /// is always zero or a power of two.
45 fn raw_capacity(&self, len: usize) -> usize {
49 // 1. Account for loading: `raw_capacity >= len * 1.1`.
50 // 2. Ensure it is a power of two.
51 // 3. Ensure it is at least the minimum size.
52 let mut raw_cap = len * 11 / 10;
53 assert!(raw_cap >= len, "raw_cap overflow");
54 raw_cap = raw_cap.checked_next_power_of_two().expect("raw_capacity overflow");
55 raw_cap = max(MIN_NONZERO_RAW_CAPACITY, raw_cap);
60 /// The capacity of the given raw capacity.
62 fn capacity(&self, raw_cap: usize) -> usize {
63 // This doesn't have to be checked for overflow since allocation size
64 // in bytes will overflow earlier than multiplication by 10.
66 // As per https://github.com/rust-lang/rust/pull/30991 this is updated
67 // to be: (raw_cap * den + den - 1) / num
68 (raw_cap * 10 + 10 - 1) / 11
72 // The main performance trick in this hashmap is called Robin Hood Hashing.
73 // It gains its excellent performance from one essential operation:
75 // If an insertion collides with an existing element, and that element's
76 // "probe distance" (how far away the element is from its ideal location)
77 // is higher than how far we've already probed, swap the elements.
79 // This massively lowers variance in probe distance, and allows us to get very
80 // high load factors with good performance. The 90% load factor I use is rather
83 // > Why a load factor of approximately 90%?
85 // In general, all the distances to initial buckets will converge on the mean.
86 // At a load factor of α, the odds of finding the target bucket after k
87 // probes is approximately 1-α^k. If we set this equal to 50% (since we converge
88 // on the mean) and set k=8 (64-byte cache line / 8-byte hash), α=0.92. I round
89 // this down to make the math easier on the CPU and avoid its FPU.
90 // Since on average we start the probing in the middle of a cache line, this
91 // strategy pulls in two cache lines of hashes on every lookup. I think that's
92 // pretty good, but if you want to trade off some space, it could go down to one
93 // cache line on average with an α of 0.84.
95 // > Wait, what? Where did you get 1-α^k from?
97 // On the first probe, your odds of a collision with an existing element is α.
98 // The odds of doing this twice in a row is approximately α^2. For three times,
99 // α^3, etc. Therefore, the odds of colliding k times is α^k. The odds of NOT
100 // colliding after k tries is 1-α^k.
102 // The paper from 1986 cited below mentions an implementation which keeps track
103 // of the distance-to-initial-bucket histogram. This approach is not suitable
104 // for modern architectures because it requires maintaining an internal data
105 // structure. This allows very good first guesses, but we are most concerned
106 // with guessing entire cache lines, not individual indexes. Furthermore, array
107 // accesses are no longer linear and in one direction, as we have now. There
108 // is also memory and cache pressure that this would entail that would be very
109 // difficult to properly see in a microbenchmark.
111 // ## Future Improvements (FIXME!)
113 // Allow the load factor to be changed dynamically and/or at initialization.
115 // Also, would it be possible for us to reuse storage when growing the
116 // underlying table? This is exactly the use case for 'realloc', and may
117 // be worth exploring.
119 // ## Future Optimizations (FIXME!)
121 // Another possible design choice that I made without any real reason is
122 // parameterizing the raw table over keys and values. Technically, all we need
123 // is the size and alignment of keys and values, and the code should be just as
124 // efficient (well, we might need one for power-of-two size and one for not...).
125 // This has the potential to reduce code bloat in rust executables, without
126 // really losing anything except 4 words (key size, key alignment, val size,
127 // val alignment) which can be passed in to every call of a `RawTable` function.
128 // This would definitely be an avenue worth exploring if people start complaining
129 // about the size of rust executables.
131 // Annotate exceedingly likely branches in `table::make_hash`
132 // and `search_hashed` to reduce instruction cache pressure
133 // and mispredictions once it becomes possible (blocked on issue #11092).
135 // Shrinking the table could simply reallocate in place after moving buckets
136 // to the first half.
138 // The growth algorithm (fragment of the Proof of Correctness)
139 // --------------------
141 // The growth algorithm is basically a fast path of the naive reinsertion-
142 // during-resize algorithm. Other paths should never be taken.
144 // Consider growing a robin hood hashtable of capacity n. Normally, we do this
145 // by allocating a new table of capacity `2n`, and then individually reinsert
146 // each element in the old table into the new one. This guarantees that the
147 // new table is a valid robin hood hashtable with all the desired statistical
148 // properties. Remark that the order we reinsert the elements in should not
149 // matter. For simplicity and efficiency, we will consider only linear
150 // reinsertions, which consist of reinserting all elements in the old table
151 // into the new one by increasing order of index. However we will not be
152 // starting our reinsertions from index 0 in general. If we start from index
153 // i, for the purpose of reinsertion we will consider all elements with real
154 // index j < i to have virtual index n + j.
156 // Our hash generation scheme consists of generating a 64-bit hash and
157 // truncating the most significant bits. When moving to the new table, we
158 // simply introduce a new bit to the front of the hash. Therefore, if an
159 // elements has ideal index i in the old table, it can have one of two ideal
160 // locations in the new table. If the new bit is 0, then the new ideal index
161 // is i. If the new bit is 1, then the new ideal index is n + i. Intuitively,
162 // we are producing two independent tables of size n, and for each element we
163 // independently choose which table to insert it into with equal probability.
164 // However the rather than wrapping around themselves on overflowing their
165 // indexes, the first table overflows into the first, and the first into the
166 // second. Visually, our new table will look something like:
168 // [yy_xxx_xxxx_xxx|xx_yyy_yyyy_yyy]
170 // Where x's are elements inserted into the first table, y's are elements
171 // inserted into the second, and _'s are empty sections. We now define a few
172 // key concepts that we will use later. Note that this is a very abstract
173 // perspective of the table. A real resized table would be at least half
176 // Theorem: A linear robin hood reinsertion from the first ideal element
177 // produces identical results to a linear naive reinsertion from the same
180 // FIXME(Gankro, pczarn): review the proof and put it all in a separate README.md
182 // Adaptive early resizing
183 // ----------------------
184 // To protect against degenerate performance scenarios (including DOS attacks),
185 // the implementation includes an adaptive behavior that can resize the map
186 // early (before its capacity is exceeded) when suspiciously long probe sequences
189 // With this algorithm in place it would be possible to turn a CPU attack into
190 // a memory attack due to the aggressive resizing. To prevent that the
191 // adaptive behavior only triggers when the map is at least half full.
192 // This reduces the effectiveness of the algorithm but also makes it completely safe.
194 // The previous safety measure also prevents degenerate interactions with
195 // really bad quality hash algorithms that can make normal inputs look like a
198 const DISPLACEMENT_THRESHOLD: usize = 128;
200 // The threshold of 128 is chosen to minimize the chance of exceeding it.
201 // In particular, we want that chance to be less than 10^-8 with a load of 90%.
202 // For displacement, the smallest constant that fits our needs is 90,
203 // so we round that up to 128.
205 // At a load factor of α, the odds of finding the target bucket after exactly n
206 // unsuccessful probes[1] are
208 // Pr_α{displacement = n} =
209 // (1 - α) / α * ∑_{k≥1} e^(-kα) * (kα)^(k+n) / (k + n)! * (1 - kα / (k + n + 1))
211 // We use this formula to find the probability of triggering the adaptive behavior
213 // Pr_0.909{displacement > 128} = 1.601 * 10^-11
215 // 1. Alfredo Viola (2005). Distributional analysis of Robin Hood linear probing
216 // hashing with buckets.
218 /// A hash map implemented with linear probing and Robin Hood bucket stealing.
220 /// By default, `HashMap` uses a hashing algorithm selected to provide
221 /// resistance against HashDoS attacks. The algorithm is randomly seeded, and a
222 /// reasonable best-effort is made to generate this seed from a high quality,
223 /// secure source of randomness provided by the host without blocking the
224 /// program. Because of this, the randomness of the seed depends on the output
225 /// quality of the system's random number generator when the seed is created.
226 /// In particular, seeds generated when the system's entropy pool is abnormally
227 /// low such as during system boot may be of a lower quality.
229 /// The default hashing algorithm is currently SipHash 1-3, though this is
230 /// subject to change at any point in the future. While its performance is very
231 /// competitive for medium sized keys, other hashing algorithms will outperform
232 /// it for small keys such as integers as well as large keys such as long
233 /// strings, though those algorithms will typically *not* protect against
234 /// attacks such as HashDoS.
236 /// The hashing algorithm can be replaced on a per-`HashMap` basis using the
237 /// [`default`], [`with_hasher`], and [`with_capacity_and_hasher`] methods. Many
238 /// alternative algorithms are available on crates.io, such as the [`fnv`] crate.
240 /// It is required that the keys implement the [`Eq`] and [`Hash`] traits, although
241 /// this can frequently be achieved by using `#[derive(PartialEq, Eq, Hash)]`.
242 /// If you implement these yourself, it is important that the following
246 /// k1 == k2 -> hash(k1) == hash(k2)
249 /// In other words, if two keys are equal, their hashes must be equal.
251 /// It is a logic error for a key to be modified in such a way that the key's
252 /// hash, as determined by the [`Hash`] trait, or its equality, as determined by
253 /// the [`Eq`] trait, changes while it is in the map. This is normally only
254 /// possible through [`Cell`], [`RefCell`], global state, I/O, or unsafe code.
256 /// Relevant papers/articles:
258 /// 1. Pedro Celis. ["Robin Hood Hashing"](https://cs.uwaterloo.ca/research/tr/1986/CS-86-14.pdf)
259 /// 2. Emmanuel Goossaert. ["Robin Hood
260 /// hashing"](http://codecapsule.com/2013/11/11/robin-hood-hashing/)
261 /// 3. Emmanuel Goossaert. ["Robin Hood hashing: backward shift
262 /// deletion"](http://codecapsule.com/2013/11/17/robin-hood-hashing-backward-shift-deletion/)
267 /// use std::collections::HashMap;
269 /// // type inference lets us omit an explicit type signature (which
270 /// // would be `HashMap<&str, &str>` in this example).
271 /// let mut book_reviews = HashMap::new();
273 /// // review some books.
274 /// book_reviews.insert("Adventures of Huckleberry Finn", "My favorite book.");
275 /// book_reviews.insert("Grimms' Fairy Tales", "Masterpiece.");
276 /// book_reviews.insert("Pride and Prejudice", "Very enjoyable.");
277 /// book_reviews.insert("The Adventures of Sherlock Holmes", "Eye lyked it alot.");
279 /// // check for a specific one.
280 /// if !book_reviews.contains_key("Les Misérables") {
281 /// println!("We've got {} reviews, but Les Misérables ain't one.",
282 /// book_reviews.len());
285 /// // oops, this review has a lot of spelling mistakes, let's delete it.
286 /// book_reviews.remove("The Adventures of Sherlock Holmes");
288 /// // look up the values associated with some keys.
289 /// let to_find = ["Pride and Prejudice", "Alice's Adventure in Wonderland"];
290 /// for book in &to_find {
291 /// match book_reviews.get(book) {
292 /// Some(review) => println!("{}: {}", book, review),
293 /// None => println!("{} is unreviewed.", book)
297 /// // iterate over everything.
298 /// for (book, review) in &book_reviews {
299 /// println!("{}: \"{}\"", book, review);
303 /// `HashMap` also implements an [`Entry API`](#method.entry), which allows
304 /// for more complex methods of getting, setting, updating and removing keys and
308 /// use std::collections::HashMap;
310 /// // type inference lets us omit an explicit type signature (which
311 /// // would be `HashMap<&str, u8>` in this example).
312 /// let mut player_stats = HashMap::new();
314 /// fn random_stat_buff() -> u8 {
315 /// // could actually return some random value here - let's just return
316 /// // some fixed value for now
320 /// // insert a key only if it doesn't already exist
321 /// player_stats.entry("health").or_insert(100);
323 /// // insert a key using a function that provides a new value only if it
324 /// // doesn't already exist
325 /// player_stats.entry("defence").or_insert_with(random_stat_buff);
327 /// // update a key, guarding against the key possibly not being set
328 /// let stat = player_stats.entry("attack").or_insert(100);
329 /// *stat += random_stat_buff();
332 /// The easiest way to use `HashMap` with a custom type as key is to derive [`Eq`] and [`Hash`].
333 /// We must also derive [`PartialEq`].
