As a rule of thumb: Naming booleans in the affirmative
One of the most challenging aspects of software development is choosing the good names for variables. This is particularly true when it comes to Boolean variables.
“Naming things is hard.”
– Some Software Developer
Affirmative names are those that start with words like is, has, or can which clearly indicate that the variable is a Boolean.
Affermative Booleans Variables
Our goal is to be consistent in the naming & to keep it readable — almost like a sentence. Take a look at these examples, “Is logged in” or “has favorites” and “has no favorites”.
| Affermative | Negative |
| isLoggedIn | !isLoggedIn |
| isEmpty | !isEmpty |
| hasFavorites | !hasFavorites |
| canEdit | !canEdit |
Reading these like a sentence is natural. “Is logged in” or “can not edit”. There is only one nation flip in your mind you must do when reading the negative cases.
Negative Booleans Variables
Now, let’s consider what happens when we deviate from the Affirmative Approach and use negative names.
| Affermative? | Negative? |
| notLoggedIn | !notLoggedIn |
| isNotEmpty | !isNotEmpty |
| hasNoFavorites | !hasNoFavorites |
| canNotEdit | !canNotEdit |
Our negative cases create a double negative! 😯
Try to read that negative statement as a sentence. “Does not have no favorites?” I think I know what that means, but that feels like an awkward way of saying “hasFavorites”.
The problem with negative named booleans is that they introduce the potential for double negatives. The Affirmative Booleans approach is more straightforward to mentally parse.
Conclusion
In general, naming Booleans in the affirmative is a practice that can significantly improve code understandability and maintainability.
Avoid no, and not, and other words that create the possible of a double negative when the boolean is flipped.
Naming things is hard, but naming boolean variables in the affirmative is a simple, yet effective way to help improve your code readability. Your future self and your teammates will thank you for it.
If you like thinking about naming, you may also enjoy thinking about pagination naming.
(Cover Photo: Factory in Sneek, Netherlands – Jonathan Stassen / JStassen Photography)