Path: utzoo!attcan!uunet!ncrlnk!ncrcae!hubcap!gatech!bbn!bbn.com!lpringle
From: lpringle@bbn.com (Lewis G. Pringle)
Newsgroups: comp.lang.c++
Subject: Re: goodbye cpp ???
Message-ID: <33617@bbn.COM>
Date: 16 Dec 88 20:57:54 GMT
References: <6590072@hplsla.HP.COM> <1106@etive.ed.ac.uk> <33528@bbn.COM> <1907@ogccse.ogc.edu>
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Reply-To: lpringle@labs-n.bbn.com (Lewis G. Pringle)
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In article <1907@ogccse.ogc.edu> wm@ogccse.UUCP (Wm Leler) writes:
>I don't think you could extend switch statements to work on strings,
>since there is some ambiguity between whether you want to compare
>the strings by comparing their contents (using strcmp) or by comparing
>their pointers (a very reasonable thing to do).
>

You seem to have missed something.  What I suggested was more general
than extending switch to work with strings. The compiler would barf on
strings unless the user had defined the approriate conversion operators
and op== functions.  The user could then define op== however he wanted
(pointer equality or strcmp() equality).

A more interesting problem is one brought up by Michael Tiemann.  He pointed
out that that the result of the evaluation of the switch() would be a
auto temp variable whose op== function would end up called a bunch of
times.  This is kosher, so long as op== is guarenteed not to modify either
of its arguments, but the compiler does not enforce this!

This leads me to another suggestion - which may already be true for all
I know - that whenever you define an op== function (or other comparitor)
it be required to have as aguements const-references.  I kind of like this
idea (I would be unhappy do discover that in some library I was using,
the op== function changed one of the things I was comparing!)  but it
would be a great departure from the current c++ definition where these
comparison operators are not assumed to have any particular semantics.


					Lewis.


"OS/2: half an operating system for half a computer."

In Real Life:		Lewis Gordon Pringle Jr.
Electronic Mail:	lpringle@labs-n.bbn.com
Phone:			(617) 873-4433