////   This file contains the C++ code from Program 16.6 of//   "Data Structures and Algorithms//    with Object-Oriented Design Patterns in C++"//   by Bruno R. Preiss.////   Copyright (c) 1998 by Bruno R. Preiss, P.Eng.  All rights reserved.////   http://www.pads.uwaterloo.ca/Bruno.Preiss/books/opus4/programs/pgm16_06.cpp//class WeightedVertex : public Vertex{    Object* weight;public:    WeightedVertex (Vertex::Number, Object&);    virtual Object& Weight () const;    // ...};    class WeightedEdge : public Edge{    Object* weight;public:    WeightedEdge (Vertex&, Vertex&, Object&);    virtual Object& Weight () const;    // ...};