"S" of SOLID — the Single Responsibility Principle (SRP).

S.O.L.I.D Principles in Real Life — Part 1: The Single Responsibility Principle (SRP)
Hey everyone,

I'm Sumit Jasuja, a Tech Lead with over 10 years of experience in .NET development. I currently lead squads at Innago and Taazaa, focusing on scalable architecture, clean code, and mentoring developers across multiple projects. I actively drive code reviews and ensure our teams follow best practices like SOLID principles to build maintainable and reliable software.

Over the years, I’ve noticed that many developers—even experienced ones—tend to overlook or underapply SOLID principles in real-world projects. These oversights might seem harmless initially but often lead to tight coupling, untestable code, and increased maintenance overhead down the road. I’ve seen this firsthand during code reviews, onboarding sessions, and even production issues.

That’s why I’m writing this series — to break down each of the SOLID principles with practical, relatable examples, and show how applying them thoughtfully can save a lot of pain later. To make things consistent and memorable, we’ll follow a recurring example from a Car Manufacturing Company as we explore each principle.

Let's start with the first and arguably most important principle:
**
**S — Single Responsibility Principle (SRP)
A class should have only one reason to change.

This means a class (or a module, or even a function) should do only one thing — and do it well.

Real-World Example: Car Manufacturing Company
Imagine you’re building a system for a Car Manufacturing Company, and you write a CarManager class that looks like this:

This violates SRP because the class handles:

• Manufacturing
• Painting
• Logistics
• Invoicing

Each of these concerns can change for different reasons. If the logistics team wants to change how cars are shipped, it shouldn’t affect the painting or manufacturing logic. But with everything in one place, you risk breaking unrelated features.

A Better, SRP-Friendly Design
Let's split responsibilities:

Now each class:

• Has one responsibility
• Is easier to test and maintain
• Changes only when that one responsibility changes

Another Analogy: Coffee Machine That Does Laundry?
Imagine if your coffee machine also tried to wash your clothes. Sounds weird, right? It might do both, but neither well — and fixing an issue in the coffee brewing logic could accidentally break the laundry cycle.

That’s exactly what happens when you overload a class with too many responsibilities.

My Approach as a Tech Lead
During code reviews, I often ask the team:

"What's the single reason this class would change?"

If there's more than one reason, we refactor it. Over time, this mindset leads to cleaner, more modular, and maintainable codebases.

Key Benefits of SRP
Modular code that's easier to test.

Less risk of unintended bugs when updating features.

Clear ownership of responsibilities among developers.

What's Next?
In the next part of this series, we’ll explore the O — Open/Closed Principle, and how to make your code flexible for extension but closed for modification. We’ll continue using the Car Company example to bring these ideas to life.

If you found this helpful or have your own SRP lessons, I'd love to hear about them in the comments. Let’s keep growing together as better developers.

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