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//! A 2Q cache //! //! This cache based on the paper entitled //! **[2Q: A Low Overhead High-Performance Buffer Management Replacement Algorithm](http://www.vldb.org/conf/1994/P439.PDF)**. #![deny( missing_docs, missing_debug_implementations, missing_copy_implementations, trivial_casts, trivial_numeric_casts, unsafe_code, unstable_features, unused_import_braces, unused_qualifications )] use std::collections::VecDeque; use std::collections::vec_deque; use std::borrow::Borrow; use std::cmp; use std::mem; use std::iter; use std::fmt; /// The type of items in the recent and frequent lists. #[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)] struct CacheEntry<K, V> { key: K, value: V, } impl<'a, K, V> Into<(&'a K, &'a V)> for &'a CacheEntry<K, V> { fn into(self) -> (&'a K, &'a V) { (&self.key, &self.value) } } impl<'a, K, V> Into<(&'a K, &'a mut V)> for &'a mut CacheEntry<K, V> { fn into(self) -> (&'a K, &'a mut V) { (&self.key, &mut self.value) } } /// A 2Q Cache which maps keys to values /// /// 2Q is an enhancement over an LRU cache by tracking both recent and frequently accessed entries /// separately. This avoids the cache being trashed by a scan of many new items: Only the recent /// list will be trashed. /// /// The cache is split into 3 sections, recent entries, frequent entries, and ghost entries /// recent contains the most recently added entries. /// frequent is an LRU cache which contains entries which are frequently accessed /// ghost contains the keys which have been recently evicted from the recent cache. /// /// New entries in the cache are initially placed in recent. /// After recent fills up, the oldest entry from recent will be removed, and its key is placed in /// ghost. When an entry is requested and not found, but its key is found in the ghost list, /// an entry is pushed to the front of frequent. /// /// # Examples /// /// ``` /// use cache_2q::Cache; /// /// // type inference lets us omit an explicit type signature (which /// // would be `Cache<&str, &str>` in this example). /// let mut book_reviews = Cache::new(1024); /// /// // review some books. /// book_reviews.insert("Adventures of Huckleberry Finn", "My favorite book."); /// book_reviews.insert("Grimms' Fairy Tales", "Masterpiece."); /// book_reviews.insert("Pride and Prejudice", "Very enjoyable."); /// book_reviews.insert("The Adventures of Sherlock Holmes", "Eye lyked it alot."); /// /// // check for a specific one. /// if !book_reviews.contains_key("Les Misérables") { /// println!("We've got {} reviews, but Les Misérables ain't one.", /// book_reviews.len()); /// } /// /// // oops, this review has a lot of spelling mistakes, let's delete it. /// book_reviews.remove("The Adventures of Sherlock Holmes"); /// /// // look up the values associated with some keys. /// let to_find = ["Pride and Prejudice", "Alice's Adventure in Wonderland"]; /// for book in &to_find { /// match book_reviews.get(book) { /// Some(review) => println!("{}: {}", book, review), /// None => println!("{} is unreviewed.", book) /// } /// } /// /// // iterate over everything. /// for (book, review) in &book_reviews { /// println!