DRY = Don’t repeat yourself
I’ve always understood DRY to be about not duplicating concepts rather than not duplicating code.
In the example here, you have separate concepts that happen to use very similar code right now. It’s not repeating yourself as the concepts are not the same. The real key is understanding that, which to be fair, is mentioned in the article.
IMO, this is where techniques like Domain-Driven Design really shine as they put the business concepts at the forefront of things.
IMO, this is where techniques like Domain-Driven Design really shine as they put the business concepts at the forefront of things.
Do you have a resource on where to learn DDD? I feel like I never understood the concept well.
As already mentioned, the blue book by Evic Evans is a good reference, but it’s a ittle dry. Vaughn Vernon has a book, “Implementing Domain-Driven Design” that is a little easier to get into.
Personally, I found that I only really grokked it when I worked on a project that used event-sourcing a few years back. When you don’t have the crutch of just doing CRUD with a relational database, you’re forced to think about business workflows - and that’s really the key to properly understanding Domain-Driven Design.
Yeah for me the understanding really came when working in a federated GraphQL API. Each team had us own little slice of overall object graph, and overlap / duplication / confusing objects across the whole domain were a lot easier to see in that environment.
“Domain Driven Design” by Eric Evans, aka the blue book. It’s very dense however and very object oriented, but concepts apply even if you dont work with object oriented languages, you might have to do more footwork to get from a domain model to services that adhere to the model.
“Head first Software Architecture” might be an easier on ramp and touches on simmiliar concepts.
That’s how DRY is described in Pragmatic Programmer, where DRY was first coined. They’re clear that just because code look similar, doesn’t necessarily mean it’s the same.
It should be about concepts but it’s more often applied to duplicate algorithms by inexperienced people (which is a huge mistake).
yes, this is exactly what you have to think about. the left example even aknowledges that deadlines for “tasks” might be different from deadlines for “payments”, which suggests that the abstraction is not “clean”.
I guess I never thought of it like this, but it resonates.
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.
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 they are really important points.
Another older blog post saying the same: https://sandimetz.com/blog/2016/1/20/the-wrong-abstraction
