## With a callback
class Foo < ActiveRecord::Base
  attr_reader :thing, :thang
  def after_initialize
    @thing = nasty_computation
    @thang = other_nasty_computation
  end
end

## without a callback
class Foo < ActiveRecord::Base
  def thing
    @thing ||= nasty_computation
  end

  def thang
    @thang ||= other_nasty_computation
  end
end