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extern crate weak_table;
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);
}
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