("{}: \"{}\"", book, review); /// } /// ``` /// /// Cache also implements an Entry API, which allows for more complex methods of getting, /// setting, updating and removing keys and their values: /// /// ``` /// use cache_2q::Cache; /// /// // type inference lets us omit an explicit type signature (which /// // would be `Cache<&str, u8>` in this example). /// let mut player_stats = Cache::new(32); /// /// fn random_stat_buff() -> u8 { /// // could actually return some random value here - let's just return /// // some fixed value for now /// 42 /// } /// /// // insert a key only if it doesn't already exist /// player_stats.entry("health").or_insert(100); /// /// // insert a key using a function that provides a new value only if it /// // doesn't already exist /// player_stats.entry("defence").or_insert_with(random_stat_buff); /// /// // update a key, guarding against the key possibly not being set /// let stat = player_stats.entry("attack").or_insert(100); /// *stat += random_stat_buff(); /// ``` #[derive(Debug, Clone, PartialEq, Eq)] pub struct Cache<K, V> { frequent: VecDeque<CacheEntry<K, V>>, recent: VecDeque<CacheEntry<K, V>>, ghost: VecDeque<K>, max_frequent: usize, max_recent: usize, max_ghost: usize, } impl<K: Eq, V> Cache<K, V> { /// Creates an empty cache, with the specified size /// /// # Notes /// `size` defines the maximum number of entries, but there can be /// an additional `size / 2` instances of `K` /// /// # Examples /// /// ``` /// use cache_2q::Cache; /// /// let mut cache: Cache<u64, Vec<u8>> = Cache::new(8); /// cache.insert(1, vec![1,2,3,4]); /// assert_eq!(*cache.get(&1).unwrap(), &[1,2,3,4]); /// ``` pub fn new(size: usize) -> Cache<K, V> { assert!(size >= 2); let k_in = cmp::max(1, size / 4); let k_out = cmp::max(1, size / 2); let k = size - k_in; Cache { frequent: VecDeque::with_capacity(k), recent: VecDeque::with_capacity(k_in), ghost: VecDeque::with_capacity(k_out), max_frequent: k, max_recent: k_in, max_ghost: k_out, } } /// Returns true if the cache contains a value for the specified key. /// /// The key may be any borrowed form of the cache's key type, but /// Eq on the borrowed form must match those for the key type. /// /// # Examples /// /// ``` /// use cache_2q::Cache; /// /// let mut cache = Cache::new(8); /// cache.insert(1, "a"); /// assert_eq!(cache.contains_key(&1), true); /// assert_eq!(cache.contains_key(&2), false); /// ``` pub fn contains_key<Q: ?Sized>(&self, key: &Q) -> bool where K: Borrow<Q>, Q: Eq, { self.recent.iter().any(|entry| entry.key.borrow() == key) || self.frequent.iter().any(|entry| entry.key.borrow() == key) } /// Returns a reference to the value corresponding to the key. /// /// The key may be any borrowed form of the cache's key type, but Eq on the borrowed form /// must match those for the key type. /// /// # Examples /// /// ``` /// use cache_2q::Cache; /// /// let mut cache = Cache::new(32); /// cache.insert(1, "a"); /// assert_eq!(cache.get(&1), Some(&"a")); /// assert_eq!(cache.get(&2), None); /// ``` pub fn get<Q: ?Sized>(&mut self, key: &Q) -> Option<&V> where K: Borrow<Q>, Q: Eq, { if let Some(&CacheEntry { ref value, .. }) = self.recent.iter().find(|entry| entry.key.borrow() == key) { Some(value) } else if let Some(i) = self.frequent.iter().position(|entry| entry.key.borrow() == key) { let old = self.frequent.remove(i).unwrap(); self.frequent.push_front(old); Some(&self.frequent[0].value) } else { None } } /// Returns a mutable reference to the value corresponding to the key. /// /// The key may be any borrowed form of the cache's key type, but /// Eq on the borrowed form *must* match those for /// the key type. /// /// # Examples /// /// ``` /// use cache_2q::Cache; /// /// let mut cache = Cache::new(8); /// cache.insert(1, "a"); /// if let Some(x) = cache.get_mut(&1) { /// *x = "b"; /// } /// assert_eq!