335 /// [`Eq`]: ../../std/cmp/trait.Eq.html
336 /// [`Hash`]: ../../std/hash/trait.Hash.html
337 /// [`PartialEq`]: ../../std/cmp/trait.PartialEq.html
338 /// [`RefCell`]: ../../std/cell/struct.RefCell.html
339 /// [`Cell`]: ../../std/cell/struct.Cell.html
340 /// [`default`]: #method.default
341 /// [`with_hasher`]: #method.with_hasher
342 /// [`with_capacity_and_hasher`]: #method.with_capacity_and_hasher
343 /// [`fnv`]: https://crates.io/crates/fnv
346 /// use std::collections::HashMap;
348 /// #[derive(Hash, Eq, PartialEq, Debug)]
355 /// /// Create a new Viking.
356 /// fn new(name: &str, country: &str) -> Viking {
357 /// Viking { name: name.to_string(), country: country.to_string() }
361 /// // Use a HashMap to store the vikings' health points.
362 /// let mut vikings = HashMap::new();
364 /// vikings.insert(Viking::new("Einar", "Norway"), 25);
365 /// vikings.insert(Viking::new("Olaf", "Denmark"), 24);
366 /// vikings.insert(Viking::new("Harald", "Iceland"), 12);
368 /// // Use derived implementation to print the status of the vikings.
369 /// for (viking, health) in &vikings {
370 /// println!("{:?} has {} hp", viking, health);
374 /// A `HashMap` with fixed list of elements can be initialized from an array:
377 /// use std::collections::HashMap;
380 /// let timber_resources: HashMap<&str, i32> =
381 /// [("Norway", 100),
384 /// .iter().cloned().collect();
385 /// // use the values stored in map
390 #[stable(feature = "rust1", since = "1.0.0")]
391 pub struct HashMap<K, V, S = RandomState> {
392 // All hashes are keyed on these values, to prevent hash collision attacks.
395 table: RawTable<K, V>,
397 resize_policy: DefaultResizePolicy,
400 /// Search for a pre-hashed key.
402 fn search_hashed<K, V, M, F>(table: M, hash: SafeHash, mut is_match: F) -> InternalEntry<K, V, M>
403 where M: Deref<Target = RawTable<K, V>>,
406 // This is the only function where capacity can be zero. To avoid
407 // undefined behavior when Bucket::new gets the raw bucket in this
408 // case, immediately return the appropriate search result.
409 if table.capacity() == 0 {
410 return InternalEntry::TableIsEmpty;
413 let size = table.size();
414 let mut probe = Bucket::new(table, hash);
415 let mut displacement = 0;
418 let full = match probe.peek() {
421 return InternalEntry::Vacant {
423 elem: NoElem(bucket, displacement),
426 Full(bucket) => bucket,
429 let probe_displacement = full.displacement();
431 if probe_displacement < displacement {
432 // Found a luckier bucket than me.
433 // We can finish the search early if we hit any bucket
434 // with a lower distance to initial bucket than we've probed.
435 return InternalEntry::Vacant {
437 elem: NeqElem(full, probe_displacement),
441 // If the hash doesn't match, it can't be this one..
442 if hash == full.hash() {
443 // If the key doesn't match, it can't be this one..
444 if is_match(full.read().0) {
445 return InternalEntry::Occupied { elem: full };
450 debug_assert!(displacement <= size);
454 fn pop_internal<K, V>(starting_bucket: FullBucketMut<K, V>)
455 -> (K, V, &mut RawTable<K, V>)
457 let (empty, retkey, retval) = starting_bucket.take();
458 let mut gap = match empty.gap_peek() {
460 Err(b) => return (retkey, retval, b.into_table()),
463 while gap.full().displacement() != 0 {
464 gap = match gap.shift() {
467 return (retkey, retval, b.into_table());
472 // Now we've done all our shifting. Return the value we grabbed earlier.
473 (retkey, retval, gap.into_table())
476 /// Perform robin hood bucket stealing at the given `bucket`. You must
477 /// also pass that bucket's displacement so we don't have to recalculate it.
479 /// `hash`, `key`, and `val` are the elements to "robin hood" into the hashtable.
480 fn robin_hood<'a, K: 'a, V: 'a>(bucket: FullBucketMut<'a, K, V>,
481 mut displacement: usize,
485 -> FullBucketMut<'a, K, V> {
486 let size = bucket.table().size();
487 let raw_capacity = bucket.table().capacity();
488 // There can be at most `size - dib` buckets to displace, because
489 // in the worst case, there are `size` elements and we already are
490 // `displacement` buckets away from the initial one.
491 let idx_end = (bucket.index() + size - bucket.displacement()) % raw_capacity;
492 // Save the *starting point*.
493 let mut bucket = bucket.stash();
496 let (old_hash, old_key, old_val) = bucket.replace(hash, key, val);
503 let probe = bucket.next();
504 debug_assert!(probe.index() != idx_end);
506 let full_bucket = match probe.peek() {
509 let bucket = bucket.put(hash, key, val);
510 // Now that it's stolen, just read the value's pointer
511 // right out of the table! Go back to the *starting point*.
513 // This use of `into_table` is misleading. It turns the
514 // bucket, which is a FullBucket on top of a
515 // FullBucketMut, into just one FullBucketMut. The "table"
516 // refers to the inner FullBucketMut in this context.
517 return bucket.into_table();
519 Full(bucket) => bucket,
522 let probe_displacement = full_bucket.displacement();
524 bucket = full_bucket;
526 // Robin hood! Steal the spot.
527 if probe_displacement < displacement {
528 displacement = probe_displacement;
535 impl<K, V, S> HashMap<K, V, S>
539 fn make_hash<X: ?Sized>(&self, x: &X) -> SafeHash
542 table::make_hash(&self.hash_builder, x)
545 /// Search for a key, yielding the index if it's found in the hashtable.
546 /// If you already have the hash for the key lying around, use
549 fn search<'a, Q: ?Sized>(&'a self, q: &Q) -> InternalEntry<K, V, &'a RawTable<K, V>>
553 let hash = self.make_hash(q);
554 search_hashed(&self.table, hash, |k| q.eq(k.borrow()))
558 fn search_mut<'a, Q: ?Sized>(&'a mut self, q: &Q) -> InternalEntry<K, V, &'a mut RawTable<K, V>>
562 let hash = self.make_hash(q);
563 search_hashed(&mut self.table, hash, |k| q.eq(k.borrow()))
566 // The caller should ensure that invariants by Robin Hood Hashing hold
567 // and that there's space in the underlying table.
568 fn insert_hashed_ordered(&mut self, hash: SafeHash, k: K, v: V) {
569 let mut buckets = Bucket::new(&mut self.table, hash);
570 let start_index = buckets.index();
573 // We don't need to compare hashes for value swap.
574 // Not even DIBs for Robin Hood.
575 buckets = match buckets.peek() {
577 empty.put(hash, k, v);
580 Full(b) => b.into_bucket(),
583 debug_assert!(buckets.index() != start_index);
588 impl<K: Hash + Eq, V> HashMap<K, V, RandomState> {
589 /// Creates an empty `HashMap`.
591 /// The hash map is initially created with a capacity of 0, so it will not allocate until it
592 /// is first inserted into.
597 /// use std::collections::HashMap;
598 /// let mut map: HashMap<&str, isize> = HashMap::new();
601 #[stable(feature = "rust1", since = "1.0.0")]
602 pub fn new() -> HashMap<K, V, RandomState> {
606 /// Creates an empty `HashMap` with the specified capacity.
608 /// The hash map will be able to hold at least `capacity` elements without
609 /// reallocating. If `capacity` is 0, the hash map will not allocate.
614 /// use std::collections::HashMap;
615 /// let mut map: HashMap<&str, isize> = HashMap::with_capacity(10);
618 #[stable(feature = "rust1", since = "1.0.0")]
619 pub fn with_capacity(capacity: usize) -> HashMap<K, V, RandomState> {
620 HashMap::with_capacity_and_hasher(capacity, Default::default())
624 impl<K, V, S> HashMap<K, V, S>
628 /// Creates an empty `HashMap` which will use the given hash builder to hash
631 /// The created map has the default initial capacity.
633 /// Warning: `hash_builder` is normally randomly generated, and
634 /// is designed to allow HashMaps to be resistant to attacks that
635 /// cause many collisions and very poor performance. Setting it
636 /// manually using this function can expose a DoS attack vector.
641 /// use std::collections::HashMap;
642 /// use std::collections::hash_map::RandomState;
644 /// let s = RandomState::new();
645 /// let mut map = HashMap::with_hasher(s);
646 /// map.insert(1, 2);
649 #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
650 pub fn with_hasher(hash_builder: S) -> HashMap<K, V, S> {
653 resize_policy: DefaultResizePolicy::new(),
654 table: RawTable::new(0),
658 /// Creates an empty `HashMap` with the specified capacity, using `hash_builder`
659 /// to hash the keys.
661 /// The hash map will be able to hold at least `capacity` elements without
662 /// reallocating. If `capacity` is 0, the hash map will not allocate.
664 /// Warning: `hash_builder` is normally randomly generated, and
665 /// is designed to allow HashMaps to be resistant to attacks that
666 /// cause many collisions and very poor performance. Setting it
667 /// manually using this function can expose a DoS attack vector.
672 /// use std::collections::HashMap;
673 /// use std::collections::hash_map::RandomState;
675 /// let s = RandomState::new();
676 /// let mut map = HashMap::with_capacity_and_hasher(10, s);
677 /// map.insert(1, 2);
680 #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
681 pub fn with_capacity_and_hasher(capacity: usize, hash_builder: S) -> HashMap<K, V, S> {
682 let resize_policy = DefaultResizePolicy::new();
683 let raw_cap = resize_policy.raw_capacity(capacity);
687 table: RawTable::new(raw_cap),
691 /// Returns a reference to the map's [`BuildHasher`].
693 /// [`BuildHasher`]: ../../std/hash/trait.BuildHasher.html
698 /// use std::collections::HashMap;
699 /// use std::collections::hash_map::RandomState;
701 /// let hasher = RandomState::new();
702 /// let map: HashMap<isize, isize> = HashMap::with_hasher(hasher);
703 /// let hasher: &RandomState = map.hasher();
705 #[stable(feature = "hashmap_public_hasher", since = "1.9.0")]
706 pub fn hasher(&self) -> &S {
710 /// Returns the number of elements the map can hold without reallocating.
712 /// This number is a lower bound; the `HashMap<K, V>` might be able to hold
713 /// more, but is guaranteed to be able to hold at least this many.
718 /// use std::collections::HashMap;
719 /// let map: HashMap<isize, isize> = HashMap::with_capacity(100);
720 /// assert!(map.capacity() >= 100);
723 #[stable(feature = "rust1", since = "1.0.0")]
724 pub fn capacity(&self) -> usize {
725 self.resize_policy.capacity(self.raw_capacity())
728 /// Returns the hash map's raw capacity.
730 fn raw_capacity(&self) -> usize {
731 self.table.capacity()
734 /// Reserves capacity for at least `additional` more elements to be inserted
735 /// in the `HashMap`. The collection may reserve more space to avoid
736 /// frequent reallocations.
740 /// Panics if the new allocation size overflows [`usize`].
742 /// [`usize`]: ../../std/primitive.usize.html
747 /// use std::collections::HashMap;
748 /// let mut map: HashMap<&str, isize> = HashMap::new();
751 #[stable(feature = "rust1", since = "1.0.0")]
752 pub fn reserve(&mut self, additional: usize) {
753 let remaining = self.capacity() - self.len(); // this can't overflow
754 if remaining < additional {
755 let min_cap = self.len().checked_add(additional).expect("reserve overflow");
756 let raw_cap = self.resize_policy.raw_capacity(min_cap);
757 self.resize(raw_cap);
758 } else if self.table.tag() && remaining <= self.len() {
759 // Probe sequence is too long and table is half full,
760 // resize early to reduce probing length.
761 let new_capacity = self.table.capacity() * 2;
762 self.resize(new_capacity);
766 /// Resizes the internal vectors to a new capacity. It's your
767 /// responsibility to:
768 /// 1) Ensure `new_raw_cap` is enough for all the elements, accounting
769 /// for the load factor.
770 /// 2) Ensure `new_raw_cap` is a power of two or zero.
