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};
23 use rand::{self, Rng};
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`.
594 /// use std::collections::HashMap;
595 /// let mut map: HashMap<&str, isize> = HashMap::new();
598 #[stable(feature = "rust1", since = "1.0.0")]
599 pub fn new() -> HashMap<K, V, RandomState> {
603 /// Creates an empty `HashMap` with the specified capacity.
605 /// The hash map will be able to hold at least `capacity` elements without
606 /// reallocating. If `capacity` is 0, the hash map will not allocate.
611 /// use std::collections::HashMap;
612 /// let mut map: HashMap<&str, isize> = HashMap::with_capacity(10);
615 #[stable(feature = "rust1", since = "1.0.0")]
616 pub fn with_capacity(capacity: usize) -> HashMap<K, V, RandomState> {
617 HashMap::with_capacity_and_hasher(capacity, Default::default())
621 impl<K, V, S> HashMap<K, V, S>
625 /// Creates an empty `HashMap` which will use the given hash builder to hash
628 /// The created map has the default initial capacity.
630 /// Warning: `hash_builder` is normally randomly generated, and
631 /// is designed to allow HashMaps to be resistant to attacks that
632 /// cause many collisions and very poor performance. Setting it
633 /// manually using this function can expose a DoS attack vector.
638 /// use std::collections::HashMap;
639 /// use std::collections::hash_map::RandomState;
641 /// let s = RandomState::new();
642 /// let mut map = HashMap::with_hasher(s);
643 /// map.insert(1, 2);
646 #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
647 pub fn with_hasher(hash_builder: S) -> HashMap<K, V, S> {
650 resize_policy: DefaultResizePolicy::new(),
651 table: RawTable::new(0),
655 /// Creates an empty `HashMap` with the specified capacity, using `hash_builder`
656 /// to hash the keys.
658 /// The hash map will be able to hold at least `capacity` elements without
659 /// reallocating. If `capacity` is 0, the hash map will not allocate.
661 /// Warning: `hash_builder` is normally randomly generated, and
662 /// is designed to allow HashMaps to be resistant to attacks that
663 /// cause many collisions and very poor performance. Setting it
664 /// manually using this function can expose a DoS attack vector.
669 /// use std::collections::HashMap;
670 /// use std::collections::hash_map::RandomState;
672 /// let s = RandomState::new();
673 /// let mut map = HashMap::with_capacity_and_hasher(10, s);
674 /// map.insert(1, 2);
677 #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
678 pub fn with_capacity_and_hasher(capacity: usize, hash_builder: S) -> HashMap<K, V, S> {
679 let resize_policy = DefaultResizePolicy::new();
680 let raw_cap = resize_policy.raw_capacity(capacity);
684 table: RawTable::new(raw_cap),
688 /// Returns a reference to the map's [`BuildHasher`].
690 /// [`BuildHasher`]: ../../std/hash/trait.BuildHasher.html
691 #[stable(feature = "hashmap_public_hasher", since = "1.9.0")]
692 pub fn hasher(&self) -> &S {
696 /// Returns the number of elements the map can hold without reallocating.
698 /// This number is a lower bound; the `HashMap<K, V>` might be able to hold
699 /// more, but is guaranteed to be able to hold at least this many.
704 /// use std::collections::HashMap;
705 /// let map: HashMap<isize, isize> = HashMap::with_capacity(100);
706 /// assert!(map.capacity() >= 100);
709 #[stable(feature = "rust1", since = "1.0.0")]
710 pub fn capacity(&self) -> usize {
711 self.resize_policy.capacity(self.raw_capacity())
714 /// Returns the hash map's raw capacity.
716 fn raw_capacity(&self) -> usize {
717 self.table.capacity()
720 /// Reserves capacity for at least `additional` more elements to be inserted
721 /// in the `HashMap`. The collection may reserve more space to avoid
722 /// frequent reallocations.
726 /// Panics if the new allocation size overflows [`usize`].
728 /// [`usize`]: ../../std/primitive.usize.html
733 /// use std::collections::HashMap;
734 /// let mut map: HashMap<&str, isize> = HashMap::new();
737 #[stable(feature = "rust1", since = "1.0.0")]
738 pub fn reserve(&mut self, additional: usize) {
739 let remaining = self.capacity() - self.len(); // this can't overflow
740 if remaining < additional {
741 let min_cap = self.len().checked_add(additional).expect("reserve overflow");
742 let raw_cap = self.resize_policy.raw_capacity(min_cap);
743 self.resize(raw_cap);
744 } else if self.table.tag() && remaining <= self.len() {
745 // Probe sequence is too long and table is half full,
746 // resize early to reduce probing length.
747 let new_capacity = self.table.capacity() * 2;
748 self.resize(new_capacity);
752 /// Resizes the internal vectors to a new capacity. It's your
753 /// responsibility to:
754 /// 1) Ensure `new_raw_cap` is enough for all the elements, accounting
755 /// for the load factor.
756 /// 2) Ensure `new_raw_cap` is a power of two or zero.
759 fn resize(&mut self, new_raw_cap: usize) {
760 assert!(self.table.size() <= new_raw_cap);
761 assert!(new_raw_cap.is_power_of_two() || new_raw_cap == 0);
763 let mut old_table = replace(&mut self.table, RawTable::new(new_raw_cap));
764 let old_size = old_table.size();
766 if old_table.size() == 0 {
770 let mut bucket = Bucket::head_bucket(&mut old_table);
772 // This is how the buckets might be laid out in memory:
773 // ($ marks an initialized bucket)
775 // |$$$_$$$$$$_$$$$$|
777 // But we've skipped the entire initial cluster of buckets
778 // and will continue iteration in this order:
781 // ^ wrap around once end is reached
784 // ^ exit once table.size == 0
786 bucket = match bucket.peek() {
788 let h = bucket.hash();
789 let (b, k, v) = bucket.take();
790 self.insert_hashed_ordered(h, k, v);
791 if b.table().size() == 0 {
796 Empty(b) => b.into_bucket(),
801 assert_eq!(self.table.size(), old_size);
804 /// Shrinks the capacity of the map as much as possible. It will drop
805 /// down as much as possible while maintaining the internal rules
806 /// and possibly leaving some space in accordance with the resize policy.
811 /// use std::collections::HashMap;
813 /// let mut map: HashMap<isize, isize> = HashMap::with_capacity(100);
814 /// map.insert(1, 2);
815 /// map.insert(3, 4);
816 /// assert!(map.capacity() >= 100);
817 /// map.shrink_to_fit();
818 /// assert!(map.capacity() >= 2);
820 #[stable(feature = "rust1", since = "1.0.0")]
821 pub fn shrink_to_fit(&mut self) {
822 let new_raw_cap = self.resize_policy.raw_capacity(self.len());
823 if self.raw_capacity() != new_raw_cap {
824 let old_table = replace(&mut self.table, RawTable::new(new_raw_cap));
825 let old_size = old_table.size();
827 // Shrink the table. Naive algorithm for resizing:
828 for (h, k, v) in old_table.into_iter() {
829 self.insert_hashed_nocheck(h, k, v);
832 debug_assert_eq!(self.table.size(), old_size);
836 /// Insert a pre-hashed key-value pair, without first checking
837 /// that there's enough room in the buckets. Returns a reference to the
838 /// newly insert value.
840 /// If the key already exists, the hashtable will be returned untouched
841 /// and a reference to the existing element will be returned.
842 fn insert_hashed_nocheck(&mut self, hash: SafeHash, k: K, v: V) -> Option<V> {
843 let entry = search_hashed(&mut self.table, hash, |key| *key == k).into_entry(k);
845 Some(Occupied(mut elem)) => Some(elem.insert(v)),
846 Some(Vacant(elem)) => {
850 None => unreachable!(),
854 /// An iterator visiting all keys in arbitrary order.
855 /// The iterator element type is `&'a K`.
860 /// use std::collections::HashMap;
862 /// let mut map = HashMap::new();
863 /// map.insert("a", 1);
864 /// map.insert("b", 2);
865 /// map.insert("c", 3);
867 /// for key in map.keys() {
868 /// println!("{}", key);
871 #[stable(feature = "rust1", since = "1.0.0")]
872 pub fn keys(&self) -> Keys<K, V> {
873 Keys { inner: self.iter() }
876 /// An iterator visiting all values in arbitrary order.
877 /// The iterator element type is `&'a V`.
882 /// use std::collections::HashMap;
884 /// let mut map = HashMap::new();
885 /// map.insert("a", 1);
886 /// map.insert("b", 2);
887 /// map.insert("c", 3);
889 /// for val in map.values() {
890 /// println!("{}", val);
893 #[stable(feature = "rust1", since = "1.0.0")]
894 pub fn values(&self) -> Values<K, V> {
895 Values { inner: self.iter() }
898 /// An iterator visiting all values mutably in arbitrary order.
899 /// The iterator element type is `&'a mut V`.
904 /// use std::collections::HashMap;
906 /// let mut map = HashMap::new();
908 /// map.insert("a", 1);
909 /// map.insert("b", 2);
910 /// map.insert("c", 3);
912 /// for val in map.values_mut() {
913 /// *val = *val + 10;
916 /// for val in map.values() {
917 /// println!("{}", val);
920 #[stable(feature = "map_values_mut", since = "1.10.0")]
921 pub fn values_mut(&mut self) -> ValuesMut<K, V> {
922 ValuesMut { inner: self.iter_mut() }
925 /// An iterator visiting all key-value pairs in arbitrary order.
926 /// The iterator element type is `(&'a K, &'a V)`.
