Hack for url versioned routes in Rails.

routes.rb

Rails.application.routes.draw do
  versioned do
    resources :flights
  end

  # Using the `versioned` helper with v1/ v2/ and v3/ directories existing
  # is equivalent to doing:
  # namespace :v1 do
  #   resources :flights
  # end

  # namespace :v2 do
  #   resources :flights
  # end

  # namespace :v3 do
  #   resources :flights
  # end
  #
end

versioned.rb

# Load this somewhere in initialisation.
module ActionDispatch::Routing
  class Mapper
    def versioned(&block)
      self.instance_eval(&Versioned.new.version(&block))
    end

    class Versioned
      def initialize
        @routes = Hash.new { |h, k| h[k] = Set.new }
      end

      def version(&block)
        self.instance_eval(&block)

        routes_proc
      end

      def method_missing(method, *args)
        controller_versions.each do |version|
          @routes[version] << [method, *args]
        end
      end

      def controller_versions
        versions = Set.new

        Dir[Rails.root.join("app/controllers/api/*")].each do |dir|
          versions << File.basename(dir)[1]
        end

        versions
      end

      def routes_proc
        routes = @routes

        Proc.new do
          routes.each do |version, version_routes|
            namespace :"v#{version}" do
              version_routes.each { |route| send(*route) }
            end
          end
        end
      end
    end
  end
end