Welcome back! Today, we'll master what we learned about backward compatibility in practice. Prepare to apply all the knowledge to practical tasks, but first, let's look at two examples and analyze them.

Let's say that initially, we have a complex data processing class designed to operate on a list of maps, applying a transformation that converts all string values within the maps to uppercase. Here's the initial version:

We intend to expand this functionality, adding capabilities to filter the items based on a condition and to allow for custom transformations. The aim is to retain backward compatibility while introducing these enhancements. Here's the updated approach using function overloading:

In this evolved version, we've introduced function overloading with additional parameters: (Map<String, Any>) -> Boolean to filter the input list based on a given condition, and ((Map<String, Any>) -> Map<String, Any>)? for custom transformations of the filtered items. The default behavior processes all items, converting string values to uppercase, which ensures that the original functionality's behavior is maintained for existing code paths.

Notice, that in the usage examples of the processData function, we utilize Kotlin's trailing lambda feature. This feature allows us to pass a lambda expression outside of the parentheses when it is the last parameter. For instance, in the custom transformation example:

Here, the lambda expression { item -> ... } is passed as the last argument to the processData function, demonstrating the trailing lambda syntax.

Imagine now that we are building a music player, and recently, the market demands have grown. Now, users expect support not just for MP3 and WAV but also for FLAC files within our music player system. This development poses a unique challenge: How do we extend our music player's capabilities to embrace this new format without altering its established interface?

Let's say that we currently have a MusicPlayer class that can only play MP3 files:

Let's approach this challenge by introducing a composite adapter, a design that encapsulates multiple adapters or strategies to extend functionality in a modular and maintainable manner.

This sophisticated adaptation strategy ensures that we can extend the MusicPlayer to include support for additional file formats without disturbing its original code. The MusicPlayerAdapter acts as a unified interface to the legacy MusicPlayer, capable of handling various formats by determining the appropriate conversion strategy based on the file type.

Great job! You've delved into backward compatibility while learning how to utilize function overloading and the Adapter Design Pattern. Get ready for some hands-on practice to consolidate these concepts! Remember, practice makes perfect. Happy Coding!