Welcome to "Breaking Dependencies to Improve Code"! In this lesson, we will explore the concept of refactoring tightly coupled code using abstract classes and pure virtual functions in C++. This is a crucial step in making our code more testable, maintainable, and flexible. By the end of this lesson, you'll understand how to identify tightly coupled code and refactor it using abstract classes to improve its quality.

Tight coupling occurs when classes or components in our code are heavily dependent on each other. This dependency makes it difficult to change or test individual parts of the code without affecting others. For example, in the OrderProcessor class, we see direct dependencies on DatabaseConnection and PaymentGateway:

These dependencies make it challenging to test the OrderProcessor class in isolation, as it relies on the actual implementations of these classes. This tight coupling can lead to maintenance challenges and hinder the flexibility of our code.

Abstract classes in C++ help abstract implementation details and reduce coupling by allowing us to define a contract that different classes can implement through pure virtual functions. This abstraction enables us to swap out implementations without changing the code that uses them. By using abstract classes, we can create more modular and testable code. For instance, by introducing abstract classes for DatabaseConnection and PaymentGateway, we can decouple the OrderProcessor from their concrete implementations:

Refactoring with abstract classes involves identifying direct dependencies and replacing them with abstract classes. This process begins by defining abstract classes that represent the required functionality through pure virtual functions. Once the abstract classes are in place, we can modify the dependent class to use these abstract classes instead of concrete implementations. This change allows for greater flexibility and easier testing. In our example, the OrderProcessor class can be refactored to use abstract classes:

By using abstract classes, the OrderProcessor can now work with any class that implements these abstract classes, making it more adaptable to future changes. This adjustment lays the groundwork for future refactoring.

When refactoring with abstract classes, we often face challenges such as designing classes that are too broad or too specific. It's vital to strike a balance by designing abstract classes that capture the necessary functionality without being overly restrictive. We will discuss this very topic in future courses. Additionally, we should ensure that our abstract class design aligns with future flexibility needs. By following best practices, such as keeping abstract classes focused and cohesive, we can overcome these challenges and create more maintainable code.

In this lesson, we explored the concept of refactoring tightly coupled code using abstract classes and pure virtual functions in C++. We discussed the drawbacks of tight coupling and the benefits of using abstract classes to create more modular and testable code. By refactoring the OrderProcessor class, we demonstrated how to replace direct dependencies with abstract classes, enhancing flexibility and maintainability. Now, you're ready to apply these concepts in the practice exercises, where you'll identify dependencies and implement abstract classes to improve your code.