commit	84cc89dbdd177a1d193defb64a1f03ef9bf44e87	[log] [tgz]
author	Matthew Maurer <[email protected]>	Thu Mar 09 18:06:34 2023 +0000
committer	Automerger Merge Worker <[email protected]>	Thu Mar 09 18:06:34 2023 +0000
tree	b9732a1c26db90ebe03598eddae2c757483d6044
parent	2f562b2b5eee80c9affa15c60b17c281c020be66 [diff]
parent	22d8fee7a28ecca9faf8544abcb018333790b885 [diff]

tree: b9732a1c26db90ebe03598eddae2c757483d6044

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.

Rust version support

This crate supports Rust version 1.46 and later.

Crate features

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 hasher

If the std feature is disabled (for no_std) then the ahash dependency must be enabled.

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);
}