Method Length Guidelines

Also Known As

TL;DR

Explanation

Long methods are one of the oldest and most reliable code smells. Martin Fowler recommends that any method longer than five lines is worth scrutinising; practically, methods over 20 lines should be refactored. Long methods almost always have multiple responsibilities that can be extracted into well-named helper methods. Each extracted method should be small enough to have a name that fully describes its purpose — if you cannot name it clearly, it may still be doing too much. Cyclomatic complexity is often more meaningful than raw line count — a 30-line linear method may be fine; a 10-line method with 6 branches is complex.

Common Misconception

Why It Matters

Common Mistakes

• Not extracting private methods when a function exceeds 20-30 lines.
• Comments used to separate 'sections' of a long method — each section is a candidate for extraction.
• Test methods as long as the code they test — long test methods indicate the production code does too much.
• Reducing method length by inlining logic rather than extracting it — moves complexity, doesn't reduce it.

Code Examples

// 80-line method doing too many things
public function processOrder(\$cart, \$user, \$payment) {
    // 15 lines: validate cart
    // 20 lines: apply discounts
    // 15 lines: process payment
    // 20 lines: send notifications
    // 10 lines: log audit trail
}

// Extract each concern into its own method
public function processOrder(Cart \$cart, User \$user, PaymentMethod \$payment): Order {
    \$validated = \$this->validateCart(\$cart);
    \$discounted = \$this->applyDiscounts(\$validated, \$user);
    \$charged    = \$this->processPayment(\$discounted, \$payment);
    \$this->notifyUser(\$charged, \$user);
    \$this->logAudit(\$charged, \$user);
    return \$charged;
}

// Each extracted method: 5-15 lines, one clear purpose
// Guideline: if a method needs a comment to explain sections, extract those sections

References

• ↗ https://refactoring.guru/smells/long-method

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