Re: DR handling for C++

[Matt Austern <austern@apple.com>]

On Sep 20, 2004, at 1:04 PM, Mark Mitchell wrote:

> I've been asked to provide my input on the handling of DRs in the C++ 
> front end.
>
> Unfortunately, I don't have the messages from the original thread, so 
> I'm off starting a new thread.
>
> I certainly agree with Matt and Nathan that there's no point in 
> supporting C++98 separately from C++03.  I also agree that new 
> features in future revisions of C++ should be supported only under a 
> flag.  I think that fixes for existing features, however, should be 
> incorporated into the C++03 mode, even if they don't show up in C++03 
> itself.  (A "defect repot", after all, is supposed to refer to a bug 
> in the standard.)  I think the threshold for incorporating such fixes 
> should be that the fixes are in WP status, in general, although I'd 
> consider other fixes if it seems clear that the commitee is going to 
> accept the change and the change seems important.

I'd be unhappy about taking all "WP" changes unconditionally, either 
CWG or LWG.

The fact is that the C++ committee uses DRs in several different ways.  
In some cases it's "the standard calls for something that's 
unimplementable or inconsistent, so here's a bug fix", and in other 
cases it's "we think the standard called for something that's not a 
good idea, so here's a better redesign."

Arguably the committee shouldn't ever be doing the latter, but it does. 
  That's especially true now that the committee is targeting changes at 
the C++0x working paper rather than at a C++98 technical corrigendum.  
In the committee's defense: we all know that the line between a bug fix 
and a feature redesign can sometimes be fuzzy.  The committee feels, in 
my opinion justifiably, that it has more liberty to make changes now 
that it's working on a new version of the standard.  It's using the 
issues list as one mechanism to track changes for that new version of 
the standard.

My concern is that if we implement all issues in "WP" status we'll be 
back in the bad place we were in the late 90s: tracking an unstable 
document, and claiming to implement a "standard" that hasn't actually 
been standardized.

There are some committee issues that ought to be implemented, because 
there are some cases where the standard really is unimplementable, 
vague, meaningless, or contradictory.  But at this point there is only 
only official C++ standard, and where that standard is clear and 
consistent our users have a right to expect that we'll follow it.

			--Matt