Explain the principles of SOLID.

SOLID principles are five fundamental principles of object-oriented design that help create flexible, extendable, and maintainable systems:

• S (Single Responsibility Principle) — The principle of single responsibility: each class or module should have only one reason to change, meaning it should be responsible for a specific task.

• O (Open/Closed Principle) — The principle of open/closed: software entities should be open for extension but closed for modification.

• L (Liskov Substitution Principle) — The Liskov Substitution Principle: objects of a subclass should be interchangeable with objects of the superclass without affecting the correctness of the program.

• I (Interface Segregation Principle) — The interface segregation principle: it's better to have several specific interfaces than one universal interface.

• D (Dependency Inversion Principle) — The dependency inversion principle: high-level modules should not depend on low-level modules; both should depend on abstractions.

In Go, these principles are applicable even though the language is not strictly object-oriented. For example, interfaces in Go help implement ISP and DIP, and struct composition supports SRP and OCP.