class ActionDispatch::Routing::RouteSet

def define_mounted_helper(name, script_namer = nil)
  return if MountedHelpers.method_defined?(name)
  routes = self
  helpers = routes.url_helpers
  MountedHelpers.class_eval do
    define_method "_#{name}" do
      RoutesProxy.new(routes, _routes_context, helpers, script_namer)
    end
  end
  MountedHelpers.class_eval(<<-RUBY, __FILE__, __LINE__ + 1)
    def #{name}
      @_#{name} ||= _#{name}
    end
  RUBY
end