I read your second paragraph as vagueness is fine, which sort of makes DRY not a helpful principle but a handwavy problem statement with no clear anything. As

I read your second paragraph as vagueness is fine, which sort of makes DRY not a helpful principle but a handwavy problem statement with no clear anything. As in most vague problems, two extreme solutions (join vs dup) are a wrong way to think about it. I have some ideas on how to turn this into a spectrum in a nearby comment. I think it is important because DRY-flavored problem is basically the thing you meet in the code most. At least that is my experience, as a guy who hates typing out and rediscovering knowledge from slightly different code blocks or tangled multi-path procedures and refactoring these — either in hope that nothing breaks in multiple places, or that you won’t forget to update that one semi-copy. I’m programming for a very long time and seemingly no one ever even tried to address this in any sensible way.