Maybe/lib/money/currency.rb

class Money::Currency
    include Comparable

    class UnknownCurrencyError < ArgumentError; end

    CURRENCIES_FILE_PATH = Rails.root.join("config", "currencies.yml")

    # Cached instances by iso code
    @@instances = {}

    class << self
        def new(object)
            iso_code = case object
            when String, Symbol
              object.to_s.downcase
            when Money::Currency
              object.iso_code.downcase
            else
              raise ArgumentError, "Invalid argument type"
            end

            @@instances[iso_code] ||= super(iso_code)
        end

        def all
            @all ||= YAML.load_file(CURRENCIES_FILE_PATH)
        end

        def popular
            all.values.sort_by { |currency| currency["priority"] }.first(12).map { |currency_data| new(currency_data["iso_code"]) }
        end
    end

    attr_reader :name, :priority, :iso_code, :iso_numeric, :html_code,
                :symbol, :minor_unit, :minor_unit_conversion, :smallest_denomination,
                :separator, :delimiter, :default_format, :default_precision

    def initialize(iso_code)
        currency_data = self.class.all[iso_code]
        raise UnknownCurrencyError if currency_data.nil?

        @name = currency_data["name"]
        @priority = currency_data["priority"]
        @iso_code = currency_data["iso_code"]
        @iso_numeric = currency_data["iso_numeric"]
        @html_code = currency_data["html_code"]
        @symbol = currency_data["symbol"]
        @minor_unit = currency_data["minor_unit"]
        @minor_unit_conversion = currency_data["minor_unit_conversion"]
        @smallest_denomination = currency_data["smallest_denomination"]
        @separator = currency_data["separator"]
        @delimiter = currency_data["delimiter"]
        @default_format = currency_data["default_format"]
        @default_precision = currency_data["default_precision"]
    end

    def <=>(other)
        return nil unless other.is_a?(Money::Currency)
        @iso_code <=> other.iso_code
    end
end