Re: Have you ever had a bug caused by...

[David Bolen <db3l@fitlinxx.com>]

mjsilva697@earthlink.net (Mike Silva) writes:

> While discussing (er, pushing) Ada with some C-coding co-workers today
> I asked a question to which I knew the answer (always the best kind!):
>  "Have you ever had a bug caused by accessing off the end of an
> array?"  Well, of course, they all had to say yes.  Then I started
> thinking of other bugs that they would have to admit to, and which
> wouldn't occur in Ada.  Nothing new here (Ada prevents many bugs...),
> but I thought it would be fun and useful to develop a group list as an
> Ada advocacy tool.  For example:

I'm curious as to how Ada _prevents_ such bugs.  Are you saying that
no Ada programmer has ever had a bug caused by walking off the end of
an array either?

I'll buy that Ada will catch that error more quickly than in C, and
probably help isolate the problem more quickly.  And even that by
using attributes such as Range, Low and High that you can write more
robust code to avoid the issue (which is no small benefit).  But given
that you can still compute indices and then attempt to dereference
based on those computations, there has to be the occasional bug that
is introduced through the use of indices that overflow the array.

And that's different from saying "wouldn't occur in Ada" ... there's a
difference between better handling of the bug, and not having the bug
ever occur.  Or to put it another way, if I have a bug that creates
this condition (or say, tries to set a value outside its range, as in
another example), generating an exception - even if handled - still
implies the bug exists.

Some of the suggested items appear to be language checks that are
completely possible at compile time, for which I'd buy the "can't
happen" argument.  But any issues that can occur at runtime and
require runtime checks and exceptions don't, IMHO, prevent bugs, but
simply act to make it easier to diagnose and manage them when they do
occur.

--
-- David
-- 
/-----------------------------------------------------------------------\
 \               David Bolen            \   E-mail: db3l@fitlinxx.com  /
  |             FitLinxx, Inc.            \  Phone: (203) 708-5192    |
 /  860 Canal Street, Stamford, CT  06902   \  Fax: (203) 316-5150     \
\-----------------------------------------------------------------------/