Crates.io | weak-table |
lib.rs | weak-table |
version | 0.3.2 |
source | src |
created_at | 2018-03-05 19:08:25.954147 |
updated_at | 2021-12-01 19:40:03.682836 |
description | Weak hash maps and sets |
homepage | |
repository | https://github.com/tov/weak-table-rs |
max_upload_size | |
id | 53981 |
size | 161,078 |
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);
}