773 fn resize(&mut self, new_raw_cap: usize) {
774 assert!(self.table.size() <= new_raw_cap);
775 assert!(new_raw_cap.is_power_of_two() || new_raw_cap == 0);
777 let mut old_table = replace(&mut self.table, RawTable::new(new_raw_cap));
778 let old_size = old_table.size();
780 if old_table.size() == 0 {
784 let mut bucket = Bucket::head_bucket(&mut old_table);
786 // This is how the buckets might be laid out in memory:
787 // ($ marks an initialized bucket)
789 // |$$$_$$$$$$_$$$$$|
791 // But we've skipped the entire initial cluster of buckets
792 // and will continue iteration in this order:
795 // ^ wrap around once end is reached
798 // ^ exit once table.size == 0
800 bucket = match bucket.peek() {
802 let h = bucket.hash();
803 let (b, k, v) = bucket.take();
804 self.insert_hashed_ordered(h, k, v);
805 if b.table().size() == 0 {
810 Empty(b) => b.into_bucket(),
815 assert_eq!(self.table.size(), old_size);
818 /// Shrinks the capacity of the map as much as possible. It will drop
819 /// down as much as possible while maintaining the internal rules
820 /// and possibly leaving some space in accordance with the resize policy.
825 /// use std::collections::HashMap;
827 /// let mut map: HashMap<isize, isize> = HashMap::with_capacity(100);
828 /// map.insert(1, 2);
829 /// map.insert(3, 4);
830 /// assert!(map.capacity() >= 100);
831 /// map.shrink_to_fit();
832 /// assert!(map.capacity() >= 2);
834 #[stable(feature = "rust1", since = "1.0.0")]
835 pub fn shrink_to_fit(&mut self) {
836 let new_raw_cap = self.resize_policy.raw_capacity(self.len());
837 if self.raw_capacity() != new_raw_cap {
838 let old_table = replace(&mut self.table, RawTable::new(new_raw_cap));
839 let old_size = old_table.size();
841 // Shrink the table. Naive algorithm for resizing:
842 for (h, k, v) in old_table.into_iter() {
843 self.insert_hashed_nocheck(h, k, v);
846 debug_assert_eq!(self.table.size(), old_size);
850 /// Insert a pre-hashed key-value pair, without first checking
851 /// that there's enough room in the buckets. Returns a reference to the
852 /// newly insert value.
854 /// If the key already exists, the hashtable will be returned untouched
855 /// and a reference to the existing element will be returned.
856 fn insert_hashed_nocheck(&mut self, hash: SafeHash, k: K, v: V) -> Option<V> {
857 let entry = search_hashed(&mut self.table, hash, |key| *key == k).into_entry(k);
859 Some(Occupied(mut elem)) => Some(elem.insert(v)),
860 Some(Vacant(elem)) => {
864 None => unreachable!(),
868 /// An iterator visiting all keys in arbitrary order.
869 /// The iterator element type is `&'a K`.
874 /// use std::collections::HashMap;
876 /// let mut map = HashMap::new();
877 /// map.insert("a", 1);
878 /// map.insert("b", 2);
879 /// map.insert("c", 3);
881 /// for key in map.keys() {
882 /// println!("{}", key);
885 #[stable(feature = "rust1", since = "1.0.0")]
886 pub fn keys(&self) -> Keys<K, V> {
887 Keys { inner: self.iter() }
890 /// An iterator visiting all values in arbitrary order.
891 /// The iterator element type is `&'a V`.
896 /// use std::collections::HashMap;
898 /// let mut map = HashMap::new();
899 /// map.insert("a", 1);
900 /// map.insert("b", 2);
901 /// map.insert("c", 3);
903 /// for val in map.values() {
904 /// println!("{}", val);
907 #[stable(feature = "rust1", since = "1.0.0")]
908 pub fn values(&self) -> Values<K, V> {
909 Values { inner: self.iter() }
912 /// An iterator visiting all values mutably in arbitrary order.
913 /// The iterator element type is `&'a mut V`.
918 /// use std::collections::HashMap;
920 /// let mut map = HashMap::new();
922 /// map.insert("a", 1);
923 /// map.insert("b", 2);
924 /// map.insert("c", 3);
926 /// for val in map.values_mut() {
927 /// *val = *val + 10;
930 /// for val in map.values() {
931 /// println!("{}", val);
934 #[stable(feature = "map_values_mut", since = "1.10.0")]
935 pub fn values_mut(&mut self) -> ValuesMut<K, V> {
936 ValuesMut { inner: self.iter_mut() }
939 /// An iterator visiting all key-value pairs in arbitrary order.
940 /// The iterator element type is `(&'a K, &'a V)`.
945 /// use std::collections::HashMap;
947 /// let mut map = HashMap::new();
948 /// map.insert("a", 1);
949 /// map.insert("b", 2);
950 /// map.insert("c", 3);
952 /// for (key, val) in map.iter() {
953 /// println!("key: {} val: {}", key, val);
956 #[stable(feature = "rust1", since = "1.0.0")]
957 pub fn iter(&self) -> Iter<K, V> {
958 Iter { inner: self.table.iter() }
961 /// An iterator visiting all key-value pairs in arbitrary order,
962 /// with mutable references to the values.
963 /// The iterator element type is `(&'a K, &'a mut V)`.
968 /// use std::collections::HashMap;
970 /// let mut map = HashMap::new();
971 /// map.insert("a", 1);
972 /// map.insert("b", 2);
973 /// map.insert("c", 3);
975 /// // Update all values
976 /// for (_, val) in map.iter_mut() {
980 /// for (key, val) in &map {
981 /// println!("key: {} val: {}", key, val);
984 #[stable(feature = "rust1", since = "1.0.0")]
985 pub fn iter_mut(&mut self) -> IterMut<K, V> {
986 IterMut { inner: self.table.iter_mut() }
989 /// Gets the given key's corresponding entry in the map for in-place manipulation.
994 /// use std::collections::HashMap;
996 /// let mut letters = HashMap::new();
998 /// for ch in "a short treatise on fungi".chars() {
999 /// let counter = letters.entry(ch).or_insert(0);
1003 /// assert_eq!(letters[&'s'], 2);
1004 /// assert_eq!(letters[&'t'], 3);
1005 /// assert_eq!(letters[&'u'], 1);
1006 /// assert_eq!(letters.get(&'y'), None);
1008 #[stable(feature = "rust1", since = "1.0.0")]
1009 pub fn entry(&mut self, key: K) -> Entry<K, V> {
1010 // Gotta resize now.
1012 let hash = self.make_hash(&key);
1013 search_hashed(&mut self.table, hash, |q| q.eq(&key))
1014 .into_entry(key).expect("unreachable")
1017 /// Returns the number of elements in the map.
1022 /// use std::collections::HashMap;
1024 /// let mut a = HashMap::new();
1025 /// assert_eq!(a.len(), 0);
1026 /// a.insert(1, "a");
1027 /// assert_eq!(a.len(), 1);
1029 #[stable(feature = "rust1", since = "1.0.0")]
1030 pub fn len(&self) -> usize {
1034 /// Returns true if the map contains no elements.
1039 /// use std::collections::HashMap;
1041 /// let mut a = HashMap::new();
1042 /// assert!(a.is_empty());
1043 /// a.insert(1, "a");
1044 /// assert!(!a.is_empty());
1047 #[stable(feature = "rust1", since = "1.0.0")]
1048 pub fn is_empty(&self) -> bool {
1052 /// Clears the map, returning all key-value pairs as an iterator. Keeps the
1053 /// allocated memory for reuse.
1058 /// use std::collections::HashMap;
1060 /// let mut a = HashMap::new();
1061 /// a.insert(1, "a");
1062 /// a.insert(2, "b");
1064 /// for (k, v) in a.drain().take(1) {
1065 /// assert!(k == 1 || k == 2);
1066 /// assert!(v == "a" || v == "b");
1069 /// assert!(a.is_empty());
1072 #[stable(feature = "drain", since = "1.6.0")]
1073 pub fn drain(&mut self) -> Drain<K, V> {
1074 Drain { inner: self.table.drain() }
1077 /// Clears the map, removing all key-value pairs. Keeps the allocated memory
1083 /// use std::collections::HashMap;
1085 /// let mut a = HashMap::new();
1086 /// a.insert(1, "a");
1088 /// assert!(a.is_empty());
1090 #[stable(feature = "rust1", since = "1.0.0")]
1092 pub fn clear(&mut self) {
1096 /// Returns a reference to the value corresponding to the key.
1098 /// The key may be any borrowed form of the map's key type, but
1099 /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
1102 /// [`Eq`]: ../../std/cmp/trait.Eq.html
1103 /// [`Hash`]: ../../std/hash/trait.Hash.html
1108 /// use std::collections::HashMap;
1110 /// let mut map = HashMap::new();
1111 /// map.insert(1, "a");
1112 /// assert_eq!(map.get(&1), Some(&"a"));
1113 /// assert_eq!(map.get(&2), None);
1115 #[stable(feature = "rust1", since = "1.0.0")]
1117 pub fn get<Q: ?Sized>(&self, k: &Q) -> Option<&V>
1121 self.search(k).into_occupied_bucket().map(|bucket| bucket.into_refs().1)
1124 /// Returns true if the map contains a value for the specified key.
1126 /// The key may be any borrowed form of the map's key type, but
1127 /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
1130 /// [`Eq`]: ../../std/cmp/trait.Eq.html
1131 /// [`Hash`]: ../../std/hash/trait.Hash.html
1136 /// use std::collections::HashMap;
1138 /// let mut map = HashMap::new();
1139 /// map.insert(1, "a");
1140 /// assert_eq!(map.contains_key(&1), true);
1141 /// assert_eq!(map.contains_key(&2), false);
1143 #[stable(feature = "rust1", since = "1.0.0")]
1144 pub fn contains_key<Q: ?Sized>(&self, k: &Q) -> bool
1148 self.search(k).into_occupied_bucket().is_some()
1151 /// Returns a mutable reference to the value corresponding to the key.
1153 /// The key may be any borrowed form of the map's key type, but
1154 /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
1157 /// [`Eq`]: ../../std/cmp/trait.Eq.html
1158 /// [`Hash`]: ../../std/hash/trait.Hash.html
1163 /// use std::collections::HashMap;
1165 /// let mut map = HashMap::new();
1166 /// map.insert(1, "a");
1167 /// if let Some(x) = map.get_mut(&1) {
1170 /// assert_eq!(map[&1], "b");
1172 #[stable(feature = "rust1", since = "1.0.0")]
1173 pub fn get_mut<Q: ?Sized>(&mut self, k: &Q) -> Option<&mut V>
1177 self.search_mut(k).into_occupied_bucket().map(|bucket| bucket.into_mut_refs().1)
1180 /// Inserts a key-value pair into the map.
1182 /// If the map did not have this key present, [`None`] is returned.
1184 /// If the map did have this key present, the value is updated, and the old
1185 /// value is returned. The key is not updated, though; this matters for
1186 /// types that can be `==` without being identical. See the [module-level
1187 /// documentation] for more.
1189 /// [`None`]: ../../std/option/enum.Option.html#variant.None
1190 /// [module-level documentation]: index.html#insert-and-complex-keys
1195 /// use std::collections::HashMap;
1197 /// let mut map = HashMap::new();
1198 /// assert_eq!(map.insert(37, "a"), None);
1199 /// assert_eq!(map.is_empty(), false);
1201 /// map.insert(37, "b");
1202 /// assert_eq!(map.insert(37, "c"), Some("b"));
1203 /// assert_eq!(map[&37], "c");
1205 #[stable(feature = "rust1", since = "1.0.0")]
1206 pub fn insert(&mut self, k: K, v: V) -> Option<V> {
1207 let hash = self.make_hash(&k);
1209 self.insert_hashed_nocheck(hash, k, v)
1212 /// Removes a key from the map, returning the value at the key if the key
1213 /// was previously in the map.
1215 /// The key may be any borrowed form of the map's key type, but
1216 /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
1219 /// [`Eq`]: ../../std/cmp/trait.Eq.html
1220 /// [`Hash`]: ../../std/hash/trait.Hash.html
1225 /// use std::collections::HashMap;
1227 /// let mut map = HashMap::new();
1228 /// map.insert(1, "a");
1229 /// assert_eq!(map.remove(&1), Some("a"));
1230 /// assert_eq!(map.remove(&1), None);
1232 #[stable(feature = "rust1", since = "1.0.0")]
1233 pub fn remove<Q: ?Sized>(&mut self, k: &Q) -> Option<V>
1237 if self.table.size() == 0 {
1241 self.search_mut(k).into_occupied_bucket().map(|bucket| pop_internal(bucket).1)
1244 /// Retains only the elements specified by the predicate.
1246 /// In other words, remove all pairs `(k, v)` such that `f(&k,&mut v)` returns `false`.
