defimpl for maps

[mnussbaumer]

Hi,

can someone explain what is the idea behind having this on formatter.ex?

defimpl Bamboo.Formatter, for: Map do
  def format_email_address(invalid_address, _opts) do
    raise ArgumentError, """
    The format of the address was invalid. Got #{inspect(invalid_address)}.
    Expected a string, e.g. "foo@bar.com", a 2 item tuple {name, address}, or
    something that implements the Bamboo.Formatter protocol.
    Example:
    defimpl Bamboo.Formatter, for: MyApp.User do
      def format_email_address(user, _opts) do
        {user.name, user.email}
      end
    end
    """
  end
end

This introduces warnings and duplicated modules errors and it seems like it isn't doing anything that a non-existing defimpl would warn/error by itself?

Other than that, how can I create an implementation for the Map type?