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

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.

Conclusion

Beware of returning booleans.

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

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