// magic cast
static <A> A cget(O c, S field) {
  O o = getOpt(c, field);
  if (o instanceof Concept.Ref) ret (A) ((Concept.Ref) o).get();
  ret (A) o;
}

static <A> A mapMethodLike cget(S field, O c) {
  ret cget(c, field);
}