Minimal KVS implementation using `GenServer` in Elixir

kv.ex

defmodule Kv do
  @name :kvs

  def new() do
    GenServer.start_link(Kv.Server, %{}, name: @name)
  end

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

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

kv_impl.ex

defmodule Kv.Impl do
  def new() do
    %{}
  end

  def lookup(store, name) do
    {:ok, result} = Map.fetch(store, name)
    result
  end

  def store(store, name, value) do
    Map.put(store, name, value)
  end
end

kv_server.ex

defmodule Kv.Server do
  use GenServer
  alias Kv.Impl

  def handle_call({:lookup, name}, _, store) do
    {:reply, Impl.lookup(store, name), store}
  end

  def handle_cast({:store, name, value}, store) do
    {:noreply, Impl.store(store, name, value)}
  end
end

kv_single.ex

defmodule KvSingle do
  use GenServer
  @name :kvs

  def new() do
    GenServer.start_link(__MODULE__, %{}, name: @name)
  end

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

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

  def handle_call({:lookup, name}, _, store) do
    {:ok, result} = Map.fetch(store, name)
    {:reply, result, store}
  end

  def handle_cast({:store, name, value}, store) do
    {:noreply, Map.put(store, name, value)}
  end
end

• KvSingle
• Kv(with Kv.Server and Kv.Impl)
  • https://pragdave.me/blog/2017/07/13/decoupling-interface-and-implementation-in-elixir.html