commit | 44d8e122bb3bedd1fb323c2e021c27a6ed36f794 | [log] [tgz] |
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author | android-build-team Robot <android-build-team-robot@google.com> | Sun Feb 21 00:06:40 2021 +0000 |
committer | android-build-team Robot <android-build-team-robot@google.com> | Sun Feb 21 00:06:40 2021 +0000 |
tree | f32d89028ab9efbc8f60d4a24af0f7f26f270740 | |
parent | 8a9cbd3453d964c1002ccf8f99474de765650216 [diff] | |
parent | e62de8e6798acf87fe33c14aa1e61e228def35c9 [diff] |
Snap for 7160059 from e62de8e6798acf87fe33c14aa1e61e228def35c9 to sc-release Change-Id: I137724008d733e5d9a048fde5f95a2c1e7486749
This crate defines several kinds of weak hash maps and sets. See the full API documentation for details.
This crate supports Rust version 1.32 and later.
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); }