Reactive Programming

Reactive Programming is a declarative programming paradigm concerned with asynchronous data streams and the propagation of change. In this model, you can create data streams of anything—from user inputs and API responses to simple variable changes—and then define logic that automatically *reacts* to new values as they are emitted. This allows changes to propagate effortlessly through the application's logic, much like a spreadsheet formula automatically recalculates when a dependent cell is updated. This approach is highly effective for building responsive user interfaces and managing complex, event-driven systems where data changes unpredictably over time.

1. Introduction to Reactive Programming
   1. Definition and Overview
   2. Core Principles
      1. Declarative Programming
         1. Contrast with Imperative Programming
         2. Expressing Logic with Data Flows
      2. Asynchronous Data Streams
         1. Continuous Data Flow
         2. Event-Driven Nature
      3. Propagation of Change
         1. Automatic Updates
         2. Data Dependency Tracking
   3. Key Metaphors
      1. The Spreadsheet Analogy
         1. Cells and Formulas
         2. Automatic Recalculation
      2. The Assembly Line Analogy
         1. Stages of Processing
         2. Flow of Items
   4. Comparison with Other Paradigms
      1. Imperative vs. Declarative
         1. Control Flow
         2. State Management
      2. Traditional Event-Driven Programming
         1. Event Listeners
         2. Callback Hell
      3. The Promise/Future Model
         1. Single Value vs. Multiple Values
         2. Eager vs. Lazy Execution
   5. The Observer Design Pattern
      1. Pattern Overview
      2. Subject (Producer)
         1. Responsibilities
         2. Managing Observers
      3. Observer (Consumer)
         1. Responsibilities
         2. Receiving Updates
      4. The Subscription Contract
         1. Registering and Deregistering
         2. Notification Mechanism