How much duplicated code do you tolerate? [closed]

Question

In a recent code review I spotted a few lines of duplicated logic in a class (less than 15 lines). When I suggested that the author refactor the code, he argued that the code is simpler to understand that way. After reading the code again, I have to agree extracting the duplicated logic would hurt readability a little.

I know DRY is guideline, not an absolute rule. But in general, are you willing to hurt readability in the name of DRY?

Answer 1

Personally, I prefer keeping code understandable, first and foremost.

DRY is about easing the maintenance in code. Making your code less understandable in order to remove repeated code hurts the maintainability more, in many cases, than having some repeated lines of code.

That being said, I do agree that DRY is a good goal to follow, when practical.

Answer 2

Very difficult to say in abstract. But my own belief is that even one line of duplicated code should be made into a function. Of course, I don't always achieve this high standard myself.

Answer 3

In general, no. Not for readability anyway. There is always some way to refactor the duplicated code into an intention revealing common method that reads like a book, IMO.

If you want to make an argument for violating DRY in order to avoid introducing dependencies, that might carry more weight, and you can get Ayende's opinionated opinion along with code to illustrate the point here.

Unless your dev is actually Ayende though I would hold tight to DRY and get the readability through intention revealing methods.

BH

Answer 4

I accept NO duplicate code. If something is used in more than one place, it will be part of the framework or at least a utility library.

The best line of code is a line of code not written.

Answer 5

Readability is one of the most important things code can have, and I'm unwilling to compromise on it. Duplicated code is a bad smell, not a mortal sin.

That being said, there are issues here.

If this code is supposed to be the same, rather than is coincidentally the same, there's a maintainability risk. I'd have comments in each place pointing to the other, and if it needed to be in a third place I'd refactor it out. (I actually do have code like this, in two different programs that don't share appropriate code files, so comments in each program point to the other.)

You haven't said if the lines make a coherent whole, performing some function you can easily describe. If they do, refactor them out. This is unlikely to be the case, since you agree that the code is more readable embedded in two places. However, you could look for a larger or smaller similarity, and perhaps factor out a function to simplify the code. Just because a dozen lines of code are repeated doesn't mean a function should consist of that dozen lines and no more.

Answer 6

As soon as you repeat anything you're creating multiple places to have make edits if you find that you've made a mistake, need to extend it, edit, delete or any other of the dozens of other reasons you might come up against that force a change.

In most languages, extracting a block to a suitably named method can rarely hurt your readability.

It is your code, with your standards, but my basic answer to your "how much?" is none ...