1 use super::either_iter::EitherIter;
2 use crate::fx::FxHashMap;
3 use arrayvec::ArrayVec;
6 use std::iter::FromIterator;
9 // For pointer-sized arguments arrays
10 // are faster than set/map for up to 64
13 // On the other hand such a big array
14 // hurts cache performance, makes passing
15 // sso structures around very expensive.
17 // Biggest performance benefit is gained
18 // for reasonably small arrays that stay
19 // small in vast majority of cases.
21 // '8' is chosen as a sane default, to be
23 const SSO_ARRAY_SIZE: usize = 8;
25 /// Small-storage-optimized implementation of a map.
27 /// Stores elements in a small array up to a certain length
28 /// and switches to `HashMap` when that length is exceeded.
30 // FIXME: Implements subset of HashMap API.
32 // Missing HashMap API:
35 // shrink_to (unstable)
36 // drain_filter (unstable)
37 // into_keys/into_values (unstable)
38 // all raw_entry-related
39 // PartialEq/Eq (requires sorting the array)
40 // Entry::or_insert_with_key
41 // Vacant/Occupied entries and related
43 // FIXME: In HashMap most methods accepting key reference
44 // accept reference to generic `Q` where `K: Borrow<Q>`.
46 // However, using this approach in `HashMap::get` apparently
47 // breaks inlining and noticeably reduces performance.
49 // Performance *should* be the same given that borrow is
50 // a NOP in most cases, but in practice that's not the case.
52 // Further investigation is required.
56 // SsoHashMap::get_mut
57 // SsoHashMap::get_entry
58 // SsoHashMap::get_key_value
59 // SsoHashMap::contains_key
61 // SsoHashMap::remove_entry
66 // SsoHashSet::contains
69 pub enum SsoHashMap<K, V> {
70 Array(ArrayVec<(K, V), SSO_ARRAY_SIZE>),
74 impl<K, V> SsoHashMap<K, V> {
75 /// Creates an empty `SsoHashMap`.
77 pub fn new() -> Self {
78 SsoHashMap::Array(ArrayVec::new())
81 /// Creates an empty `SsoHashMap` with the specified capacity.
82 pub fn with_capacity(cap: usize) -> Self {
83 if cap <= SSO_ARRAY_SIZE {
86 SsoHashMap::Map(FxHashMap::with_capacity_and_hasher(cap, Default::default()))
90 /// Clears the map, removing all key-value pairs. Keeps the allocated memory
92 pub fn clear(&mut self) {
94 SsoHashMap::Array(array) => array.clear(),
95 SsoHashMap::Map(map) => map.clear(),
99 /// Returns the number of elements the map can hold without reallocating.
100 pub fn capacity(&self) -> usize {
102 SsoHashMap::Array(_) => SSO_ARRAY_SIZE,
103 SsoHashMap::Map(map) => map.capacity(),
107 /// Returns the number of elements in the map.
108 pub fn len(&self) -> usize {
110 SsoHashMap::Array(array) => array.len(),
111 SsoHashMap::Map(map) => map.len(),
115 /// Returns `true` if the map contains no elements.
116 pub fn is_empty(&self) -> bool {
118 SsoHashMap::Array(array) => array.is_empty(),
119 SsoHashMap::Map(map) => map.is_empty(),
123 /// An iterator visiting all key-value pairs in arbitrary order.
124 /// The iterator element type is `(&'a K, &'a V)`.
126 pub fn iter(&self) -> <&Self as IntoIterator>::IntoIter {
130 /// An iterator visiting all key-value pairs in arbitrary order,
131 /// with mutable references to the values.
132 /// The iterator element type is `(&'a K, &'a mut V)`.
134 pub fn iter_mut(&mut self) -> impl Iterator<Item = (&'_ K, &'_ mut V)> {
138 /// An iterator visiting all keys in arbitrary order.
139 /// The iterator element type is `&'a K`.
