Hi Everybody,

I spent some time testing and trying different ways how to pass, process and use optional opts in a function argument.

Ideally I’d like to settle on a single piece of code - something I can use in all my functions.

By searching I quickly realized that everybody has own take on this.

At the end I developed my own way and I’d like to kindly ask you if somebody can review it advise me if this is clever or stupid and I shouldn’t use it ;-).

defmodule Helper.ArgOpts do
  @spec add_argument(map, atom, keyword, atom) :: map
  def add_argument(map, map_key, keyword, keyword_key)
      when is_map(map) and is_atom(map_key) and is_list(keyword) and is_atom(keyword_key) do
    values =
      if Keyword.has_key?(keyword, keyword_key),
        do: Keyword.get_values(keyword, keyword_key),
        else: []

    Map.put(map, map_key, values)
  end
end

defmodule MySuperApp do
  @opts_default color: :red,
           engine: :standard
  @spec make_bike(atom, list) :: String.t()
  def make_bike(brand, opts \\ []) when is_atom(brand) and is_list(opts) do
    opts = @opts_default ++ opts
    all_opts = Enum.into(opts, %{})

	# stupid example how to use the `opts` args:
    "bike: #{all_opts.color} #{brand} with #{all_opts.engine} engine"
  end

  @opts_default number_of_wheels: 4,
           color: :red,
           engine_size: :standard,
           tuning?: false
  @spec make_car(atom, list) :: String.t()
  def make_car(brand, opts \\ []) when is_atom(brand) and is_list(opts) do
    opts = @opts_default ++ opts
    all_opts = Enum.into(opts, %{})
    all_opts = Helper.ArgOpts.add_argument(all_opts, :features, opts, :feature)

	# stupid example how to use the `opts` args:
    engine =
      if all_opts.tuning?,
        do: "TUNED engine",
        else: "#{all_opts.engine_size} engine"

    """
    car: #{all_opts.color} #{brand}
      with #{all_opts.number_of_wheels} wheels
      and #{engine}
      and features: #{inspect(all_opts.features)}
    """
  end
end

IO.puts(MySuperApp.make_bike(:honda))

IO.puts(MySuperApp.make_bike(:kawasaki, engine: :fastest, color: :green))

IO.puts(MySuperApp.make_car(:ferrari))

IO.puts(MySuperApp.make_car(:lamborghini, color: :yellow, feature: :air_con, feature: :shiny_wheels))

IO.puts(MySuperApp.make_car(:hummer, color: :black, number_of_wheels: 6, tuning?: true, feature: :dark_window_tint))

Basically the idea is to have an attribute @opts_default with default values on top of each function that has opts argument.

In a simple functions (like make_bike/2) the Keyword list with defaults + the keyword list with user specified values is converted into a Map. Defaults get overwritten by user specified values.

In more complicated functions (like make_car/2) it is possible to repeat a keyword (in the example feature) and then add a features key into the new map. New features key holds all values (or empty list if feature is not specified).

Can I please get feedback if this is/isn’t a good way.

Thank you ;-).

Kind regards,

Ben