def to_s
      present_rules = FILTERS.select { |sym| method(sym).call }
      present_rules.map! { |sym| "#{sym}='#{method(sym).call}'" }
      present_rules.join(",")
    end
def to_s
      present_rules = FILTERS.select { |sym| method(sym).call }
      present_rules.map! { |sym| "#{sym}='#{method(sym).call}'" }
      present_rules.join(",")
    end
Returns a match rule string version of the object. E.g.:
 "type='signal',sender='org.freedesktop.DBus'," +
 "interface='org.freedesktop.DBus',member='Foo'," +
 "path='/bar/foo',destination=':452345.34',arg2='bar'"