Code Review Ep. 1: Violating Open-Closed Principle

Welcome to the second episode of our blog post series where we make code reviews. In this episode, we will delve into the Open Closed Principle (OCP) and its significance in creating flexible and extensible payment processing code.

We will conduct a sample code review of a PaymentProcessor class to identify areas where the OCP may have been violated. Join us as we explore potential solutions to adhere to this principle and improve the design of our payment processing system.

“Like a perfectly brewed cup of coffee, bot programming awakens the digital world with its intricate flavors of code, automation, and endless possibilities.”

Understanding the Open Closed Principle:

The Open Closed Principle guides developers to write code that is open for extension but closed for modification. This principle promotes a modular and flexible codebase that can accommodate new features or functionalities without requiring extensive changes to existing, well-tested code. By adhering to the OCP, we can create code that is easier to maintain and adapt to evolving business requirements.

Code Review:

Let’s conduct a code review of the PaymentProcessor class to identify areas that violate the Open Closed Principle. We will then propose potential solutions to address these violations and enhance the extensibility of our payment processing system.

class PaymentProcessor {
    func processPayment(payment: Payment) {
        if payment.type == "CreditCard" {
            // Process credit card payment
        } else if payment.type == "PayPal" {
            // Process PayPal payment
        } else if payment.type == "BankTransfer" {
            // Process bank transfer payment
        }
        // ... more payment types and processing logic ...
    }
}

In this code snippet, the PaymentProcessor class violates the Open Closed Principle by coupling payment processing logic with conditional statements based on payment types. Adding new payment types would require modifying the existing code, leading to maintenance challenges and potential errors.

Code Review:

Let's review the code and identify the areas where the Open Closed Principle is violated:

0. Conditional Logic:

The processPayment() method contains conditional statements that handle different payment types. This violates the Open Closed Principle since it requires modifying the existing code when adding new payment types.

Suggested Solution:

• Utilize the power of abstraction and polymorphism to handle payment-specific behavior.
• Introduce a PaymentProcessor protocol or abstract base class, and let each specific payment processor subclass implement its own processPayment() method.

Sample Solution:

protocol PaymentProcessor {
    func processPayment(payment: Payment)
}

class CreditCardProcessor: PaymentProcessor {
    func processPayment(payment: Payment) {
        // Process credit card payment
    }
}

class PayPalProcessor: PaymentProcessor {
    func processPayment(payment: Payment) {
        // Process PayPal payment
    }
}

class BankTransferProcessor: PaymentProcessor {
    func processPayment(payment: Payment) {
        // Process bank transfer payment
    }
}

In the revised code, we define a PaymentProcessor protocol that declares the processPayment() method. Each specific payment processor, such as CreditCardProcessor, PayPalProcessor, and BankTransferProcessor, conforms to the PaymentProcessor protocol and implements its own version of the processPayment() method. This way, we adhere to the Open Closed Principle by enabling new payment processors to be added without modifying existing code.

Conclusion:

Adhering to the Open Closed Principle is crucial in designing flexible and maintainable code. By utilizing abstraction and polymorphism, we can encapsulate payment-specific behavior in separate classes, making our payment processing system open for extension but closed for modification.

In this blog post, we explored a code review of the PaymentProcessor class, identified violations of the Open Closed Principle, and proposed solutions to address these violations. By embracing the Open Closed Principle, we can create payment processing systems that are adaptable, scalable, and easier to maintain as new payment types are introduced.