Re: [Boost-build] [requires] cxx11_variadic_macros

Subject: Re: [Boost-build] [requires] cxx11_variadic_macros
From: Raffi Enficiaud (raffi.enficiaud_at_[hidden])
Date: 2015-10-14 14:53:51

Le 14/10/15 01:45, Edward Diener a écrit :
> On 10/13/2015 11:41 AM, Raffi Enficiaud wrote:
>> Hi all,
>>
>> I have the following requirement on my bjam:
>>
>> requirements_boost_test = [ requires cxx11_variadic_macros ] ;
>>
>> When I compile it on clang/OSX, in C++03 mode, I have this:
>>
>> ../../../b2
>>
>>      - Boost.Config Feature Check: cxx11_variadic_macros : yes
>>      - Boost.Config Feature Check: cxx11_decltype : no
>>      - Boost.Config Feature Check: cxx11_hdr_random : yes
>>      - Boost.Config Feature Check: cxx11_hdr_tuple : no
>>      - Boost.Config Feature Check: cxx11_hdr_initializer_list : no
>>
>>
>> When I compile it on clang6/OSX, in C++11 mode, I have this
>>
>> ../../../b2  cxxflags="-stdlib=libc++ -std=c++11"
>> linkflags="-stdlib=libc++"
>>
>>      - Boost.Config Feature Check: cxx11_variadic_macros : yes
>>      - Boost.Config Feature Check: cxx11_decltype : yes
>>      - Boost.Config Feature Check: cxx11_hdr_random : yes
>>      - Boost.Config Feature Check: cxx11_hdr_tuple : yes
>>      - Boost.Config Feature Check: cxx11_hdr_initializer_list : yes
>>
>>
>> The cxx11_variadic_macros is active for both configuration, but the
>> variadic macros are not available with the "b2" toolset configuration.
>
> What exactly do you mean when you say 'the
> variadic macros are not available with the "b2" toolset configuration' ?

Sorry I was unclear. I was meaning that BOOST_PP_VARIADICS is set to 0. 
I erroneously thought that it should be automatically set to 1 if the 
compiler supports variadic macros.

So you're saying that for clang, we should have BOOST_PP_VARIADICS=1. 
Why isn't it the case then? Explicitly setting toolset=clang does not help.

For info:
 > clang --version
Apple LLVM version 6.1.0 (clang-602.0.53) (based on LLVM 3.6.0svn)
Target: x86_64-apple-darwin14.5.0
Thread model: posix

>
> Variadic macro support in Boost PP ( and Boost VMD ), and libraries
> which use Boost PP, is not determined by Boost config. Instead it is
> determined internally based on the compiler and/or level of c++11
> support. In general compiling with c++11 support will turn on variadic
> macro support in Boost PP for most compilers, but both VC++ 8 on up and
> clang have variadic macro support turned on automatically in Boost PP.
> You can also force variadic macro support in Boost PP by defining
> BOOST_PP_VARIADICS to 1.
>
> Of course if you are not talking about variadic macros in Boost PP the
> preceding paragraph does not help you.

I was talking about variadic macros in general, boost.test is making 
extensive use of boost.pp, and I thought that I would have 
BOOST_PP_VARIADICS=1 as soon as the compiler supports variadic macros.

Thanks,
Raffi