GravatarHelper with module_function usage

gravatar_helper.rb

require 'digest/md5'

module GravatarHelper
  module_function
  def gravatar_for_email(email)
    "#{gravatar_endpoint}#{hash_for_email(email)}"
  end

  def hash_for_email(email)
    Digest::MD5.hexdigest(email)
  end

  def gravatar_endpoint
    'http://www.gravatar.com/avatar/'
  end
end

usage.rb

[0] (pry) main: 0> user = User.new('user@example.com');
[1] (pry) main: 0> GravatarHelper.gravatar_for_email(user.email)
=> 'http://www.gravatar.com/avatar/b58996c504c5638798eb6b511e6f49af'
[2] (pry) main: 0> user.gravatar
=> 'http://www.gravatar.com/avatar/b58996c504c5638798eb6b511e6f49af'

user.rb

class User
  include GravatarHelper

  attr_reader :email

  def initialize(email)
    @email = email
  end

  def gravatar
    gravatar_for_email @email
  end
end