Elixir Bucket module implementing the Access behaviour

bucket.ex

defmodule Bucket do
  @behaviour Access

  defstruct pid: nil

  def start_link(default \\ %{}) when is_map(default) do
    case Agent.start_link(fn -> default end) do
      {:ok, pid} ->%__MODULE__{pid: pid}
      {:error, message} -> raise message
    end
  end

  def fetch(%__MODULE__{pid: pid}, key) do
    {:ok, Agent.get(pid, &(&1))[key]}
  end

  def get_and_update(%__MODULE__{pid: pid} = handle, key, fun) do
    {Agent.get_and_update(pid, fn state ->
      {_, new_val} = fun.(key)
      {new_val, Map.put(state, key, new_val)}
    end), handle}
  end

  defimpl Inspect do
    def inspect(bucket, _) do
      Kernel.inspect(bucket.pid)
      |> String.replace("PID", "Bucket")
    end
  end
end