////   This file contains the C++ code from Program 5.19 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/pgm05_19.cpp//Association::Association (Object& _key) :    key (&_key),    value (0)    {}Association::Association (Object& _key, Object& _value) :    key (&_key),    value (&_value)    {}Association::~Association (){    if (IsOwner ())    {	delete key;	delete value;    }}