931 /// use std::collections::HashMap;
933 /// let mut map = HashMap::new();
934 /// map.insert("a", 1);
935 /// map.insert("b", 2);
936 /// map.insert("c", 3);
938 /// for (key, val) in map.iter() {
939 /// println!("key: {} val: {}", key, val);
942 #[stable(feature = "rust1", since = "1.0.0")]
943 pub fn iter(&self) -> Iter<K, V> {
944 Iter { inner: self.table.iter() }
947 /// An iterator visiting all key-value pairs in arbitrary order,
948 /// with mutable references to the values.
949 /// The iterator element type is `(&'a K, &'a mut V)`.
954 /// use std::collections::HashMap;
956 /// let mut map = HashMap::new();
957 /// map.insert("a", 1);
958 /// map.insert("b", 2);
959 /// map.insert("c", 3);
961 /// // Update all values
962 /// for (_, val) in map.iter_mut() {
966 /// for (key, val) in &map {
967 /// println!("key: {} val: {}", key, val);
970 #[stable(feature = "rust1", since = "1.0.0")]
971 pub fn iter_mut(&mut self) -> IterMut<K, V> {
972 IterMut { inner: self.table.iter_mut() }
975 /// Gets the given key's corresponding entry in the map for in-place manipulation.
980 /// use std::collections::HashMap;
982 /// let mut letters = HashMap::new();
984 /// for ch in "a short treatise on fungi".chars() {
985 /// let counter = letters.entry(ch).or_insert(0);
989 /// assert_eq!(letters[&'s'], 2);
990 /// assert_eq!(letters[&'t'], 3);
991 /// assert_eq!(letters[&'u'], 1);
992 /// assert_eq!(letters.get(&'y'), None);
994 #[stable(feature = "rust1", since = "1.0.0")]
995 pub fn entry(&mut self, key: K) -> Entry<K, V> {
998 let hash = self.make_hash(&key);
999 search_hashed(&mut self.table, hash, |q| q.eq(&key))
1000 .into_entry(key).expect("unreachable")
1003 /// Returns the number of elements in the map.
1008 /// use std::collections::HashMap;
1010 /// let mut a = HashMap::new();
1011 /// assert_eq!(a.len(), 0);
1012 /// a.insert(1, "a");
1013 /// assert_eq!(a.len(), 1);
1015 #[stable(feature = "rust1", since = "1.0.0")]
1016 pub fn len(&self) -> usize {
1020 /// Returns true if the map contains no elements.
1025 /// use std::collections::HashMap;
1027 /// let mut a = HashMap::new();
1028 /// assert!(a.is_empty());
1029 /// a.insert(1, "a");
1030 /// assert!(!a.is_empty());
1033 #[stable(feature = "rust1", since = "1.0.0")]
1034 pub fn is_empty(&self) -> bool {
1038 /// Clears the map, returning all key-value pairs as an iterator. Keeps the
1039 /// allocated memory for reuse.
1044 /// use std::collections::HashMap;
1046 /// let mut a = HashMap::new();
1047 /// a.insert(1, "a");
1048 /// a.insert(2, "b");
1050 /// for (k, v) in a.drain().take(1) {
1051 /// assert!(k == 1 || k == 2);
1052 /// assert!(v == "a" || v == "b");
1055 /// assert!(a.is_empty());
1058 #[stable(feature = "drain", since = "1.6.0")]
1059 pub fn drain(&mut self) -> Drain<K, V> {
1060 Drain { inner: self.table.drain() }
1063 /// Clears the map, removing all key-value pairs. Keeps the allocated memory
1069 /// use std::collections::HashMap;
1071 /// let mut a = HashMap::new();
1072 /// a.insert(1, "a");
1074 /// assert!(a.is_empty());
1076 #[stable(feature = "rust1", since = "1.0.0")]
1078 pub fn clear(&mut self) {
1082 /// Returns a reference to the value corresponding to the key.
1084 /// The key may be any borrowed form of the map's key type, but
1085 /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
1088 /// [`Eq`]: ../../std/cmp/trait.Eq.html
1089 /// [`Hash`]: ../../std/hash/trait.Hash.html
1094 /// use std::collections::HashMap;
1096 /// let mut map = HashMap::new();
1097 /// map.insert(1, "a");
1098 /// assert_eq!(map.get(&1), Some(&"a"));
1099 /// assert_eq!(map.get(&2), None);
1101 #[stable(feature = "rust1", since = "1.0.0")]
1102 pub fn get<Q: ?Sized>(&self, k: &Q) -> Option<&V>
1106 self.search(k).into_occupied_bucket().map(|bucket| bucket.into_refs().1)
1109 /// Returns true if the map contains a value for the specified key.
1111 /// The key may be any borrowed form of the map's key type, but
1112 /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
1115 /// [`Eq`]: ../../std/cmp/trait.Eq.html
1116 /// [`Hash`]: ../../std/hash/trait.Hash.html
1121 /// use std::collections::HashMap;
1123 /// let mut map = HashMap::new();
1124 /// map.insert(1, "a");
1125 /// assert_eq!(map.contains_key(&1), true);
1126 /// assert_eq!(map.contains_key(&2), false);
1128 #[stable(feature = "rust1", since = "1.0.0")]
1129 pub fn contains_key<Q: ?Sized>(&self, k: &Q) -> bool
1133 self.search(k).into_occupied_bucket().is_some()
1136 /// Returns a mutable reference to the value corresponding to the key.
1138 /// The key may be any borrowed form of the map's key type, but
1139 /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
1142 /// [`Eq`]: ../../std/cmp/trait.Eq.html
1143 /// [`Hash`]: ../../std/hash/trait.Hash.html
1148 /// use std::collections::HashMap;
1150 /// let mut map = HashMap::new();
1151 /// map.insert(1, "a");
1152 /// if let Some(x) = map.get_mut(&1) {
1155 /// assert_eq!(map[&1], "b");
1157 #[stable(feature = "rust1", since = "1.0.0")]
1158 pub fn get_mut<Q: ?Sized>(&mut self, k: &Q) -> Option<&mut V>
1162 self.search_mut(k).into_occupied_bucket().map(|bucket| bucket.into_mut_refs().1)
1165 /// Inserts a key-value pair into the map.
1167 /// If the map did not have this key present, [`None`] is returned.
1169 /// If the map did have this key present, the value is updated, and the old
1170 /// value is returned. The key is not updated, though; this matters for
1171 /// types that can be `==` without being identical. See the [module-level
1172 /// documentation] for more.
1174 /// [`None`]: ../../std/option/enum.Option.html#variant.None
1175 /// [module-level documentation]: index.html#insert-and-complex-keys
1180 /// use std::collections::HashMap;
1182 /// let mut map = HashMap::new();
1183 /// assert_eq!(map.insert(37, "a"), None);
1184 /// assert_eq!(map.is_empty(), false);
1186 /// map.insert(37, "b");
1187 /// assert_eq!(map.insert(37, "c"), Some("b"));
1188 /// assert_eq!(map[&37], "c");
1190 #[stable(feature = "rust1", since = "1.0.0")]
1191 pub fn insert(&mut self, k: K, v: V) -> Option<V> {
1192 let hash = self.make_hash(&k);
1194 self.insert_hashed_nocheck(hash, k, v)
1197 /// Removes a key from the map, returning the value at the key if the key
1198 /// was previously in the map.
1200 /// The key may be any borrowed form of the map's key type, but
1201 /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
1204 /// [`Eq`]: ../../std/cmp/trait.Eq.html
1205 /// [`Hash`]: ../../std/hash/trait.Hash.html
1210 /// use std::collections::HashMap;
1212 /// let mut map = HashMap::new();
1213 /// map.insert(1, "a");
1214 /// assert_eq!(map.remove(&1), Some("a"));
1215 /// assert_eq!(map.remove(&1), None);
1217 #[stable(feature = "rust1", since = "1.0.0")]
1218 pub fn remove<Q: ?Sized>(&mut self, k: &Q) -> Option<V>
1222 if self.table.size() == 0 {
1226 self.search_mut(k).into_occupied_bucket().map(|bucket| pop_internal(bucket).1)
1229 /// Retains only the elements specified by the predicate.
1231 /// In other words, remove all pairs `(k, v)` such that `f(&k,&mut v)` returns `false`.
1236 /// use std::collections::HashMap;
1238 /// let mut map: HashMap<isize, isize> = (0..8).map(|x|(x, x*10)).collect();
1239 /// map.retain(|&k, _| k % 2 == 0);
1240 /// assert_eq!(map.len(), 4);
1242 #[stable(feature = "retain_hash_collection", since = "1.18.0")]
1243 pub fn retain<F>(&mut self, mut f: F)
1244 where F: FnMut(&K, &mut V) -> bool
1246 if self.table.size() == 0 {
1249 let mut elems_left = self.table.size();
1250 let mut bucket = Bucket::head_bucket(&mut self.table);
1252 let start_index = bucket.index();
1253 while elems_left != 0 {
1254 bucket = match bucket.peek() {
1257 let should_remove = {
1258 let (k, v) = full.read_mut();
1262 let prev_raw = full.raw();
1263 let (_, _, t) = pop_internal(full);
1264 Bucket::new_from(prev_raw, t)
1273 bucket.prev(); // reverse iteration
1274 debug_assert!(elems_left == 0 || bucket.index() != start_index);
1279 #[stable(feature = "rust1", since = "1.0.0")]
1280 impl<K, V, S> PartialEq for HashMap<K, V, S>
1285 fn eq(&self, other: &HashMap<K, V, S>) -> bool {
1286 if self.len() != other.len() {
1290 self.iter().all(|(key, value)| other.get(key).map_or(false, |v| *value == *v))
1294 #[stable(feature = "rust1", since = "1.0.0")]
1295 impl<K, V, S> Eq for HashMap<K, V, S>
1302 #[stable(feature = "rust1", since = "1.0.0")]
1303 impl<K, V, S> Debug for HashMap<K, V, S>
1304 where K: Eq + Hash + Debug,
1308 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1309 f.debug_map().entries(self.iter()).finish()
1313 #[stable(feature = "rust1", since = "1.0.0")]
1314 impl<K, V, S> Default for HashMap<K, V, S>
1316 S: BuildHasher + Default
1318 /// Creates an empty `HashMap<K, V, S>`, with the `Default` value for the hasher.
