SOLID Principles in C# — I Refactored 60 Ugly Lines, One Rule at a Time

SOLID is a default, not a religion.

Most articles teach the five principles with toy examples — a Square that violates LSP, a Logger that violates SRP. You finish having memorised five acronyms with no idea what to do on Monday morning when your real order service has 11 reasons to change and a switch statement on payment type.

So I took a real, ugly 60-line order-processing service that breaks every SOLID rule, and refactored it one principle at a time.

The starting point

public class OrderService