It was on one of those rare occasions: We we’re starting a new system from scratch. The excitement was palpable. As some devs(myself included) started using TDD, some other where busy trying to figure out an architecture to hold everything in place. We decide to hold some code reviews to keep everyone on the loop. And that’s how the clash happened. I was astonished when another developer suggested that our code wasn’t generic and so it was unable to cope with the changing requirements. It was true that our code wasn’t overly generic. But it was flexible.
The quest for adaptability
Adaptability is a desired trait in software because it helps us cope with changes without having to rewrite everything from scratch. Typically you deal with this by 1) making the software so generic that there’s no need to change it, just configure it and you are done, or 2) by making the code easy to change.
The difference between the 2 strives on the abstraction level.
Generic code embraces the idea that you can have one code base to rule them all. All you need to do is make it highly reusable. The key is to work at a high level of abstraction. Doing this has the benefit that a lot of customers can use the system as long as they don’t have specific requirements. Let’s consider an Agenda application. You could use an AgendaItem to represent anything from an appointment with your boss to a reminder to pick the laundry before sunday. So let’s say you want to introduce project management. How would you tackle that? You could modify the AgendaItem to include another AgendaItems. So now every AgendaItem can represent an appointment, a reminder or a project. Can you see what the problem is? By working at a higher level of abstraction you can represent a lot of the stuff that can be put on an Agenda but this will become increasingly harder to maintain as changes required by the different concepts it represents will force the AgendaItem object to grow complex over time. Even so you’ll be fine if you don’t need to manage projects or if you create a list somewhere else to relate certain AgendaItems to a project.
On the other hand of the adaptability spectrum, we have flexible code. Flexible code in this context means code that is easy to change to accommodate new features.
The big question
So let’s say you are starting a new project, should you go for a Generic or Flexible code base? Well… it depends. Are you working on a Line Of Business application? Are you making a framework for others to use?
On a Line Of Business application
There’s 2 kinds of code: business specific and what I call plumbing code.
Business specific code is the code we are paid to write. It adds value to the business. It contains it’s particular rules. The business doesn’t care about the database choice, the technology stack or the OS on which the application runs. And the code that contains their rules and logic shouldn’t either. Don’t be afraid to model your objects to reflect your specific business even if it’s a bit different from the rest of the industry. This code is no meant to be reused outside your application.
Plumbing code refer to all the code that is common in almost every application: things like mail sender objects, ORM, frameworks… that sort of stuff. Void of logic, highly reusable.
A LOB application contains both kinds of code, but the plumbing code must serve the needs of the business code.
On an application framework
The trap of reusability
The problem arise when we want to reuse everything on a LOB application; that’s a crazy idea! The moment you decide to reuse the business specific code, you force yourself to start thinking on a higher level of abstraction thus leading to a very generic code and as we have already seen, that makes it hard to implement specific business rules. Do not fall into the trap that everything has to be reusable. Odds are that the next project you work on the same domain, you won’t be able to reuse your domain objects due to the specific client/business rules. When it comes to LOB applications, is the knowledge and not the business specific code what’s reusable.
If you are working on a LOB application, go for a generic style on the plumbing code, but take a flexible approach for the business specific code, that is do not go too abstract on this. If you are working on an Restaurant application, don’t create a “dish” object with an ingredients collection that represents everything you can serve there. Instead make explicit representations for each dish. Is that an Italian restaurant? Chinese? Thai? Then make a “spaghetti” object, or a “dumpling” object. They all may inherit from a “dish” object and contain an ingredients collection but they are not generic dishes. They are the restaurant dishes, the business products, and you want to identify them as that. Don’t be afraid to be specific.
This all may sound like common sense and it is! It’s just that in my experience, common sense is not always common practice.
Let me know your thoughts.