I suggest to move forward, and use C++17. There is no reason to stick with old libraries.
If you prefer to keep for a year or two the ability to compile with C++14, then place such obsolete code inside some #ifdef #else #endif, so that more efficient code is generated with C++17 and less efficient code when someone insists on compiling with C++14. In yade[1] we have moved to C++17 when building packages for ubuntu focal 20.04 or debian buster or bullseye. The C++14 is used only when building packages for older systems such as ubuntu xenial 16.04. Yade can compile with eigen using C++17 without any problems. Which is good. For example the coinor library had some problems with C++17: and older version worked only with C++17. best regards Janek [1] https://yade-dem.org/doc/ and https://gitlab.com/yade-dev/trunk Rasmus Munk Larsen said: (by the date of Tue, 5 May 2020 14:14:19 -0700) > I agree with you, but it seems the maintainers are very busy with other > projects, and I am guessing they do not have time for major initiatives to > clean up Eigen. We have dropped support for c++03 in the Tensor library, > but a lot of things could be cleaned up if we more fully embraced c++11 or > c++14. At this point, I only see this happening slowly, or if somebody from > the open source community is willing to help. > > On Tue, May 5, 2020 at 2:05 PM Patrik Huber <[email protected]> wrote: > > > Hi all, > > > > I'm a quite sad to see this post got no replies. I can only add that I > > fully agree and think along the very same lines. I would love to see Eigen > > move forward, move to C++14 in the 3.5 release, and drop the old cruft. > > It's 2020 now, 6 years after C++14. > > > > Best wishes, > > Patrik > > > > On Wed, 8 Apr 2020 at 17:20, Martin Beeger <[email protected]> > > wrote: > > > >> Hallo! > >> > >> This is continuation of the discussion from last year about > >> compatibility, but I wanted to bring it up again, because I have some > >> new data from my experience. > >> > >> Our company uses Eigen extensively and has a larger ecosystem built on > >> it, as do many of the voices on this list. We are in the embedded world, > >> so we are often hindered to adapt quickly to new tools, very much like > >> the HPC community has been. > >> But we managed to move to C++14 with our codebase in 2019. When doing > >> that, we somewhat monitored performance and compile time during the > >> adaption. > >> > >> When we starting compiling our C++98 codebase as is with C+14, > >> performance already went up slightly. C++14 does silently move or elide > >> copies, and modern compiler have better optimizers, and the quality of > >> implementation of STL types got better. So if you are at all bound by > >> performance of STL types, I would really recommend using a new compiler > >> in C++14 mode even with your old code. > >> > >> This was the obvious part. Another part was less obvious. We profiled > >> compile time, which didn't change much after the switch and started to > >> look into stuff which was expensive to compile. And then selectively in > >> places, where the compile time was bad we simplified the code using > >> C++14 features to improve compile time. This allowed us with very > >> localized changes to cut our compile time by almost in half, while, at > >> the same time, making the code in question often a lot simpler and new > >> features (e.g. for performance improvements) easier to implement. > >> > >> This is also the experience which was observed with other template heavy > >> codebases like boost::mpl in comparison to hana and other stuff. The > >> gains in simplicity and compile time, especially from constexpr and > >> lambda features are not minor. They can often cut your code in half and > >> more than double the compile time. > >> > >> The problem is, I am at a point where its hard to do much more to > >> improve the compile time of my codebase significantly, because most of > >> the compile time is brought in by 2 libraries: boost.test and Eigen. We > >> will most likely at some point abandon boost.test due to this, like many > >> others have already (which slowed the development and improvement of > >> boost.test further, while the alternatives got better and getting into > >> this downwards spiral). I would be vary happy if I am not forced to > >> abandon Eigen after the great 10 years we had with this library. In > >> order to avoid this I pulled a lot of tricks like explicit template > >> instatiations, tricks to reduce includes, even pimpl-like encapsulation > >> at performance cost to isolate from the problem, but that gets you only > >> so far. > >> > >> I may well be that my use case is special, but I strongly assume that > >> new users which today want to adopt Eigen and have to look into its > >> internals (as you inevitable need to do at some points), will see how > >> its written and quickly run for alternatives. This amount of macros, > >> boilerplate and similar stuff will be an argument against this great > >> library some day and this day may already have come. > >> > >> The important part is here: Eigen compile time and internal expression > >> template engine code readability it was great by 2010s standards, it was > >> ok by 2015 standards, it is borderline by 2020 standards, and unless > >> something changes, it will be unacceptable by 2025 standards, unless the > >> Eigen library moves along. > >> > >> As C++ users, we do care about backwards compatibility greatly and that > >> is even good for me, but we should not go the C way and care about too > >> ancient compilers. The C++ comittee doesn't (that why int is required to > >> be 2s complement in C++20), so Eigen library maintainers IMHO should > >> follow. > >> > >> What are the chances to get Eigen 3.4 out of the door with C++98 support > >> and drop it on the devel branch afterwards and jump to C++14? > >> What is the Eigen promises about how old yours compilers may be? > >> Can we explicitly agree on a statement like: We vow to support up to 3 > >> year old compilers (or 5 years)? > >> > >> If we could agree on clear and conservative rules like we will go 3 > >> years back or 5 years back and state these on the Eigen front page, > >> Eigen user may look at our codebase and be much more willing to accept > >> older standards code, knowing that it will improve over time and that > >> the user gets some useful guarantees about the future in return. > >> There is agrument to be made that if you use a 5+ years old compiler, > >> you really do not care about performance, something Eigen uses generally > >> care about. So you are not in a targeted user group of Eigen. Little HPC > >> clusters do not at all offer any way to install a more recent compilers > >> that 5 years (this has changed a lot from a decade ago) and even in the > >> embedded world, vendors tend to drop support or upgrade for platforms > >> with more than 5 years old toolchains too (this has also very much > >> changed from 10 years ago). > >> > >> Eigen users should be able to get a clear answer on the question when we > >> drop C++98 (of if). That belongs on the front page IMHO. > >> > >> Kind regards, > >> Martin > >> > >> > >> > >> > >> > >> > >> > >> > >> -- -- Janek Kozicki, PhD. DSc. Arch. Assoc. Prof. Gdańsk University of Technology Faculty of Applied Physics and Mathematics Department of Theoretical Physics and Quantum Information -- http://yade-dem.org/ http://pg.edu.pl/jkozicki (click English flag on top right)
