class ActionDispatch::Flash::FlashHash

def self.from_session_value(value) #:nodoc:
  flash = case value
          when FlashHash # Rails 3.1, 3.2
            new(value.instance_variable_get(:@flashes), value.instance_variable_get(:@used))
          when Hash # Rails 4.0
            new(value['flashes'], value['discard'])
          else
            new
          end
  flash.tap(&:sweep)
end