(cache.get(&1), Some(&"b")); /// ``` pub fn get_mut<Q: ?Sized>(&mut self, key: &Q) -> Option<&mut V> where K: Borrow<Q>, Q: Eq, { if let Some(&mut CacheEntry { ref mut value, .. }) = self.recent .iter_mut() .find(|entry| entry.key.borrow() == key) { Some(value) } else if let Some(i) = self.frequent.iter().position(|entry| entry.key.borrow() == key) { let old = self.frequent.remove(i).unwrap(); self.frequent.push_front(old); Some(&mut self.frequent[0].value) } else { None } } /// Inserts a key-value pair into the cache. /// /// If the cache did not have this key present, None is returned. /// /// If the cache did have this key present, the value is updated, and the old /// value is returned. /// /// # Examples /// /// ``` /// use cache_2q::Cache; /// /// let mut cache = Cache::new(8); /// assert_eq!(cache.insert(37, "a"), None); /// assert_eq!(cache.is_empty(), false); /// /// cache.insert(37, "b"); /// assert_eq!(cache.insert(37, "c"), Some("b")); /// assert_eq!(*cache.get(&37).unwrap(), "c"); /// ``` pub fn insert(&mut self, key: K, value: V) -> Option<V> { match self.entry(key) { Entry::Occupied(mut entry) => Some(entry.insert(value)), Entry::Vacant(entry) => { entry.insert(value); None } } } /// Gets the given key's corresponding entry in the cache for in-place manipulation. /// /// # Examples /// /// ``` /// use cache_2q::Cache; /// /// let mut stringified = Cache::new(8); /// /// for &i in &[1, 2, 5, 1, 2, 8, 1, 2, 102, 25, 1092, 1, 2, 82, 10, 1095] { /// let string = stringified.entry(i).or_insert_with(|| i.to_string()); /// assert_eq!(string, &i.to_string()); /// } /// ``` pub fn entry(&mut self, key: K) -> Entry<K, V> { let mut entry = self.peek_entry(key); if let Entry::Occupied(OccupiedEntry { ref mut cache, kind: OccupiedKind::Frequent(ref mut i), .. }) = entry { let old_entry = cache.frequent.remove(*i).unwrap(); cache.frequent.push_front(old_entry); *i = 0; } entry } /// Returns the number of entries currenly in the cache. /// /// # Examples /// /// ``` /// use cache_2q::Cache; /// /// let mut a = Cache::new(8); /// assert_eq!(a.len(), 0); /// a.insert(1, "a"); /// assert_eq!(a.len(), 1); /// ``` pub fn len(&self) -> usize { self.recent.len() + self.frequent.len() } /// Returns true if the cache contains no elements. /// /// # Examples /// /// ``` /// use cache_2q::Cache; /// /// let mut a = Cache::new(8); /// assert!(a.is_empty()); /// a.insert(1, "a"); /// assert!(!a.is_empty()); /// ``` pub fn is_empty(&self) -> bool { self.recent.is_empty() && self.frequent.is_empty() } /// Removes a key from the cache, returning the value associated with the key if the key /// was previously in the cache. /// /// The key may be any borrowed form of the cache's key type, but /// Eq on the borrowed form *must* match those for /// the key type. /// /// # Examples /// /// ``` /// use cache_2q::Cache; /// /// let mut cache = Cache::new(8); /// cache.insert(1, "a"); /// assert_eq!(cache.remove(&1), Some("a")); /// assert_eq!