Don't DRY Your Code Prematurely
Don't DRY Your Code Prematurely
This is another post in our Code Health series. A version of this post originally appeared in Google bathrooms worldwide as a Google Tes...
DRY = Don't repeat yourself
You're viewing a single thread.
First off, I generally don't worry about DRY until there are 3 instances, not 2. With only 2, it's really easy to over-generalize or have a bad structure for the abstraction.
But otherwise, I disagree with the article. If it's complicated enough to bother abstracting the logic, the worst that can happen in the above situation is that you just duplicate that whole class once you discover that it's not the same. And if that never happens, you only have 1 copy to maintain.
The code in the article isn't complicated enough that I'd bother. It even ends up with about the same number of lines of code, hinting that you probably haven't simplified things much.
I personally factorize as soon as there are two copies, but do not hesitate to inline the code and redo the abstraction when there is a 3rd use if it doesn't fit. I find it much easier to inline and re-abstact a bad abstraction, than check if two copies are indeed identical.
The exception is business logic. Usually I want all of them to be dupplicates because there is a very high chance that it's just accidental that part of the logic is similar. I take great care to have good primitives but the actual business logic that glue those primitives together is written as many time as needed.
Yeah, I'm reminded of how Germanic languages used to have singular, dual and plural. If we'd still had dual, we'd probably also be talking about not abstracting until we actually have a plural.
The code in the article isn't complicated enough that I'd bother. It even ends up with about the same number of lines of code, hinting that you probably haven't simplified things much.
I think it's a good example of the problem though. People take that same idea and apply it too liberally. The point isn't that specific code, it's about not apply DRY to code that's coincidentally identical.
But otherwise, I disagree with the article. If it's complicated enough to bother abstracting the logic, the worst that can happen in the above situation is that you just duplicate that whole class once you discover that it's not the same. And if that never happens, you only have 1 copy to maintain.
That's... Not at all true in practice. What often happens with these "DRY" abstractions when they've been improperly applied is you end up with an inheritance hierarchy or a crazy template or some other thing. You're really lucky if you can just copy some code and find your way out of the weeds.
There are plenty of bad abstractions in the wild and novices applying DRY is a common source of them.
There are plenty of bad abstractions in the wild and novices applying DRY is a common source of them.
You're both saying the same thing though. Novices aggressively apply DRY the moment a second bit of identical code appears, while experienced developers often wait for a third copy and then think about whether DRY fits.
That said, I think "don't apply DRY too aggressively is the whole point of this discussion, and the person you're replying to was kind of needlessly disagreeing.
You're both saying the same thing though.
We're not quite saying the same thing though because ...
It's not a 2 vs 3 issue. You can have an infinite number of instances of the same logic and it still not be a case for generalization because it's not actually general ... it's just an infinitely large program. You can also have two copies of the same code that should be reduced because they are general (e.g. you have the exact same algorithm for generating a UUID copied into two different spots). If you're thinking about it in terms of quantity you're already doing it wrong.
It's not fixable by "just" copying something.
Those two points are really important points.
If you're thinking about it in terms of quantity you're already doing it wrong.
You're ignoring that simple principles make great guidelines for not overthinking things.
And you're doing so in the context of an article about the dangers of overthinking things.
You've over thought an article about the dangers of overthinking, while alienating potential collaborators with a condescending tone.
You're coming across like one of the rookies who need this warning.
Consider counting to three, before applying DRY. It works.
You're ignoring that simple principles make great guidelines for not overthinking things.
Name some great "simple principles;" everything has nuance and trying to distill things into "well it's just this simple principle..." is a great way to get catastrophic mistakes.
And you're doing so in the context of an article about the dangers of overthinking things.
You did not understand the point of that article if you think it's about the dangers of over thinking. The issue with DRY is that it leads to making refractors without thinking about whether or not the refractor makes sense. That's the exact issue the author is warning about, think about whether or not dry makes sense.
That has ABSOLUTELY NOTHING to do with how many times the code has been repeated. It has everything to do with why it's repeated.
You're coming across like one of the rookies who need this warning.
I'll toss that right back at you bud. You don't seem to understand the actual problem.
Consider counting to three, before applying DRY. It works.
It does not. I literally fixed a bug today because the same algorithm, doing the same job, was used in two different places formatted differently, exactly two, and they got out of sync resulting in memory corruption.
That's what DRY is intended to fix. Not "I have three [or whatever number] things doing the same thing so now I should DRY this code up", I've seen HORRIBLE refractors from DRY applied to 3 things; absolute spaghetti inheritance hierarchies that were "DRY."
I hate talking about DRY because it's this principle that so many people think "oh I'm doing it correctly; I'm doing good things!" and they actually make the code SO MUCH worse.
EDIT: Here's exact quotes from the article (emphasis theirs):
Applying DRY principles too rigidly leads to premature abstractions that make future changes more complex than necessary. Consider carefully if code is truly redundant or just superficially similar. While functions or classes may look the same, they may also serve different contexts and business requirements that evolve differently over time. Think about how the functions’ purpose holds with time, not just about making the code shorter.