Unused Function

Also Known As

TL;DR

Explanation

Unused private methods are detectable by static analysis and have no legitimate use — remove them. Unused public methods are harder because they may be called dynamically or from outside the codebase, but any that are confirmed unused should also be removed. Dead methods stay in codebases because developers are afraid to delete them ('someone might need it') — version control is the safety net; delete confidently. YAGNI applies: You Aren't Gonna Need It.

Common Misconception

Why It Matters

Common Mistakes

• Keeping methods 'just in case' — git history preserves them; remove now, restore if ever needed.
• Not running dead code detection tools — PHPStan detects unused private methods automatically.
• Unused abstract method implementations left after an interface changed.
• Helper functions added during development that became unnecessary after refactoring.

Code Examples

class OrderService {
    public function processOrder(Order $o): void { /* used */ }

    private function formatOrderLegacy(Order $o): string {
        // Never called anywhere — dead code
        return $o->id . '-' . $o->total;
    }

    private function validateOrderV1(array $data): bool {
        // Replaced by validateOrder() — never called
        return isset($data['id']);
    }
}

// Remove unused private methods — git preserves the history:
class OrderService {
    public function processOrder(Order $o): void { /* used */ }
    // formatOrderLegacy() removed — was never called
    // validateOrderV1() removed — replaced by validateOrder()
}

References

• ↗ https://phpstan.org/blog/detecting-unused-private-properties-methods-constants

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