The KISS and RoP Trade-off

I’ve discussed trade-offs in software before. The more you delve into the world of design and engineering, the more evident it becomes that trade-offs are an underlying principle to rule all principles. There is no perfect software; there is no perfect solution. My aim to strive for the best software, however, led to me choose this topic to discuss.

I intended to keep it simple and focus on KISS (Keep it Simple, Stupid), which claims that a simple, straightforward solution is the better solution. But after listening to a podcast about design principles by SoftwareArchitekTOUR*, I was forced to make a trade-off between a simple blog post and a more powerful, generic one. Specifically, they mentioned the RoP (Rule of Power) principle or GP (generalization principle), which states “that a more generic solution is better than a specific one”.

You will never produce a perfect design… but you can’t typically have both [KISS and RoP]. Either it is simple and specific, or it’s very generic and flexible and therefore no longer simple but rather has a certain degree of complexity. You can typically only strive for a Pareto-Optimal Solution.”

Christian Rehn (translated from German), SoftwareArchitekTOUR Episode 60, 14:30 – 15:45

Rehn says it’s a balancing act, and neither principle is either right nor wrong. The concept of a Pareto-optimal solution is rather simple: find a solution that is better in at least one aspect, but at least as good in every other aspect. As Rehn says, you have to ask yourself what works best in your situation. What is the best compromise?

So what does this mean when choosing between KISS and RoP? Like any new concept or principle, both should be practiced in isolation, with small projects. It is only with this basic experience that you can learn how to make these decisions in more complicated systems.

In learning design principles, I have refactored code in order to make it adhere to a design pattern or principle. When new situations arise, the old solution may no longer hold water. But each time, the code was kept as simple as possible given the requirements. The Pareto-optimal solution is the simplest solution that provides the required functionality. This leads me to conclude that KISS trumps RoP, especially considering other principles such as YAGNI, which strives to prevent the code smell of unneeded complexity. But on the other hand, the simplest solution in which every class does a single, specific thing, would itself become extremely verbose, violating DRY in particular.

Determining how to make these trade-offs is an art and comes with experience. In the mean time, I plan to keep my code as simple as possible and add complexity and generalizations as needed.

* This podcast is only available in German, but the English show notes explain the topics of the podcast in detail.

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