define_mounted_helper

# File actionpack/lib/action_dispatch/routing/route_set.rb, line 372
      def define_mounted_helper(name)
        return if MountedHelpers.method_defined?(name)

        routes = self
        MountedHelpers.class_eval do
          define_method "_#{name}" do
            RoutesProxy.new(routes, _routes_context)
          end
        end

        MountedHelpers.class_eval(          def #{name}            @_#{name} ||= _#{name}          end, __FILE__, __LINE__ + 1)
      end