sub.exs

defmodule Common do

  defmacro __using__(_opts) do
    quote do
      def validate(thing) do
        Common.validate({__MODULE__, thing})
      end
    end
  end

  def validate({impl, thing}) do
    IO.puts "Validate #{inspect(thing)} with #{impl}"
  end
end

defmodule Customer do
  use Common
end

defmodule Product do
  use Common
end

Customer.validate([1,2,3])
Product.validate(%{:a => "A"})
# run with elixir sub.exs