Maybe you can replace your map with a “function lookup”. And have mappings keys be strings? Would it change anything?

defmodule SomeModule do
  @moduledoc ""
  
  mappings = %{
    "published_at" => {:date_time, "published_at"},
    "indexed_at" => {:date_time, "indexed_at"},
    "not_parent_shared_uid" => {:terms_exclusion, "parent.shared_uid"}
  }

  @spec lookup_mapping(String.t()) :: {atom, String.t()} | nil
  defp lookup_mapping(filter_name)

  Enum.map(mappings, fn {filter_name, value} ->
    defp lookup_mapping(unquote(filter_name)) do
      unquote(value) # would create :date_time and :terms_exclusion atoms during compilation
    end
  end)

  defp lookup_mapping(_unmatched), do: nil

  def parse_filter({filter_name, value}, topic_id, acc) do
    case lookup_mapping(filter_name) do
      {function, field} ->
        apply(__MODULE__, function, [value, field, topic_id, acc])
      nil -> 
        acc
    end
  end
end

@idi527: I’d rather use atoms as map keys, although it’s just a personal preference. But I’ll look more into your code, thanks

I can’t be sure, it comes from the outside. It’s not really something I can control, I have to have “good faith” in the maintainer of the app that’s queering this app of mine. He’s got no malicious intent, though, as he’s a my work colleague.

With Map.fetch! this would fail every time exactly where it should, so I may go with this instead. Thanks