public Tuple2<R2, R1> swap() {
        return new Tuple2<R2, R1>(this.r2, this.r1);
    }
@Test
    public void testSwap() {
        Tuple2 tupleOld = new Tuple2(1, 2);
        Tuple2 tupleNew = tupleOld.swap();
        Assert.assertEquals(new Tuple2(2, 1), tupleNew);
    }