YAGNI (You Aren't Gonna Need It)

Core Principle

Only implement features when you actually need them, not when you think you might need them in the future.

Examples

Premature Abstraction (Bad)

// Over-engineered solution anticipating future needs
class UserService {
    private $database;
    private $cache;
    private $logger;
    private $notifications;
    private $analytics;

    public function __construct(
        DatabaseInterface $database,
        CacheInterface $cache,
        LoggerInterface $logger,
        NotificationService $notifications,
        AnalyticsService $analytics
    ) {
        $this->database = $database;
        $this->cache = $cache;
        $this->logger = $logger;
        $this->notifications = $notifications;
        $this->analytics = $analytics;
    }

    public function createUser($data) {
        $this->logger->info('Creating user');
        $user = $this->database->insert('users', $data);
        $this->cache->set('user_' . $user->id, $user);
        $this->notifications->sendWelcomeEmail($user);
        $this->analytics->trackUserCreation($user);
        return $user;
    }
}

Simple Implementation (Good)

class UserService {
    private $database;

    public function __construct(DatabaseInterface $database) {
        $this->database = $database;
    }

    public function createUser($data) {
        return $this->database->insert('users', $data);
    }
}

Real-World Scenarios

E-commerce Example

// Bad: Implementing unused features
class Product {
    private $name;
    private $price;
    private $stock;
    private $weight;          // Not needed yet
    private $dimensions;      // Not needed yet
    private $shippingZones;   // Not needed yet
    private $taxCategories;   // Not needed yet
    private $customFields;    // Not needed yet

    public function calculateShipping($address) {
        // Complex shipping calculation that isn't required
    }

    public function calculateTax($country) {
        // Complex tax calculation that isn't required
    }
}

// Good: Implementing what's needed now
class Product {
    private $name;
    private $price;
    private $stock;

    public function __construct(string $name, float $price, int $stock) {
        $this->name = $name;
        $this->price = $price;
        $this->stock = $stock;
    }
}

Common Anti-Patterns

1. Building complex configuration systems before needed
2. Creating elaborate inheritance hierarchies for future extensibility
3. Adding database fields for potential future features
4. Implementing unneeded API endpoints
5. Creating generic solutions for specific problems

Benefits

1. Reduced codebase complexity
2. Lower maintenance cost
3. Faster development cycles
4. Better focus on current requirements
5. Less technical debt

Exception Cases

1. Core architecture decisions
2. Data structures that are expensive to change later
3. Security considerations
4. Regulatory compliance requirements