What are SOLID principles?

SOLID is an acronym from the first letters of five principles of object-oriented programming proposed by Robert Martin. They help create scalable, maintainable, and testable systems.

1. Single Responsibility Principle:

   • A module, class, or function should have only one reason to change. This means that each component of the system should perform a single, well-defined task.

2. Open/Closed Principle:

   • Software entities (classes, modules, functions, etc.) should be open for extension but closed for modification. New functionality should be added by creating new code rather than changing existing, tested code.

3. Liskov Substitution Principle:

   • Objects of a base class should be replaceable with objects of derived classes without affecting the correctness of the program. If S is a subtype of T, then an object of type T can be replaced with an object of type S without changing the desired properties of the program (correctness, functionality, etc.).

4. Interface Segregation Principle:

   • Clients should not depend on interfaces they do not use. Larger interfaces should be split into smaller, more specific ones so that clients only deal with methods they actually need.

5. Dependency Inversion Principle:

   • High-level modules should not depend on low-level modules. Both should depend on abstractions. Abstractions should not depend on details. Details should depend on abstractions. This leads to the use of patterns such as Dependency Injection.

The SOLID principles are guidelines, not strict rules, and their application requires understanding the project context.