Elixir mutable bucket via :ets

mutable_bucket.ex

defmodule Bucket do
  @moduledoc """
  A mutable "bucket" implementing the `Access` behaviour.
  """

  @behaviour Access

  defstruct [:ets]

  @type t :: %__MODULE__{ets: term}

  @doc """
  Returns a new empty bucket.
  """
  @spec new() :: t
  def new do
    Map.new
    table = :ets.new(__MODULE__, [:set, :protected])
    struct(__MODULE__, ets: table)
  end

  #
  # Callbacks
  #

  @doc false
  def fetch(%__MODULE__{ets: table}, key) do
    case :ets.lookup(table, key) do
      [{^key, val}] ->
        {:ok, val}
      _else ->
        :error
    end
  end

  @doc false
  def get(%__MODULE__{} = bucket, key, default) do
    case fetch(bucket, key) do
      {:ok, value} -> value
      :error       -> default
    end
  end

  @doc false
  def get_and_update(%__MODULE__{ets: table} = bucket, key, list) do
    val = get(bucket, key, nil)
    case list.(val) do
      {ret_val, new_val} ->
        :ets.insert(table, {key, new_val})
        {ret_val, bucket}
      :pop ->
        :ets.delete(table, key)
        {val, bucket}
    end
  end

  @doc false
  def pop(%__MODULE__{ets: table} = bucket, key) do
    case :ets.take(table, key) do
      [val] ->
        {val, bucket}
      [] ->
        {nil, bucket}
    end
  end
end