sS getStringOpt(Map map, O key) {
  ret map == null ? null : optCast(S, map.get(key));
}

sS getStringOpt(L l, int idx) {
  ret optCast(S, get(l, idx));
}

sS getStringOpt(O o, O key) {
  if (o instanceof Map) ret getStringOpt((Map) o, key);
  if (key instanceof S)
    ret optCast(S, getOpt(o, (S) key));
  throw fail("Not a string key: " + getClassName(key));
}

sS mapMethodLike getStringOpt(S key, O o) {
  ret getStringOpt(o, (O) key);
}