(cache.remove(&1), None); /// ``` pub fn remove<Q: ?Sized>(&mut self, key: &Q) -> Option<V> where K: Borrow<Q>, Q: Eq, { if let Some(i) = self.recent .iter() .position(|entry| entry.key.borrow() == key) { Some(self.recent.remove(i).unwrap().value) } else if let Some(i) = self.frequent.iter().position(|entry| entry.key.borrow() == key) { Some(self.frequent.remove(i).unwrap().value) } else { None } } /// Clears the cache, removing all key-value pairs. Keeps the allocated memory for reuse. /// /// # Examples /// /// ``` /// use cache_2q::Cache; /// /// let mut a = Cache::new(32); /// a.insert(1, "a"); /// a.clear(); /// assert!(a.is_empty()); /// ``` pub fn clear(&mut self) { self.recent.clear(); self.ghost.clear(); self.frequent.clear(); } /// Gets the given key's corresponding entry in the cache for in-place manipulation. /// The LRU portion of the cache is not updated /// /// # Examples /// /// ``` /// use cache_2q::Cache; /// /// let mut stringified = Cache::new(8); /// /// for &i in &[1, 2, 5, 1, 2, 8, 1, 2, 102, 25, 1092, 1, 2, 82, 10, 1095] { /// let string = stringified.peek_entry(i).or_insert_with(|| i.to_string()); /// assert_eq!(string, &i.to_string()); /// } /// ``` pub fn peek_entry(&mut self, key: K) -> Entry<K, V> { if let Some(i) = self.frequent.iter().position(|entry| &entry.key == &key) { Entry::Occupied(OccupiedEntry { cache: self, kind: OccupiedKind::Frequent(i), }) } else if let Some(i) = self.recent.iter().position(|entry| &entry.key == &key) { Entry::Occupied(OccupiedEntry { cache: self, kind: OccupiedKind::Recent(i), }) } else if let Some(i) = self.ghost.iter().position(|old_key| old_key == &key) { Entry::Vacant(VacantEntry { cache: self, key: key, kind: VacantKind::Ghost(i), }) } else { Entry::Vacant(VacantEntry { cache: self, key: key, kind: VacantKind::Unknown, }) } } /// An iterator visiting all key-value pairs in arbitrary order. /// The iterator element type is `(&'a K, &'a V)`. /// /// # Examples /// /// ``` /// use cache_2q::Cache; /// /// let mut cache = Cache::new(8); /// cache.insert("a", 1); /// cache.insert("b", 2); /// cache.insert("c", 3); /// /// for (key, val) in cache.iter() { /// println!("key: {} val: {}", key, val); /// } /// ``` pub fn iter(&self) -> Iter<K, V> { Iter { inner: self.recent.iter().chain(self.frequent.iter()).map(Into::into), } } } impl<'a, K: 'a + Eq, V: 'a> IntoIterator for &'a Cache<K, V> { type Item = (&'a K, &'a V); type IntoIter = Iter<'a, K, V>; fn into_iter(self) -> Iter<'a, K, V> { self.iter() } } /// A view into a single entry in a cache, which may either be vacant or occupied. /// /// This enum is constructed from the entry method on Cache. pub enum Entry<'a, K: 'a, V: 'a> { /// An occupied entry Occupied(OccupiedEntry<'a, K, V>), /// An vacant entry Vacant(VacantEntry<'a, K, V>), } impl<'a, K: 'a + fmt::Debug, V: 'a + fmt::Debug> fmt::Debug for Entry<'a, K, V> { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { match *self { Entry::Vacant(ref v) => f.debug_tuple("Entry").field(v).finish(), Entry::Occupied(ref o) => f.debug_tuple("Entry").field(o).finish(), } } } impl<'a, K: 'a + Eq, V: 'a> Entry<'a, K, V> { /// Returns a reference to this entry's key. /// /// # Examples /// /// ``` /// use cache_2q::Cache; /// /// let mut cache: Cache<&str, u32> = Cache::new(8); /// assert_eq!(cache.entry("poneyland").key(), &"poneyland"); /// ``` pub fn key(&self) -> &K { match *self { Entry::Occupied(ref entry) => entry.key(), Entry::Vacant(ref entry) => entry.key(), } } /// Ensures a value is in the entry by inserting the default if empty, and returns a mutable /// reference to the value in the entry. /// /// # Examples /// ``` /// use cache_2q::Cache; /// /// let mut cache = Cache::new(8); /// { /// let value = cache.entry(0xFF00).or_insert(0); /// assert_eq!