What is solid-project?

SOLID-Project is a study repository that shows, with actual code, how to turn a messy, tangled class into a cleanly organized one using a set of five well known software design guidelines called SOLID. Rather than explaining the ideas in the abstract, the project takes a single example, a checkout service that processes an order, and refactors it step by step. The original version of the checkout service does several things that make code hard to maintain: it decides discounts using a long chain of if and else statements, it creates its own database connections directly inside the method instead of receiving them from outside, it sends confirmation emails using one fixed email class, and it throws an error whenever an unsupported payment method, like cryptocurrency, is attempted. The project fixes each of these one at a time, mapping each fix to one of the five SOLID letters. Saving and notifying are pulled out into their own separate, swappable pieces. The discount logic is rewritten so that new customer types can be added without changing the existing checkout code at all. The payment handling is changed so it never behaves unexpectedly or throws surprise errors. One overly broad set of required methods is split into smaller, more focused groups. Finally, the checkout service is changed to depend only on general descriptions of what it needs, with the actual connections wired together in one central place using a dependency injection container, a common .NET tool for assembling an application's pieces at startup. To run the project, you clone the repository, open it in Visual Studio or VS Code, restore any needed packages, and run it as a .NET console application. The code is organized into separate folders for interfaces, data models, and business logic services, with the application's startup and wiring kept in one file. The README does not mention a license.