1251 /// use std::collections::HashMap;
1253 /// let mut map: HashMap<isize, isize> = (0..8).map(|x|(x, x*10)).collect();
1254 /// map.retain(|&k, _| k % 2 == 0);
1255 /// assert_eq!(map.len(), 4);
1257 #[stable(feature = "retain_hash_collection", since = "1.18.0")]
1258 pub fn retain<F>(&mut self, mut f: F)
1259 where F: FnMut(&K, &mut V) -> bool
1261 if self.table.size() == 0 {
1264 let mut elems_left = self.table.size();
1265 let mut bucket = Bucket::head_bucket(&mut self.table);
1267 let start_index = bucket.index();
1268 while elems_left != 0 {
1269 bucket = match bucket.peek() {
1272 let should_remove = {
1273 let (k, v) = full.read_mut();
1277 let prev_raw = full.raw();
1278 let (_, _, t) = pop_internal(full);
1279 Bucket::new_from(prev_raw, t)
1288 bucket.prev(); // reverse iteration
1289 debug_assert!(elems_left == 0 || bucket.index() != start_index);
1294 #[stable(feature = "rust1", since = "1.0.0")]
1295 impl<K, V, S> PartialEq for HashMap<K, V, S>
1300 fn eq(&self, other: &HashMap<K, V, S>) -> bool {
1301 if self.len() != other.len() {
1305 self.iter().all(|(key, value)| other.get(key).map_or(false, |v| *value == *v))
1309 #[stable(feature = "rust1", since = "1.0.0")]
1310 impl<K, V, S> Eq for HashMap<K, V, S>
1317 #[stable(feature = "rust1", since = "1.0.0")]
1318 impl<K, V, S> Debug for HashMap<K, V, S>
1319 where K: Eq + Hash + Debug,
1323 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1324 f.debug_map().entries(self.iter()).finish()
1328 #[stable(feature = "rust1", since = "1.0.0")]
1329 impl<K, V, S> Default for HashMap<K, V, S>
1331 S: BuildHasher + Default
1333 /// Creates an empty `HashMap<K, V, S>`, with the `Default` value for the hasher.
1334 fn default() -> HashMap<K, V, S> {
1335 HashMap::with_hasher(Default::default())
1339 #[stable(feature = "rust1", since = "1.0.0")]
1340 impl<'a, K, Q: ?Sized, V, S> Index<&'a Q> for HashMap<K, V, S>
1341 where K: Eq + Hash + Borrow<Q>,
1348 fn index(&self, index: &Q) -> &V {
1349 self.get(index).expect("no entry found for key")
1353 /// An iterator over the entries of a `HashMap`.
1355 /// This `struct` is created by the [`iter`] method on [`HashMap`]. See its
1356 /// documentation for more.
1358 /// [`iter`]: struct.HashMap.html#method.iter
1359 /// [`HashMap`]: struct.HashMap.html
1360 #[stable(feature = "rust1", since = "1.0.0")]
1361 pub struct Iter<'a, K: 'a, V: 'a> {
1362 inner: table::Iter<'a, K, V>,
1365 // FIXME(#26925) Remove in favor of `#[derive(Clone)]`
1366 #[stable(feature = "rust1", since = "1.0.0")]
1367 impl<'a, K, V> Clone for Iter<'a, K, V> {
1368 fn clone(&self) -> Iter<'a, K, V> {
1369 Iter { inner: self.inner.clone() }
1373 #[stable(feature = "std_debug", since = "1.16.0")]
1374 impl<'a, K: Debug, V: Debug> fmt::Debug for Iter<'a, K, V> {
1375 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1377 .entries(self.clone())
1382 /// A mutable iterator over the entries of a `HashMap`.
1384 /// This `struct` is created by the [`iter_mut`] method on [`HashMap`]. See its
1385 /// documentation for more.
1387 /// [`iter_mut`]: struct.HashMap.html#method.iter_mut
1388 /// [`HashMap`]: struct.HashMap.html
1389 #[stable(feature = "rust1", since = "1.0.0")]
1390 pub struct IterMut<'a, K: 'a, V: 'a> {
1391 inner: table::IterMut<'a, K, V>,
1394 /// An owning iterator over the entries of a `HashMap`.
1396 /// This `struct` is created by the [`into_iter`] method on [`HashMap`][`HashMap`]
1397 /// (provided by the `IntoIterator` trait). See its documentation for more.
1399 /// [`into_iter`]: struct.HashMap.html#method.into_iter
1400 /// [`HashMap`]: struct.HashMap.html
1401 #[stable(feature = "rust1", since = "1.0.0")]
1402 pub struct IntoIter<K, V> {
1403 pub(super) inner: table::IntoIter<K, V>,
1406 /// An iterator over the keys of a `HashMap`.
1408 /// This `struct` is created by the [`keys`] method on [`HashMap`]. See its
1409 /// documentation for more.
1411 /// [`keys`]: struct.HashMap.html#method.keys
1412 /// [`HashMap`]: struct.HashMap.html
1413 #[stable(feature = "rust1", since = "1.0.0")]
1414 pub struct Keys<'a, K: 'a, V: 'a> {
1415 inner: Iter<'a, K, V>,
1418 // FIXME(#26925) Remove in favor of `#[derive(Clone)]`
1419 #[stable(feature = "rust1", since = "1.0.0")]
1420 impl<'a, K, V> Clone for Keys<'a, K, V> {
1421 fn clone(&self) -> Keys<'a, K, V> {
1422 Keys { inner: self.inner.clone() }
1426 #[stable(feature = "std_debug", since = "1.16.0")]
1427 impl<'a, K: Debug, V> fmt::Debug for Keys<'a, K, V> {
1428 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1430 .entries(self.clone())
1435 /// An iterator over the values of a `HashMap`.
1437 /// This `struct` is created by the [`values`] method on [`HashMap`]. See its
1438 /// documentation for more.
1440 /// [`values`]: struct.HashMap.html#method.values
1441 /// [`HashMap`]: struct.HashMap.html
1442 #[stable(feature = "rust1", since = "1.0.0")]
1443 pub struct Values<'a, K: 'a, V: 'a> {
1444 inner: Iter<'a, K, V>,
1447 // FIXME(#26925) Remove in favor of `#[derive(Clone)]`
1448 #[stable(feature = "rust1", since = "1.0.0")]
1449 impl<'a, K, V> Clone for Values<'a, K, V> {
1450 fn clone(&self) -> Values<'a, K, V> {
1451 Values { inner: self.inner.clone() }
1455 #[stable(feature = "std_debug", since = "1.16.0")]
1456 impl<'a, K, V: Debug> fmt::Debug for Values<'a, K, V> {
1457 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1459 .entries(self.clone())
1464 /// A draining iterator over the entries of a `HashMap`.
1466 /// This `struct` is created by the [`drain`] method on [`HashMap`]. See its
1467 /// documentation for more.
1469 /// [`drain`]: struct.HashMap.html#method.drain
1470 /// [`HashMap`]: struct.HashMap.html
1471 #[stable(feature = "drain", since = "1.6.0")]
1472 pub struct Drain<'a, K: 'a, V: 'a> {
1473 pub(super) inner: table::Drain<'a, K, V>,
1476 /// A mutable iterator over the values of a `HashMap`.
1478 /// This `struct` is created by the [`values_mut`] method on [`HashMap`]. See its
1479 /// documentation for more.
1481 /// [`values_mut`]: struct.HashMap.html#method.values_mut
1482 /// [`HashMap`]: struct.HashMap.html
1483 #[stable(feature = "map_values_mut", since = "1.10.0")]
1484 pub struct ValuesMut<'a, K: 'a, V: 'a> {
1485 inner: IterMut<'a, K, V>,
1488 enum InternalEntry<K, V, M> {
1489 Occupied { elem: FullBucket<K, V, M> },
1492 elem: VacantEntryState<K, V, M>,
1497 impl<K, V, M> InternalEntry<K, V, M> {
1499 fn into_occupied_bucket(self) -> Option<FullBucket<K, V, M>> {
1501 InternalEntry::Occupied { elem } => Some(elem),
1507 impl<'a, K, V> InternalEntry<K, V, &'a mut RawTable<K, V>> {
1509 fn into_entry(self, key: K) -> Option<Entry<'a, K, V>> {
1511 InternalEntry::Occupied { elem } => {
1512 Some(Occupied(OccupiedEntry {
1517 InternalEntry::Vacant { hash, elem } => {
1518 Some(Vacant(VacantEntry {
1524 InternalEntry::TableIsEmpty => None,
1529 /// A view into a single entry in a map, which may either be vacant or occupied.
1531 /// This `enum` is constructed from the [`entry`] method on [`HashMap`].
1533 /// [`HashMap`]: struct.HashMap.html
1534 /// [`entry`]: struct.HashMap.html#method.entry
1535 #[stable(feature = "rust1", since = "1.0.0")]
1536 pub enum Entry<'a, K: 'a, V: 'a> {
1537 /// An occupied entry.
1538 #[stable(feature = "rust1", since = "1.0.0")]
1539 Occupied(#[stable(feature = "rust1", since = "1.0.0")]
1540 OccupiedEntry<'a, K, V>),
1543 #[stable(feature = "rust1", since = "1.0.0")]
1544 Vacant(#[stable(feature = "rust1", since = "1.0.0")]
1545 VacantEntry<'a, K, V>),
1548 #[stable(feature= "debug_hash_map", since = "1.12.0")]
1549 impl<'a, K: 'a + Debug, V: 'a + Debug> Debug for Entry<'a, K, V> {
1550 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1553 f.debug_tuple("Entry")
1557 Occupied(ref o) => {
1558 f.debug_tuple("Entry")
1566 /// A view into an occupied entry in a `HashMap`.
1567 /// It is part of the [`Entry`] enum.
1569 /// [`Entry`]: enum.Entry.html
1570 #[stable(feature = "rust1", since = "1.0.0")]
1571 pub struct OccupiedEntry<'a, K: 'a, V: 'a> {
1573 elem: FullBucket<K, V, &'a mut RawTable<K, V>>,
1576 #[stable(feature= "debug_hash_map", since = "1.12.0")]
1577 impl<'a, K: 'a + Debug, V: 'a + Debug> Debug for OccupiedEntry<'a, K, V> {
1578 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1579 f.debug_struct("OccupiedEntry")
1580 .field("key", self.key())
1581 .field("value", self.get())
1586 /// A view into a vacant entry in a `HashMap`.
1587 /// It is part of the [`Entry`] enum.
1589 /// [`Entry`]: enum.Entry.html
1590 #[stable(feature = "rust1", since = "1.0.0")]
1591 pub struct VacantEntry<'a, K: 'a, V: 'a> {
1594 elem: VacantEntryState<K, V, &'a mut RawTable<K, V>>,
1597 #[stable(feature= "debug_hash_map", since = "1.12.0")]
1598 impl<'a, K: 'a + Debug, V: 'a> Debug for VacantEntry<'a, K, V> {
1599 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1600 f.debug_tuple("VacantEntry")
1606 /// Possible states of a VacantEntry.
1607 enum VacantEntryState<K, V, M> {
1608 /// The index is occupied, but the key to insert has precedence,
1609 /// and will kick the current one out on insertion.
1610 NeqElem(FullBucket<K, V, M>, usize),
1611 /// The index is genuinely vacant.
