My impression is that since it returns `this`, multiple invocations can be chained like `obj.add(X).add(Y).add(Z)`. However the test on line 92 fails and if I do a `writeln`, only "p1" and "p2" records show up.
What am I missing here? Thanks in advance.[1] https://github.com/bahmanm/d-etudes/blob/master/source/e002/models.d
