Use fused types to avoid tempita

[jbrockmendel]

A lot of the cython code is templated to avoid duplication, but is not especially readable (see anything in _libs with filename ending in ".pxi.in").

AFAICT we can use fused types and cython will internally generate all of the relevant functions. If this understanding is correct, the code can be made a lot friendlier.

[WillAyd]

Would be interested in seeing how this works - the templating system is sparsely documented so I'd definitely be +1 if there is a viable alternative

[jreback]

tried this a while back
though we had a lower cython version

personally i don’t think this makes it more readable because of the special cases for object

but certainly give a try

note we for example already have numeric fused types

[jbrockmendel]

but certainly give a try

OK, I'll poke at this after #22329, #22287, #22283 go through; any earlier and I'd be swimming in merge conflicts.

personally i don’t think this makes it more readable because of the special cases for object

It may turn out that way in the end; my intuition is that the learning curve for someone not familiar with tempita will make a pretty big difference.

[gfyoung]

If there were no special cases, I would prefer fused types over tempita as @jbrockmendel is proposing. Curious to see how many functions do not have special cases though...

[jbrockmendel]

AFAICT this process has gone as far as it can go. Closing.

[jreback]

ok!