svoid test_optOutParam() {
  embedded void bla(int i, O... _) {
    optOutParam(_, out := str(i));
  }
  
  bla();
  new Var v;
  bla(5, out := v);
  assertEqualsVerbose(5, v!);
  bla(10, litmapparams(out := v));
  assertEqualsVerbose(10, v!);
}