Data Structures and Algorithms
with Object-Oriented Design Patterns in C++ 
A NullIterator is a concrete iterator that does nothing.
As discussed in Section 
,
every container has a NewIterator member function
that returns a reference to an iterator instance.
If a particular concrete container class does not provide
an associated iterator class,
its NewIterator member function returns a reference
to a NullIterator.
Program gives the declaration of the NullIterator class.
Program: NullIterator Class Definition
Because it is a concrete class,
NullIterator provides implementations for all
the pure virtual member functions of the Iterator class.
As shown in Program ,
the implementation is trivial:
The IsDone member function always returns true;
the operator* member function always returns a reference
to the NullObject instance;
and the remaining functions do nothing at all.
Program: NullIterator Class Member Function Definitions
The default behavior of the NewIterator function
of the Container class is to
return a reference to a a new NullIterator instance
as shown in Program .
Program: Container Class NewIterator Member Function Definition
Copyright © 1997 by Bruno R. Preiss, P.Eng. All rights reserved.