port Merb's :identify routing option to Rails 3 router

gistfile1.rb

# see actionpack/lib/action_dispatch/routing/route_set.rb
module ActionDispatch
  module Routing
    class RouteSet
      class Generator
        # modified to allow :identify option ala Merb routing
        def opts                # :nodoc:
          parameterize = lambda do |name, value|
            to_param = lambda do |val|
              if options[:identify] and name == :id and not val.is_a?(String)
                val.send options[:identify]
              else
                val.to_param
              end
            end

            if name == :controller
              value
            elsif value.is_a?(Array)
              value.map { |v| Rack::Mount::Utils.escape_uri(to_param[v]) }.join('/')
            else
              return nil unless param = to_param[value]
              param.split('/').map { |v| Rack::Mount::Utils.escape_uri(v) }.join("/")
            end
          end
          {:parameterize => parameterize}
        end
      end
    end
  end
end