eval_block

# File actionpack/lib/action_dispatch/routing/route_set.rb, line 273
      def eval_block(block)
        if block.arity == 1
          raise "You are using the old router DSL which has been removed in Rails 3.1. " <<
            "Please check how to update your routes file at: http://www.engineyard.com/blog/2010/the-lowdown-on-routes-in-rails-3/"
        end
        mapper = Mapper.new(self)
        if default_scope
          mapper.with_default_scope(default_scope, &block)
        else
          mapper.instance_exec(&block)
        end
      end