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`.
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
694 #[stable(feature = "hashmap_public_hasher", since = "1.9.0")]
695 pub fn hasher(&self) -> &S {
699 /// Returns the number of elements the map can hold without reallocating.
701 /// This number is a lower bound; the `HashMap<K, V>` might be able to hold
702 /// more, but is guaranteed to be able to hold at least this many.
707 /// use std::collections::HashMap;
708 /// let map: HashMap<isize, isize> = HashMap::with_capacity(100);
709 /// assert!(map.capacity() >= 100);
712 #[stable(feature = "rust1", since = "1.0.0")]
713 pub fn capacity(&self) -> usize {
714 self.resize_policy.capacity(self.raw_capacity())
717 /// Returns the hash map's raw capacity.
719 fn raw_capacity(&self) -> usize {
720 self.table.capacity()
723 /// Reserves capacity for at least `additional` more elements to be inserted
724 /// in the `HashMap`. The collection may reserve more space to avoid
725 /// frequent reallocations.
729 /// Panics if the new allocation size overflows [`usize`].
731 /// [`usize`]: ../../std/primitive.usize.html
736 /// use std::collections::HashMap;
737 /// let mut map: HashMap<&str, isize> = HashMap::new();
740 #[stable(feature = "rust1", since = "1.0.0")]
741 pub fn reserve(&mut self, additional: usize) {
742 let remaining = self.capacity() - self.len(); // this can't overflow
743 if remaining < additional {
744 let min_cap = self.len().checked_add(additional).expect("reserve overflow");
745 let raw_cap = self.resize_policy.raw_capacity(min_cap);
746 self.resize(raw_cap);
747 } else if self.table.tag() && remaining <= self.len() {
748 // Probe sequence is too long and table is half full,
749 // resize early to reduce probing length.
750 let new_capacity = self.table.capacity() * 2;
751 self.resize(new_capacity);
755 /// Resizes the internal vectors to a new capacity. It's your
756 /// responsibility to:
757 /// 1) Ensure `new_raw_cap` is enough for all the elements, accounting
758 /// for the load factor.
759 /// 2) Ensure `new_raw_cap` is a power of two or zero.
762 fn resize(&mut self, new_raw_cap: usize) {
763 assert!(self.table.size() <= new_raw_cap);
764 assert!(new_raw_cap.is_power_of_two() || new_raw_cap == 0);
766 let mut old_table = replace(&mut self.table, RawTable::new(new_raw_cap));
767 let old_size = old_table.size();
769 if old_table.size() == 0 {
773 let mut bucket = Bucket::head_bucket(&mut old_table);
775 // This is how the buckets might be laid out in memory:
776 // ($ marks an initialized bucket)
778 // |$$$_$$$$$$_$$$$$|
780 // But we've skipped the entire initial cluster of buckets
781 // and will continue iteration in this order:
784 // ^ wrap around once end is reached
787 // ^ exit once table.size == 0
789 bucket = match bucket.peek() {
791 let h = bucket.hash();
792 let (b, k, v) = bucket.take();
793 self.insert_hashed_ordered(h, k, v);
794 if b.table().size() == 0 {
799 Empty(b) => b.into_bucket(),
804 assert_eq!(self.table.size(), old_size);
807 /// Shrinks the capacity of the map as much as possible. It will drop
808 /// down as much as possible while maintaining the internal rules
809 /// and possibly leaving some space in accordance with the resize policy.
814 /// use std::collections::HashMap;
816 /// let mut map: HashMap<isize, isize> = HashMap::with_capacity(100);
817 /// map.insert(1, 2);
818 /// map.insert(3, 4);
819 /// assert!(map.capacity() >= 100);
820 /// map.shrink_to_fit();
821 /// assert!(map.capacity() >= 2);
823 #[stable(feature = "rust1", since = "1.0.0")]
824 pub fn shrink_to_fit(&mut self) {
825 let new_raw_cap = self.resize_policy.raw_capacity(self.len());
826 if self.raw_capacity() != new_raw_cap {
827 let old_table = replace(&mut self.table, RawTable::new(new_raw_cap));
828 let old_size = old_table.size();
830 // Shrink the table. Naive algorithm for resizing:
831 for (h, k, v) in old_table.into_iter() {
832 self.insert_hashed_nocheck(h, k, v);
835 debug_assert_eq!(self.table.size(), old_size);
839 /// Insert a pre-hashed key-value pair, without first checking
840 /// that there's enough room in the buckets. Returns a reference to the
841 /// newly insert value.
843 /// If the key already exists, the hashtable will be returned untouched
844 /// and a reference to the existing element will be returned.
845 fn insert_hashed_nocheck(&mut self, hash: SafeHash, k: K, v: V) -> Option<V> {
846 let entry = search_hashed(&mut self.table, hash, |key| *key == k).into_entry(k);
848 Some(Occupied(mut elem)) => Some(elem.insert(v)),
849 Some(Vacant(elem)) => {
853 None => unreachable!(),
857 /// An iterator visiting all keys in arbitrary order.
858 /// The iterator element type is `&'a K`.
863 /// use std::collections::HashMap;
865 /// let mut map = HashMap::new();
866 /// map.insert("a", 1);
867 /// map.insert("b", 2);
868 /// map.insert("c", 3);
870 /// for key in map.keys() {
871 /// println!("{}", key);
874 #[stable(feature = "rust1", since = "1.0.0")]
875 pub fn keys(&self) -> Keys<K, V> {
876 Keys { inner: self.iter() }
879 /// An iterator visiting all values in arbitrary order.
880 /// The iterator element type is `&'a V`.
885 /// use std::collections::HashMap;
887 /// let mut map = HashMap::new();
888 /// map.insert("a", 1);
889 /// map.insert("b", 2);
890 /// map.insert("c", 3);
892 /// for val in map.values() {
893 /// println!("{}", val);
896 #[stable(feature = "rust1", since = "1.0.0")]
897 pub fn values(&self) -> Values<K, V> {
898 Values { inner: self.iter() }
901 /// An iterator visiting all values mutably in arbitrary order.
902 /// The iterator element type is `&'a mut V`.
907 /// use std::collections::HashMap;
909 /// let mut map = HashMap::new();
911 /// map.insert("a", 1);
912 /// map.insert("b", 2);
913 /// map.insert("c", 3);
915 /// for val in map.values_mut() {
916 /// *val = *val + 10;
919 /// for val in map.values() {
920 /// println!("{}", val);
923 #[stable(feature = "map_values_mut", since = "1.10.0")]
924 pub fn values_mut(&mut self) -> ValuesMut<K, V> {
925 ValuesMut { inner: self.iter_mut() }
928 /// An iterator visiting all key-value pairs in arbitrary order.
929 /// The iterator element type is `(&'a K, &'a V)`.
934 /// use std::collections::HashMap;
936 /// let mut map = HashMap::new();
937 /// map.insert("a", 1);
938 /// map.insert("b", 2);
939 /// map.insert("c", 3);
941 /// for (key, val) in map.iter() {
942 /// println!("key: {} val: {}", key, val);
945 #[stable(feature = "rust1", since = "1.0.0")]
946 pub fn iter(&self) -> Iter<K, V> {
947 Iter { inner: self.table.iter() }
950 /// An iterator visiting all key-value pairs in arbitrary order,
951 /// with mutable references to the values.
952 /// The iterator element type is `(&'a K, &'a mut V)`.
957 /// use std::collections::HashMap;
959 /// let mut map = HashMap::new();
960 /// map.insert("a", 1);
961 /// map.insert("b", 2);
962 /// map.insert("c", 3);
964 /// // Update all values
965 /// for (_, val) in map.iter_mut() {
969 /// for (key, val) in &map {
970 /// println!("key: {} val: {}", key, val);
973 #[stable(feature = "rust1", since = "1.0.0")]
974 pub fn iter_mut(&mut self) -> IterMut<K, V> {
975 IterMut { inner: self.table.iter_mut() }
978 /// Gets the given key's corresponding entry in the map for in-place manipulation.
983 /// use std::collections::HashMap;
985 /// let mut letters = HashMap::new();
987 /// for ch in "a short treatise on fungi".chars() {
988 /// let counter = letters.entry(ch).or_insert(0);
992 /// assert_eq!(letters[&'s'], 2);
993 /// assert_eq!(letters[&'t'], 3);
994 /// assert_eq!(letters[&'u'], 1);
995 /// assert_eq!(letters.get(&'y'), None);
997 #[stable(feature = "rust1", since = "1.0.0")]
998 pub fn entry(&mut self, key: K) -> Entry<K, V> {
1001 let hash = self.make_hash(&key);
1002 search_hashed(&mut self.table, hash, |q| q.eq(&key))
1003 .into_entry(key).expect("unreachable")
1006 /// Returns the number of elements in the map.
1011 /// use std::collections::HashMap;
1013 /// let mut a = HashMap::new();
1014 /// assert_eq!(a.len(), 0);
1015 /// a.insert(1, "a");
1016 /// assert_eq!(a.len(), 1);
1018 #[stable(feature = "rust1", since = "1.0.0")]
1019 pub fn len(&self) -> usize {
1023 /// Returns true if the map contains no elements.
1028 /// use std::collections::HashMap;
1030 /// let mut a = HashMap::new();
1031 /// assert!(a.is_empty());
1032 /// a.insert(1, "a");
1033 /// assert!(!a.is_empty());
1036 #[stable(feature = "rust1", since = "1.0.0")]
1037 pub fn is_empty(&self) -> bool {
1041 /// Clears the map, returning all key-value pairs as an iterator. Keeps the
1042 /// allocated memory for reuse.
