commit | 3f9b4dcdddbffc850f58568b6d0c58f3aa2a1b87 | [log] [tgz] |
---|---|---|
author | David LeGare <legare@google.com> | Fri Mar 04 02:06:26 2022 +0000 |
committer | Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com> | Fri Mar 04 02:06:26 2022 +0000 |
tree | 93f36fb91d268cdae444791dbbdcc6bd50de9034 | |
parent | 36edcf7680eebed7193d1f8da65a2e4099606607 [diff] | |
parent | 0a3ad2af3d278464a330f0d2a111aaf052b046c5 [diff] |
Update weak-table to 0.3.2 am: 77e4bb9dcd am: 0a3ad2af3d Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/weak-table/+/2005833 Change-Id: Ibbd47050f040c884679eb89fbd516ba9ab3f87bf
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); }