Use constructor functions

Create a function that initializes a Company with a properly initialized Department implementation.

This solution fixes the nil interface problem in several ways:

1. Guaranteed Initialization: The constructor function NewCompany requires a Department as an argument, ensuring that a Company is always created with a non-nil PrimaryDepartment.

2. Encapsulation: The creation logic is encapsulated in the constructor, reducing the chance of incorrect initialization elsewhere in the code.

3. Clear Intent: Using a constructor function makes it clear to other developers that proper initialization is required and how it should be done.

4. Compile-time Safety: If a developer tries to create a Company without providing a Department, they'll get a compile-time error rather than a runtime panic.

5. Flexibility: The constructor can be easily extended to include additional initialization logic or validation if needed in the future.

By using this pattern, we shift the responsibility of providing a valid Department to the caller of NewCompany, making the code more robust and less prone to runtime errors. This approach aligns with Go's philosophy of making the zero value useful, as a Company created with the constructor is immediately usable without risk of nil pointer dereferences.

package core

import (
   "fmt"

   "github.com/go-logr/logr"
)

type Department interface {
   GetName() string
}

type Company struct {
   PrimaryDepartment Department
}

func (c *Company) DisplayInfo() {
   fmt.Printf("Company's primary department: %s\n", c.PrimaryDepartment.GetName())
}

func NewCompany(dept Department) *Company {
   return &Company{
   	PrimaryDepartment: dept,
   }
}

type StandardDepartment struct {
   name string
}

func (d *StandardDepartment) GetName() string {
   return d.name
}

func NewStandardDepartment(name string) *StandardDepartment {
   return &StandardDepartment{name: name}
}

func Main(logger logr.Logger) {
   logger.V(1).Info("Debug: Entering Main function")
   dept := NewStandardDepartment("Engineering")
   myCompany := NewCompany(dept)
   myCompany.DisplayInfo()
}