1319 fn default() -> HashMap<K, V, S> {
1320 HashMap::with_hasher(Default::default())
1324 #[stable(feature = "rust1", since = "1.0.0")]
1325 impl<'a, K, Q: ?Sized, V, S> Index<&'a Q> for HashMap<K, V, S>
1326 where K: Eq + Hash + Borrow<Q>,
1333 fn index(&self, index: &Q) -> &V {
1334 self.get(index).expect("no entry found for key")
1338 /// An iterator over the entries of a `HashMap`.
1340 /// This `struct` is created by the [`iter`] method on [`HashMap`]. See its
1341 /// documentation for more.
1343 /// [`iter`]: struct.HashMap.html#method.iter
1344 /// [`HashMap`]: struct.HashMap.html
1345 #[stable(feature = "rust1", since = "1.0.0")]
1346 pub struct Iter<'a, K: 'a, V: 'a> {
1347 inner: table::Iter<'a, K, V>,
1350 // FIXME(#19839) Remove in favor of `#[derive(Clone)]`
1351 #[stable(feature = "rust1", since = "1.0.0")]
1352 impl<'a, K, V> Clone for Iter<'a, K, V> {
1353 fn clone(&self) -> Iter<'a, K, V> {
1354 Iter { inner: self.inner.clone() }
1358 #[stable(feature = "std_debug", since = "1.16.0")]
1359 impl<'a, K: Debug, V: Debug> fmt::Debug for Iter<'a, K, V> {
1360 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1362 .entries(self.clone())
1367 /// A mutable iterator over the entries of a `HashMap`.
1369 /// This `struct` is created by the [`iter_mut`] method on [`HashMap`]. See its
1370 /// documentation for more.
1372 /// [`iter_mut`]: struct.HashMap.html#method.iter_mut
1373 /// [`HashMap`]: struct.HashMap.html
1374 #[stable(feature = "rust1", since = "1.0.0")]
1375 pub struct IterMut<'a, K: 'a, V: 'a> {
1376 inner: table::IterMut<'a, K, V>,
1379 /// An owning iterator over the entries of a `HashMap`.
1381 /// This `struct` is created by the [`into_iter`] method on [`HashMap`][`HashMap`]
1382 /// (provided by the `IntoIterator` trait). See its documentation for more.
1384 /// [`into_iter`]: struct.HashMap.html#method.into_iter
1385 /// [`HashMap`]: struct.HashMap.html
1386 #[stable(feature = "rust1", since = "1.0.0")]
1387 pub struct IntoIter<K, V> {
1388 pub(super) inner: table::IntoIter<K, V>,
1391 /// An iterator over the keys of a `HashMap`.
1393 /// This `struct` is created by the [`keys`] method on [`HashMap`]. See its
1394 /// documentation for more.
1396 /// [`keys`]: struct.HashMap.html#method.keys
1397 /// [`HashMap`]: struct.HashMap.html
1398 #[stable(feature = "rust1", since = "1.0.0")]
1399 pub struct Keys<'a, K: 'a, V: 'a> {
1400 inner: Iter<'a, K, V>,
1403 // FIXME(#19839) Remove in favor of `#[derive(Clone)]`
1404 #[stable(feature = "rust1", since = "1.0.0")]
1405 impl<'a, K, V> Clone for Keys<'a, K, V> {
1406 fn clone(&self) -> Keys<'a, K, V> {
1407 Keys { inner: self.inner.clone() }
1411 #[stable(feature = "std_debug", since = "1.16.0")]
1412 impl<'a, K: Debug, V> fmt::Debug for Keys<'a, K, V> {
1413 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1415 .entries(self.clone())
1420 /// An iterator over the values of a `HashMap`.
1422 /// This `struct` is created by the [`values`] method on [`HashMap`]. See its
1423 /// documentation for more.
1425 /// [`values`]: struct.HashMap.html#method.values
1426 /// [`HashMap`]: struct.HashMap.html
1427 #[stable(feature = "rust1", since = "1.0.0")]
1428 pub struct Values<'a, K: 'a, V: 'a> {
1429 inner: Iter<'a, K, V>,
1432 // FIXME(#19839) Remove in favor of `#[derive(Clone)]`
1433 #[stable(feature = "rust1", since = "1.0.0")]
1434 impl<'a, K, V> Clone for Values<'a, K, V> {
1435 fn clone(&self) -> Values<'a, K, V> {
1436 Values { inner: self.inner.clone() }
1440 #[stable(feature = "std_debug", since = "1.16.0")]
1441 impl<'a, K, V: Debug> fmt::Debug for Values<'a, K, V> {
1442 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1444 .entries(self.clone())
1449 /// A draining iterator over the entries of a `HashMap`.
1451 /// This `struct` is created by the [`drain`] method on [`HashMap`]. See its
1452 /// documentation for more.
1454 /// [`drain`]: struct.HashMap.html#method.drain
1455 /// [`HashMap`]: struct.HashMap.html
1456 #[stable(feature = "drain", since = "1.6.0")]
1457 pub struct Drain<'a, K: 'a, V: 'a> {
1458 pub(super) inner: table::Drain<'a, K, V>,
1461 /// A mutable iterator over the values of a `HashMap`.
1463 /// This `struct` is created by the [`values_mut`] method on [`HashMap`]. See its
1464 /// documentation for more.
1466 /// [`values_mut`]: struct.HashMap.html#method.values_mut
1467 /// [`HashMap`]: struct.HashMap.html
1468 #[stable(feature = "map_values_mut", since = "1.10.0")]
1469 pub struct ValuesMut<'a, K: 'a, V: 'a> {
1470 inner: IterMut<'a, K, V>,
1473 enum InternalEntry<K, V, M> {
1474 Occupied { elem: FullBucket<K, V, M> },
1477 elem: VacantEntryState<K, V, M>,
1482 impl<K, V, M> InternalEntry<K, V, M> {
1484 fn into_occupied_bucket(self) -> Option<FullBucket<K, V, M>> {
1486 InternalEntry::Occupied { elem } => Some(elem),
1492 impl<'a, K, V> InternalEntry<K, V, &'a mut RawTable<K, V>> {
1494 fn into_entry(self, key: K) -> Option<Entry<'a, K, V>> {
1496 InternalEntry::Occupied { elem } => {
1497 Some(Occupied(OccupiedEntry {
1502 InternalEntry::Vacant { hash, elem } => {
1503 Some(Vacant(VacantEntry {
1509 InternalEntry::TableIsEmpty => None,
1514 /// A view into a single entry in a map, which may either be vacant or occupied.
1516 /// This `enum` is constructed from the [`entry`] method on [`HashMap`].
1518 /// [`HashMap`]: struct.HashMap.html
1519 /// [`entry`]: struct.HashMap.html#method.entry
1520 #[stable(feature = "rust1", since = "1.0.0")]
1521 pub enum Entry<'a, K: 'a, V: 'a> {
1522 /// An occupied entry.
1523 #[stable(feature = "rust1", since = "1.0.0")]
1524 Occupied(#[stable(feature = "rust1", since = "1.0.0")]
1525 OccupiedEntry<'a, K, V>),
1528 #[stable(feature = "rust1", since = "1.0.0")]
1529 Vacant(#[stable(feature = "rust1", since = "1.0.0")]
1530 VacantEntry<'a, K, V>),
1533 #[stable(feature= "debug_hash_map", since = "1.12.0")]
1534 impl<'a, K: 'a + Debug, V: 'a + Debug> Debug for Entry<'a, K, V> {
1535 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1538 f.debug_tuple("Entry")
1542 Occupied(ref o) => {
1543 f.debug_tuple("Entry")
1551 /// A view into an occupied entry in a `HashMap`.
1552 /// It is part of the [`Entry`] enum.
1554 /// [`Entry`]: enum.Entry.html
1555 #[stable(feature = "rust1", since = "1.0.0")]
1556 pub struct OccupiedEntry<'a, K: 'a, V: 'a> {
1558 elem: FullBucket<K, V, &'a mut RawTable<K, V>>,
1561 #[stable(feature= "debug_hash_map", since = "1.12.0")]
1562 impl<'a, K: 'a + Debug, V: 'a + Debug> Debug for OccupiedEntry<'a, K, V> {
1563 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1564 f.debug_struct("OccupiedEntry")
1565 .field("key", self.key())
1566 .field("value", self.get())
1571 /// A view into a vacant entry in a `HashMap`.
1572 /// It is part of the [`Entry`] enum.
1574 /// [`Entry`]: enum.Entry.html
1575 #[stable(feature = "rust1", since = "1.0.0")]
1576 pub struct VacantEntry<'a, K: 'a, V: 'a> {
1579 elem: VacantEntryState<K, V, &'a mut RawTable<K, V>>,
1582 #[stable(feature= "debug_hash_map", since = "1.12.0")]
1583 impl<'a, K: 'a + Debug, V: 'a> Debug for VacantEntry<'a, K, V> {
1584 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1585 f.debug_tuple("VacantEntry")
1591 /// Possible states of a VacantEntry.
1592 enum VacantEntryState<K, V, M> {
1593 /// The index is occupied, but the key to insert has precedence,
1594 /// and will kick the current one out on insertion.
1595 NeqElem(FullBucket<K, V, M>, usize),
1596 /// The index is genuinely vacant.
