Observer Pattern in Ruby: Decoupling Objects With Event-Driven Design

The Observer Pattern is a behavioral design pattern that establishes a one-to-many relationship between objects, automatically notifying all dependents when a subject's state changes. Without it, a single method like a user signup can accumulate unrelated responsibilities, violating the Single Responsibility Principle and making code harder to maintain. The pattern separates concerns by letting the subject simply broadcast a change while registered observers independently decide how to respond. A practical Ruby example demonstrates a weather station that notifies multiple display objects whenever temperature updates, without knowing anything about those displays. Rails developers encounter this pattern regularly through features like Active Record callbacks, which follow the same notify-on-change principle.