cache the cache key...

lib/declarative_policy/condition.rb

@@ -82,6 +82,7 @@ module DeclarativePolicy
     # depending on the scope, we may cache only by the user or only by
     # the subject, resulting in sharing across different policy objects.
     def cache_key
+      @cache_key ||=
         case @condition.scope
         when :normal  then "/dp/condition/#{@condition.key}/#{user_key},#{subject_key}"
         when :user    then "/dp/condition/#{@condition.key}/#{user_key}"