140 pub fn keys(&self) -> impl Iterator<Item = &'_ K> {
142 SsoHashMap::Array(array) => EitherIter::Left(array.iter().map(|(k, _v)| k)),
143 SsoHashMap::Map(map) => EitherIter::Right(map.keys()),
147 /// An iterator visiting all values in arbitrary order.
148 /// The iterator element type is `&'a V`.
149 pub fn values(&self) -> impl Iterator<Item = &'_ V> {
151 SsoHashMap::Array(array) => EitherIter::Left(array.iter().map(|(_k, v)| v)),
152 SsoHashMap::Map(map) => EitherIter::Right(map.values()),
156 /// An iterator visiting all values mutably in arbitrary order.
157 /// The iterator element type is `&'a mut V`.
158 pub fn values_mut(&mut self) -> impl Iterator<Item = &'_ mut V> {
160 SsoHashMap::Array(array) => EitherIter::Left(array.iter_mut().map(|(_k, v)| v)),
161 SsoHashMap::Map(map) => EitherIter::Right(map.values_mut()),
165 /// Clears the map, returning all key-value pairs as an iterator. Keeps the
166 /// allocated memory for reuse.
167 pub fn drain(&mut self) -> impl Iterator<Item = (K, V)> + '_ {
169 SsoHashMap::Array(array) => EitherIter::Left(array.drain(..)),
170 SsoHashMap::Map(map) => EitherIter::Right(map.drain()),
175 impl<K: Eq + Hash, V> SsoHashMap<K, V> {
176 /// Changes underlying storage from array to hashmap
177 /// if array is full.
178 fn migrate_if_full(&mut self) {
179 if let SsoHashMap::Array(array) = self {
181 *self = SsoHashMap::Map(array.drain(..).collect());
186 /// Reserves capacity for at least `additional` more elements to be inserted
187 /// in the `SsoHashMap`. The collection may reserve more space to avoid
188 /// frequent reallocations.
189 pub fn reserve(&mut self, additional: usize) {
191 SsoHashMap::Array(array) => {
192 if SSO_ARRAY_SIZE < (array.len() + additional) {
193 let mut map: FxHashMap<K, V> = array.drain(..).collect();
194 map.reserve(additional);
195 *self = SsoHashMap::Map(map);
198 SsoHashMap::Map(map) => map.reserve(additional),
202 /// Shrinks the capacity of the map as much as possible. It will drop
203 /// down as much as possible while maintaining the internal rules
204 /// and possibly leaving some space in accordance with the resize policy.
205 pub fn shrink_to_fit(&mut self) {
206 if let SsoHashMap::Map(map) = self {
207 if map.len() <= SSO_ARRAY_SIZE {
208 *self = SsoHashMap::Array(map.drain().collect());
215 /// Retains only the elements specified by the predicate.
216 pub fn retain<F>(&mut self, mut f: F)
218 F: FnMut(&K, &mut V) -> bool,
221 SsoHashMap::Array(array) => array.retain(|(k, v)| f(k, v)),
222 SsoHashMap::Map(map) => map.retain(f),
226 /// Inserts a key-value pair into the map.
228 /// If the map did not have this key present, [`None`] is returned.
230 /// If the map did have this key present, the value is updated, and the old
231 /// value is returned. The key is not updated, though; this matters for
232 /// types that can be `==` without being identical. See the [module-level
233 /// documentation] for more.
234 pub fn insert(&mut self, key: K, value: V) -> Option<V> {
236 SsoHashMap::Array(array) => {
237 for (k, v) in array.iter_mut() {
239 let old_value = std::mem::replace(v, value);
240 return Some(old_value);
243 if let Err(error) = array.try_push((key, value)) {
244 let mut map: FxHashMap<K, V> = array.drain(..).collect();
245 let (key, value) = error.element();
246 map.insert(key, value);
247 *self = SsoHashMap::Map(map);
251 SsoHashMap::Map(map) => map.insert(key, value),
255 /// Removes a key from the map, returning the value at the key if the key
256 /// was previously in the map.
