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From: ok@goanna.cs.rmit.edu.au (Richard A. O'Keefe)
Subject: Re: Uninitialized variables, Java example
Date: 1996/07/25
Message-ID: <4t7g2q$ee0@goanna.cs.rmit.edu.au>#1/1
X-Deja-AN: 170506203
references: <31EEACDA.64880EEB@sage.inel.gov>
 <4t3f1u$t0u@newsbf02.news.aol.com> <Dv0qo4.JoE@world.std.com>
 <Dv1sME.1u4.0.-s@inmet.camb.inmet.com>
organization: Comp Sci, RMIT, Melbourne, Australia
nntp-posting-user: ok
newsgroups: comp.lang.ada
Date: 1996-07-25T00:00:00+00:00
List-Id: <comp.lang.ada>


arra@inmet.com (Arra Avakian) writes:
>Some may view this as extreme, since the compiler can not know statically the 
>"truth", and forces a statically knowable work-around on the programmer. Is 
>this what some people want for Ada 0x? It seems to me to be a tradeoff between 
>efficiency (an unnecessary initialization to satisfy the compiler) and safety 
>(the compiler is then allowed to detect statically known cases of 
>uninitialized variables, i.e. true programming errors.)

Wrong.  If the problem is that the programmer knows that the default:
case can never be executed and the compiler doesn't, then the programmer
should TELL the compiler.  For example, in the same situation in C, one
does

	int x;

	switch (e) {
	    case ..: ... x = ..; break;

	    case ..: ... x = ..; break;
	    default: abort();
	}

I actually use a "shouldnt" macro (name stolen with thanks from Interlisp)
which is like assert(0) but cannot be suppressed by NDEBUG.

Now the compiler knows that path can't be traversed too.
Better still, a human reader knows that the original programmmer *thought*
about the problem and didn't just accidentally leave out the default:
And there is no unncessary initialisation anywhere.

In short, this is a perfect example of where a warning about a possibly
uninitialised variable is _really_ a warning about badly written code.
-- 
Fifty years of programming language research, and we end up with C++ ???
Richard A. O'Keefe; http://www.cs.rmit.edu.au/~ok; RMIT Comp.Sci.