1047 /// use std::collections::HashMap;
1049 /// let mut a = HashMap::new();
1050 /// a.insert(1, "a");
1051 /// a.insert(2, "b");
1053 /// for (k, v) in a.drain().take(1) {
1054 /// assert!(k == 1 || k == 2);
1055 /// assert!(v == "a" || v == "b");
1058 /// assert!(a.is_empty());
1061 #[stable(feature = "drain", since = "1.6.0")]
1062 pub fn drain(&mut self) -> Drain<K, V> {
1063 Drain { inner: self.table.drain() }
1066 /// Clears the map, removing all key-value pairs. Keeps the allocated memory
1072 /// use std::collections::HashMap;
1074 /// let mut a = HashMap::new();
1075 /// a.insert(1, "a");
1077 /// assert!(a.is_empty());
1079 #[stable(feature = "rust1", since = "1.0.0")]
1081 pub fn clear(&mut self) {
1085 /// Returns a reference to the value corresponding to the key.
1087 /// The key may be any borrowed form of the map's key type, but
1088 /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
1091 /// [`Eq`]: ../../std/cmp/trait.Eq.html
1092 /// [`Hash`]: ../../std/hash/trait.Hash.html
1097 /// use std::collections::HashMap;
1099 /// let mut map = HashMap::new();
1100 /// map.insert(1, "a");
1101 /// assert_eq!(map.get(&1), Some(&"a"));
1102 /// assert_eq!(map.get(&2), None);
1104 #[stable(feature = "rust1", since = "1.0.0")]
1105 pub fn get<Q: ?Sized>(&self, k: &Q) -> Option<&V>
1109 self.search(k).into_occupied_bucket().map(|bucket| bucket.into_refs().1)
1112 /// Returns true if the map contains a value for the specified key.
1114 /// The key may be any borrowed form of the map's key type, but
1115 /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
1118 /// [`Eq`]: ../../std/cmp/trait.Eq.html
1119 /// [`Hash`]: ../../std/hash/trait.Hash.html
1124 /// use std::collections::HashMap;
1126 /// let mut map = HashMap::new();
1127 /// map.insert(1, "a");
1128 /// assert_eq!(map.contains_key(&1), true);
1129 /// assert_eq!(map.contains_key(&2), false);
1131 #[stable(feature = "rust1", since = "1.0.0")]
1132 pub fn contains_key<Q: ?Sized>(&self, k: &Q) -> bool
1136 self.search(k).into_occupied_bucket().is_some()
1139 /// Returns a mutable reference to the value corresponding to the key.
1141 /// The key may be any borrowed form of the map's key type, but
1142 /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
1145 /// [`Eq`]: ../../std/cmp/trait.Eq.html
1146 /// [`Hash`]: ../../std/hash/trait.Hash.html
1151 /// use std::collections::HashMap;
1153 /// let mut map = HashMap::new();
1154 /// map.insert(1, "a");
1155 /// if let Some(x) = map.get_mut(&1) {
1158 /// assert_eq!(map[&1], "b");
1160 #[stable(feature = "rust1", since = "1.0.0")]
1161 pub fn get_mut<Q: ?Sized>(&mut self, k: &Q) -> Option<&mut V>
1165 self.search_mut(k).into_occupied_bucket().map(|bucket| bucket.into_mut_refs().1)
1168 /// Inserts a key-value pair into the map.
1170 /// If the map did not have this key present, [`None`] is returned.
1172 /// If the map did have this key present, the value is updated, and the old
1173 /// value is returned. The key is not updated, though; this matters for
1174 /// types that can be `==` without being identical. See the [module-level
1175 /// documentation] for more.
1177 /// [`None`]: ../../std/option/enum.Option.html#variant.None
1178 /// [module-level documentation]: index.html#insert-and-complex-keys
1183 /// use std::collections::HashMap;
1185 /// let mut map = HashMap::new();
1186 /// assert_eq!(map.insert(37, "a"), None);
1187 /// assert_eq!(map.is_empty(), false);
1189 /// map.insert(37, "b");
1190 /// assert_eq!(map.insert(37, "c"), Some("b"));
1191 /// assert_eq!(map[&37], "c");
1193 #[stable(feature = "rust1", since = "1.0.0")]
1194 pub fn insert(&mut self, k: K, v: V) -> Option<V> {
1195 let hash = self.make_hash(&k);
1197 self.insert_hashed_nocheck(hash, k, v)
1200 /// Removes a key from the map, returning the value at the key if the key
1201 /// was previously in the map.
1203 /// The key may be any borrowed form of the map's key type, but
1204 /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
1207 /// [`Eq`]: ../../std/cmp/trait.Eq.html
1208 /// [`Hash`]: ../../std/hash/trait.Hash.html
1213 /// use std::collections::HashMap;
1215 /// let mut map = HashMap::new();
1216 /// map.insert(1, "a");
1217 /// assert_eq!(map.remove(&1), Some("a"));
1218 /// assert_eq!(map.remove(&1), None);
1220 #[stable(feature = "rust1", since = "1.0.0")]
1221 pub fn remove<Q: ?Sized>(&mut self, k: &Q) -> Option<V>
1225 if self.table.size() == 0 {
1229 self.search_mut(k).into_occupied_bucket().map(|bucket| pop_internal(bucket).1)
1232 /// Retains only the elements specified by the predicate.
1234 /// In other words, remove all pairs `(k, v)` such that `f(&k,&mut v)` returns `false`.
1239 /// use std::collections::HashMap;
1241 /// let mut map: HashMap<isize, isize> = (0..8).map(|x|(x, x*10)).collect();
1242 /// map.retain(|&k, _| k % 2 == 0);
1243 /// assert_eq!(map.len(), 4);
1245 #[stable(feature = "retain_hash_collection", since = "1.18.0")]
1246 pub fn retain<F>(&mut self, mut f: F)
1247 where F: FnMut(&K, &mut V) -> bool
1249 if self.table.size() == 0 {
1252 let mut elems_left = self.table.size();
1253 let mut bucket = Bucket::head_bucket(&mut self.table);
1255 let start_index = bucket.index();
1256 while elems_left != 0 {
1257 bucket = match bucket.peek() {
1260 let should_remove = {
1261 let (k, v) = full.read_mut();
1265 let prev_raw = full.raw();
1266 let (_, _, t) = pop_internal(full);
1267 Bucket::new_from(prev_raw, t)
1276 bucket.prev(); // reverse iteration
1277 debug_assert!(elems_left == 0 || bucket.index() != start_index);
1282 #[stable(feature = "rust1", since = "1.0.0")]
1283 impl<K, V, S> PartialEq for HashMap<K, V, S>
1288 fn eq(&self, other: &HashMap<K, V, S>) -> bool {
1289 if self.len() != other.len() {
1293 self.iter().all(|(key, value)| other.get(key).map_or(false, |v| *value == *v))
1297 #[stable(feature = "rust1", since = "1.0.0")]
1298 impl<K, V, S> Eq for HashMap<K, V, S>
1305 #[stable(feature = "rust1", since = "1.0.0")]
1306 impl<K, V, S> Debug for HashMap<K, V, S>
1307 where K: Eq + Hash + Debug,
1311 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1312 f.debug_map().entries(self.iter()).finish()
1316 #[stable(feature = "rust1", since = "1.0.0")]
1317 impl<K, V, S> Default for HashMap<K, V, S>
1319 S: BuildHasher + Default
1321 /// Creates an empty `HashMap<K, V, S>`, with the `Default` value for the hasher.
1322 fn default() -> HashMap<K, V, S> {
1323 HashMap::with_hasher(Default::default())
1327 #[stable(feature = "rust1", since = "1.0.0")]
1328 impl<'a, K, Q: ?Sized, V, S> Index<&'a Q> for HashMap<K, V, S>
1329 where K: Eq + Hash + Borrow<Q>,
1336 fn index(&self, index: &Q) -> &V {
1337 self.get(index).expect("no entry found for key")
1341 /// An iterator over the entries of a `HashMap`.
1343 /// This `struct` is created by the [`iter`] method on [`HashMap`]. See its
1344 /// documentation for more.
1346 /// [`iter`]: struct.HashMap.html#method.iter
1347 /// [`HashMap`]: struct.HashMap.html
1348 #[stable(feature = "rust1", since = "1.0.0")]
1349 pub struct Iter<'a, K: 'a, V: 'a> {
1350 inner: table::Iter<'a, K, V>,
1353 // FIXME(#19839) Remove in favor of `#[derive(Clone)]`
1354 #[stable(feature = "rust1", since = "1.0.0")]
1355 impl<'a, K, V> Clone for Iter<'a, K, V> {
1356 fn clone(&self) -> Iter<'a, K, V> {
1357 Iter { inner: self.inner.clone() }
1361 #[stable(feature = "std_debug", since = "1.16.0")]
1362 impl<'a, K: Debug, V: Debug> fmt::Debug for Iter<'a, K, V> {
1363 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1365 .entries(self.clone())
1370 /// A mutable iterator over the entries of a `HashMap`.
1372 /// This `struct` is created by the [`iter_mut`] method on [`HashMap`]. See its
1373 /// documentation for more.