1612 NoElem(EmptyBucket<K, V, M>, usize),
1615 #[stable(feature = "rust1", since = "1.0.0")]
1616 impl<'a, K, V, S> IntoIterator for &'a HashMap<K, V, S>
1620 type Item = (&'a K, &'a V);
1621 type IntoIter = Iter<'a, K, V>;
1623 fn into_iter(self) -> Iter<'a, K, V> {
1628 #[stable(feature = "rust1", since = "1.0.0")]
1629 impl<'a, K, V, S> IntoIterator for &'a mut HashMap<K, V, S>
1633 type Item = (&'a K, &'a mut V);
1634 type IntoIter = IterMut<'a, K, V>;
1636 fn into_iter(self) -> IterMut<'a, K, V> {
1641 #[stable(feature = "rust1", since = "1.0.0")]
1642 impl<K, V, S> IntoIterator for HashMap<K, V, S>
1647 type IntoIter = IntoIter<K, V>;
1649 /// Creates a consuming iterator, that is, one that moves each key-value
1650 /// pair out of the map in arbitrary order. The map cannot be used after
1656 /// use std::collections::HashMap;
1658 /// let mut map = HashMap::new();
1659 /// map.insert("a", 1);
1660 /// map.insert("b", 2);
1661 /// map.insert("c", 3);
1663 /// // Not possible with .iter()
1664 /// let vec: Vec<(&str, isize)> = map.into_iter().collect();
1666 fn into_iter(self) -> IntoIter<K, V> {
1667 IntoIter { inner: self.table.into_iter() }
1671 #[stable(feature = "rust1", since = "1.0.0")]
1672 impl<'a, K, V> Iterator for Iter<'a, K, V> {
1673 type Item = (&'a K, &'a V);
1676 fn next(&mut self) -> Option<(&'a K, &'a V)> {
1680 fn size_hint(&self) -> (usize, Option<usize>) {
1681 self.inner.size_hint()
1684 #[stable(feature = "rust1", since = "1.0.0")]
1685 impl<'a, K, V> ExactSizeIterator for Iter<'a, K, V> {
1687 fn len(&self) -> usize {
1692 #[unstable(feature = "fused", issue = "35602")]
1693 impl<'a, K, V> FusedIterator for Iter<'a, K, V> {}
1695 #[stable(feature = "rust1", since = "1.0.0")]
1696 impl<'a, K, V> Iterator for IterMut<'a, K, V> {
1697 type Item = (&'a K, &'a mut V);
1700 fn next(&mut self) -> Option<(&'a K, &'a mut V)> {
1704 fn size_hint(&self) -> (usize, Option<usize>) {
1705 self.inner.size_hint()
1708 #[stable(feature = "rust1", since = "1.0.0")]
1709 impl<'a, K, V> ExactSizeIterator for IterMut<'a, K, V> {
1711 fn len(&self) -> usize {
1715 #[unstable(feature = "fused", issue = "35602")]
1716 impl<'a, K, V> FusedIterator for IterMut<'a, K, V> {}
1718 #[stable(feature = "std_debug", since = "1.16.0")]
1719 impl<'a, K, V> fmt::Debug for IterMut<'a, K, V>
1720 where K: fmt::Debug,
1723 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1725 .entries(self.inner.iter())
1730 #[stable(feature = "rust1", since = "1.0.0")]
1731 impl<K, V> Iterator for IntoIter<K, V> {
1735 fn next(&mut self) -> Option<(K, V)> {
1736 self.inner.next().map(|(_, k, v)| (k, v))
1739 fn size_hint(&self) -> (usize, Option<usize>) {
1740 self.inner.size_hint()
1743 #[stable(feature = "rust1", since = "1.0.0")]
1744 impl<K, V> ExactSizeIterator for IntoIter<K, V> {
1746 fn len(&self) -> usize {
1750 #[unstable(feature = "fused", issue = "35602")]
1751 impl<K, V> FusedIterator for IntoIter<K, V> {}
1753 #[stable(feature = "std_debug", since = "1.16.0")]
1754 impl<K: Debug, V: Debug> fmt::Debug for IntoIter<K, V> {
1755 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1757 .entries(self.inner.iter())
1762 #[stable(feature = "rust1", since = "1.0.0")]
1763 impl<'a, K, V> Iterator for Keys<'a, K, V> {
1767 fn next(&mut self) -> Option<(&'a K)> {
1768 self.inner.next().map(|(k, _)| k)
1771 fn size_hint(&self) -> (usize, Option<usize>) {
1772 self.inner.size_hint()
1775 #[stable(feature = "rust1", since = "1.0.0")]
1776 impl<'a, K, V> ExactSizeIterator for Keys<'a, K, V> {
1778 fn len(&self) -> usize {
1782 #[unstable(feature = "fused", issue = "35602")]
1783 impl<'a, K, V> FusedIterator for Keys<'a, K, V> {}
1785 #[stable(feature = "rust1", since = "1.0.0")]
1786 impl<'a, K, V> Iterator for Values<'a, K, V> {
1790 fn next(&mut self) -> Option<(&'a V)> {
1791 self.inner.next().map(|(_, v)| v)
1794 fn size_hint(&self) -> (usize, Option<usize>) {
1795 self.inner.size_hint()
1798 #[stable(feature = "rust1", since = "1.0.0")]
1799 impl<'a, K, V> ExactSizeIterator for Values<'a, K, V> {
1801 fn len(&self) -> usize {
1805 #[unstable(feature = "fused", issue = "35602")]
1806 impl<'a, K, V> FusedIterator for Values<'a, K, V> {}
1808 #[stable(feature = "map_values_mut", since = "1.10.0")]
1809 impl<'a, K, V> Iterator for ValuesMut<'a, K, V> {
1810 type Item = &'a mut V;
1813 fn next(&mut self) -> Option<(&'a mut V)> {
1814 self.inner.next().map(|(_, v)| v)
1817 fn size_hint(&self) -> (usize, Option<usize>) {
1818 self.inner.size_hint()
1821 #[stable(feature = "map_values_mut", since = "1.10.0")]
1822 impl<'a, K, V> ExactSizeIterator for ValuesMut<'a, K, V> {
1824 fn len(&self) -> usize {
1828 #[unstable(feature = "fused", issue = "35602")]
1829 impl<'a, K, V> FusedIterator for ValuesMut<'a, K, V> {}
1831 #[stable(feature = "std_debug", since = "1.16.0")]
1832 impl<'a, K, V> fmt::Debug for ValuesMut<'a, K, V>
1833 where K: fmt::Debug,
1836 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1838 .entries(self.inner.inner.iter())
1843 #[stable(feature = "drain", since = "1.6.0")]
1844 impl<'a, K, V> Iterator for Drain<'a, K, V> {
1848 fn next(&mut self) -> Option<(K, V)> {
1849 self.inner.next().map(|(_, k, v)| (k, v))
1852 fn size_hint(&self) -> (usize, Option<usize>) {
1853 self.inner.size_hint()
1856 #[stable(feature = "drain", since = "1.6.0")]
1857 impl<'a, K, V> ExactSizeIterator for Drain<'a, K, V> {
1859 fn len(&self) -> usize {
1863 #[unstable(feature = "fused", issue = "35602")]
1864 impl<'a, K, V> FusedIterator for Drain<'a, K, V> {}
1866 #[stable(feature = "std_debug", since = "1.16.0")]
1867 impl<'a, K, V> fmt::Debug for Drain<'a, K, V>
1868 where K: fmt::Debug,
1871 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1873 .entries(self.inner.iter())
1878 /// A place for insertion to a `Entry`.
1880 /// See [`HashMap::entry`](struct.HashMap.html#method.entry) for details.
1881 #[must_use = "places do nothing unless written to with `<-` syntax"]
1882 #[unstable(feature = "collection_placement",
1883 reason = "struct name and placement protocol is subject to change",
1885 pub struct EntryPlace<'a, K: 'a, V: 'a> {
1886 bucket: FullBucketMut<'a, K, V>,
1889 #[unstable(feature = "collection_placement",
1890 reason = "struct name and placement protocol is subject to change",
1892 impl<'a, K: 'a + Debug, V: 'a + Debug> Debug for EntryPlace<'a, K, V> {
1893 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1894 f.debug_struct("EntryPlace")
1895 .field("key", self.bucket.read().0)
1896 .field("value", self.bucket.read().1)
1901 #[unstable(feature = "collection_placement",
1902 reason = "struct name and placement protocol is subject to change",
1904 impl<'a, K, V> Drop for EntryPlace<'a, K, V> {
1905 fn drop(&mut self) {
1906 // Inplacement insertion failed. Only key need to drop.
1907 // The value is failed to insert into map.
1908 unsafe { self.bucket.remove_key() };
1912 #[unstable(feature = "collection_placement",
1913 reason = "placement protocol is subject to change",
1915 impl<'a, K, V> Placer<V> for Entry<'a, K, V> {
1916 type Place = EntryPlace<'a, K, V>;
1918 fn make_place(self) -> EntryPlace<'a, K, V> {
1919 let b = match self {
1920 Occupied(mut o) => {
1921 unsafe { ptr::drop_in_place(o.elem.read_mut().1); }
1925 unsafe { v.insert_key() }
1928 EntryPlace { bucket: b }
1932 #[unstable(feature = "collection_placement",
1933 reason = "placement protocol is subject to change",
1935 impl<'a, K, V> Place<V> for EntryPlace<'a, K, V> {
1936 fn pointer(&mut self) -> *mut V {
1937 self.bucket.read_mut().1
1941 #[unstable(feature = "collection_placement",
1942 reason = "placement protocol is subject to change",
1944 impl<'a, K, V> InPlace<V> for EntryPlace<'a, K, V> {
1947 unsafe fn finalize(self) {
1952 impl<'a, K, V> Entry<'a, K, V> {
1953 #[stable(feature = "rust1", since = "1.0.0")]
1954 /// Ensures a value is in the entry by inserting the default if empty, and returns
1955 /// a mutable reference to the value in the entry.
1960 /// use std::collections::HashMap;
1962 /// let mut map: HashMap<&str, u32> = HashMap::new();
1963 /// map.entry("poneyland").or_insert(12);
1965 /// assert_eq!(map["poneyland"], 12);
1967 /// *map.entry("poneyland").or_insert(12) += 10;
1968 /// assert_eq!(map["poneyland"], 22);
1970 pub fn or_insert(self, default: V) -> &'a mut V {
1972 Occupied(entry) => entry.into_mut(),
1973 Vacant(entry) => entry.insert(default),
1977 #[stable(feature = "rust1", since = "1.0.0")]
1978 /// Ensures a value is in the entry by inserting the result of the default function if empty,
1979 /// and returns a mutable reference to the value in the entry.
1984 /// use std::collections::HashMap;
1986 /// let mut map: HashMap<&str, String> = HashMap::new();
1987 /// let s = "hoho".to_string();
1989 /// map.entry("poneyland").or_insert_with(|| s);
1991 /// assert_eq!(map["poneyland"], "hoho".to_string());
1993 pub fn or_insert_with<F: FnOnce() -> V>(self, default: F) -> &'a mut V {
1995 Occupied(entry) => entry.into_mut(),
1996 Vacant(entry) => entry.insert(default()),
2000 /// Returns a reference to this entry's key.
2005 /// use std::collections::HashMap;
2007 /// let mut map: HashMap<&str, u32> = HashMap::new();
2008 /// assert_eq!(map.entry("poneyland").key(), &"poneyland");
2010 #[stable(feature = "map_entry_keys", since = "1.10.0")]
2011 pub fn key(&self) -> &K {
2013 Occupied(ref entry) => entry.key(),
2014 Vacant(ref entry) => entry.key(),
2018 /// Provides in-place mutable access to an occupied entry before any
2019 /// potential inserts into the map.
2024 /// #![feature(entry_and_modify)]
2025 /// use std::collections::HashMap;
2027 /// let mut map: HashMap<&str, u32> = HashMap::new();
2029 /// map.entry("poneyland")
2030 /// .and_modify(|e| { *e += 1 })
2032 /// assert_eq!(map["poneyland"], 42);
2034 /// map.entry("poneyland")
2035 /// .and_modify(|e| { *e += 1 })
2037 /// assert_eq!(map["poneyland"], 43);
2039 #[unstable(feature = "entry_and_modify", issue = "44733")]
2040 pub fn and_modify<F>(self, mut f: F) -> Self
2041 where F: FnMut(&mut V)
2044 Occupied(mut entry) => {
2048 Vacant(entry) => Vacant(entry),
2054 impl<'a, K, V: Default> Entry<'a, K, V> {
2055 #[unstable(feature = "entry_or_default", issue = "44324")]
2056 /// Ensures a value is in the entry by inserting the default value if empty,
2057 /// and returns a mutable reference to the value in the entry.
2062 /// #![feature(entry_or_default)]
2064 /// use std::collections::HashMap;
2066 /// let mut map: HashMap<&str, Option<u32>> = HashMap::new();
2067 /// map.entry("poneyland").or_default();
2069 /// assert_eq!(map["poneyland"], None);
2072 pub fn or_default(self) -> &'a mut V {
2074 Occupied(entry) => entry.into_mut(),
2075 Vacant(entry) => entry.insert(Default::default()),
2081 impl<'a, K, V> OccupiedEntry<'a, K, V> {
2082 /// Gets a reference to the key in the entry.
2087 /// use std::collections::HashMap;
2089 /// let mut map: HashMap<&str, u32> = HashMap::new();
2090 /// map.entry("poneyland").or_insert(12);
2091 /// assert_eq!(map.entry("poneyland").key(), &"poneyland");
2093 #[stable(feature = "map_entry_keys", since = "1.10.0")]
2094 pub fn key(&self) -> &K {
2098 /// Take the ownership of the key and value from the map.
