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From: "Nick Roberts" <Nick.Roberts@dial.pipex.com>
Subject: Re: Equality operator overloading in ADA 83
Date: 1997/05/02
Message-ID: <01bc54ef$2621d680$LocalHost@xhv46.dial.pipex.com>#1/1
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References: <01bc4e9b$ac0e7fa0$72041dc2@lightning>
 <335F5971.6375@elca-matrix.ch> <E95y9L.AK1@world.std.com>
 <dewar.861930356@merv> <E973qr.89t@world.std.com>
 <01bc5244$315f1560$28f982c1@xhv46.dial.pipex.com> <dewar.862079014@merv>
 <mheaney-ya023680002604971931400001@news.ni.net>
Organization: UUNet PIPEX server (post doesn't reflect views of UUNet PIPEX)
Newsgroups: comp.lang.ada
Date: 1997-05-02T00:00:00+00:00
List-Id: <comp.lang.ada>




Matthew Heaney <mheaney@ni.net> wrote in article
<mheaney-ya023680002604971931400001@news.ni.net>...
> In article <dewar.862079014@merv>, dewar@merv.cs.nyu.edu (Robert Dewar)
wrote:
> 
> ><<As to the property of mutual exclusion - this is the 'essence' of the
case
> >statement - the implementation would probably have to test ...>>
> >
> >This is only 50% of the essence. The other half is full coverage, which
can
> >have no meaning for extended case statements - so I think it is a bad
idea
> >to try to extend case statements to non-discrete types.
> 
> Ah, Robert brings order to chaos.  I heartily agree.  There are *much*
more
> important issues to consider than changing case statements so that they
> work for non-discrete types.


I agree that full coverage is an essential part of the case statement, but,
with respect, I think Robert is wrong to say that therefore this idea can
have 'no meaning' for extended case statements: it seems to me that there
would simply have to be a requirement (in the language rules) that there
was an 'others' alternative in any such extended case statement, and this
would then guarantee coverage (similarly to the rules for case statements
whose control expression is of a type which is a formal generic (discrete)
type).

On the other hand, it could perhaps be argued that one of the precepts of
the case statement in Ada has always been that the choices are all static
(except for 'others') so that special optimisation could be applied (e.g. a
jump table) to increase speed. This would, of course, be impossible for
extended case statements (except by overly clever optimisation techniques).

Finally, I think I would agree with Matthew that this is probably not a
very important issue concerning the design of the Ada language! (So maybe I
should shut up now? :-)

Nick.