Give each module one reason to change

How to do it

Name the person or team who would ask for a change. If a class answers to two, such as finance and the design team, split it. Keep calculation, storage and presentation apart.

Example

// Bad: pricing, storage and email in one class
class OrderService {
    public function place(Order $order): void { /* price, save, send email */ }
}

// Good: one reason to change each
final class OrderPricer { public function total(Order $order): Money { /* ... */ } }
final class OrderRepository { public function save(Order $order): void { /* ... */ } }
final class OrderMailer { public function sendConfirmation(Order $order): void { /* ... */ } }

How to check

In review, describe the module in one sentence without "and". A linter limit on class size, such as PHPMD ExcessiveClassLength, flags likely offenders.