def stringified_exchange_date
      value = (@exchange_date || Time.now.send(:to_date))
      [value.day, value.month, value.year].join('-')
    end
def stringified_exchange_date
      value = (@exchange_date || Time.now.send(:to_date))
      [value.day, value.month, value.year].join('-')
    end
Cache helper methods (only useful in a Rails app)

 Returns a suitable string-like date (like "25-8-2010"),
 aware of possible @exchange_date set by :at method