Why SOLID Matters Everywhere

The five SOLID rules were first described for object‑oriented languages, but their intent is to guide clear, maintainable design. That intent shows up in many places you might not expect.

1. Tailwind CSS and the Single Responsibility Idea

Each utility class in Tailwind does one thing and does it well. text-center aligns text, p-4 adds padding, bg-white sets a background colour. Because the class never tries to do more, you can combine them without side effects. This mirrors the Single Responsibility Principle.

The Open/Closed idea also appears: you cannot change the definition of p-4 at runtime, but you can extend the visual language by adding new utilities or by composing existing ones (md:p-8, lg:p-12). The original utilities stay untouched.

2. Functional Programming and Interface Segregation

Pure functions accept a small, well‑defined set of arguments and return a value without altering external state. This matches the Interface Segregation Principle - callers depend only on the behavior they need.

Higher‑order functions let you inject dependencies, satisfying the Dependency Inversion Principle. Instead of a function reaching directly for a global variable, you pass the required resource as an argument, keeping the high‑level logic independent of low‑level details.

3. AI Agents as Modular Systems

When building an AI agent, you often split responsibilities: a planner decides what to do, a executor carries out actions, and a monitor observes outcomes. Each module follows the Single Responsibility Principle.

The planner can be swapped for a more capable version without touching the executor - an example of the Open/Closed rule. Executors receive abstract interfaces for tools, which means the high‑level planning code does not depend on concrete tool implementations, reflecting Dependency Inversion.

Takeaway

Whether you are styling a button, composing pure functions, or orchestrating an autonomous system, the spirit of SOLID helps keep the codebase understandable and adaptable. Recognising these patterns outside traditional class hierarchies can improve the quality of any software project.