257 pub fn remove(&mut self, key: &K) -> Option<V> {
259 SsoHashMap::Array(array) => {
260 if let Some(index) = array.iter().position(|(k, _v)| k == key) {
261 Some(array.swap_remove(index).1)
266 SsoHashMap::Map(map) => map.remove(key),
270 /// Removes a key from the map, returning the stored key and value if the
271 /// key was previously in the map.
272 pub fn remove_entry(&mut self, key: &K) -> Option<(K, V)> {
274 SsoHashMap::Array(array) => {
275 if let Some(index) = array.iter().position(|(k, _v)| k == key) {
276 Some(array.swap_remove(index))
281 SsoHashMap::Map(map) => map.remove_entry(key),
285 /// Returns a reference to the value corresponding to the key.
286 pub fn get(&self, key: &K) -> Option<&V> {
288 SsoHashMap::Array(array) => {
289 for (k, v) in array {
296 SsoHashMap::Map(map) => map.get(key),
300 /// Returns a mutable reference to the value corresponding to the key.
301 pub fn get_mut(&mut self, key: &K) -> Option<&mut V> {
303 SsoHashMap::Array(array) => {
304 for (k, v) in array {
311 SsoHashMap::Map(map) => map.get_mut(key),
315 /// Returns the key-value pair corresponding to the supplied key.
316 pub fn get_key_value(&self, key: &K) -> Option<(&K, &V)> {
318 SsoHashMap::Array(array) => {
319 for (k, v) in array {
326 SsoHashMap::Map(map) => map.get_key_value(key),
330 /// Returns `true` if the map contains a value for the specified key.
331 pub fn contains_key(&self, key: &K) -> bool {
333 SsoHashMap::Array(array) => array.iter().any(|(k, _v)| k == key),
334 SsoHashMap::Map(map) => map.contains_key(key),
338 /// Gets the given key's corresponding entry in the map for in-place manipulation.
340 pub fn entry(&mut self, key: K) -> Entry<'_, K, V> {
341 Entry { ssomap: self, key }
345 impl<K, V> Default for SsoHashMap<K, V> {
347 fn default() -> Self {
352 impl<K: Eq + Hash, V> FromIterator<(K, V)> for SsoHashMap<K, V> {
353 fn from_iter<I: IntoIterator<Item = (K, V)>>(iter: I) -> SsoHashMap<K, V> {
354 let mut map: SsoHashMap<K, V> = Default::default();
360 impl<K: Eq + Hash, V> Extend<(K, V)> for SsoHashMap<K, V> {
361 fn extend<I>(&mut self, iter: I)
363 I: IntoIterator<Item = (K, V)>,
365 for (key, value) in iter.into_iter() {
366 self.insert(key, value);
371 fn extend_one(&mut self, (k, v): (K, V)) {
375 fn extend_reserve(&mut self, additional: usize) {
377 SsoHashMap::Array(array) => {
378 if SSO_ARRAY_SIZE < (array.len() + additional) {
379 let mut map: FxHashMap<K, V> = array.drain(..).collect();
380 map.extend_reserve(additional);
381 *self = SsoHashMap::Map(map);
384 SsoHashMap::Map(map) => map.extend_reserve(additional),
389 impl<'a, K, V> Extend<(&'a K, &'a V)> for SsoHashMap<K, V>
394 fn extend<T: IntoIterator<Item = (&'a K, &'a V)>>(&mut self, iter: T) {
395 self.extend(iter.into_iter().map(|(k, v)| (*k, *v)))
399 fn extend_one(&mut self, (&k, &v): (&'a K, &'a V)) {
404 fn extend_reserve(&mut self, additional: usize) {
405 Extend::<(K, V)>::extend_reserve(self, additional)
409 impl<K, V> IntoIterator for SsoHashMap<K, V> {
410 type IntoIter = EitherIter<
411 <ArrayVec<(K, V), 8> as IntoIterator>::IntoIter,
412 <FxHashMap<K, V> as IntoIterator>::IntoIter,
414 type Item = <Self::IntoIter as Iterator>::Item;
416 fn into_iter(self) -> Self::IntoIter {
418 SsoHashMap::Array(array) => EitherIter::Left(array.into_iter()),
419 SsoHashMap::Map(map) => EitherIter::Right(map.into_iter()),
424 /// adapts Item of array reference iterator to Item of hashmap reference iterator.
