README.md

$ iex -S mix
iex(1)> B.new_hoge
:fuga

a.ex

defmodule A do
  @ignore_attributes [:macrocallback, :before_compile, :opaque, :spec, :behaviour, :on_definition,
  :type, :dialyzer, :external_resource, :after_compile, :callback,
  :derive, :compile, :optional_callbacks, :moduledoc, :typep]

  defmacro __using__(_opts \\ []) do
    quote do
      @before_compile A
    end
  end

  defmacro __before_compile__(env) do
    Module.attributes_in(env.module)
    |> Enum.reject(&(&1 in @ignore_attributes))
    |> Enum.map(fn attr ->
      quote do
        def unquote(:"new_#{attr}")() do
          unquote(Module.get_attribute(env.module, attr))
        end
      end
    end)
  end
end

b.ex

defmodule B do
  use A

  @hoge :fuga

  @moduledoc """
  Documentation for `Metatest`.
  """

  @doc """
  Hello world.

  ## Examples

      iex> Metatest.hello()
      :world

  """
  def hello do
    :world
  end
end