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 >> >> >> >> >> >> >> >> >>
