Tbh I disagree with the idea of Repo.insert(%Reminder{}) needing to support dynamic defaults as well. Elixir is very much about being explicit. If you need your data to come from side effects I expect the code to tell me. %Reminder{} |> with_default_target_datetime() |> Repo.insert() is a lot better code than Repo.insert(%Reminder{}) automatically messing around with struct fields.
You’re argueing that struct defaults being a compile time thing prevent libraries from introducing dynamic field defaults. I’d counter that with dynamic defaults being something you want to have an explicit api for and once you do there’s no longer any limitation. I don’t expect ecto ever wanted to provide you with a dynamic defaults feature to begin with.
In the end your argument comes down to “I want to introduce dynamically calculated default values without changing my codebase” – not a great argument imo, such a change should be made explicit by changing code.
