Re: [Boost-users] boost 1.47: gcc file dependency generation trips over BOOST_PARAMETER_MAX_ARITY

Subject: Re: [Boost-users] boost 1.47: gcc file dependency generation trips over BOOST_PARAMETER_MAX_ARITY
From: Dave Abrahams (dave_at_[hidden])
Date: 2011-09-17 02:34:43

on Thu Sep 15 2011, Ivan Le Lann <ivan.lelann-AT-free.fr> wrote:

> ----- "Ytsen de Boer" <yrdeboer_at_[hidden]> a écrit:
>
>> Thank you for your answer.
>>   I believe we are not on the same page.
>>   Obviously, when I define the max arity to a value of 7 or more, the
>> preprocessor will finish properly.
>> 
>>   But the point I am trying to make is more subtle, namely, that the
>> generation of the project dependencies has not a thing to do with the
>> boost max arity.
>
> I think it does actually.
> How could gcc track inclusions without preprocessing ?
>
> #ifdef USE_LIB_A
> #  include "a.h"
> #else
> #  include "b.h"
> #endif
>
> It seems very dangerous to me to use "-MMD" with different 
> preprocessor definitions than at real compile time.
> But I'm not an expert.

Maybe not, but you've hit the nail on the head.

>> 
>>   I don't know what the boost max arity means or what its for, but it
>> seems to me that it is a run time variable.

It couldn't possibly be a runtime variable.  It's a preprocessor macro,
and runtime variables can't affect preprocessing.

-- 
Dave Abrahams
BoostPro Computing
http://www.boostpro.com