2103 /// use std::collections::HashMap;
2104 /// use std::collections::hash_map::Entry;
2106 /// let mut map: HashMap<&str, u32> = HashMap::new();
2107 /// map.entry("poneyland").or_insert(12);
2109 /// if let Entry::Occupied(o) = map.entry("poneyland") {
2110 /// // We delete the entry from the map.
2111 /// o.remove_entry();
2114 /// assert_eq!(map.contains_key("poneyland"), false);
2116 #[stable(feature = "map_entry_recover_keys2", since = "1.12.0")]
2117 pub fn remove_entry(self) -> (K, V) {
2118 let (k, v, _) = pop_internal(self.elem);
2122 /// Gets a reference to the value in the entry.
2127 /// use std::collections::HashMap;
2128 /// use std::collections::hash_map::Entry;
2130 /// let mut map: HashMap<&str, u32> = HashMap::new();
2131 /// map.entry("poneyland").or_insert(12);
2133 /// if let Entry::Occupied(o) = map.entry("poneyland") {
2134 /// assert_eq!(o.get(), &12);
2137 #[stable(feature = "rust1", since = "1.0.0")]
2138 pub fn get(&self) -> &V {
2142 /// Gets a mutable reference to the value in the entry.
2147 /// use std::collections::HashMap;
2148 /// use std::collections::hash_map::Entry;
2150 /// let mut map: HashMap<&str, u32> = HashMap::new();
2151 /// map.entry("poneyland").or_insert(12);
2153 /// assert_eq!(map["poneyland"], 12);
2154 /// if let Entry::Occupied(mut o) = map.entry("poneyland") {
2155 /// *o.get_mut() += 10;
2158 /// assert_eq!(map["poneyland"], 22);
2160 #[stable(feature = "rust1", since = "1.0.0")]
2161 pub fn get_mut(&mut self) -> &mut V {
2162 self.elem.read_mut().1
2165 /// Converts the OccupiedEntry into a mutable reference to the value in the entry
2166 /// with a lifetime bound to the map itself.
2171 /// use std::collections::HashMap;
2172 /// use std::collections::hash_map::Entry;
2174 /// let mut map: HashMap<&str, u32> = HashMap::new();
2175 /// map.entry("poneyland").or_insert(12);
2177 /// assert_eq!(map["poneyland"], 12);
2178 /// if let Entry::Occupied(o) = map.entry("poneyland") {
2179 /// *o.into_mut() += 10;
2182 /// assert_eq!(map["poneyland"], 22);
2184 #[stable(feature = "rust1", since = "1.0.0")]
2185 pub fn into_mut(self) -> &'a mut V {
2186 self.elem.into_mut_refs().1
2189 /// Sets the value of the entry, and returns the entry's old value.
2194 /// use std::collections::HashMap;
2195 /// use std::collections::hash_map::Entry;
2197 /// let mut map: HashMap<&str, u32> = HashMap::new();
2198 /// map.entry("poneyland").or_insert(12);
2200 /// if let Entry::Occupied(mut o) = map.entry("poneyland") {
2201 /// assert_eq!(o.insert(15), 12);
2204 /// assert_eq!(map["poneyland"], 15);
2206 #[stable(feature = "rust1", since = "1.0.0")]
2207 pub fn insert(&mut self, mut value: V) -> V {
2208 let old_value = self.get_mut();
2209 mem::swap(&mut value, old_value);
2213 /// Takes the value out of the entry, and returns it.
2218 /// use std::collections::HashMap;
2219 /// use std::collections::hash_map::Entry;
2221 /// let mut map: HashMap<&str, u32> = HashMap::new();
2222 /// map.entry("poneyland").or_insert(12);
2224 /// if let Entry::Occupied(o) = map.entry("poneyland") {
2225 /// assert_eq!(o.remove(), 12);
2228 /// assert_eq!(map.contains_key("poneyland"), false);
2230 #[stable(feature = "rust1", since = "1.0.0")]
2231 pub fn remove(self) -> V {
2232 pop_internal(self.elem).1
2235 /// Returns a key that was used for search.
2237 /// The key was retained for further use.
2238 fn take_key(&mut self) -> Option<K> {
2242 /// Replaces the entry, returning the old key and value. The new key in the hash map will be
2243 /// the key used to create this entry.
2248 /// #![feature(map_entry_replace)]
2249 /// use std::collections::hash_map::{Entry, HashMap};
2251 /// let mut map: HashMap<String, u32> = HashMap::new();
2252 /// map.insert("poneyland".to_string(), 15);
2254 /// if let Entry::Occupied(entry) = map.entry("poneyland".to_string()) {
2255 /// let (old_key, old_value): (String, u32) = entry.replace_entry(16);
2256 /// assert_eq!(old_key, "poneyland");
2257 /// assert_eq!(old_value, 15);
2260 /// assert_eq!(map.get("poneyland"), Some(&16));
2262 #[unstable(feature = "map_entry_replace", issue = "44286")]
2263 pub fn replace_entry(mut self, value: V) -> (K, V) {
2264 let (old_key, old_value) = self.elem.read_mut();
2266 let old_key = mem::replace(old_key, self.key.unwrap());
2267 let old_value = mem::replace(old_value, value);
2269 (old_key, old_value)
2272 /// Replaces the key in the hash map with the key used to create this entry.
2277 /// #![feature(map_entry_replace)]
2278 /// use std::collections::hash_map::{Entry, HashMap};
2280 /// let mut map: HashMap<String, u32> = HashMap::new();
2281 /// map.insert("poneyland".to_string(), 15);
2283 /// if let Entry::Occupied(entry) = map.entry("poneyland".to_string()) {
2284 /// let old_key = entry.replace_key();
2285 /// assert_eq!(old_key, "poneyland");
2288 #[unstable(feature = "map_entry_replace", issue = "44286")]
2289 pub fn replace_key(mut self) -> K {
2290 let (old_key, _) = self.elem.read_mut();
2291 mem::replace(old_key, self.key.unwrap())
2295 impl<'a, K: 'a, V: 'a> VacantEntry<'a, K, V> {
2296 /// Gets a reference to the key that would be used when inserting a value
2297 /// through the `VacantEntry`.
2302 /// use std::collections::HashMap;
2304 /// let mut map: HashMap<&str, u32> = HashMap::new();
2305 /// assert_eq!(map.entry("poneyland").key(), &"poneyland");
2307 #[stable(feature = "map_entry_keys", since = "1.10.0")]
2308 pub fn key(&self) -> &K {
2312 /// Take ownership of the key.
2317 /// use std::collections::HashMap;
2318 /// use std::collections::hash_map::Entry;
2320 /// let mut map: HashMap<&str, u32> = HashMap::new();
2322 /// if let Entry::Vacant(v) = map.entry("poneyland") {
2326 #[stable(feature = "map_entry_recover_keys2", since = "1.12.0")]
2327 pub fn into_key(self) -> K {
2331 /// Sets the value of the entry with the VacantEntry's key,
2332 /// and returns a mutable reference to it.
2337 /// use std::collections::HashMap;
2338 /// use std::collections::hash_map::Entry;
2340 /// let mut map: HashMap<&str, u32> = HashMap::new();
2342 /// if let Entry::Vacant(o) = map.entry("poneyland") {
2345 /// assert_eq!(map["poneyland"], 37);
2347 #[stable(feature = "rust1", since = "1.0.0")]
2348 pub fn insert(self, value: V) -> &'a mut V {
2349 let b = match self.elem {
2350 NeqElem(mut bucket, disp) => {
2351 if disp >= DISPLACEMENT_THRESHOLD {
2352 bucket.table_mut().set_tag(true);
2354 robin_hood(bucket, disp, self.hash, self.key, value)
2356 NoElem(mut bucket, disp) => {
2357 if disp >= DISPLACEMENT_THRESHOLD {
2358 bucket.table_mut().set_tag(true);
2360 bucket.put(self.hash, self.key, value)
2366 // Only used for InPlacement insert. Avoid unnecessary value copy.
2367 // The value remains uninitialized.
2368 unsafe fn insert_key(self) -> FullBucketMut<'a, K, V> {
2370 NeqElem(mut bucket, disp) => {
2371 if disp >= DISPLACEMENT_THRESHOLD {
2372 bucket.table_mut().set_tag(true);
2374 let uninit = mem::uninitialized();
2375 robin_hood(bucket, disp, self.hash, self.key, uninit)
2377 NoElem(mut bucket, disp) => {
2378 if disp >= DISPLACEMENT_THRESHOLD {
2379 bucket.table_mut().set_tag(true);
2381 bucket.put_key(self.hash, self.key)
2387 #[stable(feature = "rust1", since = "1.0.0")]
2388 impl<K, V, S> FromIterator<(K, V)> for HashMap<K, V, S>
2390 S: BuildHasher + Default
2392 fn from_iter<T: IntoIterator<Item = (K, V)>>(iter: T) -> HashMap<K, V, S> {
2393 let mut map = HashMap::with_hasher(Default::default());
2399 #[stable(feature = "rust1", since = "1.0.0")]
2400 impl<K, V, S> Extend<(K, V)> for HashMap<K, V, S>
2404 fn extend<T: IntoIterator<Item = (K, V)>>(&mut self, iter: T) {
2405 // Keys may be already present or show multiple times in the iterator.
2406 // Reserve the entire hint lower bound if the map is empty.
2407 // Otherwise reserve half the hint (rounded up), so the map
2408 // will only resize twice in the worst case.
2409 let iter = iter.into_iter();
2410 let reserve = if self.is_empty() {
2413 (iter.size_hint().0 + 1) / 2
2415 self.reserve(reserve);
2416 for (k, v) in iter {
2422 #[stable(feature = "hash_extend_copy", since = "1.4.0")]
2423 impl<'a, K, V, S> Extend<(&'a K, &'a V)> for HashMap<K, V, S>
2424 where K: Eq + Hash + Copy,
2428 fn extend<T: IntoIterator<Item = (&'a K, &'a V)>>(&mut self, iter: T) {
2429 self.extend(iter.into_iter().map(|(&key, &value)| (key, value)));
2433 /// `RandomState` is the default state for [`HashMap`] types.
2435 /// A particular instance `RandomState` will create the same instances of
2436 /// [`Hasher`], but the hashers created by two different `RandomState`
2437 /// instances are unlikely to produce the same result for the same values.
2439 /// [`HashMap`]: struct.HashMap.html
2440 /// [`Hasher`]: ../../hash/trait.Hasher.html
2445 /// use std::collections::HashMap;
2446 /// use std::collections::hash_map::RandomState;
2448 /// let s = RandomState::new();
2449 /// let mut map = HashMap::with_hasher(s);
2450 /// map.insert(1, 2);
2453 #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
2454 pub struct RandomState {
2460 /// Constructs a new `RandomState` that is initialized with random keys.
2465 /// use std::collections::hash_map::RandomState;
2467 /// let s = RandomState::new();
2470 #[allow(deprecated)]
2472 #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
2473 pub fn new() -> RandomState {
2474 // Historically this function did not cache keys from the OS and instead
2475 // simply always called `rand::thread_rng().gen()` twice. In #31356 it
2476 // was discovered, however, that because we re-seed the thread-local RNG
2477 // from the OS periodically that this can cause excessive slowdown when
2478 // many hash maps are created on a thread. To solve this performance
2479 // trap we cache the first set of randomly generated keys per-thread.
2481 // Later in #36481 it was discovered that exposing a deterministic
2482 // iteration order allows a form of DOS attack. To counter that we
2483 // increment one of the seeds on every RandomState creation, giving
2484 // every corresponding HashMap a different iteration order.
2485 thread_local!(static KEYS: Cell<(u64, u64)> = {
2486 Cell::new(sys::hashmap_random_keys())
2490 let (k0, k1) = keys.get();
2491 keys.set((k0.wrapping_add(1), k1));
2492 RandomState { k0: k0, k1: k1 }
2497 #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
2498 impl BuildHasher for RandomState {
2499 type Hasher = DefaultHasher;
2501 #[allow(deprecated)]
2502 fn build_hasher(&self) -> DefaultHasher {
2503 DefaultHasher(SipHasher13::new_with_keys(self.k0, self.k1))
2507 /// The default [`Hasher`] used by [`RandomState`].
2509 /// The internal algorithm is not specified, and so it and its hashes should
2510 /// not be relied upon over releases.
2512 /// [`RandomState`]: struct.RandomState.html
2513 /// [`Hasher`]: ../../hash/trait.Hasher.html
2514 #[stable(feature = "hashmap_default_hasher", since = "1.13.0")]
2515 #[allow(deprecated)]
2516 #[derive(Clone, Debug)]
2517 pub struct DefaultHasher(SipHasher13);
2519 impl DefaultHasher {
2520 /// Creates a new `DefaultHasher`.
