The “don’t repeat yourself” principle is well established, but over-aggressive refactorizarions to extract common code are also widely known for creating hard to maintain code due to the introduction of tight coupling between components that should not be coupled. A passing resemblance between code blocks is reason enough to extract them away, even if that ends up breaking Liskov’s substitution principle.
To mitigate problems caused by DRY fundamentalisms, the “write everything twice” (WET) principle was coined. WET works by postponing aggressive refactorizarions, the kind that introduces complexity and couples unrelated code just because it bears some resemblance, by creating a rule of thumb where similar code blocks showing up twice in the code should not be refactored, and only code that shows up multiple times should be considered for this task. However, this rule ignores context and nuances, and can dissuade developers from cleaning up code.
So, where do you stand on the topic? How do you deal with duplicate code? Do you follow any specific rule of thumb?
- When writing new code: make a good faith attempt to DRY (obviously not fucking with Liskov in the process). First draft is very WET - deleting things is easiet at this stage anyway and accidentally prematurely DRYing causes headaches. Repeat the mantra “don’t let perfect be the enemy of good” to prevent impulsive DRYing.
- When maintaining existing code I wrote: Refactor to DRY things up where it’s clear I’ve made a conceptual misjudgement or oversight. Priority goes to whatever irritates me most in the moment rather than what would be most efficient.
- When altering other people’s code: Assume they had a reason to WET (if you’re lucky, read the docs that discuss the decision) but be a little suspicious and consider DRYing things up if it seems like a misjudgement or oversight. Likely realise 50% of the way through that this is going to take much longer and be way more painful than you hoped because of some esoteric bullshit compatibility issue. Curse yourself for not letting sleeping dogs lie but still start engaging in sunk cost fallacy.
- When reviewing PRs: Attempt to politely influence the writer to DRY it up but don’t take too much offence to WET if it has a decentish reason in context. Throw in an inline one-liner to not make other maintainers question their sanity or competence when they realise they’re reading duplicate code. Also to more reliably establish git blame rather than blaming the next poor fool who comes along and make a minor reformatting revision across the file. Include a date so that someone can stumble across it in 10 years as an archaeological curiosity and their own personal esoteric bullshit compatibility issue.
- Long term maintenance: Live with your irritatingly damp mouldy code. There’s new code that needs to be written!