Re: [Boost-users] Problem with variadic BOOST_PP_TUPLE_REM in Clang

Subject: Re: [Boost-users] Problem with variadic BOOST_PP_TUPLE_REM in Clang
From: Paul Mensonides (pmenso57_at_[hidden])
Date: 2013-11-20 08:39:13

On Thu, 14 Nov 2013 18:59:39 -0500, Edward Diener wrote:

> On 11/14/2013 5:40 PM, Matt Calabrese wrote:
>> On Thu, Nov 14, 2013 at 5:26 AM, Edward Diener <eldiener_at_[hidden]
>> <mailto:eldiener_at_[hidden]>> wrote:
>>
>>     Currently Boost PP does not depend on any other Boost library, not
>>     even Config.
>>
>>     I imagine that Paul might respond to this issue. If he does not I
>>     will notify him of it.
>>
>>
>> Regardless, since both C99+ and C++11+ have variadic macros, it should
>> probably be updated to a new BOOST_PP_NO_VARIADICS macro so that we
>> assume compliance by default.
> 
> I think that adding another macro confuses the issue even if it mimics
> the style of config macros.
> 
> It is not my call to change the code for determining what compiler
> should automatically have variadic support enabled in Boost PP, even if
> I worked prettily heavily on variadic macro support in general in Boost
> PP with Paul. It's still his library to decide on this IMO and, even
> though the change is fairly trivial in a single header file, I feel on
> principal he has to agree to it. I will point this thread out to him.
> 
> The end-user can always currently set BOOST_PP_VARIADICS to 1 for any
> compiler to override the Boost PP automatic setting for that particular
> compiler, but I do understand your feeling that nearly all compilers now
> support variadic macros so it should be on, unless set off.

The basic problem here is that BOOST_PP_VARIADICS is a lot stronger than 
just "compiler supports variadic macros in some form".  The pp-lib doesn't 
pull Boost.Config for two main reasons.  First, Boost.Config's variadic 
macros support macro is much weaker than what is required by a 
preprocessor metaprogramming library.  Second, unlike the rest of Boost, 
the pp-lib is used outside of just C++ contexts--in real code in the real 
world.  I.e. it is a C/C++ library, so it cannot pull in code assumed to 
target C++ only.  Even if this is not the case with current Boost.Config, 
the pp-lib cannot place this restriction on Boost.Config (and vice versa).

I just checked and the showstopper bug in clang has apparently been 
fixed.  However, I have not personally confirmed this.  Can someone that 
has a current clang build confirm?

http://llvm.org/bugs/show_bug.cgi?id=12767

Otherwise, if everything is working properly as far as we can tell, I have 
no issue with enabling by default on clang.

Regarding the pp-lib in general... it is legacy code that is fundamentally 
gimped by several preprocessors--notably msvc.  If all of the 
preprocessors were good, the entire library would be different--i.e. it 
would be more like chaos-pp.  Perhaps after this git modularization stuff, 
chaos-pp goes into Boost (though I personally think that git is an 
abomination and I'm not at all certain about what "Boost" will even mean 
at that time).  It is also possible that MS makes good on their promise to 
fix their preprocessor, but I'll believe that when I see it (and then look 
for ulterior motives).

Otherwise, for code outside of Boost, if you only have to target non-crap 
compilers, use chaos-pp.  It is a far superior library distributed under 
the same license.

Regards,
Paul Mensonides