static <A, B, C> Map<B, C> lambdaMapLike mapToWeakHashMap(IF1<A, Pair<B, C>> f, Iterable<A> l) {
  Map<B, C> map = weakHashMap();
  fOr (A o : l) {
    Pair<B, C> p = callF(f, o);
    mapPut(map, p.a, p.b);
  }
  ret map;
}

static <A, B, C> Map<B, C> lambdaMapLike mapToWeakHashMap(Iterable<A> l, IF1<A, Pair<B, C>> f) {
  ret mapToWeakHashMap(f, l);
}

Began life as a copy of #1024294