Welcome to today's lesson! We're exploring how to introduce complex features while maintaining backward compatibility in software systems. Our journey will take us through a Potluck Dinner organization system where participants and their dishes are tracked for each round. Get ready to dive into Kotlin programming, unveiling strategies and crafting solutions. Let's embark on this exciting adventure!

Our Potluck Dinner organization system currently lets us add and remove participants and manage their dishes for each round. Here are the essential functions:

• fun addParticipant(memberId: String): Boolean: Adds a participant if they don't already exist. Returns true if successful, or false if the participant is already in the system.
• fun removeParticipant(memberId: String): Boolean: Removes a participant and their dish if they exist. Returns true if successful, false otherwise.
• fun addDish(memberId: String, dishName: String): Boolean: Allows a participant to add a dish. Returns true if added successfully, false if the participant is invalid or has already added a dish.

Let's implement these methods using Kotlin, following the initial state of our system:

With this setup, we use Kotlin's mutableSetOf for unique participant IDs and mutableMapOf to associate dishes with participant IDs. Now, let's extend our system with advanced features.

Currently, our Potluck Dinner organization system is simple yet effective. To enhance its capabilities, we're introducing a "Dish of the Day" feature. This allows participants to vote for a dish, with the most voted dish earning the title "Dish of the Day."

The new functionalities introduce these methods:

• fun vote(memberId: String, voteId: String): Boolean: Allows a participant to cast a vote. Each participant can vote only once per round. Returns false if the participant or vote action is invalid.
• fun dishOfTheDay(): String?: Calculates and returns the "Dish of the Day." In cases of ties, the earliest joining participant's dish is prioritized. Returns null if no votes exist.

To accommodate these features, we'll modify our class:

Kotlin's mutableMapOf efficiently suits our need to track participant IDs with their join time.

The vote function confirms the existence of memberId and checks whether a vote has been cast. If valid, it stores the vote; otherwise, it returns false.

Here, Kotlin's grouping and filtering methods elegantly compute vote counts and resolve ties while maintaining readability and leveraging Kotlin's safety features.

The addParticipant function requires modification to integrate join times, maintaining our system's functionality:

Updating it ensures join times are tracked for our new features.

Ensure the removeParticipant function is comprehensive to maintain data integrity:

Maintaining correctness across interactions remains pivotal, so addDish functions are similarly concise:

Here is your final Potluck implementation in Kotlin:

Congratulations on integrating complex functionalities within Kotlin while ensuring backward compatibility! This showcases how Kotlin's concise syntax and modern features can efficiently solve real-world engineering problems. Continue to hone these skills, and explore more Kotlin adventures ahead! Happy coding!