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SOLID Principles in .NET: A Practical Guide with C# Examples
Write cleaner, more maintainable, and more testable C# by applying five simple design rules
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If you’ve been writing C# for a while, you’ve probably heard the word SOLID thrown around in code reviews, architecture meetings, or job interviews. It sounds like just another buzzword — until the day you inherit a 3,000-line OrderManager class that does everything, and suddenly you understand exactly why these principles exist.
SOLID is an acronym coined by Robert C. Martin (“Uncle Bob”) for five object-oriented design principles that, together, make software easier to understand, extend, and maintain:
- S — Single Responsibility Principle
- O — Open/Closed Principle
- L — Liskov Substitution Principle
- I — Interface Segregation Principle
- D — Dependency Inversion Principle
In this article, we’ll walk through each principle with a before/after C# example, a diagram, and practical notes on where .NET’s own ecosystem (dependency injection, interfaces, IEnumerable, etc.) already leans on these ideas.
