namespace

# File actionpack/lib/action_dispatch/routing/mapper.rb, line 929
        def namespace(path, options = {}, &block)
          path = path.to_s

          defaults = {
            module:         path,
            as:             options.fetch(:as, path),
            shallow_path:   options.fetch(:path, path),
            shallow_prefix: options.fetch(:as, path)
          }

          path_scope(options.delete(:path) { path }) do
            scope(defaults.merge!(options), &block)
          end
        end

        # === Parameter Restriction
        # Allows you to constrain the nested routes based on a set of rules.
        # For instance, in order to change the routes to allow for a dot character in the +id+ parameter:
        #
        #   constraints(id: /\d+\.\d+/) do
        #     resources :posts
        #   end
        #
        # Now routes such as +/posts/1+ will no longer be valid, but +/posts/1.1+ will be.
        # The +id+ parameter must match the constraint passed in for this example.
        #
        # You may use this to also restrict other parameters:
        #
        #   resources :posts do
        #     constraints(post_id: /\d+\.\d+/) do
        #       resources :comments
        #     end
        #   end
        #
        # === Restricting based on IP
        #
        # Routes can also be constrained to an IP or a certain range of IP addresses:
        #
        #   constraints(ip: /192\.168\.\d+\.\d+/) do
        #     resources :posts
        #   end
        #
        # Any user connecting from the 192.168.* range will be able to see this resource,
        # where as any user connecting outside of this range will be told there is no such route.
        #
        # === Dynamic request matching
        #
        # Requests to routes can be constrained based on specific criteria:
        #
        #    constraints(-> (req) { /iPhone/.match?(req.env["HTTP_USER_AGENT"]) }) do
        #      resources :iphones
        #    end
        #
        # You are able to move this logic out into a class if it is too complex for routes.
        # This class must have a +matches?+ method defined on it which either returns +true+
        # if the user should be given access to that route, or +false+ if the user should not.
        #
        #    class Iphone
        #      def self.matches?(request)
        #        /iPhone/.match?(request.env["HTTP_USER_AGENT"])
        #      end
        #    end
        #
        # An expected place for this code would be +lib/constraints+.
        #
        # This class is then used like this:
        #
        #    constraints(Iphone) do
        #      resources :iphones
        #    end
        def constraints(constraints = {}, &block)
          scope(constraints: constraints, &block)
        end

        # Allows you to set default parameters for a route, such as this:
        #   defaults id: 'home' do
        #     match 'scoped_pages/(:id)', to: 'pages#show'
        #   end
        # Using this, the +:id+ parameter here will default to 'home'.
        def defaults(defaults = {})
          @scope = @scope.new(defaults: merge_defaults_scope(@scope[:defaults], defaults))
          yield
        ensure
          @scope = @scope.parent
        end

        private
          def merge_path_scope(parent, child)
            Mapper.normalize_path("#{parent}/#{child}")
          end

          def merge_shallow_path_scope(parent, child)
            Mapper.normalize_path("#{parent}/#{child}")
          end

          def merge_as_scope(parent, child)
            parent ? "#{parent}_#{child}" : child
          end

          def merge_shallow_prefix_scope(parent, child)
            parent ? "#{parent}_#{child}" : child
          end

          def merge_module_scope(parent, child)
            parent ? "#{parent}/#{child}" : child
          end

          def merge_controller_scope(parent, child)
            child
          end

          def merge_action_scope(parent, child)
            child
          end

          def merge_via_scope(parent, child)
            child
          end

          def merge_format_scope(parent, child)
            child
          end

          def merge_path_names_scope(parent, child)
            merge_options_scope(parent, child)
          end

          def merge_constraints_scope(parent, child)
            merge_options_scope(parent, child)
          end

          def merge_defaults_scope(parent, child)
            merge_options_scope(parent, child)
          end

          def merge_blocks_scope(parent, child)
            merged = parent ? parent.dup : []
            merged << child if child
            merged
          end

          def merge_options_scope(parent, child)
            (parent || {}).merge(child)
          end

          def merge_shallow_scope(parent, child)
            child ? true : false
          end

          def merge_to_scope(parent, child)
            child
          end
      end