Re: [Boost-users] xpressive

Subject: Re: [Boost-users] xpressive
From: Paul A. Bristow (pbristow_at_[hidden])
Date: 2011-05-16 11:50:36

> -----Original Message-----
> From: boost-users-bounces_at_[hidden] [mailto:boost-users-bounces_at_[hidden]] On Behalf
Of
> Eric Niebler
> Sent: Saturday, May 07, 2011 2:57 PM
> To: boost-users_at_[hidden]
> Subject: Re: [Boost-users] xpressive
> 
> On 5/7/2011 7:42 PM, Louis Lavery wrote:
> > On 07/05/2011 11:27, Eric Niebler wrote:
> >> On 5/7/2011 1:56 AM, Louis Lavery wrote:
> >>> Apart from the C4701 warning (which I can suppress for now) it seems
> >>> happy compiling stuff like this...
> >>>
> >>> sregex rex = as_xpr("foo")>>  _d>>  "xyz";
> >>>
> >>> ...so long as I enable language extensions and use the pragma.
> >>
> >> Oh, you were using /Za? This switch is useless.
> >
> > It changes the compiler's behaviour so is surely not completely useless?
> 
> It's worse than useless. See below.
> 
> >> Even Microsoft's own
> >> headers don't compiler with language extensions disabled.
> >
> > As far as I remember I've always used /Za with out any problems, maybe
> > I've been lucky and never needed to #include the MS headers that
> > require no /Za. I tend to use just the std containers, algorithm,
> > iostream, string and such, just std C++ stuff.
> >
> > Maybe by "Microsoft's own headers" you mean those specific to
> > Microsoft, in which case case I can see that /Za should be off.
> > But then I don't use MS not standard code/headers as I need my code to
> > compile under other compilers - so I want to stick to pure C++.
> >
> >> I used to work
> >> in the MSVC group at Microsoft. Every time a customer complained
> >> about /Za, they were told to simply stop using it.
> >
> > Well, yeah, they would say that wouldn't they.
> >
> > I would be a lot happier using xpressive if I didn't have to enable
> > language extensions. I'm not sure exactly how I'm going to use it. It
> > might be that I build a static lib, using xpressive, that I can link
> > to and so still use /Za in my main code. If that restricts the power
> > of xpressive and I need to use the templates directly, and so have to
> > enable MS language extensions, I'll have to have a rethink.
> >
> > Please don't take this as criticism of xpressive (it's meant to be
> > constructive criticism at worst), I'm keen on it. From what I've seen
> > so far it's intuitive and easy to use.
> 
> The /Za switch breaks standard-conforming code. I even filed a bug about it:
> 
> https://connect.microsoft.com/VisualStudio/feedback/details/486253/name-lookup-broken-with-za
> 
> This is exactly the problem in xpressive that you're running into. (I just confirmed it.) As you
can see, that
> bug was closed "won't fix."
> 
> I'll say it again: don't use /Za for ANYTHING. It's broken.

I second this (from recent bad experience), and have updated and strengthened the recommendations at

https://svn.boost.org/trac/boost/wiki/Guidelines/WarningsGuidelines

to say loudly

"Don't use /Za for ANYTHING. It's BROKEN - and won't be fixed."

Paul

---
Paul A. Bristow,
Prizet Farmhouse, Kendal LA8 8AB  UK
[phone]  07714330204
pbristow_at_[hidden]