rails_dynamic_routes.rb

# Maps a Rails route to a dynamic action name using interpolation.
#
#   get 'experiments/ajax/:endpoint', to: dynamic('experiments#ajax_%{endpoint}')

class Dynamic
  def initialize(to)
    @to = to
  end
  def call(env)
    params = env['action_dispatch.request.path_parameters']
    controller, action = @to.split('#')
    params[:action] = action = action % params 
    params[:controller] = controller
    "#{controller.camelize}Controller".constantize.action(action).call(env)
  end
  def to_s
    @to
  end
end

def dynamic(to)
  Dynamic.new(to)
end