1375 /// [`iter_mut`]: struct.HashMap.html#method.iter_mut
1376 /// [`HashMap`]: struct.HashMap.html
1377 #[stable(feature = "rust1", since = "1.0.0")]
1378 pub struct IterMut<'a, K: 'a, V: 'a> {
1379 inner: table::IterMut<'a, K, V>,
1382 /// An owning iterator over the entries of a `HashMap`.
1384 /// This `struct` is created by the [`into_iter`] method on [`HashMap`][`HashMap`]
1385 /// (provided by the `IntoIterator` trait). See its documentation for more.
1387 /// [`into_iter`]: struct.HashMap.html#method.into_iter
1388 /// [`HashMap`]: struct.HashMap.html
1389 #[stable(feature = "rust1", since = "1.0.0")]
1390 pub struct IntoIter<K, V> {
1391 pub(super) inner: table::IntoIter<K, V>,
1394 /// An iterator over the keys of a `HashMap`.
1396 /// This `struct` is created by the [`keys`] method on [`HashMap`]. See its
1397 /// documentation for more.
1399 /// [`keys`]: struct.HashMap.html#method.keys
1400 /// [`HashMap`]: struct.HashMap.html
1401 #[stable(feature = "rust1", since = "1.0.0")]
1402 pub struct Keys<'a, K: 'a, V: 'a> {
1403 inner: Iter<'a, K, V>,
1406 // FIXME(#19839) Remove in favor of `#[derive(Clone)]`
1407 #[stable(feature = "rust1", since = "1.0.0")]
1408 impl<'a, K, V> Clone for Keys<'a, K, V> {
1409 fn clone(&self) -> Keys<'a, K, V> {
1410 Keys { inner: self.inner.clone() }
1414 #[stable(feature = "std_debug", since = "1.16.0")]
1415 impl<'a, K: Debug, V> fmt::Debug for Keys<'a, K, V> {
1416 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1418 .entries(self.clone())
1423 /// An iterator over the values of a `HashMap`.
1425 /// This `struct` is created by the [`values`] method on [`HashMap`]. See its
1426 /// documentation for more.
1428 /// [`values`]: struct.HashMap.html#method.values
1429 /// [`HashMap`]: struct.HashMap.html
1430 #[stable(feature = "rust1", since = "1.0.0")]
1431 pub struct Values<'a, K: 'a, V: 'a> {
1432 inner: Iter<'a, K, V>,
1435 // FIXME(#19839) Remove in favor of `#[derive(Clone)]`
1436 #[stable(feature = "rust1", since = "1.0.0")]
1437 impl<'a, K, V> Clone for Values<'a, K, V> {
1438 fn clone(&self) -> Values<'a, K, V> {
1439 Values { inner: self.inner.clone() }
1443 #[stable(feature = "std_debug", since = "1.16.0")]
1444 impl<'a, K, V: Debug> fmt::Debug for Values<'a, K, V> {
1445 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1447 .entries(self.clone())
1452 /// A draining iterator over the entries of a `HashMap`.
1454 /// This `struct` is created by the [`drain`] method on [`HashMap`]. See its
1455 /// documentation for more.
1457 /// [`drain`]: struct.HashMap.html#method.drain
1458 /// [`HashMap`]: struct.HashMap.html
1459 #[stable(feature = "drain", since = "1.6.0")]
1460 pub struct Drain<'a, K: 'a, V: 'a> {
1461 pub(super) inner: table::Drain<'a, K, V>,
1464 /// A mutable iterator over the values of a `HashMap`.
1466 /// This `struct` is created by the [`values_mut`] method on [`HashMap`]. See its
1467 /// documentation for more.
1469 /// [`values_mut`]: struct.HashMap.html#method.values_mut
1470 /// [`HashMap`]: struct.HashMap.html
1471 #[stable(feature = "map_values_mut", since = "1.10.0")]
1472 pub struct ValuesMut<'a, K: 'a, V: 'a> {
1473 inner: IterMut<'a, K, V>,
1476 enum InternalEntry<K, V, M> {
1477 Occupied { elem: FullBucket<K, V, M> },
1480 elem: VacantEntryState<K, V, M>,
1485 impl<K, V, M> InternalEntry<K, V, M> {
1487 fn into_occupied_bucket(self) -> Option<FullBucket<K, V, M>> {
1489 InternalEntry::Occupied { elem } => Some(elem),
1495 impl<'a, K, V> InternalEntry<K, V, &'a mut RawTable<K, V>> {
1497 fn into_entry(self, key: K) -> Option<Entry<'a, K, V>> {
1499 InternalEntry::Occupied { elem } => {
1500 Some(Occupied(OccupiedEntry {
1505 InternalEntry::Vacant { hash, elem } => {
1506 Some(Vacant(VacantEntry {
1512 InternalEntry::TableIsEmpty => None,
1517 /// A view into a single entry in a map, which may either be vacant or occupied.
1519 /// This `enum` is constructed from the [`entry`] method on [`HashMap`].
1521 /// [`HashMap`]: struct.HashMap.html
1522 /// [`entry`]: struct.HashMap.html#method.entry
1523 #[stable(feature = "rust1", since = "1.0.0")]
1524 pub enum Entry<'a, K: 'a, V: 'a> {
1525 /// An occupied entry.
1526 #[stable(feature = "rust1", since = "1.0.0")]
1527 Occupied(#[stable(feature = "rust1", since = "1.0.0")]
1528 OccupiedEntry<'a, K, V>),
1531 #[stable(feature = "rust1", since = "1.0.0")]
1532 Vacant(#[stable(feature = "rust1", since = "1.0.0")]
1533 VacantEntry<'a, K, V>),
1536 #[stable(feature= "debug_hash_map", since = "1.12.0")]
1537 impl<'a, K: 'a + Debug, V: 'a + Debug> Debug for Entry<'a, K, V> {
1538 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1541 f.debug_tuple("Entry")
1545 Occupied(ref o) => {
1546 f.debug_tuple("Entry")
1554 /// A view into an occupied entry in a `HashMap`.
1555 /// It is part of the [`Entry`] enum.
1557 /// [`Entry`]: enum.Entry.html
1558 #[stable(feature = "rust1", since = "1.0.0")]
1559 pub struct OccupiedEntry<'a, K: 'a, V: 'a> {
1561 elem: FullBucket<K, V, &'a mut RawTable<K, V>>,
1564 #[stable(feature= "debug_hash_map", since = "1.12.0")]
1565 impl<'a, K: 'a + Debug, V: 'a + Debug> Debug for OccupiedEntry<'a, K, V> {
1566 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1567 f.debug_struct("OccupiedEntry")
1568 .field("key", self.key())
1569 .field("value", self.get())
1574 /// A view into a vacant entry in a `HashMap`.
1575 /// It is part of the [`Entry`] enum.
1577 /// [`Entry`]: enum.Entry.html
1578 #[stable(feature = "rust1", since = "1.0.0")]
1579 pub struct VacantEntry<'a, K: 'a, V: 'a> {
1582 elem: VacantEntryState<K, V, &'a mut RawTable<K, V>>,
1585 #[stable(feature= "debug_hash_map", since = "1.12.0")]
1586 impl<'a, K: 'a + Debug, V: 'a> Debug for VacantEntry<'a, K, V> {
1587 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1588 f.debug_tuple("VacantEntry")
1594 /// Possible states of a VacantEntry.
1595 enum VacantEntryState<K, V, M> {
1596 /// The index is occupied, but the key to insert has precedence,
1597 /// and will kick the current one out on insertion.
1598 NeqElem(FullBucket<K, V, M>, usize),
1599 /// The index is genuinely vacant.
