update demo to include an external library dependency (eg, google re2)

[sarnold]

This works, but only includes a header file and requires re2-config.cmake (I couldn't make it find a random non-cmake lib, so I had to respin the gentoo ebuild to use cmake so it installed the .cmake files)

[sarnold]

This is only a proof-of-concept but hopefully it's better than just complaining about something...

[henryiii]

A few things to keep in mind:

a) Eigen has no compiled component, so there's nothing to link.
b) The example is intended to be simple and show pybind11 interaction; adding an external library to link adds a complication that is not pybind11 specific at all.
c) Bundling shared libraries is somewhat (Unix) to very (Windows) complicated for wheels (a bit easier with Conda).
d) The CMake example is somewhat discouraged in favor of the superior Scikit-Build example or the works-everywhere python_example.
e) A more complex example can be found here: scikit-build/scikit-build-sample-projects#8

I don't want to discourage you, but would like to set expectations correctly.

[sarnold]

I think I get the points you're making (and this one is apparently very incomplete) so probably not worth keeping open. That said, I managed to iron out the wrinkles in my non-example build here: https://github.com/freepn/google-re2

Take a look if you have some time; feedback is welcome (and thanks for the examples ;)