Why do so many developers get DRY wrong?

Dan Abramov’s excellent Goodbye, Clean Code post (wherein he learned it was wise to walk back an overzealous refactoring) reminded me of somethingDave Thomas said when we interviewed him and Andy Hunt about the Pragmatic Programmer’s 20th edition:

We’ve also looked at the reaction to various parts of the book, and discovered that we weren’t really communicating as well as we thought we were some of the ideas that we had. A classic one is DRY. DRY has come to mean “Don’t cut and paste”, butthe original “Don’t repeat yourself” was nothing to do with code, it was to do with knowledge. So we’ve had to go through and update that…[:headphones:]

Young Dan’s misguided refactoring began the same way so many of ours do. With these four little words:

But it was repetitive.

I’m not picking on Dan here, by any means. I’ve fallen into this trap countless times in my career and I even heard Feross talking about the same thing on a recentJS Party episode about refactoring.

This got me thinking: why do we so often get DRY wrong? I have a few thoughts on the subject…

Names really matter

One of the reasons why DRY is a thing that most of us think about is it’s so easy to remember! It’s a great acronym. Except.

“Don’t Repeat Yourself” as a name is, itself, a leaky abstraction .

Lets refer back to what Dave Thomas said above:

the original “Don’t repeat yourself” was nothing to do with code, it was to do with knowledge

The trouble with DRY is it has no reference to the knowledge bit, which is arguablythe most important part! I can’t blame the guys for going with DRY, though. DRK just doesn’t have the same ring to it…

We’re good at pattern matching

Humans are pattern matchers. Developers, especially so.

The more code you write (and read), the more patterns just pop out of your editor and stare you in the face.

I don’t know about you, but I appreciate patterns so much that I want to pull them out, give them a name, (the best ones even get their own file), and refer to them.

Lowest common refactoring

Another reason why we’re so eager to DRY up our code is that itfeels so goodto do it.

Think back to your early days of programming. You likely copy/pasted code from one area of your program to another. You did this out of necessity, because subroutines/functions/etc just weren’t a tool you knew how to wield yet.

Once you eeked out enough XP to reach Level 2 , condensing that copy pasta down felt amazing . Suddenly your code looked more impressive. Efficient! Clean!Simple! This is like the lowest common form of refactoring. But it feels good …

Those are a few of my thoughts on the matter. And to be clear, I’m not pro code duplication. I’m a Rule of Three person. I just find it interesting thatone of the most widely cited best practices in software is so misunderstood.

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