Indifferent access in elixir

access.ex

defmodule Access do
  def indifferent_key(key) do
    fn
      :get, data, next ->
        get_atom_or_string_key!(data, key)
        |> case do
          nil -> next.(nil)
          key -> next.(Map.get(data, key))
        end

      :get_and_update, data, next ->
        {key, value} =
          get_atom_or_string_key!(data, key)
          |> case do
            nil -> {key, nil}
            key -> {key, Map.get(data, key)}
          end

        case next.(value) do
          {get, update} -> {get, Map.put(data, key, update)}
          :pop -> {value, Map.delete(data, key)}
        end
    end
  end

  defp map_indifferent_get(data, key) do
    get_atom_or_string_key!(data, key)
    |> case do
      nil -> nil
      key -> Map.get(data, key)
    end
  end

  defp get_atom_or_string_key!(data, key) do
    {atom_key, string_key} =
      cond do
        is_atom(key) -> {key, to_string(key)}
        is_binary(key) -> {String.to_existing_atom(key), key}
        true -> raise "Indifferent key must be an atom or string"
      end

    {Map.has_key?(data, atom_key), Map.has_key?(data, string_key)}
    |> case do
      {true, true} -> raise "Map contains both string and atom key: #{string_key}"
      {false, false} -> nil
      {true, false} -> atom_key
      {false, true} -> string_key
    end
  end
end

iex.exs

update_in(attrs, [City.Access.indifferent_key(field)], fn value ->
...
end)