async callback

example.exs

defmodule Example do
  use GenServer

  def start_link(_) do
    GenServer.start_link __MODULE__, :ok, []
  end 

  def init(:ok) do
    {:ok, []}
  end

  def add(pid,{first_name,last_name}) do
    GenServer.cast(pid,{:add, first_name, last_name})
    IO.puts("after calling add")
  end

  def handle_cast({:add, first_name, last_name},state) do
    task = Task.async(fn -> 
      :timer.sleep(5_000)
      Enum.join([first_name,last_name]," ") 
    end)
    {:noreply, state}
  end

  def handle_info({_ref, first_and_last_name}=msg,state) do
    IO.inspect(msg, label: "handle_info")
    {:noreply, [first_and_last_name | state]}
  end

  def handle_info(_, state), do: {:noreply, state}
end