variable.c:789
static VALUE
generic_ivar_get(obj, id)
    VALUE obj;
    ID id;
{
    st_table *tbl;
    VALUE val;

    if (generic_iv_tbl) {
      if (st_lookup(generic_iv_tbl, obj, (st_data_t *)&tbl)) {
	if (st_lookup(tbl, id, &val)) {
	  return val;
	}
      }
    }

    rb_warning("instance variable %s not initialized", rb_id2name(id));
    return Qnil;
}
