Rosetta Example: Abstract type
Define a class without instances and without implemented methods. For detailed description of this example see http://rosettacode.org/wiki/Abstract_type
Define a class AbstractQueue
Define a concrete queue (named ListQueue) based on the Abstract Queue
Demonstrating the behavior in a shell:
Trying to create an instance of the AbstraceQueue returns an error message:
Create an instance of the concrete queue:
Enqueue and dequeue items