Clean Code - Magic Numbers

Sometimes we think that to refactor a code and make it more readable we need to do something complex, but that’s not always the case — sometimes just renaming a variable to a name that matches what it really does is already a big step.

Last weekend, I was studying TDD and decided to write a simple login code. In that algorithm there were some HTTP response status codes — 400, 401, 403, 422, and so on — that I had added directly into the code. Then I thought: “Would someone who doesn’t know HTTP status codes know what this means?”

With that in mind, I started thinking about how to solve it, and I remembered something I had read in Clean Code about eliminating magic numbers. According to Robert Martin, this should be avoided in your code because it leads to bugs and makes the code harder to understand.

For those unfamiliar with the term, a magic number is one of those numbers we put in our code that requires an explanation to understand why it’s there.

To fix this code smell, you should use constants to represent those values.

In the first image I show how the code looked with the magic numbers.

I created a new class where I defined some constants to represent the response codes:

Then I swapped the numbers for the constants, and you can see how much the code’s readability improved: