commit	35a2c1fdb55b17c76f64a2265ff08b80f68411b5	[log] [tgz]
author	Joel Galenson <jgalenson@google.com>	Wed Dec 15 16:02:06 2021 +0000
committer	Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>	Wed Dec 15 16:02:06 2021 +0000
tree	db428e02daefd369d8c754a70557de3b39686571
parent	e62de8e6798acf87fe33c14aa1e61e228def35c9 [diff]
parent	93d924b9bab5b33fa2d3af0a2695e55dfa43f228 [diff]

tree: db428e02daefd369d8c754a70557de3b39686571

README.md

weak-table: weak hash maps and sets for Rust

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.

Examples

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);
}