Maintainability

Want the PDF version? Click here to download S: Single Responsibility Principle (SRP) Real Meaning: One reason to change, not one “thing” it does. Why It Matters: Avoids “God classes” that block clean PRs & slow refactoring. Personal Analogy: “If you can’t give a clean commit message for the change, it’s violating SRP.” Code Smell: Method/class summary has multiple and/or. Actionable: Before adding a method, ask: “Is this a different concern?” Read more on SRP Short link: bytecrafted.dev/solid-srp O: Open/Closed Principle (OCP) Real Meaning: Add features by extension, not by editing old code. Why It Matters: Keeps legacy code stable; new business rules plug in cleanly. Personal Analogy: “If a new requirement means touching brittle switch statements, you’re not OCP.” Code Smell: Growing switch/if chains for types or behaviors. Actionable: When adding a rule, prefer new handler/class over changing the old one. Read more on OCP Short link: bytecrafted.dev/solid-ocp L: Liskov Substitution Principle (LSP) Real Meaning: Subtypes must behave as expected, no surprises for callers. Why It Matters: Swapping implementations shouldn’t break existing tests or runtime logic. Personal Analogy: “If a subclass throws where the base returns null, that’s an LSP landmine.” Code Smell: Derived classes override with different exceptions, parameters, or semantics. Actionable: Run parent class tests on every subclass; look for broken guarantees. Read more on LSP Short link: bytecrafted.dev/solid-lsp I: Interface Segregation Principle (ISP) Real Meaning: Small, client-focused interfaces, never force unused methods. Why It Matters: Reduces coupling, makes mocks/tests trivial, avoids NotSupportedException landmines. Personal Analogy: “If your interface summary needs bullet points, it’s already too fat.” Code Smell: Implementations with empty or throw NotSupportedException methods. Actionable: Extract groups of related methods into separate interfaces as soon as a client skips one. Read more on ISP Short link: bytecrafted.dev/solid-isp D: Dependency Inversion Principle (DIP) Real Meaning: Depend on abstractions, not concrete implementations, flip the usual control. Why It Matters: Makes business logic testable, swappable, and free of infrastructure glue. Personal Analogy: “If you see new SqlRepo() in a service, that’s DIP going up in flames.” Code Smell: Direct instantiation of dependencies inside business logic. Actionable: Use constructor injection for every external dependency; mock in tests, swap in production. Read more on DIP Short link: bytecrafted.dev/solid-dip Read full series: bytecrafted.dev/series/solid. ...

TL;DR ISP means interfaces should be small and focused on client needs. Avoid “God” interfaces that force clients to implement unused methods. Split large interfaces into cohesive, role-based interfaces. Use C# 12 features like default interface methods for flexibility. ISP improves maintainability, testability, and reduces coupling. Refactor fat interfaces by extracting related methods into separate interfaces. Interface Segregation Principle stops you from creating huge interfaces that force clients to implement methods they’ll never use. When interfaces get too big, your implementations end up filled with empty methods and unnecessary dependencies. ...

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. ...

Discover how guard clauses in C# simplify validation and error handling. Learn to write fail-fast code, avoid nested conditionals, and keep business logic clean with modern language features and reusable helpers.