1597 NoElem(EmptyBucket<K, V, M>, usize),
1600 #[stable(feature = "rust1", since = "1.0.0")]
1601 impl<'a, K, V, S> IntoIterator for &'a HashMap<K, V, S>
1605 type Item = (&'a K, &'a V);
1606 type IntoIter = Iter<'a, K, V>;
1608 fn into_iter(self) -> Iter<'a, K, V> {
1613 #[stable(feature = "rust1", since = "1.0.0")]
1614 impl<'a, K, V, S> IntoIterator for &'a mut HashMap<K, V, S>
1618 type Item = (&'a K, &'a mut V);
1619 type IntoIter = IterMut<'a, K, V>;
1621 fn into_iter(self) -> IterMut<'a, K, V> {
1626 #[stable(feature = "rust1", since = "1.0.0")]
1627 impl<K, V, S> IntoIterator for HashMap<K, V, S>
1632 type IntoIter = IntoIter<K, V>;
1634 /// Creates a consuming iterator, that is, one that moves each key-value
1635 /// pair out of the map in arbitrary order. The map cannot be used after
1641 /// use std::collections::HashMap;
1643 /// let mut map = HashMap::new();
1644 /// map.insert("a", 1);
1645 /// map.insert("b", 2);
1646 /// map.insert("c", 3);
1648 /// // Not possible with .iter()
1649 /// let vec: Vec<(&str, isize)> = map.into_iter().collect();
1651 fn into_iter(self) -> IntoIter<K, V> {
1652 IntoIter { inner: self.table.into_iter() }
1656 #[stable(feature = "rust1", since = "1.0.0")]
1657 impl<'a, K, V> Iterator for Iter<'a, K, V> {
1658 type Item = (&'a K, &'a V);
1661 fn next(&mut self) -> Option<(&'a K, &'a V)> {
1665 fn size_hint(&self) -> (usize, Option<usize>) {
1666 self.inner.size_hint()
1669 #[stable(feature = "rust1", since = "1.0.0")]
1670 impl<'a, K, V> ExactSizeIterator for Iter<'a, K, V> {
1672 fn len(&self) -> usize {
1677 #[unstable(feature = "fused", issue = "35602")]
1678 impl<'a, K, V> FusedIterator for Iter<'a, K, V> {}
1680 #[stable(feature = "rust1", since = "1.0.0")]
1681 impl<'a, K, V> Iterator for IterMut<'a, K, V> {
1682 type Item = (&'a K, &'a mut V);
1685 fn next(&mut self) -> Option<(&'a K, &'a mut V)> {
1689 fn size_hint(&self) -> (usize, Option<usize>) {
1690 self.inner.size_hint()
1693 #[stable(feature = "rust1", since = "1.0.0")]
1694 impl<'a, K, V> ExactSizeIterator for IterMut<'a, K, V> {
1696 fn len(&self) -> usize {
1700 #[unstable(feature = "fused", issue = "35602")]
1701 impl<'a, K, V> FusedIterator for IterMut<'a, K, V> {}
1703 #[stable(feature = "std_debug", since = "1.16.0")]
1704 impl<'a, K, V> fmt::Debug for IterMut<'a, K, V>
1705 where K: fmt::Debug,
1708 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1710 .entries(self.inner.iter())
1715 #[stable(feature = "rust1", since = "1.0.0")]
1716 impl<K, V> Iterator for IntoIter<K, V> {
1720 fn next(&mut self) -> Option<(K, V)> {
1721 self.inner.next().map(|(_, k, v)| (k, v))
1724 fn size_hint(&self) -> (usize, Option<usize>) {
1725 self.inner.size_hint()
1728 #[stable(feature = "rust1", since = "1.0.0")]
1729 impl<K, V> ExactSizeIterator for IntoIter<K, V> {
1731 fn len(&self) -> usize {
1735 #[unstable(feature = "fused", issue = "35602")]
1736 impl<K, V> FusedIterator for IntoIter<K, V> {}
1738 #[stable(feature = "std_debug", since = "1.16.0")]
1739 impl<K: Debug, V: Debug> fmt::Debug for IntoIter<K, V> {
1740 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1742 .entries(self.inner.iter())
1747 #[stable(feature = "rust1", since = "1.0.0")]
1748 impl<'a, K, V> Iterator for Keys<'a, K, V> {
1752 fn next(&mut self) -> Option<(&'a K)> {
1753 self.inner.next().map(|(k, _)| k)
1756 fn size_hint(&self) -> (usize, Option<usize>) {
1757 self.inner.size_hint()
1760 #[stable(feature = "rust1", since = "1.0.0")]
1761 impl<'a, K, V> ExactSizeIterator for Keys<'a, K, V> {
1763 fn len(&self) -> usize {
1767 #[unstable(feature = "fused", issue = "35602")]
1768 impl<'a, K, V> FusedIterator for Keys<'a, K, V> {}
1770 #[stable(feature = "rust1", since = "1.0.0")]
1771 impl<'a, K, V> Iterator for Values<'a, K, V> {
1775 fn next(&mut self) -> Option<(&'a V)> {
1776 self.inner.next().map(|(_, v)| v)
1779 fn size_hint(&self) -> (usize, Option<usize>) {
1780 self.inner.size_hint()
1783 #[stable(feature = "rust1", since = "1.0.0")]
1784 impl<'a, K, V> ExactSizeIterator for Values<'a, K, V> {
1786 fn len(&self) -> usize {
1790 #[unstable(feature = "fused", issue = "35602")]
1791 impl<'a, K, V> FusedIterator for Values<'a, K, V> {}
1793 #[stable(feature = "map_values_mut", since = "1.10.0")]
1794 impl<'a, K, V> Iterator for ValuesMut<'a, K, V> {
1795 type Item = &'a mut V;
1798 fn next(&mut self) -> Option<(&'a mut V)> {
1799 self.inner.next().map(|(_, v)| v)
1802 fn size_hint(&self) -> (usize, Option<usize>) {
1803 self.inner.size_hint()
1806 #[stable(feature = "map_values_mut", since = "1.10.0")]
1807 impl<'a, K, V> ExactSizeIterator for ValuesMut<'a, K, V> {
1809 fn len(&self) -> usize {
1813 #[unstable(feature = "fused", issue = "35602")]
1814 impl<'a, K, V> FusedIterator for ValuesMut<'a, K, V> {}
1816 #[stable(feature = "std_debug", since = "1.16.0")]
1817 impl<'a, K, V> fmt::Debug for ValuesMut<'a, K, V>
1818 where K: fmt::Debug,
1821 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1823 .entries(self.inner.inner.iter())
1828 #[stable(feature = "drain", since = "1.6.0")]
1829 impl<'a, K, V> Iterator for Drain<'a, K, V> {
1833 fn next(&mut self) -> Option<(K, V)> {
1834 self.inner.next().map(|(_, k, v)| (k, v))
1837 fn size_hint(&self) -> (usize, Option<usize>) {
1838 self.inner.size_hint()
1841 #[stable(feature = "drain", since = "1.6.0")]
1842 impl<'a, K, V> ExactSizeIterator for Drain<'a, K, V> {
1844 fn len(&self) -> usize {
1848 #[unstable(feature = "fused", issue = "35602")]
1849 impl<'a, K, V> FusedIterator for Drain<'a, K, V> {}
1851 #[stable(feature = "std_debug", since = "1.16.0")]
1852 impl<'a, K, V> fmt::Debug for Drain<'a, K, V>
1853 where K: fmt::Debug,
1856 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1858 .entries(self.inner.iter())
1863 /// A place for insertion to a `Entry`.
1865 /// See [`HashMap::entry`](struct.HashMap.html#method.entry) for details.
1866 #[must_use = "places do nothing unless written to with `<-` syntax"]
1867 #[unstable(feature = "collection_placement",
1868 reason = "struct name and placement protocol is subject to change",
1870 pub struct EntryPlace<'a, K: 'a, V: 'a> {
1871 bucket: FullBucketMut<'a, K, V>,
1874 #[unstable(feature = "collection_placement",
1875 reason = "struct name and placement protocol is subject to change",
1877 impl<'a, K: 'a + Debug, V: 'a + Debug> Debug for EntryPlace<'a, K, V> {
1878 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1879 f.debug_struct("EntryPlace")
1880 .field("key", self.bucket.read().0)
1881 .field("value", self.bucket.read().1)
1886 #[unstable(feature = "collection_placement",
1887 reason = "struct name and placement protocol is subject to change",
1889 impl<'a, K, V> Drop for EntryPlace<'a, K, V> {
1890 fn drop(&mut self) {
1891 // Inplacement insertion failed. Only key need to drop.
1892 // The value is failed to insert into map.
1893 unsafe { self.bucket.remove_key() };
1897 #[unstable(feature = "collection_placement",
1898 reason = "placement protocol is subject to change",
1900 impl<'a, K, V> Placer<V> for Entry<'a, K, V> {
1901 type Place = EntryPlace<'a, K, V>;
1903 fn make_place(self) -> EntryPlace<'a, K, V> {
1904 let b = match self {
1905 Occupied(mut o) => {
1906 unsafe { ptr::drop_in_place(o.elem.read_mut().1); }
1910 unsafe { v.insert_key() }
1913 EntryPlace { bucket: b }
1917 #[unstable(feature = "collection_placement",
1918 reason = "placement protocol is subject to change",
1920 impl<'a, K, V> Place<V> for EntryPlace<'a, K, V> {
1921 fn pointer(&mut self) -> *mut V {
1922 self.bucket.read_mut().1
1926 #[unstable(feature = "collection_placement",
1927 reason = "placement protocol is subject to change",
1929 impl<'a, K, V> InPlace<V> for EntryPlace<'a, K, V> {
1932 unsafe fn finalize(self) {
1937 impl<'a, K, V> Entry<'a, K, V> {
1938 #[stable(feature = "rust1", since = "1.0.0")]
1939 /// Ensures a value is in the entry by inserting the default if empty, and returns
1940 /// a mutable reference to the value in the entry.
