What is SOLID?

SOLID is a set of five basic rules that help programmers write code that is easier to understand, change, and keep working correctly. Each rule focuses on a different way to organize code so that parts of a program don’t get tangled together.

Let's break it down

  • S (Single Responsibility Principle): Every piece of code (like a class) should do just one thing and have only one reason to change.
  • O (Open/Closed Principle): Code should be open for adding new features but closed for changing the old, stable parts.
  • L (Liskov Substitution Principle): Objects of a child type must be usable anywhere the parent type is expected, without breaking anything.
  • I (Interface Segregation Principle): Instead of one big “everything” interface, create many small, specific ones so users only need what they actually use.
  • D (Dependency Inversion Principle): High-level parts of a program should not depend on low-level details; both should rely on simple, abstract contracts.

Why does it matter?

Following SOLID makes software less buggy, easier to fix, and quicker to add new features. For beginners, it gives a clear checklist to write clean, maintainable code from the start, saving time and frustration later.

Where is it used?

  • Building large web applications (e.g., e-commerce sites) where many developers work on the same codebase.
  • Developing mobile apps that need frequent updates without breaking existing functionality.
  • Creating libraries or frameworks that other programmers will reuse, such as logging or authentication modules.
  • Designing game engines where performance and modularity are critical.

Good things about it

  • Encourages code that is easy to read and understand.
  • Reduces the risk of bugs when adding new features.
  • Makes testing simpler because components are isolated.
  • Helps teams collaborate without stepping on each other’s code.
  • Increases the lifespan of a project by keeping it adaptable.

Not-so-good things

  • The rules can feel restrictive for very small or simple projects, adding unnecessary complexity.
  • Learning and applying all five principles takes time, which may slow down early development.
  • Over-engineering can happen if developers try to force SOLID onto code that doesn’t need it.
  • Some principles (like Dependency Inversion) may require extra tooling or patterns that beginners find confusing.