Are you familiar with Hexagonal Architecture? Tell about its structure.

Hexagonal Architecture, or Ports and Adapters, is an architectural style that separates the application into a core and external interfaces. The core contains business logic (domain) that does not depend on external systems such as databases, UI, or external services.

The structure includes:

• Domain (core) — contains business rules and logic.
• Ports — interfaces through which the core interacts with the outside world (e.g., repositories, services).
• Adapters — implementations of ports for specific technologies (DB, web, UI).

This allows easy replacement of external components without changing business logic, improving testability and maintainability.

Example in Go:

// Port
type UserRepository interface {
    GetUser(id string) (*User, error)
}

// Domain
func GetUserName(repo UserRepository, id string) (string, error) {
    user, err := repo.GetUser(id)
    if err != nil {
        return "", err
    }
    return user.Name, nil
}

// Adapter
type InMemoryUserRepo struct {
    users map[string]*User
}

func (r *InMemoryUserRepo) GetUser(id string) (*User, error) {
    user, ok := r.users[id]
    if !ok {
        return nil, errors.New("user not found")
    }
    return user, nil
}

This approach isolates business logic from implementation details.