form_object.rb

class InvoiceForm
  attr_reader :params
  def initialize(params)
    @params = params
  end
  
  def billing_date
    Time.new(*[:year, :month, :day].map { |k| params[k] or raise ArgumentError})
  rescue ArgumentError
  end
  
  def company_name
    params[:_messed_up_company_name] || params[:company_name]
  end
  
  def valid?
    billing_date.present? && company_name.present?
  end
  
  private

end

form = InvoiceForm.new({year: "2014", month: "07", day: "18"})
form.billing_date # => Time instance