[Cython] CEP1000: Native dispatch through callables

Robert Bradshaw robertwb at gmail.com
Sun Apr 15 08:32:10 CEST 2012

On Sat, Apr 14, 2012 at 11:16 PM, Stefan Behnel <stefan_ml at behnel.de> wrote:
> Robert Bradshaw, 15.04.2012 07:59:
>> On Sat, Apr 14, 2012 at 2:00 PM, mark florisson wrote:
>>> There may be a lot of promotion/demotion (you likely only want the
>>> former) combinations, especially for multiple arguments, so perhaps it
>>> makes sense to limit ourselves a bit. For instance for numeric scalar
>>> argument types we could limit to long (and the unsigned counterparts),
>>> double and double complex.
>>> So char, short and int scalars will be
>>> promoted to long, float to double and float complex to double complex.
>>> Anything bigger, like long long etc will be matched specifically.
>>> Promotions and associated demotions if necessary in the callee should
>>> be fairly cheap compared to checking all combinations or going through
>>> the python layer.
>> True, though this could be a convention rather than a requirement of
>> the spec. Long vs. < long seems natural, but are there any systems
>> where (scalar) float still has an advantage over double?
>> Of course pointers like float* vs double* can't be promoted, so we
>> would still need this kind of type declaration.
> Yes, passing data sets as C arrays requires proper knowledge about their
> memory layout on both sides.
> OTOH, we are talking about functions that would otherwise be called through
> Python, so this could only apply for buffers anyway. So why not require a
> Py_buffer* as argument for them?

That's certainly our (initial?) usecase, but there's no need to limit
the protocol to this.

- Robert

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