noalias (was: Re: the "const" qualifier)

[dmr at alice.UUCP]

Bill Plauger first used the phrase "politically impossible" during
X3J11's noalias showdown meeting, in May 1988.  It's become evident
that it is, at least in part, a code for "Dennis won't stand for it."
The situation (especially then) was pretty complex.

During Dec-Jan 1987-88, Prosser, with help from a central group
of X3J11 members and suggestions from me, rewrote the "noalias"
paragraphs several times, and the collective wisdom was never
able to come up with a proposal that both made sense
and was compatible with the design that X3J11 had voted in during
the preceding fall.

The problem at that point was that this was supposed to
be the penultimate draft (only editorial changes), and everyone
wanted things to happen as rapidly as possible.  The two choices
I saw were to try to work something out on my own and present
an alternative proposal, or simply to try to rip the thing
out altogether.   You may think me naive or lacking in self-confidence,
but I was genuinely worried that X3J11 would be so impelled to
finish things up without another public review that I decided
on the second course.  The reasoning was that if I
said, "I would like you to fiddle the draft in this way,"
I would be taken less seriously than if I said "Noalias must go.
This is non-negotiable."  I feared that the committee would
decide to go with their previous decision unless I credibly
pulled a full tantrum.

I decided to handle things this way after talking to several
of the insiders on X3J11 who were all somewhat pessimistic
of the likelihood that the committee would change its mind
(and commit itself to another review).  It wasn't a decision
taken lightly--I brooded about it throughout early 1988.

In retrospect, it seems possible that if I had worked harder
and perhaps done more lobbying, it would have been possible
to have a "noalias" that was linguistically defensible
and generally acceptable.  On the whole, though, I don't
regret taking the course I did.

I have been careful to point out to groups like the Numerical
C Extensions Group convened by Rex Jaeschke that I will not
cause them "political problems" if someone can come up
with a coherent noalias notion that does not cause unbearable
problems in the rest of the language.

Incidentally, my general dislike of type qualifiers, to which
Gwyn referred, was noticeably stimulated by important faults
in the definition of "const" in the same Dec. 1987 draft
that introduced "noalias."  As it turned out, the draft had
leftover language in it that was simply unintended, and
the committee dealt with these complaints by saying (in effect)
"Whoops, we didn't mean to say that."

BTW, I think X3J11 did an excellent job, though there are
legitimate criticisms.  If you want to see others in greater
anguish and wrangling, check out Fortran 8X, or the Ada 9X
or C++ discussions.

	Dennis Ritchie
	dmr at research.att.com
	att!research!dmr