1945 /// use std::collections::HashMap;
1947 /// let mut map: HashMap<&str, u32> = HashMap::new();
1948 /// map.entry("poneyland").or_insert(12);
1950 /// assert_eq!(map["poneyland"], 12);
1952 /// *map.entry("poneyland").or_insert(12) += 10;
1953 /// assert_eq!(map["poneyland"], 22);
1955 pub fn or_insert(self, default: V) -> &'a mut V {
1957 Occupied(entry) => entry.into_mut(),
1958 Vacant(entry) => entry.insert(default),
1962 #[stable(feature = "rust1", since = "1.0.0")]
1963 /// Ensures a value is in the entry by inserting the result of the default function if empty,
1964 /// and returns a mutable reference to the value in the entry.
1969 /// use std::collections::HashMap;
1971 /// let mut map: HashMap<&str, String> = HashMap::new();
1972 /// let s = "hoho".to_string();
1974 /// map.entry("poneyland").or_insert_with(|| s);
1976 /// assert_eq!(map["poneyland"], "hoho".to_string());
1978 pub fn or_insert_with<F: FnOnce() -> V>(self, default: F) -> &'a mut V {
1980 Occupied(entry) => entry.into_mut(),
1981 Vacant(entry) => entry.insert(default()),
1985 /// Returns a reference to this entry's key.
1990 /// use std::collections::HashMap;
1992 /// let mut map: HashMap<&str, u32> = HashMap::new();
1993 /// assert_eq!(map.entry("poneyland").key(), &"poneyland");
1995 #[stable(feature = "map_entry_keys", since = "1.10.0")]
1996 pub fn key(&self) -> &K {
1998 Occupied(ref entry) => entry.key(),
1999 Vacant(ref entry) => entry.key(),
2004 impl<'a, K, V: Default> Entry<'a, K, V> {
2005 #[unstable(feature = "entry_or_default", issue = "44324")]
2006 /// Ensures a value is in the entry by inserting the default value if empty,
2007 /// and returns a mutable reference to the value in the entry.
2012 /// #![feature(entry_or_default)]
2014 /// use std::collections::HashMap;
2016 /// let mut map: HashMap<&str, Option<u32>> = HashMap::new();
2017 /// map.entry("poneyland").or_default();
2019 /// assert_eq!(map["poneyland"], None);
2022 pub fn or_default(self) -> &'a mut V {
2024 Occupied(entry) => entry.into_mut(),
2025 Vacant(entry) => entry.insert(Default::default()),
2031 impl<'a, K, V> OccupiedEntry<'a, K, V> {
2032 /// Gets a reference to the key in the entry.
2037 /// use std::collections::HashMap;
2039 /// let mut map: HashMap<&str, u32> = HashMap::new();
2040 /// map.entry("poneyland").or_insert(12);
2041 /// assert_eq!(map.entry("poneyland").key(), &"poneyland");
2043 #[stable(feature = "map_entry_keys", since = "1.10.0")]
2044 pub fn key(&self) -> &K {
2048 /// Take the ownership of the key and value from the map.
2053 /// use std::collections::HashMap;
2054 /// use std::collections::hash_map::Entry;
2056 /// let mut map: HashMap<&str, u32> = HashMap::new();
2057 /// map.entry("poneyland").or_insert(12);
2059 /// if let Entry::Occupied(o) = map.entry("poneyland") {
2060 /// // We delete the entry from the map.
2061 /// o.remove_entry();
2064 /// assert_eq!(map.contains_key("poneyland"), false);
2066 #[stable(feature = "map_entry_recover_keys2", since = "1.12.0")]
2067 pub fn remove_entry(self) -> (K, V) {
2068 let (k, v, _) = pop_internal(self.elem);
2072 /// Gets a reference to the value in the entry.
2077 /// use std::collections::HashMap;
2078 /// use std::collections::hash_map::Entry;
2080 /// let mut map: HashMap<&str, u32> = HashMap::new();
2081 /// map.entry("poneyland").or_insert(12);
2083 /// if let Entry::Occupied(o) = map.entry("poneyland") {
2084 /// assert_eq!(o.get(), &12);
2087 #[stable(feature = "rust1", since = "1.0.0")]
2088 pub fn get(&self) -> &V {
2092 /// Gets a mutable reference to the value in the entry.
2097 /// use std::collections::HashMap;
2098 /// use std::collections::hash_map::Entry;
2100 /// let mut map: HashMap<&str, u32> = HashMap::new();
2101 /// map.entry("poneyland").or_insert(12);
2103 /// assert_eq!(map["poneyland"], 12);
2104 /// if let Entry::Occupied(mut o) = map.entry("poneyland") {
2105 /// *o.get_mut() += 10;
2108 /// assert_eq!(map["poneyland"], 22);
2110 #[stable(feature = "rust1", since = "1.0.0")]
2111 pub fn get_mut(&mut self) -> &mut V {
2112 self.elem.read_mut().1
2115 /// Converts the OccupiedEntry into a mutable reference to the value in the entry
2116 /// with a lifetime bound to the map itself.
2121 /// use std::collections::HashMap;
2122 /// use std::collections::hash_map::Entry;
2124 /// let mut map: HashMap<&str, u32> = HashMap::new();
2125 /// map.entry("poneyland").or_insert(12);
2127 /// assert_eq!(map["poneyland"], 12);
2128 /// if let Entry::Occupied(o) = map.entry("poneyland") {
2129 /// *o.into_mut() += 10;
2132 /// assert_eq!(map["poneyland"], 22);
2134 #[stable(feature = "rust1", since = "1.0.0")]
2135 pub fn into_mut(self) -> &'a mut V {
2136 self.elem.into_mut_refs().1
2139 /// Sets the value of the entry, and returns the entry's old value.
2144 /// use std::collections::HashMap;
2145 /// use std::collections::hash_map::Entry;
2147 /// let mut map: HashMap<&str, u32> = HashMap::new();
2148 /// map.entry("poneyland").or_insert(12);
2150 /// if let Entry::Occupied(mut o) = map.entry("poneyland") {
2151 /// assert_eq!(o.insert(15), 12);
2154 /// assert_eq!(map["poneyland"], 15);
2156 #[stable(feature = "rust1", since = "1.0.0")]
2157 pub fn insert(&mut self, mut value: V) -> V {
2158 let old_value = self.get_mut();
2159 mem::swap(&mut value, old_value);
2163 /// Takes the value out of the entry, and returns it.
2168 /// use std::collections::HashMap;
2169 /// use std::collections::hash_map::Entry;
2171 /// let mut map: HashMap<&str, u32> = HashMap::new();
2172 /// map.entry("poneyland").or_insert(12);
2174 /// if let Entry::Occupied(o) = map.entry("poneyland") {
2175 /// assert_eq!(o.remove(), 12);
2178 /// assert_eq!(map.contains_key("poneyland"), false);
2180 #[stable(feature = "rust1", since = "1.0.0")]
2181 pub fn remove(self) -> V {
2182 pop_internal(self.elem).1
2185 /// Returns a key that was used for search.
2187 /// The key was retained for further use.
2188 fn take_key(&mut self) -> Option<K> {
2193 impl<'a, K: 'a, V: 'a> VacantEntry<'a, K, V> {
2194 /// Gets a reference to the key that would be used when inserting a value
2195 /// through the `VacantEntry`.
2200 /// use std::collections::HashMap;
2202 /// let mut map: HashMap<&str, u32> = HashMap::new();
2203 /// assert_eq!(map.entry("poneyland").key(), &"poneyland");
2205 #[stable(feature = "map_entry_keys", since = "1.10.0")]
2206 pub fn key(&self) -> &K {
2210 /// Take ownership of the key.
2215 /// use std::collections::HashMap;
2216 /// use std::collections::hash_map::Entry;
2218 /// let mut map: HashMap<&str, u32> = HashMap::new();
2220 /// if let Entry::Vacant(v) = map.entry("poneyland") {
2224 #[stable(feature = "map_entry_recover_keys2", since = "1.12.0")]
2225 pub fn into_key(self) -> K {
2229 /// Sets the value of the entry with the VacantEntry's key,
2230 /// and returns a mutable reference to it.
2235 /// use std::collections::HashMap;
2236 /// use std::collections::hash_map::Entry;
2238 /// let mut map: HashMap<&str, u32> = HashMap::new();
2240 /// if let Entry::Vacant(o) = map.entry("poneyland") {
2243 /// assert_eq!(map["poneyland"], 37);
2245 #[stable(feature = "rust1", since = "1.0.0")]
2246 pub fn insert(self, value: V) -> &'a mut V {
2247 let b = match self.elem {
2248 NeqElem(mut bucket, disp) => {
2249 if disp >= DISPLACEMENT_THRESHOLD {
2250 bucket.table_mut().set_tag(true);
2252 robin_hood(bucket, disp, self.hash, self.key, value)
2254 NoElem(mut bucket, disp) => {
2255 if disp >= DISPLACEMENT_THRESHOLD {
2256 bucket.table_mut().set_tag(true);
2258 bucket.put(self.hash, self.key, value)
2264 // Only used for InPlacement insert. Avoid unnecessary value copy.
2265 // The value remains uninitialized.
2266 unsafe fn insert_key(self) -> FullBucketMut<'a, K, V> {
2268 NeqElem(mut bucket, disp) => {
2269 if disp >= DISPLACEMENT_THRESHOLD {
2270 bucket.table_mut().set_tag(true);
2272 let uninit = mem::uninitialized();
2273 robin_hood(bucket, disp, self.hash, self.key, uninit)
2275 NoElem(mut bucket, disp) => {
2276 if disp >= DISPLACEMENT_THRESHOLD {
2277 bucket.table_mut().set_tag(true);
2279 bucket.put_key(self.hash, self.key)
2285 #[stable(feature = "rust1", since = "1.0.0")]
2286 impl<K, V, S> FromIterator<(K, V)> for HashMap<K, V, S>
2288 S: BuildHasher + Default
2290 fn from_iter<T: IntoIterator<Item = (K, V)>>(iter: T) -> HashMap<K, V, S> {
2291 let mut map = HashMap::with_hasher(Default::default());
2297 #[stable(feature = "rust1", since = "1.0.0")]
2298 impl<K, V, S> Extend<(K, V)> for HashMap<K, V, S>
2302 fn extend<T: IntoIterator<Item = (K, V)>>(&mut self, iter: T) {
2303 // Keys may be already present or show multiple times in the iterator.
