# File test/unit/util/observable.rb, line 31

                                def add_listener(channel_name, listener_key=NOTHING, &listener) # :yields: value

                                        unless(block_given?)

                                                raise ArgumentError.new("No callback was passed as a listener")

                                        end

                        

                                        key = listener_key

                                        if (listener_key == NOTHING)

                                                listener_key = listener

                                                key = ProcWrapper.new(listener)

                                        end

                        

                                        channels[channel_name] ||= Hash.new

                                        channels[channel_name][key] = listener

                                        return listener_key

                                end