1600 NoElem(EmptyBucket<K, V, M>, usize),
1603 #[stable(feature = "rust1", since = "1.0.0")]
1604 impl<'a, K, V, S> IntoIterator for &'a HashMap<K, V, S>
1608 type Item = (&'a K, &'a V);
1609 type IntoIter = Iter<'a, K, V>;
1611 fn into_iter(self) -> Iter<'a, K, V> {
1616 #[stable(feature = "rust1", since = "1.0.0")]
1617 impl<'a, K, V, S> IntoIterator for &'a mut HashMap<K, V, S>
1621 type Item = (&'a K, &'a mut V);
1622 type IntoIter = IterMut<'a, K, V>;
1624 fn into_iter(self) -> IterMut<'a, K, V> {
1629 #[stable(feature = "rust1", since = "1.0.0")]
1630 impl<K, V, S> IntoIterator for HashMap<K, V, S>
1635 type IntoIter = IntoIter<K, V>;
1637 /// Creates a consuming iterator, that is, one that moves each key-value
1638 /// pair out of the map in arbitrary order. The map cannot be used after
1644 /// use std::collections::HashMap;
1646 /// let mut map = HashMap::new();
1647 /// map.insert("a", 1);
1648 /// map.insert("b", 2);
1649 /// map.insert("c", 3);
1651 /// // Not possible with .iter()
1652 /// let vec: Vec<(&str, isize)> = map.into_iter().collect();
1654 fn into_iter(self) -> IntoIter<K, V> {
1655 IntoIter { inner: self.table.into_iter() }
1659 #[stable(feature = "rust1", since = "1.0.0")]
1660 impl<'a, K, V> Iterator for Iter<'a, K, V> {
1661 type Item = (&'a K, &'a V);
1664 fn next(&mut self) -> Option<(&'a K, &'a V)> {
1668 fn size_hint(&self) -> (usize, Option<usize>) {
1669 self.inner.size_hint()
1672 #[stable(feature = "rust1", since = "1.0.0")]
1673 impl<'a, K, V> ExactSizeIterator for Iter<'a, K, V> {
1675 fn len(&self) -> usize {
1680 #[unstable(feature = "fused", issue = "35602")]
1681 impl<'a, K, V> FusedIterator for Iter<'a, K, V> {}
1683 #[stable(feature = "rust1", since = "1.0.0")]
1684 impl<'a, K, V> Iterator for IterMut<'a, K, V> {
1685 type Item = (&'a K, &'a mut V);
1688 fn next(&mut self) -> Option<(&'a K, &'a mut V)> {
1692 fn size_hint(&self) -> (usize, Option<usize>) {
1693 self.inner.size_hint()
1696 #[stable(feature = "rust1", since = "1.0.0")]
1697 impl<'a, K, V> ExactSizeIterator for IterMut<'a, K, V> {
1699 fn len(&self) -> usize {
1703 #[unstable(feature = "fused", issue = "35602")]
1704 impl<'a, K, V> FusedIterator for IterMut<'a, K, V> {}
1706 #[stable(feature = "std_debug", since = "1.16.0")]
1707 impl<'a, K, V> fmt::Debug for IterMut<'a, K, V>
1708 where K: fmt::Debug,
1711 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1713 .entries(self.inner.iter())
1718 #[stable(feature = "rust1", since = "1.0.0")]
1719 impl<K, V> Iterator for IntoIter<K, V> {
1723 fn next(&mut self) -> Option<(K, V)> {
1724 self.inner.next().map(|(_, k, v)| (k, v))
1727 fn size_hint(&self) -> (usize, Option<usize>) {
1728 self.inner.size_hint()
1731 #[stable(feature = "rust1", since = "1.0.0")]
1732 impl<K, V> ExactSizeIterator for IntoIter<K, V> {
1734 fn len(&self) -> usize {
1738 #[unstable(feature = "fused", issue = "35602")]
1739 impl<K, V> FusedIterator for IntoIter<K, V> {}
1741 #[stable(feature = "std_debug", since = "1.16.0")]
1742 impl<K: Debug, V: Debug> fmt::Debug for IntoIter<K, V> {
1743 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1745 .entries(self.inner.iter())
1750 #[stable(feature = "rust1", since = "1.0.0")]
1751 impl<'a, K, V> Iterator for Keys<'a, K, V> {
1755 fn next(&mut self) -> Option<(&'a K)> {
1756 self.inner.next().map(|(k, _)| k)
1759 fn size_hint(&self) -> (usize, Option<usize>) {
1760 self.inner.size_hint()
1763 #[stable(feature = "rust1", since = "1.0.0")]
1764 impl<'a, K, V> ExactSizeIterator for Keys<'a, K, V> {
1766 fn len(&self) -> usize {
1770 #[unstable(feature = "fused", issue = "35602")]
1771 impl<'a, K, V> FusedIterator for Keys<'a, K, V> {}
1773 #[stable(feature = "rust1", since = "1.0.0")]
1774 impl<'a, K, V> Iterator for Values<'a, K, V> {
1778 fn next(&mut self) -> Option<(&'a V)> {
1779 self.inner.next().map(|(_, v)| v)
1782 fn size_hint(&self) -> (usize, Option<usize>) {
1783 self.inner.size_hint()
1786 #[stable(feature = "rust1", since = "1.0.0")]
1787 impl<'a, K, V> ExactSizeIterator for Values<'a, K, V> {
1789 fn len(&self) -> usize {
1793 #[unstable(feature = "fused", issue = "35602")]
1794 impl<'a, K, V> FusedIterator for Values<'a, K, V> {}
1796 #[stable(feature = "map_values_mut", since = "1.10.0")]
1797 impl<'a, K, V> Iterator for ValuesMut<'a, K, V> {
1798 type Item = &'a mut V;
1801 fn next(&mut self) -> Option<(&'a mut V)> {
1802 self.inner.next().map(|(_, v)| v)
1805 fn size_hint(&self) -> (usize, Option<usize>) {
1806 self.inner.size_hint()
1809 #[stable(feature = "map_values_mut", since = "1.10.0")]
1810 impl<'a, K, V> ExactSizeIterator for ValuesMut<'a, K, V> {
1812 fn len(&self) -> usize {
1816 #[unstable(feature = "fused", issue = "35602")]
1817 impl<'a, K, V> FusedIterator for ValuesMut<'a, K, V> {}
1819 #[stable(feature = "std_debug", since = "1.16.0")]
1820 impl<'a, K, V> fmt::Debug for ValuesMut<'a, K, V>
1821 where K: fmt::Debug,
1824 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1826 .entries(self.inner.inner.iter())
1831 #[stable(feature = "drain", since = "1.6.0")]
1832 impl<'a, K, V> Iterator for Drain<'a, K, V> {
1836 fn next(&mut self) -> Option<(K, V)> {
1837 self.inner.next().map(|(_, k, v)| (k, v))
1840 fn size_hint(&self) -> (usize, Option<usize>) {
1841 self.inner.size_hint()
1844 #[stable(feature = "drain", since = "1.6.0")]
1845 impl<'a, K, V> ExactSizeIterator for Drain<'a, K, V> {
1847 fn len(&self) -> usize {
1851 #[unstable(feature = "fused", issue = "35602")]
1852 impl<'a, K, V> FusedIterator for Drain<'a, K, V> {}
1854 #[stable(feature = "std_debug", since = "1.16.0")]
1855 impl<'a, K, V> fmt::Debug for Drain<'a, K, V>
1856 where K: fmt::Debug,
1859 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1861 .entries(self.inner.iter())
1866 /// A place for insertion to a `Entry`.
1868 /// See [`HashMap::entry`](struct.HashMap.html#method.entry) for details.
1869 #[must_use = "places do nothing unless written to with `<-` syntax"]
1870 #[unstable(feature = "collection_placement",
1871 reason = "struct name and placement protocol is subject to change",
1873 pub struct EntryPlace<'a, K: 'a, V: 'a> {
1874 bucket: FullBucketMut<'a, K, V>,
1877 #[unstable(feature = "collection_placement",
1878 reason = "struct name and placement protocol is subject to change",
1880 impl<'a, K: 'a + Debug, V: 'a + Debug> Debug for EntryPlace<'a, K, V> {
1881 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1882 f.debug_struct("EntryPlace")
1883 .field("key", self.bucket.read().0)
1884 .field("value", self.bucket.read().1)
1889 #[unstable(feature = "collection_placement",
1890 reason = "struct name and placement protocol is subject to change",
1892 impl<'a, K, V> Drop for EntryPlace<'a, K, V> {
1893 fn drop(&mut self) {
1894 // Inplacement insertion failed. Only key need to drop.
1895 // The value is failed to insert into map.
1896 unsafe { self.bucket.remove_key() };
1900 #[unstable(feature = "collection_placement",
1901 reason = "placement protocol is subject to change",
1903 impl<'a, K, V> Placer<V> for Entry<'a, K, V> {
1904 type Place = EntryPlace<'a, K, V>;
1906 fn make_place(self) -> EntryPlace<'a, K, V> {
1907 let b = match self {
1908 Occupied(mut o) => {
1909 unsafe { ptr::drop_in_place(o.elem.read_mut().1); }
1913 unsafe { v.insert_key() }
1916 EntryPlace { bucket: b }
1920 #[unstable(feature = "collection_placement",
1921 reason = "placement protocol is subject to change",
1923 impl<'a, K, V> Place<V> for EntryPlace<'a, K, V> {
1924 fn pointer(&mut self) -> *mut V {
1925 self.bucket.read_mut().1
1929 #[unstable(feature = "collection_placement",
1930 reason = "placement protocol is subject to change",
1932 impl<'a, K, V> InPlace<V> for EntryPlace<'a, K, V> {
1935 unsafe fn finalize(self) {
1940 impl<'a, K, V> Entry<'a, K, V> {
1941 #[stable(feature = "rust1", since = "1.0.0")]
1942 /// Ensures a value is in the entry by inserting the default if empty, and returns
1943 /// a mutable reference to the value in the entry.
1948 /// use std::collections::HashMap;
1950 /// let mut map: HashMap<&str, u32> = HashMap::new();
1951 /// map.entry("poneyland").or_insert(12);
1953 /// assert_eq!(map["poneyland"], 12);
1955 /// *map.entry("poneyland").or_insert(12) += 10;
1956 /// assert_eq!(map["poneyland"], 22);
1958 pub fn or_insert(self, default: V) -> &'a mut V {
1960 Occupied(entry) => entry.into_mut(),
1961 Vacant(entry) => entry.insert(default),
1965 #[stable(feature = "rust1", since = "1.0.0")]
1966 /// Ensures a value is in the entry by inserting the result of the default function if empty,
1967 /// and returns a mutable reference to the value in the entry.
1972 /// use std::collections::HashMap;
1974 /// let mut map: HashMap<&str, String> = HashMap::new();
1975 /// let s = "hoho".to_string();
1977 /// map.entry("poneyland").or_insert_with(|| s);
1979 /// assert_eq!(map["poneyland"], "hoho".to_string());
1981 pub fn or_insert_with<F: FnOnce() -> V>(self, default: F) -> &'a mut V {
1983 Occupied(entry) => entry.into_mut(),
1984 Vacant(entry) => entry.insert(default()),
1988 /// Returns a reference to this entry's key.
