Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!odi!dlw
From: dlw@odi.com (Dan Weinreb)
Newsgroups: comp.object
Subject: Re: Do we really need types in OOPL's?
Message-ID: <1990Oct10.041259.1123@odi.com>
Date: 10 Oct 90 04:12:59 GMT
References: <0yw10qr@Unify.Com> <60700003@inmet>
Reply-To: dlw@odi.com
Organization: Object Design, Inc.
Lines: 21
In-Reply-To: stt@inmet.inmet.com's message of 7 Oct 90 15:32:00 GMT

In article <60700003@inmet> stt@inmet.inmet.com writes:

   In general, I would argue that if there are no
   machine-enforceable static constraints on a complex
   system, then the programmers themselves must have no
   idea whether any given line of code is right or wrong,
   except through (inherently infeasible) exhaustive testing.

While I don't disagree with this, I'd like to point out that even if
every single static constraint passes, the programmer still does not
know (is that the same as "has no idea"?) whether the code is correct,
has one subtle bug, or is ridden through with bugs.  Many bugs are not
found by static tests.  So, while the checking of static constraints
probably increases your confidence in the correctness of your code by
some amount, you would still be well advised to test it -- including
the parts that are rarely used -- to see if all the array references
are within bounds, that you don't re-use freed storage, that there
aren't logical errors at a higher level, and so on.  The implied
assertion above, that a lot of testing is needed in the absence
of static checks but that testing can be dispensed with in the
presence of static checks, is an exagguration.