SOLID & Design Patterns Interview Question #150

What are the most important principles for maintainable .NET application design?

Anti-Patterns, Refactoring, DI Lifetimes & Senior Design Scenarios Senior Advanced

Quick Interview Answer

Maintainable .NET applications keep responsibilities cohesive, dependencies explicit, domain rules protected, and infrastructure concerns separated from core policies. They use abstractions where they create a real boundary and keep simpler code where additional indirection provides no benefit.

Detailed Explanation

Maintainable .NET applications keep responsibilities cohesive, dependencies explicit, domain rules protected, and infrastructure concerns separated from core policies. They use abstractions where they create a real boundary and keep simpler code where additional indirection provides no benefit.

SOLID, design patterns, DDD, Clean Architecture, and related techniques are tools rather than mandatory checklists. A strong design balances clarity, correctness, testability, performance, operational needs, and the expected rate of change.

For interviews, explain why a design was chosen, what alternatives exist, and what tradeoffs it introduces. That reasoning is more important than applying the maximum number of patterns.

Code Example

Maintainable design =
    clear responsibilities
  + explicit dependencies
  + protected invariants
  + appropriate boundaries
  + measurable performance
  + testability
  + simple solutions where possible;