Decorator?

invoice.rb

class Invoice
  attr_accessor :a, :b, :c, :name
  
  def to_s
    name
  end
  
end

report.rb

class Report
  
  class Invoice < ::Invoice
    def to_s
      [name]
    end
  end
  
  def build_csv
    
    # CSV Setup
    # 
    # csv.is_a? Array
    # => true
    # 
    csv += Invoice.all.inject([]) do |lines, invoice|
      lines << invoice
    end
    
    # CSV Finish
    # 
  end
  
end