Re: [Boost-bugs] Fwd: [Boost C++ Libraries] #11211: Fusion example no longer compiles

Subject: Re: [Boost-bugs] Fwd: [Boost C++ Libraries] #11211: Fusion example no longer compiles
From: Damien Buhl (damien.buhl_at_[hidden])
Date: 2015-04-21 07:06:08

Sorry for this message, I just saw after sending that Flast already
replied about the problem :

https://svn.boost.org/trac/boost/ticket/11211?replyto=3#comment:3

Shouldn't we make some bugfix release ? Because it is a seriously weird
issue.

On 21/04/2015 09:01, Damien Buhl wrote:
> Hi Joel,
> 
> Thanks for forwarding.
> 
> Looks like the support for BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED was
> added to DEFINE_STRUCT in a too strong way, which makes it impossible to
> use non-constexpr enabled types (namely std::string).
> 
> I think the problem comes from the addition of BOOST_CONSTEXPR where
> BOOST_FUSION_GPU_ENABLED already was.
> 
> In this commit
> https://github.com/boostorg/fusion/commit/2114bfca6c8d5e4f7fe2439346e1feddfd550ea6
> 
> there is BOOST_CONSTEXPR added for the constructors and assignment
> operators.
> 
> I think we have to remove the constexpr for this part, because we cannot
> add the requirements that the types the users gives to DEFINE_STRUCT are
> valid within constant expression.
> 
> It also didn't come out by unit-tests runs, because our test are only
> done with int types. We have to add types which aren't constant-enabled
> to the tests for DEFINE_STRUCT and by the way for ADAPT also.
> 
> I understand the idea behind adding BOOST_CONSTEXPR everywhere where
> BOOST_FUSION_GPU_ENABLED was, but actually it's not the same : on GPU
> there isn't any scenarii where one uses std::string I think, while it is
> typical in normal execution platform, and by the way BOOST_CONSTEXPR
> shouldn't be in this file.
> 
> I've pushed a small commit where it then compiles for me on clang + g++
> with C++03,11,14 :
>> https://github.com/boostorg/fusion/compare/boostorg:master...daminetreg:feature/fix-for-11211?expand=1
> 
> 
> Cheers,
> 
> --
> Damien Buhl
> 
> On 20/04/2015 21:18, Joel de Guzman wrote:
>> Hello Kohei, Damien,
>>
>> Uh oh. Do you know what's happening here?
>> I'm getting:
>>
>> Constexpr constructor never produces a constant expression
>>
>> How did this slip?
>>
>> -------- Forwarded Message --------
>> Subject: [Boost C++ Libraries] #11211: Fusion example no longer compiles
>> Date: Mon, 20 Apr 2015 19:01:29 -0000
>> From: Boost C++ Libraries <noreply_at_[hidden]>
>> CC: boost-bugs_at_[hidden]
>>
>> #11211: Fusion example no longer compiles
>> -----------------------------------------------------+---------------------
>>  Reporter:  Adrián Etchevarne <adrian.etchevarne@…>  |      Owner:  djowel
>>      Type:  Bugs                                     |     Status:  new
>> Milestone:  To Be Determined                         |  Component:  fusion
>>   Version:  Boost 1.58.0                             |   Severity:  Problem
>>  Keywords:  fusion                                   |
>> -----------------------------------------------------+---------------------
>>  From the manual:
>>
>>  {{{
>>
>>  #include <string>
>>  #include "boost/fusion/adapted/struct/define_struct.hpp"
>>
>>  // demo::employee is a Fusion sequence
>>  BOOST_FUSION_DEFINE_STRUCT(
>>       (demo), employee,
>>       (std::string, name)
>>       (int, age))
>>
>>
>>  int main()
>>  {
>>  }
>>
>>  }}}
>>
>>  It fails to compile with boost 1.58. With boost 1.57, compiles
>>  successfully.
>>
>>   g++ --std=c++11 test.cpp -I /home/saknussemm/downloads/boost_1_58_0
>>
>>  clang fails with a similar error.
>>
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