variable.c:1372
void*
rb_mod_const_at(mod, data)
    VALUE mod;
    void *data;
{
    st_table *tbl = data;
    if (!tbl) {
	tbl = st_init_numtable();
    }
    if (RCLASS(mod)->iv_tbl) {
	st_foreach(RCLASS(mod)->iv_tbl, sv_i, (st_data_t)tbl);
    }
    return tbl;
}
