@Override
  public SelArray assignOps(SelOp op, SelType rhs) {
    if (op == SelOp.ASSIGN) {
      SelTypeUtil.checkTypeMatch(this.type(), rhs.type());
      this.val = ((SelArray) rhs).val; // direct assignment
      return this;
    }
    throw new UnsupportedOperationException(
        this.type() + " DO NOT support assignment operation " + op);
  }
@Test
  public void testAssignOps() {
    one.assignOps(SelOp.ASSIGN, new SelArray(1, SelTypes.STRING_ARRAY));
    assertEquals("STRING_ARRAY: [null]", one.type() + ": " + one);
  }