phanalist

E0009: The “Choose Your Own Adventure” Rule (Cyclomatic Complexity)

Imagine a method is like a “Choose Your Own Adventure” book. Every time there is an if, else, switch, or loop, the reader has to keep track of a new path the story could take.

Cyclomatic Complexity is just a fancy way of counting how many different paths exist through your code.

How the rule works

The rule starts at 1, and adds +1 for every “branching” word it sees:

1. Every if or elseif is +1 path.
2. Every case in a switch is +1 path.
3. Every loop (for, foreach, while) is +1 path.
4. Every catch block is +1 path.

If your score gets too high (default > 10), it means your method has too many possible stories. It’s too hard to test, and too hard for a human to read!

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❌ The “Too Many Paths” Example

This code has so many if statements that it’s impossible to know all the outcomes.

public function getChapter(int $number, Character $character): bool {
    if ($number > 0) {                 // +1 path
        switch ($number) {
            case 1:                    // +1 path
            case 2:                    // +1 path
                if ($character->isAlive()) { // +1 path
                    return true;
                }
                break;
        }
        if ($character->hasSword()) {  // +1 path
            if ($character->isStrong()) { // +1 path
                return true;
            }
        }
    }
    return false;
}

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✅ The “Simple Story” Example (Refactored)

We can flatten this by extracting logic or returning early. Now there are fewer paths to think about at once!

public function getChapter(int $number, Character $character): bool {
    if ($number <= 0) {
        return false;
    }

    if ($this->isEarlyChapter($number) && $character->isAlive()) {
        return true;
    }

    return $character->hasSword() && $character->isStrong();
}

private function isEarlyChapter(int $number): bool {
    return $number === 1 || $number === 2;
}

---

Configuration

rules:
  E0009:
    max_complexity: 10

The Junior’s Rule of Thumb:

If Phanalist flags your method for Cyclomatic Complexity, it means your method is trying to make too many decisions. Break the complex parts out into smaller, well-named helper methods!

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