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From: ndiamond@watdaisy.UUCP (Norman Diamond)
Newsgroups: net.lang
Subject: Re: Nil dereferencing protection
Message-ID: <6916@watdaisy.UUCP>
Date: Mon, 4-Feb-85 12:49:02 EST
Article-I.D.: watdaisy.6916
Posted: Mon Feb  4 12:49:02 1985
Date-Received: Tue, 5-Feb-85 04:37:23 EST
References: <1934@inmet.UUCP>
Organization: U of Waterloo, Ontario
Lines: 23

> > > > For instance, it is possible to statically guarantee that nil
> > > > pointers are never dereferenced  --Pemberton
> > > Ada supports this...  --Steinman
> > Unfortunately, this is not and cannot be true.  (consider "a := if
> > program P halts, then nil else new foo; deref(a)")  [--?]
> Excuse me for putting words into Mr. Pemberton's terminal but I
> think that what he was trying to say was NOT that you can guarantee
> that a nil dereference WILL occur, but that it WILL NOT occur.
> In the above example a compiler can warn you that a nil dereference
> MAY occur. In many situations this information can help you to
> discover bugs. In other situations you may just say "so what."  [--bobo(?)]

In that case, nearly every dereferencing operation in the source program
will draw that warning message.  Of course, programmers would have to ignore
the warnings, and their content of usable information would be near zero.

-- Norman Diamond

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