ENH, SIMD: Add support for dispatching C++ sources

[seiko2plus]

Same usage as the C dispatch-able sources except files extensions
should be `.dispatcher.cpp` or `.dispatch.cxx` rather than `.dispatch.c`

[charris]

Hmm, this brings up the question of how we want to support c++. Do we want to modify the ccompiler or make a new cppcompiler. Or use meson :) @rgommers @mattip @seberg Thoughts?

[seberg]

Wouldn't meson be more of a mid- to longerterm solution/replacement, while we would like to try function templates fairly soon? And I guess most of distutils does all of this already and this is just generalizes the same things to the simd dispatching?

So, I know neither this code well nor the C++ deployment in general, but it seems fine to just go with it.

[rgommers]

And I guess most of distutils does all of this already and this is just generalizes the same things to the simd dispatching?

Exactly, SciPy has lots of C++ code and happily uses numpy.distutils. There's nothing missing aside from this PR AFAIK.

[rgommers]

@seiko2plus this PR looks good, but since there's no C++ code yet it's hard to test. I'm not suggesting you add in C++ code here (that would make it large and hard to merge). But did you test it locally? Is there a branch or WIP PR you could share to test this? Or would you prefer to just merge this and iterate on it if it later turns out to be incomplete?

[seiko2plus]

@rgommers,

But did you test it locally?

Sure, I did.

Is there a branch or WIP PR you could share to test this?

The current work is kinda a miss a little bit and I'm working on splitting them into 4 PRs:

• Add support for dispatching C++ sources(this one)
• Add support for Doxygen through Breathe
• Several fixes to the C headers that brings compatibility with c++
• C++ wrappers for C universal intrinsics(NPYV) [documented]

Or would you prefer to just merge this and iterate on it

Yes, that what I prefer but I can add a testing unit for C++ dispatching if it's nesseary. What do you think?

[charris]

but I can add a testing unit for C++ dispatching

Let's wait until the rest gets in and is working. I'm not sure what we should be testing at this point.

Thanks Sayed.

[rgommers]

Add support for Doxygen through Breathe

That seems fine, it looks like Breathe is pretty actively maintained right now.

The related Exhale (https://github.com/svenevs/exhale) is best avoided, it's unmaintained.