1993 /// use std::collections::HashMap;
1995 /// let mut map: HashMap<&str, u32> = HashMap::new();
1996 /// assert_eq!(map.entry("poneyland").key(), &"poneyland");
1998 #[stable(feature = "map_entry_keys", since = "1.10.0")]
1999 pub fn key(&self) -> &K {
2001 Occupied(ref entry) => entry.key(),
2002 Vacant(ref entry) => entry.key(),
2007 impl<'a, K, V: Default> Entry<'a, K, V> {
2008 #[unstable(feature = "entry_or_default", issue = "44324")]
2009 /// Ensures a value is in the entry by inserting the default value if empty,
2010 /// and returns a mutable reference to the value in the entry.
2015 /// #![feature(entry_or_default)]
2017 /// use std::collections::HashMap;
2019 /// let mut map: HashMap<&str, Option<u32>> = HashMap::new();
2020 /// map.entry("poneyland").or_default();
2022 /// assert_eq!(map["poneyland"], None);
2025 pub fn or_default(self) -> &'a mut V {
2027 Occupied(entry) => entry.into_mut(),
2028 Vacant(entry) => entry.insert(Default::default()),
2034 impl<'a, K, V> OccupiedEntry<'a, K, V> {
2035 /// Gets a reference to the key in the entry.
2040 /// use std::collections::HashMap;
2042 /// let mut map: HashMap<&str, u32> = HashMap::new();
2043 /// map.entry("poneyland").or_insert(12);
2044 /// assert_eq!(map.entry("poneyland").key(), &"poneyland");
2046 #[stable(feature = "map_entry_keys", since = "1.10.0")]
2047 pub fn key(&self) -> &K {
2051 /// Take the ownership of the key and value from the map.
2056 /// use std::collections::HashMap;
2057 /// use std::collections::hash_map::Entry;
2059 /// let mut map: HashMap<&str, u32> = HashMap::new();
2060 /// map.entry("poneyland").or_insert(12);
2062 /// if let Entry::Occupied(o) = map.entry("poneyland") {
2063 /// // We delete the entry from the map.
2064 /// o.remove_entry();
2067 /// assert_eq!(map.contains_key("poneyland"), false);
2069 #[stable(feature = "map_entry_recover_keys2", since = "1.12.0")]
2070 pub fn remove_entry(self) -> (K, V) {
2071 let (k, v, _) = pop_internal(self.elem);
2075 /// Gets a reference to the value in the entry.
2080 /// use std::collections::HashMap;
2081 /// use std::collections::hash_map::Entry;
2083 /// let mut map: HashMap<&str, u32> = HashMap::new();
2084 /// map.entry("poneyland").or_insert(12);
2086 /// if let Entry::Occupied(o) = map.entry("poneyland") {
2087 /// assert_eq!(o.get(), &12);
2090 #[stable(feature = "rust1", since = "1.0.0")]
2091 pub fn get(&self) -> &V {
2095 /// Gets a mutable reference to the value in the entry.
2100 /// use std::collections::HashMap;
2101 /// use std::collections::hash_map::Entry;
2103 /// let mut map: HashMap<&str, u32> = HashMap::new();
2104 /// map.entry("poneyland").or_insert(12);
2106 /// assert_eq!(map["poneyland"], 12);
2107 /// if let Entry::Occupied(mut o) = map.entry("poneyland") {
2108 /// *o.get_mut() += 10;
2111 /// assert_eq!(map["poneyland"], 22);
2113 #[stable(feature = "rust1", since = "1.0.0")]
2114 pub fn get_mut(&mut self) -> &mut V {
2115 self.elem.read_mut().1
2118 /// Converts the OccupiedEntry into a mutable reference to the value in the entry
2119 /// with a lifetime bound to the map itself.
2124 /// use std::collections::HashMap;
2125 /// use std::collections::hash_map::Entry;
2127 /// let mut map: HashMap<&str, u32> = HashMap::new();
2128 /// map.entry("poneyland").or_insert(12);
2130 /// assert_eq!(map["poneyland"], 12);
2131 /// if let Entry::Occupied(o) = map.entry("poneyland") {
2132 /// *o.into_mut() += 10;
2135 /// assert_eq!(map["poneyland"], 22);
2137 #[stable(feature = "rust1", since = "1.0.0")]
2138 pub fn into_mut(self) -> &'a mut V {
2139 self.elem.into_mut_refs().1
2142 /// Sets the value of the entry, and returns the entry's old value.
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 /// if let Entry::Occupied(mut o) = map.entry("poneyland") {
2154 /// assert_eq!(o.insert(15), 12);
2157 /// assert_eq!(map["poneyland"], 15);
2159 #[stable(feature = "rust1", since = "1.0.0")]
2160 pub fn insert(&mut self, mut value: V) -> V {
2161 let old_value = self.get_mut();
2162 mem::swap(&mut value, old_value);
2166 /// Takes the value out of the entry, and returns it.
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 /// if let Entry::Occupied(o) = map.entry("poneyland") {
2178 /// assert_eq!(o.remove(), 12);
2181 /// assert_eq!(map.contains_key("poneyland"), false);
2183 #[stable(feature = "rust1", since = "1.0.0")]
2184 pub fn remove(self) -> V {
2185 pop_internal(self.elem).1
2188 /// Returns a key that was used for search.
2190 /// The key was retained for further use.
2191 fn take_key(&mut self) -> Option<K> {
2196 impl<'a, K: 'a, V: 'a> VacantEntry<'a, K, V> {
2197 /// Gets a reference to the key that would be used when inserting a value
2198 /// through the `VacantEntry`.
2203 /// use std::collections::HashMap;
2205 /// let mut map: HashMap<&str, u32> = HashMap::new();
2206 /// assert_eq!(map.entry("poneyland").key(), &"poneyland");
2208 #[stable(feature = "map_entry_keys", since = "1.10.0")]
2209 pub fn key(&self) -> &K {
2213 /// Take ownership of the key.
2218 /// use std::collections::HashMap;
2219 /// use std::collections::hash_map::Entry;
2221 /// let mut map: HashMap<&str, u32> = HashMap::new();
2223 /// if let Entry::Vacant(v) = map.entry("poneyland") {
2227 #[stable(feature = "map_entry_recover_keys2", since = "1.12.0")]
2228 pub fn into_key(self) -> K {
2232 /// Sets the value of the entry with the VacantEntry's key,
2233 /// and returns a mutable reference to it.
2238 /// use std::collections::HashMap;
2239 /// use std::collections::hash_map::Entry;
2241 /// let mut map: HashMap<&str, u32> = HashMap::new();
2243 /// if let Entry::Vacant(o) = map.entry("poneyland") {
2246 /// assert_eq!(map["poneyland"], 37);
2248 #[stable(feature = "rust1", since = "1.0.0")]
2249 pub fn insert(self, value: V) -> &'a mut V {
2250 let b = match self.elem {
2251 NeqElem(mut bucket, disp) => {
2252 if disp >= DISPLACEMENT_THRESHOLD {
2253 bucket.table_mut().set_tag(true);
2255 robin_hood(bucket, disp, self.hash, self.key, value)
2257 NoElem(mut bucket, disp) => {
2258 if disp >= DISPLACEMENT_THRESHOLD {
2259 bucket.table_mut().set_tag(true);
2261 bucket.put(self.hash, self.key, value)
2267 // Only used for InPlacement insert. Avoid unnecessary value copy.
2268 // The value remains uninitialized.
2269 unsafe fn insert_key(self) -> FullBucketMut<'a, K, V> {
2271 NeqElem(mut bucket, disp) => {
2272 if disp >= DISPLACEMENT_THRESHOLD {
2273 bucket.table_mut().set_tag(true);
2275 let uninit = mem::uninitialized();
2276 robin_hood(bucket, disp, self.hash, self.key, uninit)
2278 NoElem(mut bucket, disp) => {
2279 if disp >= DISPLACEMENT_THRESHOLD {
2280 bucket.table_mut().set_tag(true);
2282 bucket.put_key(self.hash, self.key)
2288 #[stable(feature = "rust1", since = "1.0.0")]
2289 impl<K, V, S> FromIterator<(K, V)> for HashMap<K, V, S>
2291 S: BuildHasher + Default
2293 fn from_iter<T: IntoIterator<Item = (K, V)>>(iter: T) -> HashMap<K, V, S> {
2294 let mut map = HashMap::with_hasher(Default::default());
2300 #[stable(feature = "rust1", since = "1.0.0")]
2301 impl<K, V, S> Extend<(K, V)> for HashMap<K, V, S>
2305 fn extend<T: IntoIterator<Item = (K, V)>>(&mut self, iter: T) {
2306 // Keys may be already present or show multiple times in the iterator.
2307 // Reserve the entire hint lower bound if the map is empty.
2308 // Otherwise reserve half the hint (rounded up), so the map
2309 // will only resize twice in the worst case.
2310 let iter = iter.into_iter();
2311 let reserve = if self.is_empty() {
2314 (iter.size_hint().0 + 1) / 2
2316 self.reserve(reserve);
2317 for (k, v) in iter {
2323 #[stable(feature = "hash_extend_copy", since = "1.4.0")]
2324 impl<'a, K, V, S> Extend<(&'a K, &'a V)> for HashMap<K, V, S>
2325 where K: Eq + Hash + Copy,
2329 fn extend<T: IntoIterator<Item = (&'a K, &'a V)>>(&mut self, iter: T) {
2330 self.extend(iter.into_iter().map(|(&key, &value)| (key, value)));
2334 /// `RandomState` is the default state for [`HashMap`] types.
