ActiveSupport::Memoizable will be removed from Rails and has a lot of strange caveats that will ruin your day.
Use the 
  Memoizer gem
  
    Show archive.org snapshot
  
 instead. It works in all past and future Railses and has none of the annoying "features" of ActiveSupport::Memoizable. It just does memoization and does it well.
The syntax is similiar also:
class Foo
  include Memoizer
  
  def bar
      ...
  end
  
  memoize :bar
  
end
If you're using Ruby 2.1+, you can write this even shorter:
class Foo
  include Memoizer
  
  memoize def bar
      ...
  end
end
This is because def 
  returns the method name as a symbol
  
    Show archive.org snapshot
  
 in 2.1+.
Posted by Henning Koch to makandra dev (2012-07-02 18:22)