SOLID in Practice: Real-World Examples with Ruby on Rails

Every developer has seen it: a codebase that started small and clean… and after some months turned into a giant mess. 😅 New features break old ones, testing becomes painful, and onboarding a new teammate feels like an impossible task.

So, how do we avoid this? One classic answer is SOLID — five design principles that help us create software that is easier to maintain and extend.

But here’s the truth: 👉 Most developers know the theory, but struggle to apply it in real projects. 👉 Others think SOLID is “old school” and not useful anymore.

In this first article of a new series, I want to challenge both views. I’ll show you how SOLID still matters today, with practical and realistic examples from modern development (Rails, APIs, services).

We’ll explore the benefits, the downsides, and when it’s better to bend the rules.

🔹 What SOLID stands for: S — Single Responsibility Principle O — Open/Closed Principle L — Liskov Substitution Principle I — Interface Segregation Principle D — Dependency Inversion Principle

📖 My promise: this is not a “copy-paste definition” series. It’s about real-life coding problems and how SOLID can (or cannot) help solve them.

👉 In the next article, we’ll start with the Single Responsibility Principle (SRP), and why “God classes” can silently kill your project.

📌 Question for you: Have you ever worked on a project that became too hard to change? Did SOLID help — or do you think it’s overrated?