module A
  def hello
    puts "hola"
  end
end

# Instead of module_function, let's include A in its own metaclass so we
# can both include the methods in other classes and call the methods a class methods of the module
module A
  class << self
    include ::A
  end
end

class B
  include A
end

A.hello     # => "hola"
B.new.hello # => "hola"