What is the best practice for matching function return values when the value isn't expected to be used?

Questions / Help
1

As I run dialyzer on my code, I see instances of the following warning:

Expression produces a value of type 'ok' | {'error',_}, but this value is unmatched

I often execute functions in my code in which I don’t use the return value. An instance like this my be in a GenServer when I log a message from a downed task.

def handle_info({:DOWN, ref, _proc, _pid, reason}, state) do
  Process.demonitor(ref)
  Logger.warn "#{__MODULE__} Task failed expectedly: #{inspect(reason)}"
  {:noreply, state}
end

Dialyzer will complain that Process.demonitor/1 and Logger.warn/2 are unmatched. So I might change my code to the following:

def handle_info({:DOWN, ref, _proc, _pid, reason}, state) do
  _bool = Process.demonitor(ref)
  :ok = Logger.warn "#{__MODULE__} Task failed expectedly: #{inspect(reason)}"
  {:noreply, state}
end

However, now if Logger returns {:error, any} it could crash my server.

So I’m curious, what is the best practice for matching function return values when the value isn’t expected to be used?

2

Well, you already did the verbose way in _bool = Processs.demonitor(ref), a instead of prefixing a name by _, you can use _ alone, eg: _ = Process.demonitor(ref).

And yes, _ = f.() is the idiomatic way to say “I do not care for fs return value, but call it solely for its sideeffects.”

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