t.rb

class EmailAddress
  def initialize(user, disallowed_email_domains, paid_via_ach)
    @user = user
    @disallowed_email_domains = disallowed_email_domains
    @paid_via_ach = paid_via_ach
  end

  def self.generate(user, disallowed_email_domains: [], paid_via_ach:)
    new(user, disallowed_email_domains, paid_via_ach)
  end

  private

  attr_reader :user, :disallowed_email_domains, :paid_via_ach

  def generate
    if paid_via_ach
      generate_for_paid_via_ach
    else
      generate_for_non_paid_via_ach
    end
  end
end