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From: jls@netcom.COM (Jim Showalter)
Newsgroups: comp.object
Subject: Re: Objects and Interactions: Separate Definitions
Message-ID: <1991May21.064913.16149@netcom.COM>
Date: 21 May 91 06:49:13 GMT
References: <3999@motcsd.csd.mot.com>
Distribution: comp
Organization: Netcom - Online Communication Services  UNIX System {408 241-9760 guest}
Lines: 25

]>>OK, let me expose my ignorance[1].  I'd like to see how object-oriented
]>>design works.  Would you care to sketch the design for this?  My naive
]>>model would be that a heap is an object and that it has add and remove
]>>methods to take objects of unspecified type and stick them into the heap
]>>in the right place.  So where do the comparison and exchange procedures
]>>go?  I see two alternatives[2]: (1) the heap object has compare and
]>>exchange methods that "know about" all of the types, figure out what's
]>>involved, and operate on the member objects or (2) the objects have
]>>methods that report their "comparable value" and size in canonical forms
]>>that a generic routine in the heap object can operate on.  Neither of
]>>these makes me awfully happy.  

Why does 2 make you unhappy? This is a perfect example of what is called
genericity in Ada and templates in latest-greatest C++. The basic principle
is "separation of concerns": one program entity knows how to quicksort
stuff (arbitrary stuff), but since it doesn't know a priori what the stuff
being sorted is, the responsibility for providing a "<" operation belongs
to the client providing the stuff. This is a first-rate way to achieve a
high degree of reuse--one optimized and fully-debugged quicksort that can
be used to sort any kind of object.
-- 
**************** JIM SHOWALTER, jls@netcom.com, (408) 243-0630 ****************
*Proven solutions to software problems. Consulting and training on all aspects*
*of software development. Management/process/methodology. Architecture/design/*
*reuse. Quality/productivity. Risk reduction. EFFECTIVE OO usage. Ada/C++.    *