426 fn adapt_array_ref_it<K, V>(pair: &'a (K, V)) -> (&'a K, &'a V) {
431 /// adapts Item of array mut reference iterator to Item of hashmap mut reference iterator.
433 fn adapt_array_mut_it<K, V>(pair: &'a mut (K, V)) -> (&'a K, &'a mut V) {
438 impl<'a, K, V> IntoIterator for &'a SsoHashMap<K, V> {
439 type IntoIter = EitherIter<
441 <&'a ArrayVec<(K, V), 8> as IntoIterator>::IntoIter,
442 fn(&'a (K, V)) -> (&'a K, &'a V),
444 <&'a FxHashMap<K, V> as IntoIterator>::IntoIter,
446 type Item = <Self::IntoIter as Iterator>::Item;
448 fn into_iter(self) -> Self::IntoIter {
450 SsoHashMap::Array(array) => EitherIter::Left(array.into_iter().map(adapt_array_ref_it)),
451 SsoHashMap::Map(map) => EitherIter::Right(map.iter()),
456 impl<'a, K, V> IntoIterator for &'a mut SsoHashMap<K, V> {
457 type IntoIter = EitherIter<
459 <&'a mut ArrayVec<(K, V), 8> as IntoIterator>::IntoIter,
460 fn(&'a mut (K, V)) -> (&'a K, &'a mut V),
462 <&'a mut FxHashMap<K, V> as IntoIterator>::IntoIter,
464 type Item = <Self::IntoIter as Iterator>::Item;
466 fn into_iter(self) -> Self::IntoIter {
468 SsoHashMap::Array(array) => EitherIter::Left(array.into_iter().map(adapt_array_mut_it)),
469 SsoHashMap::Map(map) => EitherIter::Right(map.iter_mut()),
474 impl<K, V> fmt::Debug for SsoHashMap<K, V>
479 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
480 f.debug_map().entries(self.iter()).finish()
484 impl<'a, K, V> Index<&'a K> for SsoHashMap<K, V>
491 fn index(&self, key: &K) -> &V {
492 self.get(key).expect("no entry found for key")
496 /// A view into a single entry in a map.
497 pub struct Entry<'a, K, V> {
498 ssomap: &'a mut SsoHashMap<K, V>,
502 impl<'a, K: Eq + Hash, V> Entry<'a, K, V> {
503 /// Provides in-place mutable access to an occupied entry before any
504 /// potential inserts into the map.
505 pub fn and_modify<F>(self, f: F) -> Self
509 if let Some(value) = self.ssomap.get_mut(&self.key) {
515 /// Ensures a value is in the entry by inserting the default if empty, and returns
516 /// a mutable reference to the value in the entry.
518 pub fn or_insert(self, value: V) -> &'a mut V {
519 self.or_insert_with(|| value)
522 /// Ensures a value is in the entry by inserting the result of the default function if empty,
523 /// and returns a mutable reference to the value in the entry.
524 pub fn or_insert_with<F: FnOnce() -> V>(self, default: F) -> &'a mut V {
525 self.ssomap.migrate_if_full();
527 SsoHashMap::Array(array) => {
528 let key_ref = &self.key;
529 let found_index = array.iter().position(|(k, _v)| k == key_ref);
530 let index = if let Some(index) = found_index {
533 let index = array.len();
534 array.try_push((self.key, default())).unwrap();
539 SsoHashMap::Map(map) => map.entry(self.key).or_insert_with(default),
543 /// Returns a reference to this entry's key.
545 pub fn key(&self) -> &K {
550 impl<'a, K: Eq + Hash, V: Default> Entry<'a, K, V> {
551 /// Ensures a value is in the entry by inserting the default value if empty,
552 /// and returns a mutable reference to the value in the entry.
554 pub fn or_default(self) -> &'a mut V {
555 self.or_insert_with(Default::default)