Simple cache using GenServer in Elixir

cache_server.exs

defmodule CacheServer do
  use GenServer

  @name CS

  ## Client API
  def start_link(opts \\ []) do
    GenServer.start_link(__MODULE__, :ok, opts ++ [name: CS])
  end

  def write(key, val) do
    GenServer.cast(@name, {:write, key, val})
  end

  def read(key) do
    GenServer.call(@name, {:read, key})
  end

  def delete(key) do
    GenServer.cast(@name, {:delete, key})
  end

  def clear() do
    GenServer.cast(@name, {:clear})
  end

  def exists?(key) do
    GenServer.call(@name, {:exists?, key})
  end

  ## Server API

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

  def handle_call({:read, key}, _from, cache) do
    {:reply, Map.fetch(cache, key), cache}
  end

  def handle_call({:exists?, key}, _from, cache) do
    {:reply, Map.has_key?(cache, key), cache}
  end

  def handle_cast({:write, key, val}, cache) do
    {:noreply, Map.put(cache, key, val)}
  end

  def handle_cast({:delete, key}, cache) do
    {:noreply, Map.delete(cache, key)}
  end

  def handle_cast({:clear}, _cache) do
    {:noreply, %{}}
  end

end