Disguised as a friendly shortcut is another coupling smell.

TL;DR: Optional Arguments generate a hidden coupling in the name of smaller code.

Problems

• Coupling

• Unexpected results

• Side effects

• Ripple Effect

• In languages with optional arguments but limited to basic types, we need to set a flag and add an accidental IF (another smell).

Solutions

1. Make arguments explicit.
2. All function calls must have the same arity.
3. Use Named Parameters if your language supports them.

Sample Code

Wrong

<?

final class Poll {

    function _construct(array $questions, bool $annonymousAllowed = false, $validationPolicy = 'Normal') {

        if ($validationPolicy == 'Normal') {
          $validationPolicy = new NormalValidationPolicy();
        }
        //...
    }
}

//Valid
new Poll([]);
new Poll([], true);
new Poll([], true , new NormalValidationPolicy());
new Poll([], , new StrictValidationPolicy());

Right

<? 

final class Poll {

    function _construct(array $questions, AnonnyomousStrategy $annonymousStrategy, ValidationPolicy $validationPolicy) {            
        //...
    }
}


//invalid
new Poll([]);
new Poll([], new NoAnonnyomousValidStrategy());
new Poll([], , new StrictValidationPolicy());

//Valid
new Poll([], new NoAnonnyomousValidStrategy(), new StrictValidationPolicy());

Detection

Detection is easy if the language supports optional arguments.

Tags

• Optional

• Laziness

Conclusion

Be explicit. Favor readability over shorter (and more coupled) function calls.

More info

• Function Arity

• Decoupling a Legacy System

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The trouble with programmers is that you can never tell what a programmer is doing until it’s too late.

Seymour Cray

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This article is part of the CodeSmell Series.

Last update: 2021/06/30