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From: vaughan@mcc.com (Paul Vaughan)
Newsgroups: comp.lang.c++,comp.software-eng
Subject: Re: Project experience with C++
Message-ID: <10329@cadillac.CAD.MCC.COM>
Date: 10 Aug 90 15:12:57 GMT
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Reply-To: vaughan@mcc.com (Paul Vaughan)
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In-reply-to: klimas@astro.pc.ab.com

klimas@astro.pc.ab.com wrote:

	I saw some confidential statistics on a large software project that
	indicated that strong typing in a rather large (~ 1 million lines of
	code) caught only 10% of the errors.  I believe that this is an area
	that others' contributions would be very helpfull in sorting out the 
	relevant issues from the noise.

I'd be highly skeptical of this.  Type checking catches a lot of
errors in a way that gets them fixed immediately.  Programmers tend to
forget they even made them.  It's like leaving out a semi-colon.  Most
people don't record that as a programming error.  They just fix it.
Having come from a LISP background, I find that it seemed a lot easier
to modify a program in LISP, but that after having done it, bugs
associated with the "fix" would keep popping up forever and stringent
testing after every change was required to maintain robustness.  Type
checking totally eliminates most of the errors that would plague us
then.

On the other hand, there certainly are several categories of frequent
errors that type checking doesn't help with.  Memory
allocation/deallocation misunderstandings come prominently to mind
(ah, LISP . . .).

Does anyone have any experience, intuition, or statistics concerning
the use of const?  Does it really help clear up errors or not?  It's
certainly a bag of worms to get a program const correct--it just
ripples and ripples through your code and then you wind up finding a
place in some library or system function where something really should
have been const but can't be changed and you have to cast around it in
the end.  So what's the verdict is const worth it?


 Paul Vaughan, MCC CAD Program | ARPA: vaughan@mcc.com | Phone: [512] 338-3639
 Box 200195, Austin, TX 78720  | UUCP: ...!cs.utexas.edu!milano!cadillac!vaughan