Photo by Anh Tuan To on Unsplash
Code Smell 241- Referential Transparency Violation
Pure functions produce the same output for the same input and have no side effects
TL;DR: Your functions should be replaceable by the computation result.
Problems
Readability
Principle of least astonishment violation
Testability
Solutions
- Avoid side effects and erratic behavior
Context
Breaking referential transparency occurs when the code introduces side effects or relies on a mutable state.
This violates the principle that an expression or function can be replaced with its value without changing the program's behavior.
Sample Code
Wrong
# Global mutable variable
counter = 0
# Function with side effect
def increment_counter():
global counter
counter += 1
return counter
# Function with implicit dependency and non-deterministic
def get_random_number():
import random
return random.randint(1, 100)
# Function with non-deterministic behavior
def get_current_time():
import time
return time.time()
Right
import random
import time
# Function without side effects
def increment_counter(counter):
return counter + 1
# Function without side effects (but not deterministic)
def get_random_number():
return random.randint(1, 100)
# Function without side effects (can also be injected)
def get_current_time(timesource):
return timesource.time()
Detection
[X] Semi-Automatic
Many linters warn you when you violate referential transparency
Tags
- Coupling
Level
[x] Intermediate
AI Assistants
Most AI assistants will avoid violating referential transparency.
Conclusion
Functional programming is known for its ability to enable concise, expressive, and maintainable code, as well as facilitating parallel and concurrent programming due to its emphasis on immutable data and pure functions.
There are many concepts to borrow from it.
Relations
More Info
Disclaimer
Code Smells are my opinion.
Credits
Photo by Wilhelm Gunkel on Unsplash
Referential transparency is a very desirable property: it implies that functions consistently yield the same results given the same input, irrespective of where and when they are invoked.
Edward Garson
This article is part of the CodeSmell Series.