Code Smell 02 - Constants and Magic Numbers
A method makes calculations with lots of numbers without describing their semantics
TL;DR: Avoid Magic numbers without explanation. We don't know their source and are afraid to change them.
Problems
- Coupling
- Low testability
- Low readability
Solutions
1) Rename the constant with a semantic and name (meaningful and intention revealing).
2) Replace constants with parameters, so you can mock them from the outside.
3) The constant definition is often a different object than the constant (ab)user.
Examples
- Algorithms Hyper Parameters
Sample Code
Wrong
def energy(mass)
mass * 299792458 ** 2
end
Right
# Storing magnitudes without units is another smell
class PhysicsConstants
LIGHT_SPEED = 299792458.freeze
end
def energy(mass)
mass * PhysicsConstants::LIGHT_SPEED ** 2
end
Detection
Many linters can detect number literals in attributes and methods.
Tags
- Hard coded
- Constants
More info
Credits
Photo by Kristopher Roller on Unsplash
In a purely functional program, the value of a [constant] never changes, and yet, it changes all the time! A paradox!
Joel Spolsky
This article is part of the CodeSmell Series.