(*value, 0); /// } /// /// *cache.entry(0xFF00).or_insert(100) += 1; /// assert_eq!(*cache.get(&0xFF00).unwrap(), 1); /// ``` pub fn or_insert(self, default: V) -> &'a mut V { match self { Entry::Occupied(entry) => entry.into_mut(), Entry::Vacant(entry) => entry.insert(default), } } /// Ensures a value is in the entry by inserting the result of the default function if empty, /// and returns a mutable reference to the value in the entry. /// /// # Examples /// /// ``` /// use cache_2q::Cache; /// /// let mut cache: Cache<&'static str, String> = Cache::new(8); /// cache.entry("key").or_insert_with(|| "value".to_string()); /// /// assert_eq!(cache.get(&"key").unwrap(), &"value".to_string()); /// ``` pub fn or_insert_with<F: FnOnce() -> V>(self, default: F) -> &'a mut V { match self { Entry::Occupied(entry) => entry.into_mut(), Entry::Vacant(entry) => entry.insert(default()), } } } /// A view into an occupied entry in a [`Cache`]. /// It is part of the [`Entry`] enum. /// /// [`Cache`]: struct.Cache.html /// [`Entry`]: enum.Entry.html pub struct OccupiedEntry<'a, K: 'a, V: 'a> { cache: &'a mut Cache<K, V>, kind: OccupiedKind, } impl<'a, K: 'a + fmt::Debug, V: 'a + fmt::Debug> fmt::Debug for OccupiedEntry<'a, K, V> { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { f.debug_struct("OccupiedEntry") .field("key", self.key()) .field("value", self.get()) .field( "kind", &if let OccupiedKind::Frequent(_) = self.kind { "frequent" } else { "recent" }, ) .finish() } } impl<'a, K: 'a, V: 'a> OccupiedEntry<'a, K, V> { fn entry(&self) -> &CacheEntry<K, V> { match self.kind { OccupiedKind::Recent(idx) => &self.cache.recent[idx], OccupiedKind::Frequent(idx) => &self.cache.frequent[idx], } } fn entry_mut(&mut self) -> &mut CacheEntry<K, V> { match self.kind { OccupiedKind::Recent(idx) => &mut self.cache.recent[idx], OccupiedKind::Frequent(idx) => &mut self.cache.frequent[idx], } } /// Gets a reference to the key in the entry. /// /// # Examples /// /// ``` /// use cache_2q::{Cache, Entry}; /// /// let mut cache: Cache<&str, u32> = Cache::new(8); /// cache.entry("poneyland").or_insert(12); /// match cache.entry("poneyland") { /// Entry::Vacant(_) => { /// panic!("Should be occupied"); /// }, /// Entry::Occupied(occupied) => { /// assert_eq!(occupied.key(), &"poneyland"); /// }, /// } /// ``` pub fn key(&self) -> &K { &self.entry().key } /// Gets a reference to the value in the entry. /// /// # Examples /// /// ``` /// use cache_2q::{Cache, Entry}; /// /// let mut cache: Cache<&str, u32> = Cache::new(8); /// cache.entry("poneyland").or_insert(12); /// /// if let Entry::Occupied(o) = cache.entry("poneyland") { /// assert_eq!(o.get(), &12); /// } else { /// panic!("Entry should be occupied"); /// } /// ``` pub fn get(&self) -> &V { &self.entry().value } /// Gets a mutable reference to the value in the entry. /// /// # Examples /// /// ``` /// use cache_2q::{Cache, Entry}; /// /// let mut cache: Cache<&str, u32> = Cache::new(8); /// cache.entry("poneyland").or_insert(12); /// /// assert_eq!(*cache.get("poneyland").unwrap(), 12); /// if let Entry::Occupied(mut o) = cache.entry("poneyland") { /// *o.get_mut() += 10; /// } else { /// panic!