You should be able to add a new payment method (e.g., Stripe) by creating a new class that extends a base interface, rather than rewriting your existing checkout logic. L: Liskov Substitution Principle (LSP)
If a Bird class has a fly() method, a Penguin subclass shouldn't override it to throw an error, as this violates the expectation that all birds in the system can fly. I: Interface Segregation Principle (ISP) php-guide.7z
A class should have one, and only one, reason to change. You should be able to add a new payment method (e
Instead of one massive WorkerInterface , create smaller interfaces like WorkableInterface and SleepableInterface so a robot class isn't forced to implement a sleep() method. D: Dependency Inversion Principle (DIP) and only one
