Yes, I've seen too many unfortunate template libraries, which never work in combination with a different template library.

I've used some quite reasonable academic C++ for geometry processing and meshing.

Note that I'm not saying that science academic C++ is never great; I'm saying that it's often unfortunate. Is the code you're talking about code that's progressed through several maintainers without becoming sad? That's often where things go wrong, not the initial code, but keeping it going, cleanly, through multiple collaborators / post-docs / grad students.

I agree that meshing is definitely a difficult situation; I've never seen a solution (for unusual geometry) that I liked much. Things that can pretend to be rectangular? No problem. Very adaptive meshes? Argh.

Hard to say, but I'm looking at 39 contributors, 539 stars, 3,005 commits [1]. Nicely documented, pretty extensive list of users, CI on Linux and Windows. But with that said, yes, I've also dealt with absolutely horrendous academic C++.

[1] https://github.com/libigl/libigl/

Are there any users that are science academics? I wasn't talking about computer scientists / computer graphics / visualization researchers at all in this thread; they do great with C++. I clicked on a bunch of links of the users of this library and didn't see any physics, astronomy, chemistry, fluid dynamics, etc.

Not sure! We are using it in (non-academic) CFD work.

So it sounds like you're somewhat like the folks I'm talking about, even if the other users of this code are not... but have you had a lot of turnover of your coders, like grad students and postdocs that turn over every 2-4 years? Because that was the full nature of my complaint: science not-computer-scientists over several maintainers doing better in Fortran.