adding documentation for cached_attributes

activerecord/lib/active_record/attribute_methods.rb

@@ -104,17 +104,19 @@ module ActiveRecord
 
       # +cache_attributes+ allows you to declare which converted attribute values should
       # be cached. Usually caching only pays off for attributes with expensive conversion
-      # methods, like date columns (e.g. created_at, updated_at).
+      # methods, like time related columns (e.g. created_at, updated_at).
       def cache_attributes(*attribute_names)
         attribute_names.each {|attr| cached_attributes << attr.to_s}
       end
 
-      # returns the attributes where
+      # returns the attributes which are cached.
+      # By default time related columns with datatype <tt>:datetime, :timestamp, :time, :date</tt> are cached
       def cached_attributes
         @cached_attributes ||=
           columns.select{|c| attribute_types_cached_by_default.include?(c.type)}.map(&:name).to_set
       end
 
+      # returns true if the provided attribute is being cached
       def cache_attribute?(attr_name)
         cached_attributes.include?(attr_name)
       end