2304 // Reserve the entire hint lower bound if the map is empty.
2305 // Otherwise reserve half the hint (rounded up), so the map
2306 // will only resize twice in the worst case.
2307 let iter = iter.into_iter();
2308 let reserve = if self.is_empty() {
2311 (iter.size_hint().0 + 1) / 2
2313 self.reserve(reserve);
2314 for (k, v) in iter {
2320 #[stable(feature = "hash_extend_copy", since = "1.4.0")]
2321 impl<'a, K, V, S> Extend<(&'a K, &'a V)> for HashMap<K, V, S>
2322 where K: Eq + Hash + Copy,
2326 fn extend<T: IntoIterator<Item = (&'a K, &'a V)>>(&mut self, iter: T) {
2327 self.extend(iter.into_iter().map(|(&key, &value)| (key, value)));
2331 /// `RandomState` is the default state for [`HashMap`] types.
2333 /// A particular instance `RandomState` will create the same instances of
2334 /// [`Hasher`], but the hashers created by two different `RandomState`
2335 /// instances are unlikely to produce the same result for the same values.
2337 /// [`HashMap`]: struct.HashMap.html
2338 /// [`Hasher`]: ../../hash/trait.Hasher.html
2343 /// use std::collections::HashMap;
2344 /// use std::collections::hash_map::RandomState;
2346 /// let s = RandomState::new();
2347 /// let mut map = HashMap::with_hasher(s);
2348 /// map.insert(1, 2);
2351 #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
2352 pub struct RandomState {
2358 /// Constructs a new `RandomState` that is initialized with random keys.
2363 /// use std::collections::hash_map::RandomState;
2365 /// let s = RandomState::new();
2368 #[allow(deprecated)]
2370 #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
2371 pub fn new() -> RandomState {
2372 // Historically this function did not cache keys from the OS and instead
2373 // simply always called `rand::thread_rng().gen()` twice. In #31356 it
2374 // was discovered, however, that because we re-seed the thread-local RNG
2375 // from the OS periodically that this can cause excessive slowdown when
2376 // many hash maps are created on a thread. To solve this performance
2377 // trap we cache the first set of randomly generated keys per-thread.
2379 // Later in #36481 it was discovered that exposing a deterministic
2380 // iteration order allows a form of DOS attack. To counter that we
2381 // increment one of the seeds on every RandomState creation, giving
2382 // every corresponding HashMap a different iteration order.
2383 thread_local!(static KEYS: Cell<(u64, u64)> = {
2384 let r = rand::OsRng::new();
2385 let mut r = r.expect("failed to create an OS RNG");
2386 Cell::new((r.gen(), r.gen()))
2390 let (k0, k1) = keys.get();
2391 keys.set((k0.wrapping_add(1), k1));
2392 RandomState { k0: k0, k1: k1 }
2397 #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
2398 impl BuildHasher for RandomState {
2399 type Hasher = DefaultHasher;
2401 #[allow(deprecated)]
2402 fn build_hasher(&self) -> DefaultHasher {
2403 DefaultHasher(SipHasher13::new_with_keys(self.k0, self.k1))
2407 /// The default [`Hasher`] used by [`RandomState`].
2409 /// The internal algorithm is not specified, and so it and its hashes should
2410 /// not be relied upon over releases.
2412 /// [`RandomState`]: struct.RandomState.html
2413 /// [`Hasher`]: ../../hash/trait.Hasher.html
2414 #[stable(feature = "hashmap_default_hasher", since = "1.13.0")]
2415 #[allow(deprecated)]
2416 #[derive(Clone, Debug)]
2417 pub struct DefaultHasher(SipHasher13);
2419 impl DefaultHasher {
2420 /// Creates a new `DefaultHasher`.
2422 /// This hasher is not guaranteed to be the same as all other
2423 /// `DefaultHasher` instances, but is the same as all other `DefaultHasher`
2424 /// instances created through `new` or `default`.
2425 #[stable(feature = "hashmap_default_hasher", since = "1.13.0")]
2426 #[allow(deprecated)]
2427 pub fn new() -> DefaultHasher {
2428 DefaultHasher(SipHasher13::new_with_keys(0, 0))
2432 #[stable(feature = "hashmap_default_hasher", since = "1.13.0")]
2433 impl Default for DefaultHasher {
2434 /// Creates a new `DefaultHasher` using [`new`]. See its documentation for more.
2436 /// [`new`]: #method.new
2437 fn default() -> DefaultHasher {
2438 DefaultHasher::new()
2442 #[stable(feature = "hashmap_default_hasher", since = "1.13.0")]
2443 impl Hasher for DefaultHasher {
2445 fn write(&mut self, msg: &[u8]) {
2450 fn finish(&self) -> u64 {
2455 #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
2456 impl Default for RandomState {
2457 /// Constructs a new `RandomState`.
2459 fn default() -> RandomState {
2464 #[stable(feature = "std_debug", since = "1.16.0")]
2465 impl fmt::Debug for RandomState {
2466 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2467 f.pad("RandomState { .. }")
2471 impl<K, S, Q: ?Sized> super::Recover<Q> for HashMap<K, (), S>
2472 where K: Eq + Hash + Borrow<Q>,
2478 fn get(&self, key: &Q) -> Option<&K> {
2479 self.search(key).into_occupied_bucket().map(|bucket| bucket.into_refs().0)
2482 fn take(&mut self, key: &Q) -> Option<K> {
2483 if self.table.size() == 0 {
2487 self.search_mut(key).into_occupied_bucket().map(|bucket| pop_internal(bucket).0)
2490 fn replace(&mut self, key: K) -> Option<K> {
2493 match self.entry(key) {
2494 Occupied(mut occupied) => {
2495 let key = occupied.take_key().unwrap();
2496 Some(mem::replace(occupied.elem.read_mut().0, key))
2507 fn assert_covariance() {
2508 fn map_key<'new>(v: HashMap<&'static str, u8>) -> HashMap<&'new str, u8> {
2511 fn map_val<'new>(v: HashMap<u8, &'static str>) -> HashMap<u8, &'new str> {
2514 fn iter_key<'a, 'new>(v: Iter<'a, &'static str, u8>) -> Iter<'a, &'new str, u8> {
2517 fn iter_val<'a, 'new>(v: Iter<'a, u8, &'static str>) -> Iter<'a, u8, &'new str> {
2520 fn into_iter_key<'new>(v: IntoIter<&'static str, u8>) -> IntoIter<&'new str, u8> {
2523 fn into_iter_val<'new>(v: IntoIter<u8, &'static str>) -> IntoIter<u8, &'new str> {
2526 fn keys_key<'a, 'new>(v: Keys<'a, &'static str, u8>) -> Keys<'a, &'new str, u8> {
2529 fn keys_val<'a, 'new>(v: Keys<'a, u8, &'static str>) -> Keys<'a, u8, &'new str> {
2532 fn values_key<'a, 'new>(v: Values<'a, &'static str, u8>) -> Values<'a, &'new str, u8> {
2535 fn values_val<'a, 'new>(v: Values<'a, u8, &'static str>) -> Values<'a, u8, &'new str> {
2538 fn drain<'new>(d: Drain<'static, &'static str, &'static str>)
2539 -> Drain<'new, &'new str, &'new str> {
2547 use super::Entry::{Occupied, Vacant};
2548 use super::RandomState;
2550 use rand::{thread_rng, Rng};
2554 fn test_zero_capacities() {
2555 type HM = HashMap<i32, i32>;
2558 assert_eq!(m.capacity(), 0);
2560 let m = HM::default();
2561 assert_eq!(m.capacity(), 0);
2563 let m = HM::with_hasher(RandomState::new());
2564 assert_eq!(m.capacity(), 0);
2566 let m = HM::with_capacity(0);
2567 assert_eq!(m.capacity(), 0);
2569 let m = HM::with_capacity_and_hasher(0, RandomState::new());
2570 assert_eq!(m.capacity(), 0);
2572 let mut m = HM::new();
2578 assert_eq!(m.capacity(), 0);
2580 let mut m = HM::new();
2582 assert_eq!(m.capacity(), 0);
2586 fn test_create_capacity_zero() {
2587 let mut m = HashMap::with_capacity(0);
2589 assert!(m.insert(1, 1).is_none());
2591 assert!(m.contains_key(&1));
2592 assert!(!m.contains_key(&0));
2597 let mut m = HashMap::new();
2598 assert_eq!(m.len(), 0);
2599 assert!(m.insert(1, 2).is_none());
2600 assert_eq!(m.len(), 1);
2601 assert!(m.insert(2, 4).is_none());
2602 assert_eq!(m.len(), 2);
2603 assert_eq!(*m.get(&1).unwrap(), 2);
2604 assert_eq!(*m.get(&2).unwrap(), 4);
2609 let mut m = HashMap::new();
2610 assert_eq!(m.len(), 0);
2611 assert!(m.insert(1, 2).is_none());
2612 assert_eq!(m.len(), 1);
2613 assert!(m.insert(2, 4).is_none());
2614 assert_eq!(m.len(), 2);
2616 assert_eq!(*m2.get(&1).unwrap(), 2);
2617 assert_eq!(*m2.get(&2).unwrap(), 4);
2618 assert_eq!(m2.len(), 2);
2621 thread_local! { static DROP_VECTOR: RefCell<Vec<isize>> = RefCell::new(Vec::new()) }
2623 #[derive(Hash, PartialEq, Eq)]
2629 fn new(k: usize) -> Dropable {
2630 DROP_VECTOR.with(|slot| {
2631 slot.borrow_mut()[k] += 1;
2638 impl Drop for Dropable {
2639 fn drop(&mut self) {
2640 DROP_VECTOR.with(|slot| {
2641 slot.borrow_mut()[self.k] -= 1;
2646 impl Clone for Dropable {
2647 fn clone(&self) -> Dropable {
2648 Dropable::new(self.k)
2654 DROP_VECTOR.with(|slot| {
2655 *slot.borrow_mut() = vec![0; 200];
2659 let mut m = HashMap::new();
2661 DROP_VECTOR.with(|v| {
2663 assert_eq!(v.borrow()[i], 0);
2668 let d1 = Dropable::new(i);
2669 let d2 = Dropable::new(i + 100);
2673 DROP_VECTOR.with(|v| {
2675 assert_eq!(v.borrow()[i], 1);
2680 let k = Dropable::new(i);
2681 let v = m.remove(&k);
2683 assert!(v.is_some());
2685 DROP_VECTOR.with(|v| {
2686 assert_eq!(v.borrow()[i], 1);
2687 assert_eq!(v.borrow()[i+100], 1);
2691 DROP_VECTOR.with(|v| {
2693 assert_eq!(v.borrow()[i], 0);
2694 assert_eq!(v.borrow()[i+100], 0);
2698 assert_eq!(v.borrow()[i], 1);
2699 assert_eq!(v.borrow()[i+100], 1);
2704 DROP_VECTOR.with(|v| {
2706 assert_eq!(v.borrow()[i], 0);
2712 fn test_into_iter_drops() {
2713 DROP_VECTOR.with(|v| {
2714 *v.borrow_mut() = vec![0; 200];
2718 let mut hm = HashMap::new();
2720 DROP_VECTOR.with(|v| {
2722 assert_eq!(v.borrow()[i], 0);
2727 let d1 = Dropable::new(i);
2728 let d2 = Dropable::new(i + 100);
2732 DROP_VECTOR.with(|v| {
2734 assert_eq!(v.borrow()[i], 1);
2741 // By the way, ensure that cloning doesn't screw up the dropping.
