rust/src/comp/syntax/util/interner.rs

// An "interner" is a data structure that associates values with uint tags and
// allows bidirectional lookup; i.e. given a value, one can easily find the
// type, and vice versa.
import std::ivec;
import std::map;
import std::map::hashmap;
import std::map::hashfn;
import std::map::eqfn;
import std::option;
import std::option::none;
import std::option::some;

type interner[T] =
    {map: hashmap[T, uint],
     mutable vect: T[],
     hasher: hashfn[T],
     eqer: eqfn[T]};

fn mk[@T](hasher: hashfn[T], eqer: eqfn[T]) -> interner[T] {
    let m = map::mk_hashmap[T, uint](hasher, eqer);
    ret {map: m, mutable vect: ~[], hasher: hasher, eqer: eqer};
}
fn intern[@T](itr: &interner[T], val: &T) -> uint {
    alt itr.map.find(val) {
      some(idx) { ret idx; }
      none. {
        let new_idx = ivec::len[T](itr.vect);
        itr.map.insert(val, new_idx);
        itr.vect += ~[val];
        ret new_idx;
      }
    }
}
fn get[T](itr: &interner[T], idx: uint) -> T { ret itr.vect.(idx); }