module ActiveRecord::Persistence::ClassMethods

how this "single-table" inheritance mapping is implemented.
See ActiveRecord::Inheritance#discriminate_class_for_record to see

instances of the appropriate class for each record.
+instantiate+ instead of +new+, finder methods ensure they get new
by storing the record's subclass in a +type+ attribute. By calling
For example, +Post.all+ may return Comments, Messages, and Emails

the appropriate class. Accepts only keys as strings.
Given an attributes hash, +instantiate+ returns a new instance of

def instantiate(attributes, column_types = {}, &block)
  klass = discriminate_class_for_record(attributes)
  instantiate_instance_of(klass, attributes, column_types, &block)
end