2336 /// A particular instance `RandomState` will create the same instances of
2337 /// [`Hasher`], but the hashers created by two different `RandomState`
2338 /// instances are unlikely to produce the same result for the same values.
2340 /// [`HashMap`]: struct.HashMap.html
2341 /// [`Hasher`]: ../../hash/trait.Hasher.html
2346 /// use std::collections::HashMap;
2347 /// use std::collections::hash_map::RandomState;
2349 /// let s = RandomState::new();
2350 /// let mut map = HashMap::with_hasher(s);
2351 /// map.insert(1, 2);
2354 #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
2355 pub struct RandomState {
2361 /// Constructs a new `RandomState` that is initialized with random keys.
2366 /// use std::collections::hash_map::RandomState;
2368 /// let s = RandomState::new();
2371 #[allow(deprecated)]
2373 #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
2374 pub fn new() -> RandomState {
2375 // Historically this function did not cache keys from the OS and instead
2376 // simply always called `rand::thread_rng().gen()` twice. In #31356 it
2377 // was discovered, however, that because we re-seed the thread-local RNG
2378 // from the OS periodically that this can cause excessive slowdown when
2379 // many hash maps are created on a thread. To solve this performance
2380 // trap we cache the first set of randomly generated keys per-thread.
2382 // Later in #36481 it was discovered that exposing a deterministic
2383 // iteration order allows a form of DOS attack. To counter that we
2384 // increment one of the seeds on every RandomState creation, giving
2385 // every corresponding HashMap a different iteration order.
2386 thread_local!(static KEYS: Cell<(u64, u64)> = {
2387 let r = rand::OsRng::new();
2388 let mut r = r.expect("failed to create an OS RNG");
2389 Cell::new((r.gen(), r.gen()))
2393 let (k0, k1) = keys.get();
2394 keys.set((k0.wrapping_add(1), k1));
2395 RandomState { k0: k0, k1: k1 }
2400 #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
2401 impl BuildHasher for RandomState {
2402 type Hasher = DefaultHasher;
2404 #[allow(deprecated)]
2405 fn build_hasher(&self) -> DefaultHasher {
2406 DefaultHasher(SipHasher13::new_with_keys(self.k0, self.k1))
2410 /// The default [`Hasher`] used by [`RandomState`].
2412 /// The internal algorithm is not specified, and so it and its hashes should
2413 /// not be relied upon over releases.
2415 /// [`RandomState`]: struct.RandomState.html
2416 /// [`Hasher`]: ../../hash/trait.Hasher.html
2417 #[stable(feature = "hashmap_default_hasher", since = "1.13.0")]
2418 #[allow(deprecated)]
2419 #[derive(Clone, Debug)]
2420 pub struct DefaultHasher(SipHasher13);
2422 impl DefaultHasher {
2423 /// Creates a new `DefaultHasher`.
2425 /// This hasher is not guaranteed to be the same as all other
2426 /// `DefaultHasher` instances, but is the same as all other `DefaultHasher`
2427 /// instances created through `new` or `default`.
2428 #[stable(feature = "hashmap_default_hasher", since = "1.13.0")]
2429 #[allow(deprecated)]
2430 pub fn new() -> DefaultHasher {
2431 DefaultHasher(SipHasher13::new_with_keys(0, 0))
2435 #[stable(feature = "hashmap_default_hasher", since = "1.13.0")]
2436 impl Default for DefaultHasher {
2437 /// Creates a new `DefaultHasher` using [`new`]. See its documentation for more.
2439 /// [`new`]: #method.new
2440 fn default() -> DefaultHasher {
2441 DefaultHasher::new()
2445 #[stable(feature = "hashmap_default_hasher", since = "1.13.0")]
2446 impl Hasher for DefaultHasher {
2448 fn write(&mut self, msg: &[u8]) {
2453 fn finish(&self) -> u64 {
2458 #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
2459 impl Default for RandomState {
2460 /// Constructs a new `RandomState`.
2462 fn default() -> RandomState {
2467 #[stable(feature = "std_debug", since = "1.16.0")]
2468 impl fmt::Debug for RandomState {
2469 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2470 f.pad("RandomState { .. }")
2474 impl<K, S, Q: ?Sized> super::Recover<Q> for HashMap<K, (), S>
2475 where K: Eq + Hash + Borrow<Q>,
2481 fn get(&self, key: &Q) -> Option<&K> {
2482 self.search(key).into_occupied_bucket().map(|bucket| bucket.into_refs().0)
2485 fn take(&mut self, key: &Q) -> Option<K> {
2486 if self.table.size() == 0 {
2490 self.search_mut(key).into_occupied_bucket().map(|bucket| pop_internal(bucket).0)
2493 fn replace(&mut self, key: K) -> Option<K> {
2496 match self.entry(key) {
2497 Occupied(mut occupied) => {
2498 let key = occupied.take_key().unwrap();
2499 Some(mem::replace(occupied.elem.read_mut().0, key))
2510 fn assert_covariance() {
2511 fn map_key<'new>(v: HashMap<&'static str, u8>) -> HashMap<&'new str, u8> {
2514 fn map_val<'new>(v: HashMap<u8, &'static str>) -> HashMap<u8, &'new str> {
2517 fn iter_key<'a, 'new>(v: Iter<'a, &'static str, u8>) -> Iter<'a, &'new str, u8> {
2520 fn iter_val<'a, 'new>(v: Iter<'a, u8, &'static str>) -> Iter<'a, u8, &'new str> {
2523 fn into_iter_key<'new>(v: IntoIter<&'static str, u8>) -> IntoIter<&'new str, u8> {
2526 fn into_iter_val<'new>(v: IntoIter<u8, &'static str>) -> IntoIter<u8, &'new str> {
2529 fn keys_key<'a, 'new>(v: Keys<'a, &'static str, u8>) -> Keys<'a, &'new str, u8> {
2532 fn keys_val<'a, 'new>(v: Keys<'a, u8, &'static str>) -> Keys<'a, u8, &'new str> {
2535 fn values_key<'a, 'new>(v: Values<'a, &'static str, u8>) -> Values<'a, &'new str, u8> {
2538 fn values_val<'a, 'new>(v: Values<'a, u8, &'static str>) -> Values<'a, u8, &'new str> {
2541 fn drain<'new>(d: Drain<'static, &'static str, &'static str>)
2542 -> Drain<'new, &'new str, &'new str> {
2550 use super::Entry::{Occupied, Vacant};
2551 use super::RandomState;
2553 use rand::{thread_rng, Rng};
2557 fn test_zero_capacities() {
2558 type HM = HashMap<i32, i32>;
2561 assert_eq!(m.capacity(), 0);
2563 let m = HM::default();
2564 assert_eq!(m.capacity(), 0);
2566 let m = HM::with_hasher(RandomState::new());
2567 assert_eq!(m.capacity(), 0);
2569 let m = HM::with_capacity(0);
2570 assert_eq!(m.capacity(), 0);
2572 let m = HM::with_capacity_and_hasher(0, RandomState::new());
2573 assert_eq!(m.capacity(), 0);
2575 let mut m = HM::new();
2581 assert_eq!(m.capacity(), 0);
2583 let mut m = HM::new();
2585 assert_eq!(m.capacity(), 0);
2589 fn test_create_capacity_zero() {
2590 let mut m = HashMap::with_capacity(0);
2592 assert!(m.insert(1, 1).is_none());
2594 assert!(m.contains_key(&1));
2595 assert!(!m.contains_key(&0));
2600 let mut m = HashMap::new();
2601 assert_eq!(m.len(), 0);
2602 assert!(m.insert(1, 2).is_none());
2603 assert_eq!(m.len(), 1);
2604 assert!(m.insert(2, 4).is_none());
2605 assert_eq!(m.len(), 2);
2606 assert_eq!(*m.get(&1).unwrap(), 2);
2607 assert_eq!(*m.get(&2).unwrap(), 4);
2612 let mut m = HashMap::new();
2613 assert_eq!(m.len(), 0);
2614 assert!(m.insert(1, 2).is_none());
2615 assert_eq!(m.len(), 1);
2616 assert!(m.insert(2, 4).is_none());
2617 assert_eq!(m.len(), 2);
2619 assert_eq!(*m2.get(&1).unwrap(), 2);
2620 assert_eq!(*m2.get(&2).unwrap(), 4);
2621 assert_eq!(m2.len(), 2);
2624 thread_local! { static DROP_VECTOR: RefCell<Vec<isize>> = RefCell::new(Vec::new()) }
2626 #[derive(Hash, PartialEq, Eq)]
2632 fn new(k: usize) -> Dropable {
2633 DROP_VECTOR.with(|slot| {
2634 slot.borrow_mut()[k] += 1;
2641 impl Drop for Dropable {
2642 fn drop(&mut self) {
2643 DROP_VECTOR.with(|slot| {
2644 slot.borrow_mut()[self.k] -= 1;
2649 impl Clone for Dropable {
2650 fn clone(&self) -> Dropable {
2651 Dropable::new(self.k)
2657 DROP_VECTOR.with(|slot| {
2658 *slot.borrow_mut() = vec![0; 200];
2662 let mut m = HashMap::new();
2664 DROP_VECTOR.with(|v| {
2666 assert_eq!(v.borrow()[i], 0);
2671 let d1 = Dropable::new(i);
2672 let d2 = Dropable::new(i + 100);
2676 DROP_VECTOR.with(|v| {
2678 assert_eq!(v.borrow()[i], 1);
2683 let k = Dropable::new(i);
2684 let v = m.remove(&k);
2686 assert!(v.is_some());
2688 DROP_VECTOR.with(|v| {
2689 assert_eq!(v.borrow()[i], 1);
2690 assert_eq!(v.borrow()[i+100], 1);
2694 DROP_VECTOR.with(|v| {
2696 assert_eq!(v.borrow()[i], 0);
2697 assert_eq!(v.borrow()[i+100], 0);
2701 assert_eq!(v.borrow()[i], 1);
2702 assert_eq!(v.borrow()[i+100], 1);
2707 DROP_VECTOR.with(|v| {
2709 assert_eq!(v.borrow()[i], 0);
2715 fn test_into_iter_drops() {
2716 DROP_VECTOR.with(|v| {
2717 *v.borrow_mut() = vec![0; 200];
2721 let mut hm = HashMap::new();
2723 DROP_VECTOR.with(|v| {
2725 assert_eq!(v.borrow()[i], 0);
2730 let d1 = Dropable::new(i);
2731 let d2 = Dropable::new(i + 100);
2735 DROP_VECTOR.with(|v| {
2737 assert_eq!(v.borrow()[i], 1);
2744 // By the way, ensure that cloning doesn't screw up the dropping.
