Rails 助手在 self 方法中将负号作为参数传递

Question

In my Rails 6, Ruby 2.7 app I'm using ActionView::Helpers::NumberHelper and number_to_currency method. Everything works fine but in one place I need to have negative amount instead of positive. To do so I created two methods:

formatters/document_amount_formatter.rb

module Formatters
  # Formats the amount in a suitable form to be used in PDF creator.
  class DocumentAmountFormatter
    extend ActionView::Helpers::NumberHelper

    # The method to call.
    #
    # @return [String]
    def self.call(amount)
      number_to_currency(amount.to_f, delimiter: '.', separator: ',', format: '%n €')
    end

    def self.negative_amount(amount)
      number_to_currency(-amount.to_f, delimiter: '.', separator: ',', format: '%n €')
    end
  end
end

Both works well:

Formatters::CashbookDocumentAmountFormatter.call(cash_transactions.first.gross_amount)
=> "100,00 €"
Formatters::CashbookDocumentAmountFormatter.negative_amount(cash_transactions.first.gross_amount)
=> "-100,00 €"

But I'm not so sure if this is a good approach, tbh the code seems to be smelly. Is it possible to change those two methods into one? How to pass '-' or '+' as an argument inside of one of these methods?

Answer 1

Call call from within negative_amount .

    def self.negative_amount(amount)
      call(-amount)
    end

The next question being, why have this method at all? The caller can write formatter.call(-amount) just as easily and more obviously.

Note that you probably shouldn't hard-code currency formatting and instead make use if internationalization .