This series explores the SOLID principles of object-oriented design, which are essential for creating software that is easy to maintain and extend. Each principle will be covered in detail with real-world examples and best practices.
1 Single Resposibility Principle - What’s a “Single Reason to Change” and Why It Matters?
TL;DR: SRP means each class or module should have only one reason to change. Split validation, data access, and business logic into separate classes. SRP improves maintainability, testability, and scalability. Use C# 12 features like primary constructors and records for clean separation. Avoid “God” classes and mixing unrelated responsibilities. SRP is the foundation for applying other SOLID principles. Refactor large classes by extracting focused components and using dependency injection. The Single Responsibility Principle gets misunderstood more than any other SOLID principle. It’s not about doing one thing, it’s about having one reason to change. When your class changes for multiple business reasons, you’ve violated SRP and created a maintenance nightmare. ...
2 How to Apply the Open/Closed Principle Without Turning Every Feature Into a Plugin
TL;DR: The Open/Closed Principle (OCP) states: classes should be open for extension, but closed for modification. You don’t need to create a plugin for every new feature, favor simpler patterns like strategy, inheritance, or composition. Start with well-named abstractions; introduce extensibility points only when real change is expected. Keep code maintainable by balancing extension points with simplicity. Overengineering is a bigger risk than occasional refactoring. The Open/Closed Principle isn’t about making everything extensible. It simply means that your core business logic should be closed to modification but open to extension. The real skill is knowing when to apply it and when you’re just over-engineering your code. ...
3 The Rectangle-Square Problem: What It Teaches Us About Liskov Substitution Principle (LSP)
TL;DR LSP means you can use subtype objects anywhere you use base type objects without breaking code. Square/Rectangle inheritance that breaks existing code? That’s a classic LSP problem. Watch for subclasses that throw unexpected exceptions or silently change behavior. When behaviors are too different, reach for composition instead of inheritance. Make interfaces that clearly show what objects can and can’t do to avoid surprises. LSP violations often sneak past unit tests and show up as runtime bugs. The Liskov Substitution Principle isn’t just academic theory - it helps you avoid those “it worked yesterday” bugs that show up in production. When a subclass doesn’t behave like its parent promises, your code breaks in ways that unit tests often miss. ...
4 Interface Segregation Principle
// Drafting in Progress...5 Dependency Inversion Principle
// Drafting in Progress...6 Solid Principles: conclusion
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