prepare_ivar_name(mrb_state *mrb, mrb_sym sym)
{
  sym = prepare_name_common(mrb, sym, "@", NULL);
  mrb_iv_name_sym_check(mrb, sym);
  return mrb_symbol_value(sym);
}
prepare_ivar_name(mrb_state *mrb, mrb_sym sym)
{
  sym = prepare_name_common(mrb, sym, "@", NULL);
  mrb_iv_name_sym_check(mrb, sym);
  return mrb_symbol_value(sym);
}