TL;DR: Don't use Optional Arguments before mandatory ones. In fact: Don't use Optional Arguments at all

Problems

• Fail Fast principle violation

• Readability

Solutions

1. Move your optional arguments last.

2. Avoid Optional Arguments.

Context

Optional Arguments are a code smell.

Defining optional arguments before mandatory ones is an error.

Sample Code

Wrong

<?

function buildCar($color = "red", $model){...}  
// First argument with optional argument

buildCar("Volvo")}}  
// Runtime error: Missing argument 2 in call to buildCar()

Right

<?

function buildCar($model, $color = "Red", ){...}

buildCar("Volvo")}} 
// Works as expected

def functionWithLastOptional(a, b, c='foo'):
    print(a)
    print(b)
    print(c)
functionWithLastOptional(1, 2)

def functionWithMiddleOptional(a, b='foo', c):
    print(a)
    print(b)
    print(c)
functionWithMiddleOptional(1, 2)

# SyntaxError: non-default argument follows default argument

Detection

[X] Automatic

Many Linters can enforce this rule since we can derive it from function signature.

Also, many compilers directly forbid it.

Tags

• Readability

Conclusion

Try to be strict when defining functions to avoid coupling.

Relations

More Info

Rule on Sonar Source

Disclaimer

Code Smells are just my opinion.

Credits

Photo by Manuel Torres Garcia on Unsplash

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Programs are meant to be read by humans and only incidentally for computers to execute.

Donald Knuth

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This article is part of the CodeSmell Series.