Extensibility

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: 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. ...