From: sampson@cod.NOSC.MIL (Charles H. Sampson)
Subject: Re: Pre-condition vs. Post-condition
Date: 19 Mar 91 20:38:57 GMT [thread overview]
Message-ID: <2938@cod.NOSC.MIL> (raw)
In-Reply-To: 311@nic.cerf.net
In article <311@nic.cerf.net> sss@nic.cerf.net (Marlene M. Eckert) writes:
>How about exceptions should be raised only in _EXCEPTIONAL_
>situations? Reaching the end-of-file or trying to POP off an
>empty stack are NOT exceptional conditions.
O. K., but that just pushes the issue off to deciding what the word
_exceptional_ means. The definition I prefer to use is: "An exceptional
condition is one that occurs infrequently or unexpectedly." (Not original,
but I forgot whom I stole it from. I think it was John Barnes.) When
teaching Ada, immediately after giving that definition I point out to the
students that it does not require all exceptional conditions to be handled
by exceptions.
What's happening here is that we're in an area where a lot of design
decisions have to be made. I'm not sure that there is a rule that can be
applied to all cases and I am sure that if there is one we haven't found
it yet. Unlike Mike Feldman, I have no philosophical problem with using
End_error to detect end-of-file or stack underflow to determine that the
stack is now empty, both satisfying the _infrequent_ criterion. (I doubt
that I would ever use the latter myself, but my reasons are more esthetic
than anything else.) Before I would condemn these uses in any particular
situation, I would want to hear the reasons for them.
This has been an interesting thread to follow as we grapple with
this problem. I particularly appreciate the fact that very few dogmatic
positions have been put forward.
Charlie
next prev parent reply other threads:[~1991-03-19 20:38 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
1991-03-15 3:57 Pre-condition vs. Post-condition Chris M. Little
1991-03-15 19:07 ` Michael Feldman
1991-03-17 12:26 ` George C. Harrison, Norfolk State University
1991-03-18 15:04 ` Joe Hollingsworth
1991-03-18 19:51 ` Marlene M. Eckert
1991-03-19 19:07 ` Michael Feldman
1991-03-21 3:01 ` Jim Showalter
1991-03-21 16:34 ` Exception usage design issues (was: Pre-condition vs. Post-condition) John Goodenough
1991-03-21 18:40 ` Pre-condition vs. Post-condition Michael Feldman
1991-03-19 20:38 ` Charles H. Sampson [this message]
1991-03-21 3:06 ` Jim Showalter
1991-03-19 21:07 ` Jim Showalter
1991-03-19 7:38 ` Jim Showalter
1991-03-19 14:46 ` Joe Hollingsworth
1991-03-21 2:46 ` Jim Showalter
1991-03-21 5:12 ` Explicit vs implicit checks (was Pre-condition vs. Post-condition) Scott Carter
1991-03-22 15:18 ` Pre-condition vs. Post-condition Brad Balfour
1991-03-19 18:17 ` Mike Gilbert
-- strict thread matches above, loose matches on Subject: below --
1991-03-18 15:47 "Norman H. Cohen"
1991-03-24 21:23 stt
1991-03-25 16:00 ` Arthur Evans
1991-03-25 17:05 ` Michael Feldman
1991-03-26 4:31 ` Jim Showalter
1991-03-26 10:21 ` Richard A. O'Keefe
1991-03-26 16:44 ` Michael Feldman
1991-03-26 22:03 ` Richard A. O'Keefe
1991-03-26 23:36 ` Michael Feldman
1991-03-27 21:34 ` Jim Showalter
1991-03-28 2:54 ` Michael Feldman
1991-03-29 3:28 ` Jim Showalter
1991-03-27 3:12 ` Jim Showalter
replies disabled
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox