Objects are relatively heavy weight. To be able to create efficiently
light weight objects, we introduce the notion of instances. An
instance is an object with restricted capability. It is created from
an object that is considered its class. It gets a copy of the
attributes of its class. These can be modified by get/1 and
set/1. An instance cannot be a class for other
instances. Instances are in general very efficient, both in space and
access/modification time. The attribute '$class'/1 will store
the identity of the class of the instance including parameters.