defmodule FDS.ArrayList do
  defstruct [:ral]
  def new() do
    %__MODULE__{ral: :fds_ralist.new()}
  end
end

defimpl Collectable, for: FDS.ArrayList do
  def into(%FDS.ArrayList{ral: ral}) do
    {ral, &do_into/2}
  end

  defp do_into(_ral, :halt), do: :ok
  defp do_into(ral, :done), do: %FDS.ArrayList{ral: ral}
  defp do_into(ral, {:cont, item}), do: :fds_ralist.cons(item, ral)
end

defimpl Enumerable, for: FDS.ArrayList do
  def reduce(%FDS.ArrayList{ral: ral}, acc, fun) do
    {:done, :fds_ralist.foldl(fun, acc, ral)}
  end
  def count(%FDS.ArrayList{ral: ral}), do: :fds_ralist.count(ral)
  def member?(%FDS.ArrayList{}, _item), do: {:error, @for}
  def slice(%FDS.ArrayList{}), do: {:error, @for}
end