| commit | 127e16d338f7532478aac785ef70987ab5ef2c95 | [log] [tgz] |
|---|---|---|
| author | James Farrell <jamesfarrell@google.com> | Wed Sep 18 20:37:08 2024 +0000 |
| committer | James Farrell <jamesfarrell@google.com> | Wed Sep 18 20:37:08 2024 +0000 |
| tree | c4cae01b9f1c3ddaced8853a00dde8339575f85b | |
| parent | 095b9219ab07e0cb7a51946a730735fdc5d35a5a [diff] |
Migrate 26 crates to monorepo tokio-util tower tower-layer tower-service tracing tracing-attributes tracing-core tracing-subscriber try-lock tungstenite twox-hash ucd-trie unicode-bidi unicode-normalization unicode-segmentation unicode-width unsafe-libyaml userfaultfd utf-8 uuid weak-table webpki which winnow x509-cert xml-rs Bug: http://b/339424309 Test: treehugger Change-Id: I8ae91f7ddade6107facf2e7f045704aefa6312da
This crate defines several kinds of weak hash maps and sets. See the full API documentation for details.
This crate supports Rust version 1.46 and later.
weak-table is built with the std feature, which enables functionality dependent on the std library, enabled by default. Optionally, the following dependency may be enabled:
ahash: use ahash’s hasher rather than the std hasherIf the std feature is disabled (for no_std) then the ahash dependency must be enabled.
Here we create a weak hash map and demonstrate that it forgets mappings whose keys expire:
use weak_table::WeakKeyHashMap; use std::sync::{Arc, Weak}; let mut table = <WeakKeyHashMap<Weak<str>, u32>>::new(); let one = Arc::<str>::from("one"); let two = Arc::<str>::from("two"); table.insert(one.clone(), 1); assert_eq!( table.get("one"), Some(&1) ); assert_eq!( table.get("two"), None ); table.insert(two.clone(), 2); *table.get_mut(&one).unwrap() += 10; assert_eq!( table.get("one"), Some(&11) ); assert_eq!( table.get("two"), Some(&2) ); drop(one); assert_eq!( table.get("one"), None ); assert_eq!( table.get("two"), Some(&2) );
Here we use a weak hash set to implement a simple string interning facility:
use weak_table::WeakHashSet; use std::ops::Deref; use std::rc::{Rc, Weak}; #[derive(Clone, Debug)] pub struct Symbol(Rc<str>); impl PartialEq for Symbol { fn eq(&self, other: &Symbol) -> bool { Rc::ptr_eq(&self.0, &other.0) } } impl Eq for Symbol {} impl Deref for Symbol { type Target = str; fn deref(&self) -> &str { &self.0 } } #[derive(Debug, Default)] pub struct SymbolTable(WeakHashSet<Weak<str>>); impl SymbolTable { pub fn new() -> Self { Self::default() } pub fn intern(&mut self, name: &str) -> Symbol { if let Some(rc) = self.0.get(name) { Symbol(rc) } else { let rc = Rc::<str>::from(name); self.0.insert(Rc::clone(&rc)); Symbol(rc) } } } #[test] fn interning() { let mut tab = SymbolTable::new(); let a0 = tab.intern("a"); let a1 = tab.intern("a"); let b = tab.intern("b"); assert_eq!(a0, a1); assert_ne!(a0, b); }