2748 let mut half = hm.into_iter().take(50);
2750 DROP_VECTOR.with(|v| {
2752 assert_eq!(v.borrow()[i], 1);
2756 for _ in half.by_ref() {}
2758 DROP_VECTOR.with(|v| {
2760 .filter(|&i| v.borrow()[i] == 1)
2764 .filter(|&i| v.borrow()[i + 100] == 1)
2772 DROP_VECTOR.with(|v| {
2774 assert_eq!(v.borrow()[i], 0);
2780 fn test_empty_remove() {
2781 let mut m: HashMap<isize, bool> = HashMap::new();
2782 assert_eq!(m.remove(&0), None);
2786 fn test_empty_entry() {
2787 let mut m: HashMap<isize, bool> = HashMap::new();
2789 Occupied(_) => panic!(),
2792 assert!(*m.entry(0).or_insert(true));
2793 assert_eq!(m.len(), 1);
2797 fn test_empty_iter() {
2798 let mut m: HashMap<isize, bool> = HashMap::new();
2799 assert_eq!(m.drain().next(), None);
2800 assert_eq!(m.keys().next(), None);
2801 assert_eq!(m.values().next(), None);
2802 assert_eq!(m.values_mut().next(), None);
2803 assert_eq!(m.iter().next(), None);
2804 assert_eq!(m.iter_mut().next(), None);
2805 assert_eq!(m.len(), 0);
2806 assert!(m.is_empty());
2807 assert_eq!(m.into_iter().next(), None);
2811 fn test_lots_of_insertions() {
2812 let mut m = HashMap::new();
2814 // Try this a few times to make sure we never screw up the hashmap's
2817 assert!(m.is_empty());
2820 assert!(m.insert(i, i).is_none());
2824 assert_eq!(r, Some(&j));
2827 for j in i + 1..1001 {
2829 assert_eq!(r, None);
2833 for i in 1001..2001 {
2834 assert!(!m.contains_key(&i));
2839 assert!(m.remove(&i).is_some());
2842 assert!(!m.contains_key(&j));
2845 for j in i + 1..1001 {
2846 assert!(m.contains_key(&j));
2851 assert!(!m.contains_key(&i));
2855 assert!(m.insert(i, i).is_none());
2859 for i in (1..1001).rev() {
2860 assert!(m.remove(&i).is_some());
2863 assert!(!m.contains_key(&j));
2867 assert!(m.contains_key(&j));
2874 fn test_find_mut() {
2875 let mut m = HashMap::new();
2876 assert!(m.insert(1, 12).is_none());
2877 assert!(m.insert(2, 8).is_none());
2878 assert!(m.insert(5, 14).is_none());
2880 match m.get_mut(&5) {
2882 Some(x) => *x = new,
2884 assert_eq!(m.get(&5), Some(&new));
2888 fn test_insert_overwrite() {
2889 let mut m = HashMap::new();
2890 assert!(m.insert(1, 2).is_none());
2891 assert_eq!(*m.get(&1).unwrap(), 2);
2892 assert!(!m.insert(1, 3).is_none());
2893 assert_eq!(*m.get(&1).unwrap(), 3);
2897 fn test_insert_conflicts() {
2898 let mut m = HashMap::with_capacity(4);
2899 assert!(m.insert(1, 2).is_none());
2900 assert!(m.insert(5, 3).is_none());
2901 assert!(m.insert(9, 4).is_none());
2902 assert_eq!(*m.get(&9).unwrap(), 4);
2903 assert_eq!(*m.get(&5).unwrap(), 3);
2904 assert_eq!(*m.get(&1).unwrap(), 2);
2908 fn test_conflict_remove() {
2909 let mut m = HashMap::with_capacity(4);
2910 assert!(m.insert(1, 2).is_none());
2911 assert_eq!(*m.get(&1).unwrap(), 2);
2912 assert!(m.insert(5, 3).is_none());
2913 assert_eq!(*m.get(&1).unwrap(), 2);
2914 assert_eq!(*m.get(&5).unwrap(), 3);
2915 assert!(m.insert(9, 4).is_none());
2916 assert_eq!(*m.get(&1).unwrap(), 2);
2917 assert_eq!(*m.get(&5).unwrap(), 3);
2918 assert_eq!(*m.get(&9).unwrap(), 4);
2919 assert!(m.remove(&1).is_some());
2920 assert_eq!(*m.get(&9).unwrap(), 4);
2921 assert_eq!(*m.get(&5).unwrap(), 3);
2925 fn test_is_empty() {
2926 let mut m = HashMap::with_capacity(4);
2927 assert!(m.insert(1, 2).is_none());
2928 assert!(!m.is_empty());
2929 assert!(m.remove(&1).is_some());
2930 assert!(m.is_empty());
2935 let mut m = HashMap::new();
2937 assert_eq!(m.remove(&1), Some(2));
2938 assert_eq!(m.remove(&1), None);
2943 let mut m = HashMap::with_capacity(4);
2945 assert!(m.insert(i, i*2).is_none());
2947 assert_eq!(m.len(), 32);
2949 let mut observed: u32 = 0;
2952 assert_eq!(*v, *k * 2);
2953 observed |= 1 << *k;
2955 assert_eq!(observed, 0xFFFF_FFFF);
2960 let vec = vec![(1, 'a'), (2, 'b'), (3, 'c')];
2961 let map: HashMap<_, _> = vec.into_iter().collect();
2962 let keys: Vec<_> = map.keys().cloned().collect();
2963 assert_eq!(keys.len(), 3);
2964 assert!(keys.contains(&1));
2965 assert!(keys.contains(&2));
2966 assert!(keys.contains(&3));
2971 let vec = vec![(1, 'a'), (2, 'b'), (3, 'c')];
2972 let map: HashMap<_, _> = vec.into_iter().collect();
2973 let values: Vec<_> = map.values().cloned().collect();
2974 assert_eq!(values.len(), 3);
2975 assert!(values.contains(&'a'));
2976 assert!(values.contains(&'b'));
2977 assert!(values.contains(&'c'));
2981 fn test_values_mut() {
2982 let vec = vec![(1, 1), (2, 2), (3, 3)];
2983 let mut map: HashMap<_, _> = vec.into_iter().collect();
2984 for value in map.values_mut() {
2985 *value = (*value) * 2
2987 let values: Vec<_> = map.values().cloned().collect();
2988 assert_eq!(values.len(), 3);
2989 assert!(values.contains(&2));
2990 assert!(values.contains(&4));
2991 assert!(values.contains(&6));
2996 let mut m = HashMap::new();
2997 assert!(m.get(&1).is_none());
3001 Some(v) => assert_eq!(*v, 2),
3007 let mut m1 = HashMap::new();
3012 let mut m2 = HashMap::new();
3025 let mut map = HashMap::new();
3026 let empty: HashMap<i32, i32> = HashMap::new();
3031 let map_str = format!("{:?}", map);
3033 assert!(map_str == "{1: 2, 3: 4}" ||
3034 map_str == "{3: 4, 1: 2}");
3035 assert_eq!(format!("{:?}", empty), "{}");
3040 let mut m = HashMap::new();
3042 assert_eq!(m.len(), 0);
3043 assert!(m.is_empty());
3046 let old_raw_cap = m.raw_capacity();
3047 while old_raw_cap == m.raw_capacity() {
3052 assert_eq!(m.len(), i);
3053 assert!(!m.is_empty());
3057 fn test_behavior_resize_policy() {
3058 let mut m = HashMap::new();
3060 assert_eq!(m.len(), 0);
3061 assert_eq!(m.raw_capacity(), 0);
3062 assert!(m.is_empty());
3066 assert!(m.is_empty());
3067 let initial_raw_cap = m.raw_capacity();
3068 m.reserve(initial_raw_cap);
3069 let raw_cap = m.raw_capacity();
3071 assert_eq!(raw_cap, initial_raw_cap * 2);
3074 for _ in 0..raw_cap * 3 / 4 {
3078 // three quarters full
3080 assert_eq!(m.len(), i);
3081 assert_eq!(m.raw_capacity(), raw_cap);
3083 for _ in 0..raw_cap / 4 {
3089 let new_raw_cap = m.raw_capacity();
3090 assert_eq!(new_raw_cap, raw_cap * 2);
3092 for _ in 0..raw_cap / 2 - 1 {
3095 assert_eq!(m.raw_capacity(), new_raw_cap);
3097 // A little more than one quarter full.
