class ActionDispatch::Routing::Mapper::Mapping

def app(blocks)
  if to.is_a?(Class) && to < ActionController::Metal
    Routing::RouteSet::StaticDispatcher.new to
  else
    if to.respond_to?(:call)
      Constraints.new(to, blocks, Constraints::CALL)
    elsif blocks.any?
      Constraints.new(dispatcher(defaults.key?(:controller)), blocks, Constraints::SERVE)
    else
      dispatcher(defaults.key?(:controller))
    end
  end
end