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 10:36:56

On 3/10/2015 1:54 AM, 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.
>
> In all the test I ran I got no warning under VC++, but this was on a
> pretty new version. And some of my test were run before 1.57.

The BOOST_PP_IS_EMPTY macro is undocumented in Boost PP and therefore 
was not meant to be used outside the library. I actually changed it to 
be much more reliable when using variadic macros, but unfortunately that 
mean that VC++ puts out more spurious warning messages.

Honestly just getting VC++ to work properly in Boost PP and VMD is hard 
enough. Fixing VC++ warning messages, when there is nothing wrong, is 
nearly impossible. I understand they are irritating but they are totally 
false also. They are part of VC++'s non-conformant C++ preprocessor.

>
>>
>> Turning off C4003 globally for VC++ is the only solution to the VC++
>> warnings I could ever discover. I attempted to turn off the warnings in
>> the macros where they occur, but VC++ just ignores that. Evidently the
>> warnings can only be turned off globally or possibly at the very
>> top-level macro which eventually causes them.
>
> Do you think I could add specific pragmas to disable C4003 where I use
> BOOST_PP_IS_EMPTY ?

You can try it by surrounding the top-level macro, which eventually 
calls BOOST_PP_EMPTY, with the appropriate VC++ pragmas to turn off the 
warning. But even that may not work with VC++.

I tried to use the appropriate VC++ pragmas at the Boost PP level to 
turn off the warnings but it did not succeed.