Re: [eigen] "plain": a new keyword for auto with implicit evaluation

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While we were and are adding some new features which depend on C++11/C++14, there are currently no plans to generally lose C++03 compatibility -- at least not for Eigen 3.x. There is a macro EIGEN_MAX_CPP_VER which can be used to limit the standard Eigen is allowed to use (can be 03, 11, 14, 17, etc)

Of course, `if constexpr` could simplify/replace a lot of template specialization and SFINAE code (and therefore would likely even reduce compile-times), but currently that would mean essentially writing code twice (this can't be hidden elegantly into macros).


Christoph


On 19/02/2019 12.50, Daniel.Vollmer@xxxxxx wrote:
Hello,

since we're all inserting cents:

If Eigen were to make a break with C++03 compatibility it might as well be all the way
to the latest standard in my opinion.

Not everyone is so lucky that they either already have a code-base in C++17, or can just trivially require it (with all that that entails for the host system, compiler, and other dependencies used).

I personally don't see a problem with requiring C++11 in a new major release, but anything newer than that should IMO be weighed *very* carefully against the features / simplifications / etc. it allows.


Best regards

Daniel Vollmer

--------------------------
Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR)
German Aerospace Center
Institute of Aerodynamics and Flow Technology | Lilienthalplatz 7 | 38108 Braunschweig | Germany

Daniel Vollmer | AS C²A²S²E
www.DLR.de
________________________________
Von: Wood, Tobias [tobias.wood@xxxxxxxxx]
Gesendet: Dienstag, 19. Februar 2019 12:23
An: eigen@xxxxxxxxxxxxxxxxxxx
Betreff: Re: [eigen] "plain": a new keyword for auto with implicit evaluation

Just my two cents, might be a bit off-topic here, but in my opinion it would be a real back-step if the "hypothetical" Eigen 4 was stuck on C++11. I would very strongly argue to at least make the step to full C++14 and potentially C++17

I wholeheartedly agree on this point. C++17 features have been a big help in my own code - I have a hunch that `if constexpr` has the potential to simplify parts of Eigen (but this is a vague hunch based on my own code and a poor understanding of Eigen’s template code). If Eigen were to make a break with C++03 compatibility it might as well be all the way to the latest standard in my opinion.

Toby


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