[Cython] non-virtual methods

Robert Bradshaw robertwb at math.washington.edu
Tue Aug 30 19:40:46 CEST 2011

On Tue, Aug 30, 2011 at 10:19 AM, Vitja Makarov <vitja.makarov at gmail.com> wrote:
> 2011/8/30 Stefan Behnel <stefan_ml at behnel.de>:
>> Vitja Makarov, 30.08.2011 18:39:
>>> 2011/8/30 Stefan Behnel:
>>>> Robert Bradshaw, 30.08.2011 18:18:
>>>>> On Tue, Aug 30, 2011 at 9:14 AM, Vitja Makarov wrote:
>>>>>> What about final classes with cpdef methods?
>>>>>> @cython.final
>>>>>> class Foo:
>>>>>>    cpdef bar(self):
>>>>>>        pass
>>>>>> Should that raise an error?
>>>>> That should be perfectly fine.
>>>> Well, the 'final' decorator shouldn't work on normal Python classes.
>>>> Regarding extension types, CPython has a way of declaring them 'final'
>>>> with
>>>> a type flag, which effectively prevents them from being subclassed in
>>>> Python. So the above works as just fine for cdef classes.
>>> Ok. So final class could have cpdef methods but non-final extension
>>> type couldn't, am I right?
>> All extension types can have cpdef methods, be they final or not. For final
>> classes, cpdef methods simply mean that they have a Python wrapper and will
>> otherwise be called directly when called from Cython.
>> Actually, for cpdef methods in final classes, we can even drop the override
>> check in the DefNode wrapper. I don't think that currently happens.
> Currently I drop OverrideCheckNode for all final cpdef methods, see
> https://github.com/cython/cython/pull/59/files#L2R1751
> Final classes can have cpdef method that's ok.
> Could non-final classes have final-cpdef methods?

No, as we can't prevent them from being overridden (violating the
semantics of final). We should raise an error when trying to declare
final cpdef methods in non-final classes.

> Currently final class means that all its c[p]def methods are final too.

Good point.

- Robert

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