Different styles of manipulating hierarchy in Elixir

manipulating_hierarchy.ex

defmodule Fp do
  defmodule Company do
    defrecordp :company, employees: HashDict.new
    defrecordp :employee, [:id, :name]
    
    def merge_employee(company(employees: employees), employee(id: employee_id) = employee) do
      company(company, employees: Dict.put(employees, employee_id, employee))   
    end
    
    def new, do: company()
    def new_employee(id, name), do: employee(id: id, name: name)
  end
  
  IO.inspect(
    Company.new |>
    Company.merge_employee(Company.new_employee(1, "John Doe"))
  )
end


defmodule Hybrid do
  defrecord Employee, [:id, :name]

  defrecord Company, employees: HashDict.new do
    def merge_employee(company, employee) do
      company.update_employees(Dict.put(&1, employee.id, employee))
    end
  end

  IO.inspect(
    Company.new |> 
    Company.merge_employee(Employee.new(id: 1, name: "John Doe"))
  )
end


defmodule Oop do
  defrecord Employee, [:id, :name]

  defrecord Company, employees: HashDict.new do
    def merge_employee(employee, company) do
      company.update_employees(Dict.put(&1, employee.id, employee))
    end
  end

  IO.inspect(
    Company.new.
      merge_employee(Employee.new(id: 1, name: "John Doe"))
  )
end