Sunday, July 17, 2016

Code Learnability vs. Feature Addability

I'd like to talk about made up words.

No, really I'd like to talk about the tension between making a code base easy to learn vs. the ease of adding things to it, specifically about web applications.

Imagine you had a slider control for your code that went from "easy to learn" to "easy to maintain".

When you slide the control all the way over to "easy to learn", most of the classes disappear along with all of the interfaces and many if statements appear. Methods balloon in size and contain duplicate logic because there are so few classes to encapsulate it. It's very easy to trace data and logic through calls up and down the stack. Anyone reading the code will come across all of the decisions it makes. The reader won't have a good sense of why the code does what it does, though. The lack of little methods like DetermineRanking or classes like RankingEngine mean that such code lives all over the place.

At "easy to learn", you can give a new developer your codebase and they'll be productive very quickly with little mentoring. Need to add a new data field when adding a customer? Just find the giant AddCustomer method or click button event handler and change line 654. A quick bit of functional testing shows that more related logic lives down on line 1233.

Oops, the same logic appears in SaveCustomer and now you can add a customer with a new field but users can't update it. QA or, even worse, customer support opens a bug, new developer finds duplicate logic, copy, paste, fixed. Again and again.

In some organizations, this is totally acceptable to devs, managers and customers. They can hire less skilled, cheaper developers and undercut the competition. Their customers are probably buying the software for some cost center in their business, so spending as little as possible is the goal. Everyone here operates at the low end of some market, which might make sense at the moment. As the dev shop or the customer grows they'll try to level up the software they make or use.

(The field of Economics contains an idea that ideally every product exists at every quality and price point so that everyone can afford the version of a product that fits precisely with their income. If there were only shacks and mansions to live in you'd have to live in a shack until you can afford a mansion. Better to have a wide range of housing options, especially within a neighbourhood.)

I'll bet the development shop's employee turnover is pretty high, though. As soon as a dev learns a little more about development they look for a more advanced employer. Again, some companies accept this and keep hiring from the ever growing pool of junior developers, which is fine.

I'll also bet that successfully adding features takes weeks, including writing code and back and forth with QA. Such code is not unit testable, so people find all bugs during end to end manual or automated testing.

At the other end of the slider, "easy to maintain", classes and interfaces abound, if statements largely disappear, but the structure obfuscates the code's flow. Frameworks and libraries, like inversion of control (IOC) containers and request pipeline handlers, automatically set up actions and dependencies. This means that for the app to know what to do with a class or method you only have to put a specific interface or attribute on it.

The experienced developer's productivity goes way up and bugs go way down because of unit testability and the inherent design (e.g. code no longer allows the string "0" or "1" for values, it uses booleans). However, the major trade off is the learning curve and cognitive load of the code base. The concept count goes through the roof. With so many classes and seemingly magic behaviour, new developers need a lot of guidance with the design. That could be in person or in a recorded video or design docs.

(I recently experienced this myself looking at code samples that rely exclusively on IOC containers to resolve dependencies. Some containers use an easy to follow "map interface IFoo to class Foo" syntax, while others use "map all of Foo's interfaces to Foo". The latter makes it harder to find the thing that maps IFoo to Foo with Visual Studio's Find All References because IFoo doesn't appear in the mapping. I even found one IOC container with a convention-based mapping method like "map all classes in assembly X to the interfaces matching their names". This meant that neither the classes nor the interfaces appear in the container setup code. Unless you find the conference video or series of blog posts where the author goes from original code to the heavily refactored version, you can end up puzzling over the approaches you see.)

Adding features now takes days and involves mostly one way trips through QA.Production bug counts due to actual code problems go down.

The code now requires more experienced developers who demand higher pay. This causes the software to cost more. Customers are happy to pay, though, because the software "just works", which they need to keep their profit centers working. Turnover drops.

There is a joke (belief?) in programming that the more complicated and obscure the code the more job security you have because only you know how to update it. This depends on what makes the code complicated, though, and what the benefit is to the company. Are you using well documented but advanced libraries that do a lot of heavy lifting, or are you writing 1000 line methods of bit shifting code with single letter variables?

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