Does not every member variable definition in the class have a self?

List 9.3: green to add the Remember method to the User model

class User<ApplicationRecord
  attr_accessor:remember_token
  before_save {self.email=email.downcase}
  values:name,presence:true,length:{maximum:50}
  VALID_EMAIL_REGEX=/\A[\w+\-.]+@[a-z\d\-.]+\.[a-z]+\z/i
  values:email, presence:true, length:{maximum:255},
                    format: {with:VALID_EMAIL_REGEX},
                    unity: {case_sensitive:false}
  has_secure_password
  values:password,presence:true,length:{minimum:6}

  # return the hash value of a passed string
  def User.digest(string)
    cost=ActiveModel::SecurePassword.min_cost?BCrypt::Engine::MIN_COST:
                                                  BCrypt::Engine.cost
    BCrypt::Password.create(string, cost:cost)
  end

  # return a random token
  def User.new_token
    SecureRandom.urlsafe_base64
  end

  # store users in the database for persistent sessions
  Why is it not defremember#emmemo｠User.remember?
    self.remember_token=User.new_token
    update_attribute(:remember_digest,User.digest(remember_token))
  end
end