How Should This Work?

An Object Design Epiphany

Successful software projects are always changing. Every new requirement comes with the responsibility to determine exactly how the new or changed behaviors will be codified into the system, often in the form of objects.

For the longest time, when I had to change a behavior in a codebase I followed these rough steps:

1. Locate the behavior in the application’s code, usually inside some class (hopefully just one)
2. Determine how it needed to be adjusted in order to meet the new requirements
3. Write one or more failing tests that the class must satisfy
4. Update the class to satisfy the tests

Simple, right? Eventually I realized that this simple workflow leads to messy code.

The temptation when changing an existing system is to implement the desired behavior within the structure of the current abstractions. Repeat this without adjustment, and you’ll quickly end up contorting existing concepts or working around legacy behaviors. Conditionals pile up, and shotgun surgery becomes standard operating procedure.

One day, I had an epiphany. When making a change, rather than surveying the current landscape and asking “How can I make this work like I need?”, take a step back, look at each relevant abstraction and ask, “How should this work?”.

The names of the modules, classes and methods convey meaning. When you change the behavior within them in isolation, the cohesion between those names and the implementation beneath them may begin to fray.

If you are continually ensuring that your classes work exactly as their names imply, you’ll often find that the change in behavior you seek is better represented by adjusting the landscape of types in your system. You may end up introducing a collaborator, or you might simply need to tweak the name of a class to align with it’s new behavior.

This type of conscientiousness is difficult to apply rigorously, but like any habit it can be built up over time. Your reward will be a codebase maintainable years into the future.