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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.

About the Author

Abhinaw Kumar is a software engineer who builds real-world systems: from resilient ASP.NET Core backends to clean, maintainable Angular frontends. With over 11+ years in production development, he shares what actually works when you're shipping software that has to last.

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