Coming Up for Air

Chesterton's Fence and the Software Developer

Recently at work, we found an odd scenario with a REST (-ish ;) endpoint from another team: If the request provided a list of, say, 11 IDs in the query string, the system would only return information on the first 10 of them, silently dropping anything over that seemingly odd limit. The initial reaction was of, course, "Well, let’s just increase the limit." To be honest, I had the same reaction, but then I remembered one of my favorite quotes, known as Chesteron’s Fence:

In the matter of reforming things, as distinct from deforming them, there is one plain and simple principle; a principle which will probably be called a paradox. There exists in such a case a certain institution or law; let us say, for the sake of simplicity, a fence or gate erected across a road. The more modern type of reformer goes gaily up to it and says, "I don’t see the use of this; let us clear it away." To which the more intelligent type of reformer will do well to answer: "If you don’t see the use of it, I certainly won’t let you clear it away. Go away and think. Then, when you can come back and tell me that you do see the use of it, I may allow you to destroy it."

— G.K. Chesterton

Chesterton’s context, politics in Great Britain of the 1920s, is, of course, quite different from a software development shop almost 100 years later, but the message is still extremely appropriate: Before you go tearing things down or otherwise changing something you’ve found, you really need to understand not only what you’re changing, but why it was made that way in the first place.

In the case of this REST call, we should ask questions like

  • Are there system load concerns, such as memory or processing time?

  • Are there concerns about the on-the-wire response size?

  • Was there an explicit Product Management decision to set the limit this low for business reasons we don’t see reflected in the code?

And so on. Until we can answer those questions (or reasonably rule them out as relevant), we need to be very hesitant in making the change. Once we’ve explained the original developer(s) built that fence, then we can talk about ripping it down.

tags: General


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