In this lesson, we'll focus on the sprout class technique, but this time in scenarios when we are adding new functionality, and we don't want to disrupt existing code. This approach is particularly useful when we want to expand capabilities while ensuring that the existing behavior remains intact.

As software evolves, new features are often added to meet changing requirements. However, integrating these features into existing classes can inadvertently affect their current functionality. This is where the sprout class technique comes into play. By creating a new class to handle additional responsibilities, we can preserve the original class's behavior. This approach not only maintains the integrity of the existing code but also makes the new functionality easier to manage and test independently.

When integrating new features into existing classes, common problems include increased complexity, reduced readability, and the risk of introducing bugs. The sprout class technique addresses these issues by isolating new behavior in a separate class. This separation of concerns ensures that the original class remains focused on its primary responsibilities, while the new class handles the additional functionality. By doing so, we maintain code clarity and reduce the likelihood of errors.

Let's explore how to implement a sprout class. We want to introduce a discount feature in the order processor based on customer loyalty without affecting the existing order processing logic. Here's how we can achieve this:

In this example, the OrderProcessor class processes orders by calculating the total amount. To introduce a discount feature, we create a new DiscountCalculator class (we sprout it):

The DiscountCalculator class calculates a discount based on the customer's loyalty level.

Next, we introduce another sprout class, the DiscountedOrderProcessor:

Using the unchanged logic of the OrderProcessor together with the new discount logic of the DiscountCalculator, we are able to achieve the desired new behavior. While some modifications to the model classes also happen to accommodate the new behavior, we can ensure that they are backwards compatible. The practice sessions following this lesson will demonstrate this.

The sprout class technique offers several benefits, including improved modularity, easier testing, and reduced risk of breaking existing code. By separating new functionality into its own class, we can focus on specific responsibilities, making the codebase more manageable. However, it's vital to avoid over-segmentation, which can lead to increased complexity. Striking the right balance is key to effectively using this technique.

Testing is crucial when introducing new functionality. With the sprout class technique, we can test the new class independently, ensuring that it works as expected without affecting the original class. This approach allows us to maintain comprehensive test coverage and quickly identify any issues with the new functionality.

In this lesson, we've explored the sprout class technique, a powerful tool for adding new functionality without disrupting existing code. By isolating new behavior in a separate class, we maintain code stability and enhance modularity. As we move on to the practical exercises, we'll have the opportunity to apply this technique and reinforce our understanding. Thank you for joining us on this journey, and best of luck with our coding endeavors!