("Entry should be occupied"); /// } /// /// assert_eq!(*cache.get("poneyland").unwrap(), 22); /// ``` pub fn get_mut(&mut self) -> &mut V { &mut self.entry_mut().value } /// Converts the OccupiedEntry into a mutable reference to the value in the entry /// with a lifetime bound to the cache itself. /// /// # Examples /// /// ``` /// use cache_2q::{Cache, Entry}; /// /// let mut cache: Cache<&str, u32> = Cache::new(8); /// cache.entry("poneyland").or_insert(12); /// /// assert_eq!(*cache.get("poneyland").unwrap(), 12); /// if let Entry::Occupied(o) = cache.entry("poneyland") { /// *o.into_mut() += 10; /// } else { /// panic!("Entry should be occupied"); /// } /// /// assert_eq!(*cache.get("poneyland").unwrap(), 22); /// ``` pub fn into_mut(self) -> &'a mut V { match self.kind { OccupiedKind::Recent(idx) => &mut self.cache.recent[idx].value, OccupiedKind::Frequent(idx) => &mut self.cache.frequent[idx].value, } } /// Sets the value of the entry, and returns the entry's old value. /// /// # Examples /// /// ``` /// use cache_2q::{Cache, Entry}; /// /// let mut cache: Cache<&str, u32> = Cache::new(8); /// cache.entry("poneyland").or_insert(12); /// /// if let Entry::Occupied(mut o) = cache.entry("poneyland") { /// assert_eq!(o.insert(15), 12); /// } else { /// panic!("Entry should be occupied"); /// } /// /// assert_eq!(*cache.get("poneyland").unwrap(), 15); /// ``` pub fn insert(&mut self, value: V) -> V { mem::replace(self.get_mut(), value) } /// Take the ownership of the key and value from the cache. /// /// # Examples /// /// ``` /// use cache_2q::{Cache, Entry}; /// /// let mut cache: Cache<&str, u32> = Cache::new(8); /// cache.entry("poneyland").or_insert(12); /// /// if let Entry::Occupied(o) = cache.entry("poneyland") { /// // We delete the entry from the cache. /// o.remove_entry(); /// } else { /// panic!("Entry should be occupied"); /// } /// /// assert_eq!(cache.contains_key("poneyland"), false); /// ``` pub fn remove_entry(self) -> (K, V) { match self.kind { OccupiedKind::Recent(idx) => { let entry = self.cache.recent.remove(idx).unwrap(); (entry.key, entry.value) } OccupiedKind::Frequent(idx) => { let entry = self.cache.frequent.remove(idx).unwrap(); (entry.key, entry.value) } } } /// Takes the value out of the entry, and returns it. /// /// # Examples /// /// ``` /// use cache_2q::{Cache, Entry}; /// /// let mut cache: Cache<&str, u32> = Cache::new(8); /// cache.entry("poneyland").or_insert(12); /// /// if let Entry::Occupied(o) = cache.entry("poneyland") { /// assert_eq!(o.remove(), 12); /// } else { /// panic!("Entry should be occupied"); /// } /// /// assert_eq!(cache.contains_key("poneyland"), false); /// ``` pub fn remove(self) -> V { self.remove_entry().1 } } /// A view into a vacant entry in a [`Cache`]. /// It is part of the [`Entry`] enum. /// /// [`Cache`]: struct.Cache.html /// [`Entry`]: enum.Entry.html pub struct VacantEntry<'a, K: 'a, V: 'a> { cache: &'a mut Cache<K, V>, key: K, kind: VacantKind, } impl<'a, K: 'a + fmt::Debug, V: 'a + fmt::Debug> fmt::Debug for VacantEntry<'a, K, V> { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { f.debug_struct("VacantEntry") .field("key", self.key()) .field( "remembered", &if let VacantKind::Ghost(_) = self.kind { true } else { false }, ) .finish() } } impl<'a, K: 'a, V: 'a> VacantEntry<'a, K, V> { /// Gets a reference to the key that would be used when inserting a value /// through the `VacantEntry`. /// /// # Examples /// /// ``` /// use cache_2q::{Cache, Entry}; /// /// let mut cache: Cache<&str, u32> = Cache::new(8); /// /// if let Entry::Vacant(v) = cache.entry("poneyland") { /// assert_eq!