Clean Code Principles: Write Code That Humans Can Read

// Bad
$d = 7;
$list = User::where('s', 1)->get();

// Good
$maxLoginAttempts = 7;
$activeUsers = User::where('status', 'active')->get();

// Good: each function does one thing
function processOrder(OrderRequest $request): Order
{
    $validated = $this->validateOrder($request);
    $order = $this->createOrder($validated);
    $this->chargePayment($order);
    $this->updateInventory($order);
    $this->notifyCustomer($order);
    return $order;
}

enum UserRole: int {
    case Admin = 1;
    case Editor = 2;
    case Viewer = 3;
}

enum OrderStatus: string {
    case Pending = 'pending';
    case Shipped = 'shipped';
    case Delivered = 'delivered';
}

if ($user->role === UserRole::Editor) { ... }

// Good: flat with guard clauses
function getDiscount(?User $user): float
{
    if (!$user) return 0;
    if (!$user->isPremium()) return 0.05;
    if ($user->ordersCount() <= 10) return 0.1;
    return 0.2;
}

S — Single Responsibility: One reason to change
O — Open/Closed: Open for extension, closed for modification
L — Liskov Substitution: Subtypes must be substitutable
I — Interface Segregation: Many specific > one general
D — Dependency Inversion: Depend on abstractions