WeakPair primitive ?

[Sean Eagan]

Would a WeakPair primitive be useful...

let wp = new WeakPair(key, value);
...
if(wp.hasKey(key)) {
  foo(wp.value());
}

WeakMap could be built on top of this primitive:

class WeakMap {
  constructor() {
    private pairs = new Set;
    private getPair = function(key) {
      for(i of private(this).pairs.iterator()) {
        if(i.hasKey(key)) return i;
      }
      return undefined;
    }
  }
  get(key) {
    let pair = private(this).getPair(key);
    return pair ? pair.value() : undefined;
  }
  has(key) {
    return !!private(this).getPair(key);
  }
  set(key, val) {
    if(!isObject(key)) throw new Error;
    let pair = private(this).getPair(key);
    let pairs = private(this).pairs;
    if(pair) {
      pairs.delete(pair);
    }
    pairs.add(new WeakPair(key, value));
  }
  delete(key) {
    let pair = private(this).getPair(key);
    if(pair) {
      let pairs = private(this).pairs;
      pairs.delete(pair);
    }
  }
}

Are there other useful abstractions that could be built on top of
WeakPair, beyond WeakMap ?

Thanks,
Sean Eagan