public function channel(string $channel_id) : EventChannelInterface
    {
        if (isset($this->channel_adapters[$channel_id])){
            return $this->channel_adapters[$channel_id];
        }
        $adapter = new Stk2kEventChannelAdapter(
            $this->eventstream->channel(
                $channel_id,
                function () { return new SimpleEventSource(); },
                function () { return new WildCardEventEmitter(); }
            )
        );
        $this->channel_adapters[$channel_id] = $adapter;
        return $adapter;
    }