example.ex

defmodule OtpConceptsProcesses do

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

  def init(:ok) do
    {:ok, %{}}
  end

  def add(pid, value) do
    GenServer.cast(pid, {:add, value})
  end

  def remove(pid, value) do
    GenServer.cast(pid, {:remove, value})
  end

  def value(pid) do
    GenServer.call(pid, :final)
  end

  def handle_cast({:add, value}, state) do
    new_state = Map.put(state, :add, value)
    {:noreply, new_state}
  end

  def handle_cast({:remove, value}, state) do
    new_state = Map.put(state, :remove, value)
    {:noreply, new_state}
  end

  def handle_call(:final, _from, state) do
    {:reply, state, state}
  end
end