Re: [boost] Conflicts when building libraries at root

Subject: Re: [boost] Conflicts when building libraries at root
From: Edward Diener (eldiener_at_[hidden])
Date: 2015-03-10 10:55:43

On 3/10/2015 6:23 AM, Damien Buhl wrote:
> On 10/03/2015 09:08, Andrey Semashev wrote:
>> On Tuesday 10 March 2015 06:54:30 Damien Buhl wrote:
>>> On 09/03/2015 23:20, Edward Diener wrote:
>>>> On 3/9/2015 5:09 PM, Andrey Semashev wrote:
>>>> [...]
>>>>
>>>>> There weren't any warnings before. Is this a result of a change in
>>>>> Boost.PP?
>>>>
>>>> Yes, but they were already in 1.57. The changes added some new
>>>> (BOOST_PP_IS_BEGIN_PARENS) and better functionality (the internal
>>>> BOOST_PP_IS_EMPTY) to Boost PP, as well as fixing some corner cases with
>>>> VC++ I discovered when testing VMD.
>>>
>>> The reason why this happens more in this build, is that the new
>>> BOOST_FUSION_ADAPT macros uses BOOST_PP_IS_EMPTY for each field member
>>> now. This is used to determine if the type was provided or has to be
>>> deduced.
>>
>> Is it possible to avoid BOOST_PP_IS_EMPTY? For example, use a keyword instead
>> of testing for an empty string?
>
> I'll change this to look at the implication that it has. Not sure it
> will be better on old compilers like MSVC 8, but perhaps we can avoid
> some warnings. :p
>
> What is good is that the current code allow this change easily. Because
> when BOOST_PP_VARIADICS support is active, it wouldn't be needed at all,
> and when it's not there then it currently only uses BOOST_PP_IS_EMPTY to
> check if the provided type is a macro which expands to BOOST_PP_EMPTY,
> namely BOOST_FUSION_ADAPT_AUTO.
>
> So it might be quite easy to replace it to make a check if the provided
> type is a string equal to BOOST_FUSION_ADAPT_AUTO. Actually it makes
> even more sense than the check for emptiness.
>
> The only disadvandtage is that the user cannot anymore write nothing
> instead of the type when he don't have BOOST_PP_VARIADICS support (which
> is anyway undocumented and not advised).
>
> Otherwise isn't there any possibility to fix the warnings in
> BOOST_PP_IS_EMPTY? Because the old version of BOOST_PP_IS_EMPTY didn't
> warn about anything AFAIK when used with a parameter which expands to
> BOOST_PP_EMPTY().

If you are compiling with VC++ then BOOST_PP_VARIADICS is on by default. 
Try to specifically turn it off to see if the warnings go away if that 
is an option. Of course with BOOST_PP_VARIADICS off the variadic support 
in Boost PP goes away.