To abstract or not to abstract

Posted by jordan_terry on March 24, 2021 · 1 min read

The longer I’ve written software the more I debate with myself about whether I should be adding an abstraction or not adding an abstraction.

Let us define an abstraction, it could be an interface, a trait, a protocol, or an abstract class. It is a structure that defines how a piece of code should interact with the outside. But not how that interaction is handled.

Abstractions are a powerful tool, but they should be used appropriately. They are powerful at the boundaries of your code but introduce too much indirection when used overzealously.

A good abstraction lets a developer switch out an implementation without any effort. A bad abstraction finds a developer clicking through many files trying to a lot of information in their head.

I have a few rules of thumb that I try to follow:

  1. An abstraction is useful when there is a genuine reason to swap out the implementation.

  2. If you are at a boundary of a key separation of concern use an interface to define that boundary.

  3. If you are designing a library use an abstraction to define a public API that can be added to or sensibly deprecated

  4. If you know your class isn’t going to be swapped out don’t use an abstraction

These are not a definitive set of rules but I find they rein me in from creating an abstraction for everything under the sun!