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From: diamond@jit533.swstokyo.dec.com (Norman Diamond)
Newsgroups: comp.object
Subject: Re: Objects and Interactions: Separate Definitions
Message-ID: <1991May22.012821.12048@tkou02.enet.dec.com>
Date: 22 May 91 01:28:21 GMT
References: <3999@motcsd.csd.mot.com> <1991May21.064913.16149@netcom.COM>
Sender: usenet@tkou02.enet.dec.com (USENET News System)
Reply-To: diamond@jit533.enet@tkou02.enet.dec.com (Norman Diamond)
Distribution: comp
Organization: Digital Equipment Corporation Japan , Tokyo
Lines: 33

In article <1991May21.064913.16149@netcom.COM> jls@netcom.COM (Jim Showalter) writes:
[attribution lost]:
>]>> 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? ... "separation of concerns": one program
>entity knows how to quicksort stuff (arbitrary stuff), ...  the
>responsibility for providing a "<" operation belongs to the client
>providing the stuff.

Responsibility for specifying a "<" operation belongs to the call site.

For example, people have family names and given names.  One might want
to sort people's names to create a Western-style phone book or a
Japanese-style phone book.  To create a Western-style phone book, the
key for a person's name is the family name followed by the given names.
To create a Japanese-style phone book, the key for a Japanese person's
name is the family name followed by the given name, while the key for
a foreigner's name is the given names followed by the family name.(*)

A person-object has a family name and given names, but can't construct
the correct key for a "<" operation without knowing which "<" operation
suits the call site.  I do agree that the sorter entity should not
specify the "<" operation.  I think the call site has to specify it.

(* My personal opinion is that Japanese don't know how to make a phone
book, and that the inconsistency is mildly racist; -- DISCLAIMER: my
employer has stated its disagreement with my opinion.)
--
Norman Diamond       diamond@tkov50.enet.dec.com
If this were the company's opinion, I wouldn't be allowed to post it.
Permission is granted to feel this signature, but not to look at it.