It’s a common pattern to use extend self inside ruby module to make all methods available in a static context/declared as class methods.

Instead of this, you can use module_function instead which will do the same as extend self but also have the added benefit of making those method private instance methods when they are included in another file.

module UserNameFormatter
  module_function

  def format_name(user)
    "#{user.name}"
  end
end

class User
  include UserNameFormatter

  def something
    format_name(self)
  end
end