2745 let mut half = hm.into_iter().take(50);
2747 DROP_VECTOR.with(|v| {
2749 assert_eq!(v.borrow()[i], 1);
2753 for _ in half.by_ref() {}
2755 DROP_VECTOR.with(|v| {
2757 .filter(|&i| v.borrow()[i] == 1)
2761 .filter(|&i| v.borrow()[i + 100] == 1)
2769 DROP_VECTOR.with(|v| {
2771 assert_eq!(v.borrow()[i], 0);
2777 fn test_empty_remove() {
2778 let mut m: HashMap<isize, bool> = HashMap::new();
2779 assert_eq!(m.remove(&0), None);
2783 fn test_empty_entry() {
2784 let mut m: HashMap<isize, bool> = HashMap::new();
2786 Occupied(_) => panic!(),
2789 assert!(*m.entry(0).or_insert(true));
2790 assert_eq!(m.len(), 1);
2794 fn test_empty_iter() {
2795 let mut m: HashMap<isize, bool> = HashMap::new();
2796 assert_eq!(m.drain().next(), None);
2797 assert_eq!(m.keys().next(), None);
2798 assert_eq!(m.values().next(), None);
2799 assert_eq!(m.values_mut().next(), None);
2800 assert_eq!(m.iter().next(), None);
2801 assert_eq!(m.iter_mut().next(), None);
2802 assert_eq!(m.len(), 0);
2803 assert!(m.is_empty());
2804 assert_eq!(m.into_iter().next(), None);
2808 fn test_lots_of_insertions() {
2809 let mut m = HashMap::new();
2811 // Try this a few times to make sure we never screw up the hashmap's
2814 assert!(m.is_empty());
2817 assert!(m.insert(i, i).is_none());
2821 assert_eq!(r, Some(&j));
2824 for j in i + 1..1001 {
2826 assert_eq!(r, None);
2830 for i in 1001..2001 {
2831 assert!(!m.contains_key(&i));
2836 assert!(m.remove(&i).is_some());
2839 assert!(!m.contains_key(&j));
2842 for j in i + 1..1001 {
2843 assert!(m.contains_key(&j));
2848 assert!(!m.contains_key(&i));
2852 assert!(m.insert(i, i).is_none());
2856 for i in (1..1001).rev() {
2857 assert!(m.remove(&i).is_some());
2860 assert!(!m.contains_key(&j));
2864 assert!(m.contains_key(&j));
2871 fn test_find_mut() {
2872 let mut m = HashMap::new();
2873 assert!(m.insert(1, 12).is_none());
2874 assert!(m.insert(2, 8).is_none());
2875 assert!(m.insert(5, 14).is_none());
2877 match m.get_mut(&5) {
2879 Some(x) => *x = new,
2881 assert_eq!(m.get(&5), Some(&new));
2885 fn test_insert_overwrite() {
2886 let mut m = HashMap::new();
2887 assert!(m.insert(1, 2).is_none());
2888 assert_eq!(*m.get(&1).unwrap(), 2);
2889 assert!(!m.insert(1, 3).is_none());
2890 assert_eq!(*m.get(&1).unwrap(), 3);
2894 fn test_insert_conflicts() {
2895 let mut m = HashMap::with_capacity(4);
2896 assert!(m.insert(1, 2).is_none());
2897 assert!(m.insert(5, 3).is_none());
2898 assert!(m.insert(9, 4).is_none());
2899 assert_eq!(*m.get(&9).unwrap(), 4);
2900 assert_eq!(*m.get(&5).unwrap(), 3);
2901 assert_eq!(*m.get(&1).unwrap(), 2);
2905 fn test_conflict_remove() {
2906 let mut m = HashMap::with_capacity(4);
2907 assert!(m.insert(1, 2).is_none());
2908 assert_eq!(*m.get(&1).unwrap(), 2);
2909 assert!(m.insert(5, 3).is_none());
2910 assert_eq!(*m.get(&1).unwrap(), 2);
2911 assert_eq!(*m.get(&5).unwrap(), 3);
2912 assert!(m.insert(9, 4).is_none());
2913 assert_eq!(*m.get(&1).unwrap(), 2);
2914 assert_eq!(*m.get(&5).unwrap(), 3);
2915 assert_eq!(*m.get(&9).unwrap(), 4);
2916 assert!(m.remove(&1).is_some());
2917 assert_eq!(*m.get(&9).unwrap(), 4);
2918 assert_eq!(*m.get(&5).unwrap(), 3);
2922 fn test_is_empty() {
2923 let mut m = HashMap::with_capacity(4);
2924 assert!(m.insert(1, 2).is_none());
2925 assert!(!m.is_empty());
2926 assert!(m.remove(&1).is_some());
2927 assert!(m.is_empty());
2932 let mut m = HashMap::new();
2934 assert_eq!(m.remove(&1), Some(2));
2935 assert_eq!(m.remove(&1), None);
2940 let mut m = HashMap::with_capacity(4);
2942 assert!(m.insert(i, i*2).is_none());
2944 assert_eq!(m.len(), 32);
2946 let mut observed: u32 = 0;
2949 assert_eq!(*v, *k * 2);
2950 observed |= 1 << *k;
2952 assert_eq!(observed, 0xFFFF_FFFF);
2957 let vec = vec![(1, 'a'), (2, 'b'), (3, 'c')];
2958 let map: HashMap<_, _> = vec.into_iter().collect();
2959 let keys: Vec<_> = map.keys().cloned().collect();
2960 assert_eq!(keys.len(), 3);
2961 assert!(keys.contains(&1));
2962 assert!(keys.contains(&2));
2963 assert!(keys.contains(&3));
2968 let vec = vec![(1, 'a'), (2, 'b'), (3, 'c')];
2969 let map: HashMap<_, _> = vec.into_iter().collect();
2970 let values: Vec<_> = map.values().cloned().collect();
2971 assert_eq!(values.len(), 3);
2972 assert!(values.contains(&'a'));
2973 assert!(values.contains(&'b'));
2974 assert!(values.contains(&'c'));
2978 fn test_values_mut() {
2979 let vec = vec![(1, 1), (2, 2), (3, 3)];
2980 let mut map: HashMap<_, _> = vec.into_iter().collect();
2981 for value in map.values_mut() {
2982 *value = (*value) * 2
2984 let values: Vec<_> = map.values().cloned().collect();
2985 assert_eq!(values.len(), 3);
2986 assert!(values.contains(&2));
2987 assert!(values.contains(&4));
2988 assert!(values.contains(&6));
2993 let mut m = HashMap::new();
2994 assert!(m.get(&1).is_none());
2998 Some(v) => assert_eq!(*v, 2),
3004 let mut m1 = HashMap::new();
3009 let mut m2 = HashMap::new();
3022 let mut map = HashMap::new();
3023 let empty: HashMap<i32, i32> = HashMap::new();
3028 let map_str = format!("{:?}", map);
3030 assert!(map_str == "{1: 2, 3: 4}" ||
3031 map_str == "{3: 4, 1: 2}");
3032 assert_eq!(format!("{:?}", empty), "{}");
3037 let mut m = HashMap::new();
3039 assert_eq!(m.len(), 0);
3040 assert!(m.is_empty());
3043 let old_raw_cap = m.raw_capacity();
3044 while old_raw_cap == m.raw_capacity() {
3049 assert_eq!(m.len(), i);
3050 assert!(!m.is_empty());
3054 fn test_behavior_resize_policy() {
3055 let mut m = HashMap::new();
3057 assert_eq!(m.len(), 0);
3058 assert_eq!(m.raw_capacity(), 0);
3059 assert!(m.is_empty());
3063 assert!(m.is_empty());
3064 let initial_raw_cap = m.raw_capacity();
3065 m.reserve(initial_raw_cap);
3066 let raw_cap = m.raw_capacity();
3068 assert_eq!(raw_cap, initial_raw_cap * 2);
3071 for _ in 0..raw_cap * 3 / 4 {
3075 // three quarters full
3077 assert_eq!(m.len(), i);
3078 assert_eq!(m.raw_capacity(), raw_cap);
3080 for _ in 0..raw_cap / 4 {
3086 let new_raw_cap = m.raw_capacity();
3087 assert_eq!(new_raw_cap, raw_cap * 2);
3089 for _ in 0..raw_cap / 2 - 1 {
3092 assert_eq!(m.raw_capacity(), new_raw_cap);
3094 // A little more than one quarter full.
