////   This file contains the C++ code from Program 11.21 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/pgm11_21.cpp//typedef double time;class Event : public Association{public:    enum type    {	arrival, departure    };    typedef Wrapper<type> Type;    typedef Wrapper<time> Time;    Event (type typ, time tim) :	Association (*new Time (tim), *new Type (typ)) {}    Time& Key () const	{ return dynamic_cast<Time&> (Association::Key ()); }    Type& Value () const	{ return dynamic_cast<Type&> (Association::Value()); }};