Re: [eigen] Should we require c++11 for Eigen tensor

[Christoph Hertzberg <chtz@xxxxxxxxxxxxxxxxxxxxxxxx>]

Hi!

I think some time ago there was some opposition against that step -- in 
fact, originally C++03 was only introduced after the first versions of 
the Tensor module.

I can't find a reference to that discussion at the moment, I think it 
concerned supporting Tensor for some GPU architecture. But this was a 
few years ago, and compilers likely evolved since then.

So unless there is an outcry on this list, I'm not against dropping 
C++03 support of the Tensor module.


For transitioning it would of course be nice to have a clear "latest 
working" version which still supports C++03, one possibility would be to 
make that with the 3.4 release. OTOH, this will just complicate 
maintenance and Tensors are still "unsupported" for a reason (e.g., not 
having to spend unnecessary time to support them ...)

So just making a clear cut before 3.4 sounds actually better -- this 
will also simplify to maintain the upcoming 3.4 and master versions in 
parallel (I guess the 3.3.x version of the Tensor module has barely been 
touched in recent years).


Cheers,
Christoph

On 18/10/2019 18.46, Rasmus Munk Larsen wrote:
> Dear Eigen tensor users,
>
> Today, various c++11 features are in use in many parts of Eigen tensor,
> while other parts compile with c++03 without warnings. This division is
> rather arbitrary and primarily dictated by what parts of the code gets
> compiled for the subset of tests that are enabled in c++03 mode:
>
> https://bitbucket.org/eigen/eigen/src/default/unsupported/test/CMakeLists.txt#lines-112
>
> A larger set of tests covering the majority of the code base are only
> compiled in c++11 mode:
> https://bitbucket.org/eigen/eigen/src/c4368f48fef3737ef5a48604cfc63ce946b68616/unsupported/test/CMakeLists.txt#lines-179
>
> I don't think a user can realistically use Eigen tensor and avoid the c++11
> parts of the code. Therefore I would propose that we stop pretending that
> Eigen tensor supports c++03 and simply guard all the code with
> EIGEN_HAS_CXX11 or similar. This will then allow us to start cleaning up
> the code.
>
> Please let me know if you have any objections to this.
>
> Best,
>    Rasmus

--
 Dr.-Ing. Christoph Hertzberg

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