# File lib/dbus/bus.rb, line 573
    def add_match(mr, &slot)
      # check this is a signal.
      mrs = mr.to_s
      puts "#{@signal_matchrules.size} rules, adding #{mrs.inspect}" if $DEBUG
      # don't ask for the same match if we override it
      unless @signal_matchrules.key?(mrs)
        puts "Asked for a new match" if $DEBUG
        proxy.AddMatch(mrs)
      end
      @signal_matchrules[mrs] = slot
    end