2522 /// This hasher is not guaranteed to be the same as all other
2523 /// `DefaultHasher` instances, but is the same as all other `DefaultHasher`
2524 /// instances created through `new` or `default`.
2525 #[stable(feature = "hashmap_default_hasher", since = "1.13.0")]
2526 #[allow(deprecated)]
2527 pub fn new() -> DefaultHasher {
2528 DefaultHasher(SipHasher13::new_with_keys(0, 0))
2532 #[stable(feature = "hashmap_default_hasher", since = "1.13.0")]
2533 impl Default for DefaultHasher {
2534 /// Creates a new `DefaultHasher` using [`new`]. See its documentation for more.
2536 /// [`new`]: #method.new
2537 fn default() -> DefaultHasher {
2538 DefaultHasher::new()
2542 #[stable(feature = "hashmap_default_hasher", since = "1.13.0")]
2543 impl Hasher for DefaultHasher {
2545 fn write(&mut self, msg: &[u8]) {
2550 fn finish(&self) -> u64 {
2555 #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
2556 impl Default for RandomState {
2557 /// Constructs a new `RandomState`.
2559 fn default() -> RandomState {
2564 #[stable(feature = "std_debug", since = "1.16.0")]
2565 impl fmt::Debug for RandomState {
2566 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2567 f.pad("RandomState { .. }")
2571 impl<K, S, Q: ?Sized> super::Recover<Q> for HashMap<K, (), S>
2572 where K: Eq + Hash + Borrow<Q>,
2579 fn get(&self, key: &Q) -> Option<&K> {
2580 self.search(key).into_occupied_bucket().map(|bucket| bucket.into_refs().0)
2583 fn take(&mut self, key: &Q) -> Option<K> {
2584 if self.table.size() == 0 {
2588 self.search_mut(key).into_occupied_bucket().map(|bucket| pop_internal(bucket).0)
2592 fn replace(&mut self, key: K) -> Option<K> {
2595 match self.entry(key) {
2596 Occupied(mut occupied) => {
2597 let key = occupied.take_key().unwrap();
2598 Some(mem::replace(occupied.elem.read_mut().0, key))
2609 fn assert_covariance() {
2610 fn map_key<'new>(v: HashMap<&'static str, u8>) -> HashMap<&'new str, u8> {
2613 fn map_val<'new>(v: HashMap<u8, &'static str>) -> HashMap<u8, &'new str> {
2616 fn iter_key<'a, 'new>(v: Iter<'a, &'static str, u8>) -> Iter<'a, &'new str, u8> {
2619 fn iter_val<'a, 'new>(v: Iter<'a, u8, &'static str>) -> Iter<'a, u8, &'new str> {
2622 fn into_iter_key<'new>(v: IntoIter<&'static str, u8>) -> IntoIter<&'new str, u8> {
2625 fn into_iter_val<'new>(v: IntoIter<u8, &'static str>) -> IntoIter<u8, &'new str> {
2628 fn keys_key<'a, 'new>(v: Keys<'a, &'static str, u8>) -> Keys<'a, &'new str, u8> {
2631 fn keys_val<'a, 'new>(v: Keys<'a, u8, &'static str>) -> Keys<'a, u8, &'new str> {
2634 fn values_key<'a, 'new>(v: Values<'a, &'static str, u8>) -> Values<'a, &'new str, u8> {
2637 fn values_val<'a, 'new>(v: Values<'a, u8, &'static str>) -> Values<'a, u8, &'new str> {
2640 fn drain<'new>(d: Drain<'static, &'static str, &'static str>)
2641 -> Drain<'new, &'new str, &'new str> {
2649 use super::Entry::{Occupied, Vacant};
2650 use super::RandomState;
2652 use rand::{thread_rng, Rng};
2656 fn test_zero_capacities() {
2657 type HM = HashMap<i32, i32>;
2660 assert_eq!(m.capacity(), 0);
2662 let m = HM::default();
2663 assert_eq!(m.capacity(), 0);
2665 let m = HM::with_hasher(RandomState::new());
2666 assert_eq!(m.capacity(), 0);
2668 let m = HM::with_capacity(0);
2669 assert_eq!(m.capacity(), 0);
2671 let m = HM::with_capacity_and_hasher(0, RandomState::new());
2672 assert_eq!(m.capacity(), 0);
2674 let mut m = HM::new();
2680 assert_eq!(m.capacity(), 0);
2682 let mut m = HM::new();
2684 assert_eq!(m.capacity(), 0);
2688 fn test_create_capacity_zero() {
2689 let mut m = HashMap::with_capacity(0);
2691 assert!(m.insert(1, 1).is_none());
2693 assert!(m.contains_key(&1));
2694 assert!(!m.contains_key(&0));
2699 let mut m = HashMap::new();
2700 assert_eq!(m.len(), 0);
2701 assert!(m.insert(1, 2).is_none());
2702 assert_eq!(m.len(), 1);
2703 assert!(m.insert(2, 4).is_none());
2704 assert_eq!(m.len(), 2);
2705 assert_eq!(*m.get(&1).unwrap(), 2);
2706 assert_eq!(*m.get(&2).unwrap(), 4);
2711 let mut m = HashMap::new();
2712 assert_eq!(m.len(), 0);
2713 assert!(m.insert(1, 2).is_none());
2714 assert_eq!(m.len(), 1);
2715 assert!(m.insert(2, 4).is_none());
2716 assert_eq!(m.len(), 2);
2718 assert_eq!(*m2.get(&1).unwrap(), 2);
2719 assert_eq!(*m2.get(&2).unwrap(), 4);
2720 assert_eq!(m2.len(), 2);
2723 thread_local! { static DROP_VECTOR: RefCell<Vec<isize>> = RefCell::new(Vec::new()) }
2725 #[derive(Hash, PartialEq, Eq)]
2731 fn new(k: usize) -> Dropable {
2732 DROP_VECTOR.with(|slot| {
2733 slot.borrow_mut()[k] += 1;
2740 impl Drop for Dropable {
2741 fn drop(&mut self) {
2742 DROP_VECTOR.with(|slot| {
2743 slot.borrow_mut()[self.k] -= 1;
2748 impl Clone for Dropable {
2749 fn clone(&self) -> Dropable {
2750 Dropable::new(self.k)
2756 DROP_VECTOR.with(|slot| {
2757 *slot.borrow_mut() = vec![0; 200];
2761 let mut m = HashMap::new();
2763 DROP_VECTOR.with(|v| {
2765 assert_eq!(v.borrow()[i], 0);
2770 let d1 = Dropable::new(i);
2771 let d2 = Dropable::new(i + 100);
2775 DROP_VECTOR.with(|v| {
2777 assert_eq!(v.borrow()[i], 1);
2782 let k = Dropable::new(i);
2783 let v = m.remove(&k);
2785 assert!(v.is_some());
2787 DROP_VECTOR.with(|v| {
2788 assert_eq!(v.borrow()[i], 1);
2789 assert_eq!(v.borrow()[i+100], 1);
2793 DROP_VECTOR.with(|v| {
2795 assert_eq!(v.borrow()[i], 0);
2796 assert_eq!(v.borrow()[i+100], 0);
2800 assert_eq!(v.borrow()[i], 1);
2801 assert_eq!(v.borrow()[i+100], 1);
2806 DROP_VECTOR.with(|v| {
2808 assert_eq!(v.borrow()[i], 0);
2814 fn test_into_iter_drops() {
2815 DROP_VECTOR.with(|v| {
2816 *v.borrow_mut() = vec![0; 200];
2820 let mut hm = HashMap::new();
2822 DROP_VECTOR.with(|v| {
2824 assert_eq!(v.borrow()[i], 0);
2829 let d1 = Dropable::new(i);
2830 let d2 = Dropable::new(i + 100);
2834 DROP_VECTOR.with(|v| {
2836 assert_eq!(v.borrow()[i], 1);
2843 // By the way, ensure that cloning doesn't screw up the dropping.
2847 let mut half = hm.into_iter().take(50);
2849 DROP_VECTOR.with(|v| {
2851 assert_eq!(v.borrow()[i], 1);
2855 for _ in half.by_ref() {}
2857 DROP_VECTOR.with(|v| {
2859 .filter(|&i| v.borrow()[i] == 1)
2863 .filter(|&i| v.borrow()[i + 100] == 1)
2871 DROP_VECTOR.with(|v| {
2873 assert_eq!(v.borrow()[i], 0);
2879 fn test_empty_remove() {
2880 let mut m: HashMap<isize, bool> = HashMap::new();
2881 assert_eq!(m.remove(&0), None);
2885 fn test_empty_entry() {
2886 let mut m: HashMap<isize, bool> = HashMap::new();
2888 Occupied(_) => panic!(),
2891 assert!(*m.entry(0).or_insert(true));
2892 assert_eq!(m.len(), 1);
2896 fn test_empty_iter() {
2897 let mut m: HashMap<isize, bool> = HashMap::new();
2898 assert_eq!(m.drain().next(), None);
2899 assert_eq!(m.keys().next(), None);
2900 assert_eq!(m.values().next(), None);
2901 assert_eq!(m.values_mut().next(), None);
2902 assert_eq!(m.iter().next(), None);
2903 assert_eq!(m.iter_mut().next(), None);
2904 assert_eq!(m.len(), 0);
2905 assert!(m.is_empty());
2906 assert_eq!(m.into_iter().next(), None);
2910 fn test_lots_of_insertions() {
2911 let mut m = HashMap::new();
2913 // Try this a few times to make sure we never screw up the hashmap's
2916 assert!(m.is_empty());
2919 assert!(m.insert(i, i).is_none());
2923 assert_eq!(r, Some(&j));
2926 for j in i + 1..1001 {
2928 assert_eq!(r, None);
2932 for i in 1001..2001 {
2933 assert!(!m.contains_key(&i));
2938 assert!(m.remove(&i).is_some());
2941 assert!(!m.contains_key(&j));
2944 for j in i + 1..1001 {
2945 assert!(m.contains_key(&j));
2950 assert!(!m.contains_key(&i));
2954 assert!(m.insert(i, i).is_none());
2958 for i in (1..1001).rev() {
2959 assert!(m.remove(&i).is_some());
2962 assert!(!m.contains_key(&j));
2966 assert!(m.contains_key(&j));
2973 fn test_find_mut() {
2974 let mut m = HashMap::new();
2975 assert!(m.insert(1, 12).is_none());
2976 assert!(m.insert(2, 8).is_none());
2977 assert!(m.insert(5, 14).is_none());
2979 match m.get_mut(&5) {
2981 Some(x) => *x = new,
2983 assert_eq!(m.get(&5), Some(&new));
2987 fn test_insert_overwrite() {
2988 let mut m = HashMap::new();
2989 assert!(m.insert(1, 2).is_none());
2990 assert_eq!(*m.get(&1).unwrap(), 2);
2991 assert!(!m.insert(1, 3).is_none());
2992 assert_eq!(*m.get(&1).unwrap(), 3);
2996 fn test_insert_conflicts() {
2997 let mut m = HashMap::with_capacity(4);
2998 assert!(m.insert(1, 2).is_none());
2999 assert!(m.insert(5, 3).is_none());
3000 assert!(m.insert(9, 4).is_none());
3001 assert_eq!(*m.get(&9).unwrap(), 4);
3002 assert_eq!(*m.get(&5).unwrap(), 3);
3003 assert_eq!(*m.get(&1).unwrap(), 2);
3007 fn test_conflict_remove() {
3008 let mut m = HashMap::with_capacity(4);
3009 assert!(m.insert(1, 2).is_none());
3010 assert_eq!(*m.get(&1).unwrap(), 2);
3011 assert!(m.insert(5, 3).is_none());
3012 assert_eq!(*m.get(&1).unwrap(), 2);
3013 assert_eq!(*m.get(&5).unwrap(), 3);
3014 assert!(m.insert(9, 4).is_none());
3015 assert_eq!(*m.get(&1).unwrap(), 2);
3016 assert_eq!(*m.get(&5).unwrap(), 3);
3017 assert_eq!(*m.get(&9).unwrap(), 4);
3018 assert!(m.remove(&1).is_some());
3019 assert_eq!(*m.get(&9).unwrap(), 4);
3020 assert_eq!(*m.get(&5).unwrap(), 3);
3024 fn test_is_empty() {
3025 let mut m = HashMap::with_capacity(4);
3026 assert!(m.insert(1, 2).is_none());
3027 assert!(!m.is_empty());
3028 assert!(m.remove(&1).is_some());
3029 assert!(m.is_empty());
3034 let mut m = HashMap::new();
3036 assert_eq!(m.remove(&1), Some(2));
3037 assert_eq!(m.remove(&1), None);
3042 let mut m = HashMap::with_capacity(4);
3044 assert!(m.insert(i, i*2).is_none());
3046 assert_eq!(m.len(), 32);
3048 let mut observed: u32 = 0;
3051 assert_eq!(*v, *k * 2);
3052 observed |= 1 << *k;
3054 assert_eq!(observed, 0xFFFF_FFFF);
3059 let vec = vec![(1, 'a'), (2, 'b'), (3, 'c')];
3060 let map: HashMap<_, _> = vec.into_iter().collect();
3061 let keys: Vec<_> = map.keys().cloned().collect();
3062 assert_eq!(keys.len(), 3);
3063 assert!(keys.contains(&1));
3064 assert!(keys.contains(&2));
3065 assert!(keys.contains(&3));
3070 let vec = vec![(1, 'a'), (2, 'b'), (3, 'c')];
3071 let map: HashMap<_, _> = vec.into_iter().collect();
3072 let values: Vec<_> = map.values().cloned().collect();
3073 assert_eq!(values.len(), 3);
3074 assert!(values.contains(&'a'));
3075 assert!(values.contains(&'b'));
3076 assert!(values.contains(&'c'));
3080 fn test_values_mut() {
3081 let vec = vec![(1, 1), (2, 2), (3, 3)];
3082 let mut map: HashMap<_, _> = vec.into_iter().collect();
3083 for value in map.values_mut() {
3084 *value = (*value) * 2
3086 let values: Vec<_> = map.values().cloned().collect();
3087 assert_eq!(values.len(), 3);
3088 assert!(values.contains(&2));
3089 assert!(values.contains(&4));
3090 assert!(values.contains(&6));
3095 let mut m = HashMap::new();
3096 assert!(m.get(&1).is_none());
3100 Some(v) => assert_eq!(*v, 2),
3106 let mut m1 = HashMap::new();
3111 let mut m2 = HashMap::new();
3124 let mut map = HashMap::new();
3125 let empty: HashMap<i32, i32> = HashMap::new();
3130 let map_str = format!("{:?}", map);
3132 assert!(map_str == "{1: 2, 3: 4}" ||
3133 map_str == "{3: 4, 1: 2}");
3134 assert_eq!(format!("{:?}", empty), "{}");
3139 let mut m = HashMap::new();
3141 assert_eq!(m.len(), 0);
3142 assert!(m.is_empty());
3145 let old_raw_cap = m.raw_capacity();
3146 while old_raw_cap == m.raw_capacity() {
3151 assert_eq!(m.len(), i);
3152 assert!(!m.is_empty());
3156 fn test_behavior_resize_policy() {
3157 let mut m = HashMap::new();
3159 assert_eq!(m.len(), 0);
3160 assert_eq!(m.raw_capacity(), 0);
3161 assert!(m.is_empty());
3165 assert!(m.is_empty());
3166 let initial_raw_cap = m.raw_capacity();
3167 m.reserve(initial_raw_cap);
3168 let raw_cap = m.raw_capacity();
3170 assert_eq!(raw_cap, initial_raw_cap * 2);
3173 for _ in 0..raw_cap * 3 / 4 {
3177 // three quarters full
3179 assert_eq!(m.len(), i);
3180 assert_eq!(m.raw_capacity(), raw_cap);
3182 for _ in 0..raw_cap / 4 {
3188 let new_raw_cap = m.raw_capacity();
3189 assert_eq!(new_raw_cap, raw_cap * 2);
3191 for _ in 0..raw_cap / 2 - 1 {
3194 assert_eq!(m.raw_capacity(), new_raw_cap);
3196 // A little more than one quarter full.
