An iterator over attributes, as GCC scalarizes it the code is equivalent

An iterator over attributes, as GCC scalarizes it the code is equivalent
to hand-written code that doesn't use a structure:

attr_iterator ai;
FOR_ATTRS (store, entry, &ai)
  {
    do_something (ai.name, ai.type);
    switch (ai.type)
    {
      case ATTR_STRING:   ai.as_string; break;
      case ATTR_INT:      ai.as_int;    break;
      case ATTR_LOCALIDS: iterate (ai.as_numlist); break;
    }
  }