Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!ames!think!barmar
From: barmar@think.COM (Barry Margolin)
Newsgroups: comp.arch
Subject: Re: Parity hardware for uninitialized variable checking?
Message-ID: <28866@news.Think.COM>
Date: 5 Sep 89 22:32:25 GMT
References: <14166@polyslo.CalPoly.EDU> <28784@news.Think.COM> <14206@polyslo.CalPoly.EDU>
Sender: news@Think.COM
Reply-To: barmar@kulla.UUCP (Barry Margolin)
Distribution: usa
Organization: Thinking Machines Corporation, Cambridge MA, USA
Lines: 24

In article <14206@polyslo.CalPoly.EDU> ttwang@polyslo.CalPoly.EDU (Thomas Wang) writes:
>barmar@think.COM (Barry Margolin) writes:
>>In article <14166@polyslo.CalPoly.EDU> ttwang@polyslo.CalPoly.EDU (Thomas Wang) writes:
>>>Yes.  Insist you initialize a variable when you create it.
>>What if you don't know what value it should have yet?
>You can create the variable with a default value, or delay the creation of
>the variable until you know what value it should have.

My contention is that a variable with a default value is often just as
bad as an uninitialized variable.  Sure, it has a well-defined value,
but it's not the value you really care about, and it might not make
sense to use the variable until it gets a more meaningful value.

Consider a language that automatically initializes all pointer
variables to NULL when they are created.  Strictly speaking, there are
no uninitialized pointer variables in such a language.  However, it's
still not valid to dereference a pointer until you REALLY initialize
it to point to something.

Barry Margolin
Thinking Machines Corp.

barmar@think.com
{uunet,harvard}!think!barmar