Tell me about the principles of SOLID.

SOLID principles are a set of five fundamental object-oriented design principles that help create flexible, extendable, and maintainable code. While they are universal, their application in Go is adapted to the language's features.

1. S — Single Responsibility Principle Each module or function should have one reason to change, meaning it should be responsible for a single task.

2. O — Open/Closed Principle Software entities should be open for extension but closed for modification. In Go, this is achieved through interfaces and composition.

3. L — Liskov Substitution Principle Objects in a program should be replaceable with instances of their subtypes without affecting correctness. In Go, this means that types implementing an interface should behave as expected.

4. I — Interface Segregation Principle Clients should not depend on interfaces they do not use. In Go, it is recommended to create small, specialized interfaces.

5. D — Dependency Inversion Principle High-level modules should not depend on low-level modules directly; both should depend on abstractions (interfaces). In Go, this is implemented through dependency injection and interface usage.

Example of a small interface in Go:

 type Reader interface {
     Read(p []byte) (n int, err error)
 }

This approach facilitates testing and extending code without modifying existing components.