3099 assert_eq!(m.raw_capacity(), raw_cap);
3100 // again, a little more than half full
3101 for _ in 0..raw_cap / 2 - 1 {
3107 assert_eq!(m.len(), i);
3108 assert!(!m.is_empty());
3109 assert_eq!(m.raw_capacity(), initial_raw_cap);
3113 fn test_reserve_shrink_to_fit() {
3114 let mut m = HashMap::new();
3117 assert!(m.capacity() >= m.len());
3123 let usable_cap = m.capacity();
3124 for i in 128..(128 + 256) {
3126 assert_eq!(m.capacity(), usable_cap);
3129 for i in 100..(128 + 256) {
3130 assert_eq!(m.remove(&i), Some(i));
3134 assert_eq!(m.len(), 100);
3135 assert!(!m.is_empty());
3136 assert!(m.capacity() >= m.len());
3139 assert_eq!(m.remove(&i), Some(i));
3144 assert_eq!(m.len(), 1);
3145 assert!(m.capacity() >= m.len());
3146 assert_eq!(m.remove(&0), Some(0));
3150 fn test_from_iter() {
3151 let xs = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
3153 let map: HashMap<_, _> = xs.iter().cloned().collect();
3155 for &(k, v) in &xs {
3156 assert_eq!(map.get(&k), Some(&v));
3161 fn test_size_hint() {
3162 let xs = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
3164 let map: HashMap<_, _> = xs.iter().cloned().collect();
3166 let mut iter = map.iter();
3168 for _ in iter.by_ref().take(3) {}
3170 assert_eq!(iter.size_hint(), (3, Some(3)));
3174 fn test_iter_len() {
3175 let xs = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
3177 let map: HashMap<_, _> = xs.iter().cloned().collect();
3179 let mut iter = map.iter();
3181 for _ in iter.by_ref().take(3) {}
3183 assert_eq!(iter.len(), 3);
3187 fn test_mut_size_hint() {
3188 let xs = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
3190 let mut map: HashMap<_, _> = xs.iter().cloned().collect();
3192 let mut iter = map.iter_mut();
3194 for _ in iter.by_ref().take(3) {}
3196 assert_eq!(iter.size_hint(), (3, Some(3)));
3200 fn test_iter_mut_len() {
3201 let xs = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
3203 let mut map: HashMap<_, _> = xs.iter().cloned().collect();
3205 let mut iter = map.iter_mut();
3207 for _ in iter.by_ref().take(3) {}
3209 assert_eq!(iter.len(), 3);
3214 let mut map = HashMap::new();
3220 assert_eq!(map[&2], 1);
3225 fn test_index_nonexistent() {
3226 let mut map = HashMap::new();
3237 let xs = [(1, 10), (2, 20), (3, 30), (4, 40), (5, 50), (6, 60)];
3239 let mut map: HashMap<_, _> = xs.iter().cloned().collect();
3241 // Existing key (insert)
3242 match map.entry(1) {
3243 Vacant(_) => unreachable!(),
3244 Occupied(mut view) => {
3245 assert_eq!(view.get(), &10);
3246 assert_eq!(view.insert(100), 10);
3249 assert_eq!(map.get(&1).unwrap(), &100);
3250 assert_eq!(map.len(), 6);
3253 // Existing key (update)
3254 match map.entry(2) {
3255 Vacant(_) => unreachable!(),
3256 Occupied(mut view) => {
3257 let v = view.get_mut();
3258 let new_v = (*v) * 10;
3262 assert_eq!(map.get(&2).unwrap(), &200);
3263 assert_eq!(map.len(), 6);
3265 // Existing key (take)
3266 match map.entry(3) {
3267 Vacant(_) => unreachable!(),
3269 assert_eq!(view.remove(), 30);
3272 assert_eq!(map.get(&3), None);
3273 assert_eq!(map.len(), 5);
3276 // Inexistent key (insert)
3277 match map.entry(10) {
3278 Occupied(_) => unreachable!(),
3280 assert_eq!(*view.insert(1000), 1000);
3283 assert_eq!(map.get(&10).unwrap(), &1000);
3284 assert_eq!(map.len(), 6);
3288 fn test_entry_take_doesnt_corrupt() {
3289 #![allow(deprecated)] //rand
3291 fn check(m: &HashMap<isize, ()>) {
3293 assert!(m.contains_key(k),
3294 "{} is in keys() but not in the map?", k);
3298 let mut m = HashMap::new();
3299 let mut rng = thread_rng();
3301 // Populate the map with some items.
3303 let x = rng.gen_range(-10, 10);
3308 let x = rng.gen_range(-10, 10);
3312 println!("{}: remove {}", i, x);
3322 fn test_extend_ref() {
3323 let mut a = HashMap::new();
3325 let mut b = HashMap::new();
3327 b.insert(3, "three");
3331 assert_eq!(a.len(), 3);
3332 assert_eq!(a[&1], "one");
3333 assert_eq!(a[&2], "two");
3334 assert_eq!(a[&3], "three");
3338 fn test_capacity_not_less_than_len() {
3339 let mut a = HashMap::new();
3347 assert!(a.capacity() > a.len());
3349 let free = a.capacity() - a.len();
3355 assert_eq!(a.len(), a.capacity());
3357 // Insert at capacity should cause allocation.
3359 assert!(a.capacity() > a.len());
3363 fn test_occupied_entry_key() {
3364 let mut a = HashMap::new();
3365 let key = "hello there";
3366 let value = "value goes here";
3367 assert!(a.is_empty());
3368 a.insert(key.clone(), value.clone());
3369 assert_eq!(a.len(), 1);
3370 assert_eq!(a[key], value);
3372 match a.entry(key.clone()) {
3373 Vacant(_) => panic!(),
3374 Occupied(e) => assert_eq!(key, *e.key()),
3376 assert_eq!(a.len(), 1);
3377 assert_eq!(a[key], value);
3381 fn test_vacant_entry_key() {
3382 let mut a = HashMap::new();
3383 let key = "hello there";
3384 let value = "value goes here";
3386 assert!(a.is_empty());
3387 match a.entry(key.clone()) {
3388 Occupied(_) => panic!(),
3390 assert_eq!(key, *e.key());
3391 e.insert(value.clone());
3394 assert_eq!(a.len(), 1);
3395 assert_eq!(a[key], value);
3400 let mut map: HashMap<isize, isize> = (0..100).map(|x|(x, x*10)).collect();
3402 map.retain(|&k, _| k % 2 == 0);
3403 assert_eq!(map.len(), 50);
3404 assert_eq!(map[&2], 20);
3405 assert_eq!(map[&4], 40);
3406 assert_eq!(map[&6], 60);
3410 fn test_adaptive() {
3411 const TEST_LEN: usize = 5000;
3412 // by cloning we get maps with the same hasher seed
3413 let mut first = HashMap::new();
3414 let mut second = first.clone();
3415 first.extend((0..TEST_LEN).map(|i| (i, i)));
3416 second.extend((TEST_LEN..TEST_LEN * 2).map(|i| (i, i)));
3418 for (&k, &v) in &second {
3419 let prev_cap = first.capacity();
3420 let expect_grow = first.len() == prev_cap;
3422 if !expect_grow && first.capacity() != prev_cap {
3426 panic!("Adaptive early resize failed");
3430 fn test_placement_in() {
3431 let mut map = HashMap::new();
3432 map.extend((0..10).map(|i| (i, i)));
3434 map.entry(100) <- 100;
3435 assert_eq!(map[&100], 100);
3438 assert_eq!(map[&0], 10);
3440 assert_eq!(map.len(), 11);
3444 fn test_placement_panic() {
3445 let mut map = HashMap::new();
3446 map.extend((0..10).map(|i| (i, i)));
3448 fn mkpanic() -> usize { panic!() }
3450 // modify existing key
3451 // when panic happens, previous key is removed.
3452 let _ = panic::catch_unwind(panic::AssertUnwindSafe(|| { map.entry(0) <- mkpanic(); }));
3453 assert_eq!(map.len(), 9);
3454 assert!(!map.contains_key(&0));
3457 let _ = panic::catch_unwind(panic::AssertUnwindSafe(|| { map.entry(100) <- mkpanic(); }));
3458 assert_eq!(map.len(), 9);
3459 assert!(!map.contains_key(&100));
3463 fn test_placement_drop() {
3465 struct TestV<'a>(&'a mut bool);
3466 impl<'a> Drop for TestV<'a> {
3467 fn drop(&mut self) {
3468 if !*self.0 { panic!("value double drop!"); } // no double drop
3473 fn makepanic<'a>() -> TestV<'a> { panic!() }
3475 let mut can_drop = true;
3476 let mut hm = HashMap::new();
3477 hm.insert(0, TestV(&mut can_drop));
3478 let _ = panic::catch_unwind(panic::AssertUnwindSafe(|| { hm.entry(0) <- makepanic(); }));
3479 assert_eq!(hm.len(), 0);