3198 assert_eq!(m.raw_capacity(), raw_cap);
3199 // again, a little more than half full
3200 for _ in 0..raw_cap / 2 - 1 {
3206 assert_eq!(m.len(), i);
3207 assert!(!m.is_empty());
3208 assert_eq!(m.raw_capacity(), initial_raw_cap);
3212 fn test_reserve_shrink_to_fit() {
3213 let mut m = HashMap::new();
3216 assert!(m.capacity() >= m.len());
3222 let usable_cap = m.capacity();
3223 for i in 128..(128 + 256) {
3225 assert_eq!(m.capacity(), usable_cap);
3228 for i in 100..(128 + 256) {
3229 assert_eq!(m.remove(&i), Some(i));
3233 assert_eq!(m.len(), 100);
3234 assert!(!m.is_empty());
3235 assert!(m.capacity() >= m.len());
3238 assert_eq!(m.remove(&i), Some(i));
3243 assert_eq!(m.len(), 1);
3244 assert!(m.capacity() >= m.len());
3245 assert_eq!(m.remove(&0), Some(0));
3249 fn test_from_iter() {
3250 let xs = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
3252 let map: HashMap<_, _> = xs.iter().cloned().collect();
3254 for &(k, v) in &xs {
3255 assert_eq!(map.get(&k), Some(&v));
3260 fn test_size_hint() {
3261 let xs = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
3263 let map: HashMap<_, _> = xs.iter().cloned().collect();
3265 let mut iter = map.iter();
3267 for _ in iter.by_ref().take(3) {}
3269 assert_eq!(iter.size_hint(), (3, Some(3)));
3273 fn test_iter_len() {
3274 let xs = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
3276 let map: HashMap<_, _> = xs.iter().cloned().collect();
3278 let mut iter = map.iter();
3280 for _ in iter.by_ref().take(3) {}
3282 assert_eq!(iter.len(), 3);
3286 fn test_mut_size_hint() {
3287 let xs = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
3289 let mut map: HashMap<_, _> = xs.iter().cloned().collect();
3291 let mut iter = map.iter_mut();
3293 for _ in iter.by_ref().take(3) {}
3295 assert_eq!(iter.size_hint(), (3, Some(3)));
3299 fn test_iter_mut_len() {
3300 let xs = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
3302 let mut map: HashMap<_, _> = xs.iter().cloned().collect();
3304 let mut iter = map.iter_mut();
3306 for _ in iter.by_ref().take(3) {}
3308 assert_eq!(iter.len(), 3);
3313 let mut map = HashMap::new();
3319 assert_eq!(map[&2], 1);
3324 fn test_index_nonexistent() {
3325 let mut map = HashMap::new();
3336 let xs = [(1, 10), (2, 20), (3, 30), (4, 40), (5, 50), (6, 60)];
3338 let mut map: HashMap<_, _> = xs.iter().cloned().collect();
3340 // Existing key (insert)
3341 match map.entry(1) {
3342 Vacant(_) => unreachable!(),
3343 Occupied(mut view) => {
3344 assert_eq!(view.get(), &10);
3345 assert_eq!(view.insert(100), 10);
3348 assert_eq!(map.get(&1).unwrap(), &100);
3349 assert_eq!(map.len(), 6);
3352 // Existing key (update)
3353 match map.entry(2) {
3354 Vacant(_) => unreachable!(),
3355 Occupied(mut view) => {
3356 let v = view.get_mut();
3357 let new_v = (*v) * 10;
3361 assert_eq!(map.get(&2).unwrap(), &200);
3362 assert_eq!(map.len(), 6);
3364 // Existing key (take)
3365 match map.entry(3) {
3366 Vacant(_) => unreachable!(),
3368 assert_eq!(view.remove(), 30);
3371 assert_eq!(map.get(&3), None);
3372 assert_eq!(map.len(), 5);
3375 // Inexistent key (insert)
3376 match map.entry(10) {
3377 Occupied(_) => unreachable!(),
3379 assert_eq!(*view.insert(1000), 1000);
3382 assert_eq!(map.get(&10).unwrap(), &1000);
3383 assert_eq!(map.len(), 6);
3387 fn test_entry_take_doesnt_corrupt() {
3388 #![allow(deprecated)] //rand
3390 fn check(m: &HashMap<isize, ()>) {
3392 assert!(m.contains_key(k),
3393 "{} is in keys() but not in the map?", k);
3397 let mut m = HashMap::new();
3398 let mut rng = thread_rng();
3400 // Populate the map with some items.
3402 let x = rng.gen_range(-10, 10);
3407 let x = rng.gen_range(-10, 10);
3411 println!("{}: remove {}", i, x);
3421 fn test_extend_ref() {
3422 let mut a = HashMap::new();
3424 let mut b = HashMap::new();
3426 b.insert(3, "three");
3430 assert_eq!(a.len(), 3);
3431 assert_eq!(a[&1], "one");
3432 assert_eq!(a[&2], "two");
3433 assert_eq!(a[&3], "three");
3437 fn test_capacity_not_less_than_len() {
3438 let mut a = HashMap::new();
3446 assert!(a.capacity() > a.len());
3448 let free = a.capacity() - a.len();
3454 assert_eq!(a.len(), a.capacity());
3456 // Insert at capacity should cause allocation.
3458 assert!(a.capacity() > a.len());
3462 fn test_occupied_entry_key() {
3463 let mut a = HashMap::new();
3464 let key = "hello there";
3465 let value = "value goes here";
3466 assert!(a.is_empty());
3467 a.insert(key.clone(), value.clone());
3468 assert_eq!(a.len(), 1);
3469 assert_eq!(a[key], value);
3471 match a.entry(key.clone()) {
3472 Vacant(_) => panic!(),
3473 Occupied(e) => assert_eq!(key, *e.key()),
3475 assert_eq!(a.len(), 1);
3476 assert_eq!(a[key], value);
3480 fn test_vacant_entry_key() {
3481 let mut a = HashMap::new();
3482 let key = "hello there";
3483 let value = "value goes here";
3485 assert!(a.is_empty());
3486 match a.entry(key.clone()) {
3487 Occupied(_) => panic!(),
3489 assert_eq!(key, *e.key());
3490 e.insert(value.clone());
3493 assert_eq!(a.len(), 1);
3494 assert_eq!(a[key], value);
3499 let mut map: HashMap<isize, isize> = (0..100).map(|x|(x, x*10)).collect();
3501 map.retain(|&k, _| k % 2 == 0);
3502 assert_eq!(map.len(), 50);
3503 assert_eq!(map[&2], 20);
3504 assert_eq!(map[&4], 40);
3505 assert_eq!(map[&6], 60);
3509 fn test_adaptive() {
3510 const TEST_LEN: usize = 5000;
3511 // by cloning we get maps with the same hasher seed
3512 let mut first = HashMap::new();
3513 let mut second = first.clone();
3514 first.extend((0..TEST_LEN).map(|i| (i, i)));
3515 second.extend((TEST_LEN..TEST_LEN * 2).map(|i| (i, i)));
3517 for (&k, &v) in &second {
3518 let prev_cap = first.capacity();
3519 let expect_grow = first.len() == prev_cap;
3521 if !expect_grow && first.capacity() != prev_cap {
3525 panic!("Adaptive early resize failed");
3529 fn test_placement_in() {
3530 let mut map = HashMap::new();
3531 map.extend((0..10).map(|i| (i, i)));
3533 map.entry(100) <- 100;
3534 assert_eq!(map[&100], 100);
3537 assert_eq!(map[&0], 10);
3539 assert_eq!(map.len(), 11);
3543 fn test_placement_panic() {
3544 let mut map = HashMap::new();
3545 map.extend((0..10).map(|i| (i, i)));
3547 fn mkpanic() -> usize { panic!() }
3549 // modify existing key
3550 // when panic happens, previous key is removed.
3551 let _ = panic::catch_unwind(panic::AssertUnwindSafe(|| { map.entry(0) <- mkpanic(); }));
3552 assert_eq!(map.len(), 9);
3553 assert!(!map.contains_key(&0));
3556 let _ = panic::catch_unwind(panic::AssertUnwindSafe(|| { map.entry(100) <- mkpanic(); }));
3557 assert_eq!(map.len(), 9);
3558 assert!(!map.contains_key(&100));
3562 fn test_placement_drop() {
3564 struct TestV<'a>(&'a mut bool);
3565 impl<'a> Drop for TestV<'a> {
3566 fn drop(&mut self) {
3567 if !*self.0 { panic!("value double drop!"); } // no double drop
3572 fn makepanic<'a>() -> TestV<'a> { panic!() }
3574 let mut can_drop = true;
3575 let mut hm = HashMap::new();
3576 hm.insert(0, TestV(&mut can_drop));
3577 let _ = panic::catch_unwind(panic::AssertUnwindSafe(|| { hm.entry(0) <- makepanic(); }));
3578 assert_eq!(hm.len(), 0);