////   This file contains the C++ code from Program 13.15 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/pgm13_15.cpp//typedef unsigned int time;class Event : public Association{public:    typedef Wrapper<time> Time;    typedef Wrapper<void*> VoidPtr;    Event (time t, void* ptr) :	Association (*new Time (t), *new VoidPtr (ptr)) {}    Time& Key () const	{ return dynamic_cast<Time&> (Association::Key ()); }    VoidPtr& Value () const	{ return dynamic_cast<VoidPtr&> (Association::Value()); }};