SimpleVsDCI.rb

class Human
  attr_reader :name, :amount
  
  def initialize(name, amount)
    @name = name
    @amount = amount
  end
  
  def deposit(amount)
    @amount += amount
  end
  
  def withdraw(amount)
    @amount -= amount
  end
  
  def say(text)
    puts text
  end
end

# ParentExtension.rb
class Human
  def parent_give_pocket_money_to(child)
    amount = 5 # five backs
    withdraw(amount)
    child.receive_pocket_money(amount)
  end
end

# ChildExtension.rb
class Human
  def child_receive_pocket_money(amount)
    deposit(amount)
    say('Thank you')
  end
end

# EmployeeExtension.rb
class Human
  def employee_receive_salary(amount)
    deposit(amount)
    ...
  end
  
  def employee_do_job_task()
    ...
  end
end

# ParentingController.rb
class ParentingController < ApplicationController
  
  def do_parenting
    child = Human.find params[:id]
    current_user.parent_give_pocket_money_to child
  end
    
end