shift

static VALUE
fgdbm_shift(VALUE obj)
{
    struct dbmdata *dbmp;
    GDBM_FILE dbm;
    VALUE keystr, valstr;

    rb_gdbm_modify(obj);
    GetDBM2(obj, dbmp, dbm);
    keystr = rb_gdbm_firstkey(dbm);
    if (NIL_P(keystr)) return Qnil;
    valstr = rb_gdbm_fetch2(dbm, keystr);
    rb_gdbm_delete(obj, keystr);

    return rb_assoc_new(keystr, valstr);
}