TL;DR

  • SOLID principles help write maintainable, testable, and scalable C# code.
  • Apply SOLID selectively to avoid over-engineering.
  • Use modern C# and .NET 8 features for clean, flexible architecture.
  • Refactor gradually and focus on real pain points.
  • SOLID is a guideline for better code, not a strict rulebook.

SOLID principles aren’t academic theory, they’re practical tools that solve real problems in .NET codebases. After implementing these patterns across countless enterprise applications, here’s what actually matters.

The Reality of SOLID Implementation

Single Responsibility Principle: Focus on “reasons to change” rather than “doing one thing.” Split classes when they change for multiple distinct reasons.

Open/Closed Principle: Don’t make everything extensible. Target volatile business rules and frequent switch statements with strategy patterns.

Liskov Substitution Principle: Behavioral compatibility trumps interface compatibility. When inheritance breaks contracts, use composition instead.

Interface Segregation Principle: Small, focused interfaces beat god interfaces. Design around client needs, not implementation convenience.

Dependency Inversion Principle: High-level modules depend on abstractions. Own your interfaces where you use them, not where you implement them.

When to Apply SOLID Principles in C#

SOLID principles solve specific problems, not theoretical ones. Apply them when you encounter actual pain points:

  • SRP: When a class changes for multiple business reasons
  • OCP: When you frequently add new implementations of the same concept
  • LSP: When polymorphic behavior needs to be reliable across derived types
  • ISP: When clients are forced to depend on methods they don’t use
  • DIP: When you need testable code isolated from external dependencies

The Pragmatic Approach

Start simple, identify problems, then apply SOLID principles selectively. Over-engineering with premature abstractions creates more problems than it solves. Under-applying them leaves you with rigid, untestable code.

The best .NET applications strike this balance:

  1. Write working code first
  2. Recognize pain points during development
  3. Apply relevant SOLID principles to address specific issues
  4. Refactor incrementally as requirements evolve

Measuring Success

Good SOLID implementation makes your C# code easier to understand, test, and change. The ultimate measure isn’t perfect principle compliance, it’s how well your application adapts to evolving business requirements while maintaining code quality.

Use SOLID principles as guidelines for building maintainable .NET applications, not as rigid rules. Master these patterns, and you’ll write code that scales with your team and business needs.

— Abhinaw Kumar [Read more]

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