(v.key(), &"poneyland"); /// } else { /// panic!("Entry should be vacant"); /// } /// ``` pub fn key(&self) -> &K { &self.key } /// Take ownership of the key. /// /// # Examples /// /// ``` /// use cache_2q::{Cache, Entry}; /// /// let mut cache: Cache<String, u32> = Cache::new(8); /// /// if let Entry::Vacant(v) = cache.entry("poneyland".into()) { /// assert_eq!(v.into_key(), "poneyland".to_string()); /// } else { /// panic!("Entry should be vacant"); /// } /// ``` pub fn into_key(self) -> K { self.key } } impl<'a, K: 'a + Eq, V: 'a> VacantEntry<'a, K, V> { /// Sets the value of the entry with the VacantEntry's key, /// and returns a mutable reference to it. /// /// # Examples /// /// ``` /// use cache_2q::{Cache, Entry}; /// /// let mut cache: Cache<&str, u32> = Cache::new(8); /// /// if let Entry::Vacant(o) = cache.entry("poneyland") { /// o.insert(37); /// } else { /// panic!("Entry should be vacant"); /// } /// assert_eq!(*cache.get("poneyland").unwrap(), 37); /// ``` pub fn insert(self, value: V) -> &'a mut V { let VacantEntry { cache, key, kind } = self; match kind { VacantKind::Ghost(idx) => { cache.ghost.remove(idx); if cache.frequent.len() + 1 > cache.max_frequent { cache.frequent.pop_back(); } cache.frequent.push_front(CacheEntry { key: key, value: value, }); &mut cache.frequent[0].value } VacantKind::Unknown => { if cache.recent.len() + 1 > cache.max_recent { let old_key = cache.recent.pop_back().unwrap().key; if cache.ghost.len() + 1 > cache.max_ghost { cache.ghost.pop_back(); } cache.ghost.push_front(old_key); } cache.recent.push_front(CacheEntry { key: key, value: value, }); &mut cache.recent[0].value } } } } /// An iterator over the entries of a `Cache`. /// /// This `struct` is created by the [`iter`] method on [`Cache`]. See its /// documentation for more. /// /// [`iter`]: struct.Cache.html#method.iter /// [`Cache`]: struct.Cache.html pub struct Iter<'a, K: 'a, V: 'a> { inner: iter::Map< iter::Chain<vec_deque::Iter<'a, CacheEntry<K, V>>, vec_deque::Iter<'a, CacheEntry<K, V>>>, fn(&'a CacheEntry<K, V>) -> (&K, &V), >, } impl<'a, K: 'a, V: 'a> Clone for Iter<'a, K, V> { fn clone(&self) -> Self { Iter { inner: self.inner.clone(), } } } impl<'a, K: 'a + fmt::Debug, V: 'a + fmt::Debug> fmt::Debug for Iter<'a, K, V> { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { f.debug_list().entries(self.clone()).finish() } } impl<'a, K: 'a, V: 'a> Iterator for Iter<'a, K, V> { type Item = (&'a K, &'a V); fn next(&mut self) -> Option<Self::Item> { self.inner.next() } fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() } } #[derive(Debug, Copy, Clone, PartialEq, Eq)] enum VacantKind { Ghost(usize), Unknown, } #[derive(Debug, Copy, Clone, PartialEq, Eq)] enum OccupiedKind { Recent(usize), Frequent(usize), } #[cfg(test)] mod tests { use super::Cache; #[test] fn cache_zero_size() { let mut cache = Cache::new(8); for _ in 0..1024 { cache.entry(()).or_insert_with(|| ()); } } #[test] fn get_borrowed() { let mut cache = Cache::new(8); cache.entry("hi".to_string()).or_insert(0); cache.entry("there".to_string()).or_insert(0); assert_eq!(*cache.get("hi").unwrap(), 0); } }