Dead Code

Also Known As

TL;DR

Explanation

Dead code increases the cognitive load of reading code without providing any value. It can arise from if(false) conditions left from debugging, code below an unconditional return, or logic that was superseded but never removed. Dead code is confusing because readers try to understand why it's there. Worse, if a bug exists in dead code, it may be noticed and "fixed" — causing it to become live and introduce a regression. Remove dead code; source control preserves the history.

Common Misconception

Why It Matters

Common Mistakes

• Leaving commented-out code in version control — use git; if it's commented out, delete it.
• Unreachable code after return/throw that static analysis would catch if it were run.
• Keeping old API endpoints 'just in case' without deprecation notices or removal timelines.
• Private methods that are never called — IDEs flag these but warnings are often ignored.

Code Examples

function processOrder(Order $o): void {
    if ($o->isPaid()) {
        return;
    }
    // This block can never run for a paid order:
    $this->chargeCard($o);  // dead
    $this->sendReceipt($o); // dead
}

function processOrder(Order $o): void {
    if ($o->isPaid()) {
        return;
    }
    $this->chargeCard($o);
    $this->sendReceipt($o);
}
// Or restructure so all paths are live:
function processOrder(Order $o): void {
    if (!$o->isPaid()) {
        $this->chargeCard($o);
        $this->sendReceipt($o);
    }
}

References

• ↗ https://refactoring.guru/smells/dead-code

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