Software, Work

What’s the difference between Simple and Stupid in interview code?

Kent Beck (I believe) said: “Do the simplest thing that works, not the stupidest”. What does that mean in the context of showcase code (i.e. code you have written as part of some kind of application process)?

Well firstly think of what the point of showcase code is. What is the reviewer looking for as part of the application process? They are looking for evidence of a train of thought or method of problem solving that chimes with the kind of thought processes that they think are effective. Ideally these would be the “best” processes but you have to accept that a lot of processes are about finding people who agree with what an organisation thinks is best practice rather than respecting originality and clever solutions. You should never try to tailor your showcase code to an organisation because it is too hard to double guess what someone is looking for. You can only express yourself as clearly as you can and hope that it fits well with what is being sought.

A good piece of showcase code will appropriately abstract the problem being set, illustrating the way the candidate finds solutions to problems. It will neither be too elaborate, abstracting too much of the problem, nor too literal, coding “between the lines” of the problem being set.

Let’s take an example. If the problem is to model a set of automobile configurations in an object then the problem set may explain that a car is sold with seat configurations of 2, 4 or 6. In my view a stupid solution would be to have a list of just 2, 4, 6. Clearly the reviewer is going to want some flexibility here, the solution should be able to deal with a new configuration of 5.

An obvious solution is to just model the number of seats as an integer value. You can encapsulate the data by providing an API that allows you query how many seats a configuration has and provide a way of setting that value in an immutable way (once a configuration is set then the number of seats it has is unlikely to change in the lifetime of the object, that’s simplicity not stupidity). This solution just exposes that a configuration has a number of seats which is an integer, which is logical. It is an entirely sensible solution that keeps it simple.

How might a nervous candidate overcomplicate this situation? Well the number of seats really is immutable unless the problem set says otherwise, you don’t need to supply a mutator. Similarly the number of seats is never going to be a Real number.

What about modelling the number of seats as a list of Seat objects? Well yes that works because the encapsulation should hide the implementation and the number of seats is now just the number of Seats in the Seat list. Domain-driven design fans might even say this is a better solution that an integer because it is a closer description of the domain. However I think that simplicity would tend to demand that until we have something else to model about a Seat (say, whether it has a seatbelt) then it is hard to justify having a class whose only purpose is to be counted in a list. For all the difference it makes I could put Turtle objects into the Seat list. In terms of showcase code using this technique actually gives the reviewer a bit of a headache because instead of just ticking the box and moving on the reviewer now has to ask whether the new level of abstraction introduced is valid or not, is it a good idea to have a class with no functionality or data? What if actually the seat configurations are better represented by enumerated constants? The effort of creating the Seat class is just wasted and has to be replaced.

This solution at least stays within the bounds of an existing paradigm. If a candidate starts to abstract wildly then reviewer is going to give up in frustration. If the candidate starts abstracting the model to the point where it could model a motorcycle or truck just as well as car then they have just failed the process. Unless the problem says something about having a motorcycle then you don’t want to see Vehicle With An Engine type classes. After all if you start to generalise then where do you stop? Sure you can model a motorcycle and a truck but why not a plane? Or a rocket?

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