3096 assert_eq!(m.raw_capacity(), raw_cap);
3097 // again, a little more than half full
3098 for _ in 0..raw_cap / 2 - 1 {
3104 assert_eq!(m.len(), i);
3105 assert!(!m.is_empty());
3106 assert_eq!(m.raw_capacity(), initial_raw_cap);
3110 fn test_reserve_shrink_to_fit() {
3111 let mut m = HashMap::new();
3114 assert!(m.capacity() >= m.len());
3120 let usable_cap = m.capacity();
3121 for i in 128..(128 + 256) {
3123 assert_eq!(m.capacity(), usable_cap);
3126 for i in 100..(128 + 256) {
3127 assert_eq!(m.remove(&i), Some(i));
3131 assert_eq!(m.len(), 100);
3132 assert!(!m.is_empty());
3133 assert!(m.capacity() >= m.len());
3136 assert_eq!(m.remove(&i), Some(i));
3141 assert_eq!(m.len(), 1);
3142 assert!(m.capacity() >= m.len());
3143 assert_eq!(m.remove(&0), Some(0));
3147 fn test_from_iter() {
3148 let xs = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
3150 let map: HashMap<_, _> = xs.iter().cloned().collect();
3152 for &(k, v) in &xs {
3153 assert_eq!(map.get(&k), Some(&v));
3158 fn test_size_hint() {
3159 let xs = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
3161 let map: HashMap<_, _> = xs.iter().cloned().collect();
3163 let mut iter = map.iter();
3165 for _ in iter.by_ref().take(3) {}
3167 assert_eq!(iter.size_hint(), (3, Some(3)));
3171 fn test_iter_len() {
3172 let xs = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
3174 let map: HashMap<_, _> = xs.iter().cloned().collect();
3176 let mut iter = map.iter();
3178 for _ in iter.by_ref().take(3) {}
3180 assert_eq!(iter.len(), 3);
3184 fn test_mut_size_hint() {
3185 let xs = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
3187 let mut map: HashMap<_, _> = xs.iter().cloned().collect();
3189 let mut iter = map.iter_mut();
3191 for _ in iter.by_ref().take(3) {}
3193 assert_eq!(iter.size_hint(), (3, Some(3)));
3197 fn test_iter_mut_len() {
3198 let xs = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
3200 let mut map: HashMap<_, _> = xs.iter().cloned().collect();
3202 let mut iter = map.iter_mut();
3204 for _ in iter.by_ref().take(3) {}
3206 assert_eq!(iter.len(), 3);
3211 let mut map = HashMap::new();
3217 assert_eq!(map[&2], 1);
3222 fn test_index_nonexistent() {
3223 let mut map = HashMap::new();
3234 let xs = [(1, 10), (2, 20), (3, 30), (4, 40), (5, 50), (6, 60)];
3236 let mut map: HashMap<_, _> = xs.iter().cloned().collect();
3238 // Existing key (insert)
3239 match map.entry(1) {
3240 Vacant(_) => unreachable!(),
3241 Occupied(mut view) => {
3242 assert_eq!(view.get(), &10);
3243 assert_eq!(view.insert(100), 10);
3246 assert_eq!(map.get(&1).unwrap(), &100);
3247 assert_eq!(map.len(), 6);
3250 // Existing key (update)
3251 match map.entry(2) {
3252 Vacant(_) => unreachable!(),
3253 Occupied(mut view) => {
3254 let v = view.get_mut();
3255 let new_v = (*v) * 10;
3259 assert_eq!(map.get(&2).unwrap(), &200);
3260 assert_eq!(map.len(), 6);
3262 // Existing key (take)
3263 match map.entry(3) {
3264 Vacant(_) => unreachable!(),
3266 assert_eq!(view.remove(), 30);
3269 assert_eq!(map.get(&3), None);
3270 assert_eq!(map.len(), 5);
3273 // Inexistent key (insert)
3274 match map.entry(10) {
3275 Occupied(_) => unreachable!(),
3277 assert_eq!(*view.insert(1000), 1000);
3280 assert_eq!(map.get(&10).unwrap(), &1000);
3281 assert_eq!(map.len(), 6);
3285 fn test_entry_take_doesnt_corrupt() {
3286 #![allow(deprecated)] //rand
3288 fn check(m: &HashMap<isize, ()>) {
3290 assert!(m.contains_key(k),
3291 "{} is in keys() but not in the map?", k);
3295 let mut m = HashMap::new();
3296 let mut rng = thread_rng();
3298 // Populate the map with some items.
3300 let x = rng.gen_range(-10, 10);
3305 let x = rng.gen_range(-10, 10);
3309 println!("{}: remove {}", i, x);
3319 fn test_extend_ref() {
3320 let mut a = HashMap::new();
3322 let mut b = HashMap::new();
3324 b.insert(3, "three");
3328 assert_eq!(a.len(), 3);
3329 assert_eq!(a[&1], "one");
3330 assert_eq!(a[&2], "two");
3331 assert_eq!(a[&3], "three");
3335 fn test_capacity_not_less_than_len() {
3336 let mut a = HashMap::new();
3344 assert!(a.capacity() > a.len());
3346 let free = a.capacity() - a.len();
3352 assert_eq!(a.len(), a.capacity());
3354 // Insert at capacity should cause allocation.
3356 assert!(a.capacity() > a.len());
3360 fn test_occupied_entry_key() {
3361 let mut a = HashMap::new();
3362 let key = "hello there";
3363 let value = "value goes here";
3364 assert!(a.is_empty());
3365 a.insert(key.clone(), value.clone());
3366 assert_eq!(a.len(), 1);
3367 assert_eq!(a[key], value);
3369 match a.entry(key.clone()) {
3370 Vacant(_) => panic!(),
3371 Occupied(e) => assert_eq!(key, *e.key()),
3373 assert_eq!(a.len(), 1);
3374 assert_eq!(a[key], value);
3378 fn test_vacant_entry_key() {
3379 let mut a = HashMap::new();
3380 let key = "hello there";
3381 let value = "value goes here";
3383 assert!(a.is_empty());
3384 match a.entry(key.clone()) {
3385 Occupied(_) => panic!(),
3387 assert_eq!(key, *e.key());
3388 e.insert(value.clone());
3391 assert_eq!(a.len(), 1);
3392 assert_eq!(a[key], value);
3397 let mut map: HashMap<isize, isize> = (0..100).map(|x|(x, x*10)).collect();
3399 map.retain(|&k, _| k % 2 == 0);
3400 assert_eq!(map.len(), 50);
3401 assert_eq!(map[&2], 20);
3402 assert_eq!(map[&4], 40);
3403 assert_eq!(map[&6], 60);
3407 fn test_adaptive() {
3408 const TEST_LEN: usize = 5000;
3409 // by cloning we get maps with the same hasher seed
3410 let mut first = HashMap::new();
3411 let mut second = first.clone();
3412 first.extend((0..TEST_LEN).map(|i| (i, i)));
3413 second.extend((TEST_LEN..TEST_LEN * 2).map(|i| (i, i)));
3415 for (&k, &v) in &second {
3416 let prev_cap = first.capacity();
3417 let expect_grow = first.len() == prev_cap;
3419 if !expect_grow && first.capacity() != prev_cap {
3423 panic!("Adaptive early resize failed");
3427 fn test_placement_in() {
3428 let mut map = HashMap::new();
3429 map.extend((0..10).map(|i| (i, i)));
3431 map.entry(100) <- 100;
3432 assert_eq!(map[&100], 100);
3435 assert_eq!(map[&0], 10);
3437 assert_eq!(map.len(), 11);
3441 fn test_placement_panic() {
3442 let mut map = HashMap::new();
3443 map.extend((0..10).map(|i| (i, i)));
3445 fn mkpanic() -> usize { panic!() }
3447 // modify existing key
3448 // when panic happens, previous key is removed.
3449 let _ = panic::catch_unwind(panic::AssertUnwindSafe(|| { map.entry(0) <- mkpanic(); }));
3450 assert_eq!(map.len(), 9);
3451 assert!(!map.contains_key(&0));
3454 let _ = panic::catch_unwind(panic::AssertUnwindSafe(|| { map.entry(100) <- mkpanic(); }));
3455 assert_eq!(map.len(), 9);
3456 assert!(!map.contains_key(&100));
3460 fn test_placement_drop() {
3462 struct TestV<'a>(&'a mut bool);
3463 impl<'a> Drop for TestV<'a> {
3464 fn drop(&mut self) {
3465 if !*self.0 { panic!("value double drop!"); } // no double drop
3470 fn makepanic<'a>() -> TestV<'a> { panic!() }
3472 let mut can_drop = true;
3473 let mut hm = HashMap::new();
3474 hm.insert(0, TestV(&mut can_drop));
3475 let _ = panic::catch_unwind(panic::AssertUnwindSafe(|| { hm.entry(0) <- makepanic(); }));
3476 assert_eq!(hm.len(), 0);