Code Smell 119 — Stairs Code

Nested boolean conditions express a business rule. Not an IF

TL;DR: Avoid checking for boolean expressions and returning an explicit boolean.

Problems

• Declarativeness
• Ninja Code
• Readability
• Arrow Code

Solutions

1. Return a boolean business formula value.

Context

When dealing with boolean formulas, it is more readable to show a business boolean formula than a stair of boolean checks followed by returning an explicit true/false;

Sample Code

Wrong

def is_platypus(self):
    if self.is_mammal():
        if self.has_fur():
            if self.has_beak():
                if self.has_tail():
                    if self.can_swim():
                        return True
    return False
# This is also wrong since it is polluted with IFs and not readable by a biologist
def is_platypus(self):
    if not self.is_mammal():
        return False
    if not self.has_fur():
        return False
    if not self.has_beak():
        return False
    if not self.has_tail():
        return False
    if not self.can_swim():
        return False 
    return True

Right

def is_platypus(self):
    return self.is_mammal() &&  self.has_fur() && self.has_beak() && self.has_tail() && self.can_swim()
#We can even group conditions according to animal taxonomies

Detection

[X] Automatic

Based on syntax trees, we can safely refactor the code removing the explicit boolean value.

Tags

• Boolean

Conclusion

Beware of returning booleans.

After the return, you will need an If statement which is also a code smell.

Relations

Code Smell 115 — Return True

Code Smell 97 — Error Messages Without Empathy

Code Smell 24 — Boolean Coercions

Code Smell 62 — Flag Variables

Code Smell 102 — Arrow Code

Code Smell 80 — Nested Try/Catch

More Info

• How to Get Rid of Annoying Ifs Forever

Credits

Photo by Jukan Tateisi on Unsplash

Thanks again to Nico K. for this suggestion.

The real hero of programming is the one who writes negative code.

Douglas McIlroy

Software Engineering Great Quotes

This article is part of the CodeSmell Series.

How to Find the Stinky parts of your Code