SOLID
🧠 1️⃣ SOLID Principles — Deep Dive with Examples
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- S — Single Responsibility Principle (SRP)
- O — Open/Closed Principle (OCP)
- L — Liskov Substitution Principle (LSP)
- I — Interface Segregation Principle (ISP)
- D — Dependency Inversion Principle (DIP)
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Questions & Answers
Q: Why are SOLID principles important for senior engineers?
A: They’re heuristics for keeping codebases maintainable and evolvable. Applying SOLID reduces regressions, eases testing, and makes large systems like trading platforms adaptable to new requirements.
Q: How do SOLID principles interact with Clean Architecture?
A: Clean Architecture enforces layer boundaries; SOLID guides class-level design inside those layers. Together they ensure domains stay decoupled from infrastructure and classes remain focused.
Q: Can you break SOLID intentionally?
A: Yes, when performance or simplicity demands it. Document deviations, ensure tests cover the risk, and revisit later. SOLID is guidance, not dogma.
Q: How do SOLID principles apply to microservices?
A: Each service should have a single bounded context (SRP), expose stable contracts (OCP), adhere to interface segregation for clients, and depend on abstractions so infrastructure can evolve independently.
Q: What metrics signal SOLID violations?
A: High cyclomatic complexity, low cohesion, many reasons to change a class (SRP), or ripple effects from small requirements. Code reviews and architecture fitness functions can catch these.
Q: How do SOLID principles improve testing?
A: Focused classes are easier to test (SRP), abstractions enable mocking (DIP), and segregated interfaces prevent massive fakes. This reduces flakiness and speeds CI feedback.
Q: How does LSP relate to API design?
A: Derived types must honor base contracts; otherwise substitutability fails and consumers break. In APIs, ensure new versions remain backward compatible, mirroring LSP.
Q: How does ISP influence public contracts?
A: Expose narrow interfaces tailored to specific clients so they don't depend on methods they don't use. This minimizes breaking changes and improves clarity.
Q: How does DIP show up in ASP.NET Core?
A: Services depend on abstractions registered in DI containers. Infrastructure injects concrete implementations, enabling easier testing and swapping components like data stores.
Q: How do you balance SOLID with performance?
A: Apply SOLID first, measure, and only optimize hotspots. If adding an abstraction hurts perf, encapsulate the optimized path while documenting why the deviation exists.