Phoenix Counting Application - (FunctionClauseError) no function clause matching

I’m currently learning some phoenix and built a counting app with a simple increase/decrease. Both worked fine so I decided to implement GenServers and PubSub to see how many users currently are on the page (presence).

Whole error:

GenServer #PID<0.511.0> terminating
** (FunctionClauseError) no function clause matching in CounterWeb.Counter.handle_info/2
    (counter 0.1.0) lib/counter_web/live/counter.ex:45: CounterWeb.Counter.handle_info({:count, 1}, #Phoenix.LiveView.Socket<assigns: %{__changed__: %{}, flash: %{}, live_action: nil, present: 1, val: 
1}, endpoint: CounterWeb.Endpoint, id: "phx-FtSq5dehn8AlGgAF", parent_pid: nil, root_pid: #PID<0.511.0>, router: CounterWeb.Router, transport_pid: #PID<0.506.0>, view: CounterWeb.Counter, ...>)  

I think it’s coming from my make change function

defp make_change(count, change) do
    new_count = count + change
    PubSub.broadcast(Counter.PubSub, topic(), {:count, new_count})
    {:reply, new_count, new_count}

and my handle info

def handle_info(
       %{event: "presence_diff", payload: %{joins: joins, leaves: leaves}},
       %{assigns: %{present: present}} = socket
    ) do
   new_present = present + map_size(joins) - map_size(leaves)

   {:noreply, assign(socket, :present, new_present)}

Someone recommended me to create another clause and do the same kind of setup as I did with the previous functions to handle the calls, example:

def handle_call(:reply, _from, count) do
    {:ok, count, count}

  def handle_call(:incr, _from, count) do
    make_change(count, +1)

  def handle_call(:decr, _from, count) do
    make_change(count, -1)

My first argument is the message I receive, I am sending a tuple and I have to match that tuple.

I think I have to add another handle_info, like this

def handle_info({count: count}, socket) do
   # ???
   {:noreply, socket}

How would I handle/implement that? Can anyone help me by explaining that a bit?


If you are getting function clause matching error - you have to add new handle_info/2

It should be like what is described in error message {:count, count} not {count: count}

def handle_info({:count, count}, socket) do

I am little confused - you are speaking about GenServer and the error message and your sample code refers to PhoenixLiveView.Socket.

You have implemented the GenServer and Pubsub part and you want to handle the PubSub message in LiveView ?


so just

def handle_info({:count, count}, socket) do
    {:noreply, assign(socket, val: count)}
1 Like

{:noreply, assign(socket, :val, count)} - did it work ?

I just had to add the following function to get it working, is there any better solution maybe?

def handle_info({:count, count}, socket) do
    {:noreply, assign(socket, val: count)}