lambda caching

gistfile1.rb

class Episode < ActiveRecord::Base
  scope :airs_at_in_future,       lambda{ where('episodes.airs_at > ?', Time.zone.now) }
  scope :airs_at_in_past,         lambda{ where('episodes.airs_at < ?', Time.zone.now) }

  # will cache Time.now
  scope :next_airing,             airs_at_in_future.order('episodes.airs_at asc')
  scope :last_aired,              airs_at_in_past.order('episodes.airs_at desc')

  # will not cache Time.now
  scope :next_airing,             lambda{ airs_at_in_future.order('episodes.airs_at asc') }
  scope :last_aired,              lambda{ airs_at_in_past.order('episodes.airs_at desc') }
end

I guess Arel/AR only postpones (lazyloads) the sql call, and call's procs directly
https://github.com/rails/rails/blob/master/activerecord/lib/active_record/named_scope.rb#L160