Use a Typespec function type

Questions & Help Questions
2

This is accomplished using behaviours:

defmodule A do
  @callback simple_function(integer()) :: non_neg_integer()
end

defmodule B do
  @behaviour A

  @impl A
  def simple_function(int), do: ...
end

I’ll add, however, that it’s not advisable to create behaviours if your goal is really only to re-use some typespecs. Two different functions sharing a common, duplicated typespec is not a code smell.