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From: kaz@accton.shaw.ca (Kaz Kylheku)
Newsgroups: comp.lang.lisp,comp.lang.ada,comp.lang.eiffel,comp.lang.smalltalk
Subject: Re: True faiths ( was Re: The true faith )
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Organization: Psycho-Neurotic Institute for the Very, Very Nervous
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Date: Sun, 20 Jan 2002 05:59:42 GMT
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Date: 2002-01-20T05:59:42+00:00
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In article <3C4A58B8.10304@mail.com>, Hyman Rosen wrote:
>Richard Riehle wrote:
>
>>         procedure Copy_Deep       (Source : in T; Target : in out T);
>>         procedure Copy_Shallow  (Source : in T; Target : in out T);
>
>
>I dislike the notion of providing these methods as external interfaces
>to a type. It seems wrong to me for a client to have to know what kind
>of copy to use - that's the type's business to know.

This turns out to be circular reasoning, because what a type ``knows''
is partally defined by the operations you can perform on it.

Suppose that you have N methods for copying an object. I do not take it
as a theorem that you can always make an (N + 1)-th method which unifies
the other N, magically choosing the appropriate one. How can this magic
meta-method possibly know what semantics the caller wants?