There is certainly good precedent for the approach you suggest.
Shortly after Nathaniel mentioned the rewrite to me, I looked up
d-pointers as a possible technique: https://wiki.qt.io/D-Pointer.
If we allow arbitrary kwargs for the new functions, is that something
you would want to note in the public structure? I was thinking
something along the lines of adding a hook to process additional
kwargs and return a void * that would then be passed to the loop.
To do this incrementally, perhaps opening a special development branch
on the main repository is in order?
I would love to join in the fun as time permits. Unfortunately, it is
not especially permissive right about now. I will at least throw in
some ideas that I have been mulling over.
-Joe
On Thu, Mar 31, 2016 at 4:00 PM, Jaime Fernández del Río
I have started discussing with Nathaniel the implementation of the ufunc ABI break that he proposed in a draft NEP a few months ago:
http://thread.gmane.org/gmane.comp.python.numeric.general/61270
His original proposal was to make the public portion of PyUFuncObject be:
typedef struct { PyObject_HEAD int nin, nout, nargs; } PyUFuncObject;
Of course the idea is that internally we would use a much larger struct that we could change at will, as long as its first few entries matched those of PyUFuncObject. My problem with this, and I may very well be missing something, is that in PyUFunc_Type we need to set the tp_basicsize to the size of the extended struct, so we would end up having to expose its contents. This is somewhat similar to what now happens with PyArrayObject: anyone can #include "ndarraytypes.h", cast PyArrayObject* to PyArrayObjectFields*, and access the guts of the struct without using the supplied API inline functions. Not the end of the world, but if you want to make something private, you might as well make it truly private.
I think it would be to have something similar to what NpyIter does::
typedef struct { PyObject_HEAD NpyUFunc *ufunc; } PyUFuncObject;
where NpyUFunc would, at this level, be an opaque type of which nothing would be known. We could have some of the NpyUFunc attributes cached on the PyUFuncObject struct for easier access, as is done in NewNpyArrayIterObject. This would also give us more liberty in making NpyUFunc be whatever we want it to be, including a variable-sized memory chunk that we could use and access at will. NpyIter is again a good example, where rather than storing pointers to strides and dimensions arrays, these are made part of the NpyIter memory chunk, effectively being equivalent to having variable sized arrays as part of the struct. And I think we will probably no longer trigger the Cython warnings about size changes either.
Any thoughts on this approach? Is there anything fundamentally wrong with what I'm proposing here?
Also, this is probably going to end up being a rewrite of a pretty large and complex codebase. I am not sure that working on this on my own and eventually sending a humongous PR is the best approach. Any thoughts on how best to handle turning this into a collaborative, incremental effort? Anyone who would like to join in the fun?
Jaime
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