What are the SOLID principles?
SOLID is a set of five object-oriented design principles that help you write maintainable, scalable, and testable code. Robert C. Martin popularized them, and today they're fundamental in modern software architecture.
Single Responsibility (SRP)
A class should have only one reason to change. If a class handles persistence, business logic, and formatting, it has too many responsibilities. Split into specialized classes.
// Bad: handles persistence, validation, and email sending
class UserService {
saveUser(user: User) { ... }
validateUser(user: User) { ... }
sendWelcomeEmail(user: User) { ... }
}
Open/Closed (OCP)
Entities should be open for extension but closed for modification. Use interfaces and inheritance to add behavior without modifying existing code.
Liskov Substitution (LSP)
Subtypes must be substitutable for their base types. If a subclass breaks the expected behavior of the parent class, you're violating LSP.
Interface Segregation (ISP)
No client should be forced to depend on interfaces they don't use. Prefer small, specific interfaces over a general-purpose one.
Dependency Inversion (DIP)
High-level modules should not depend on low-level modules. Both should depend on abstractions. Inject dependencies instead of creating them.
Want to apply SOLID in your project? At Vynta we design clean and maintainable architectures.