[Cython] non-virtual methods

Vitja Makarov vitja.makarov at gmail.com
Sun Aug 28 13:00:37 CEST 2011


2011/8/27 Vitja Makarov <vitja.makarov at gmail.com>:
> 2011/8/27 Vitja Makarov <vitja.makarov at gmail.com>:
>> 2011/8/26 Vitja Makarov <vitja.makarov at gmail.com>:
>>> 2011/8/25 Vitja Makarov <vitja.makarov at gmail.com>:
>>>> 2011/8/25 Vitja Makarov <vitja.makarov at gmail.com>:
>>>>> 2011/8/25 Stefan Behnel <stefan_ml at behnel.de>:
>>>>>> Vitja Makarov, 25.08.2011 20:32:
>>>>>>>
>>>>>>> 2011/8/25 Stefan Behnel<stefan_ml at behnel.de>:
>>>>>>>>
>>>>>>>> Vitja Makarov, 25.08.2011 18:11:
>>>>>>>>>
>>>>>>>>> 2011/8/24 Stefan Behnel:
>>>>>>>>>>
>>>>>>>>>> Vitja Makarov, 24.08.2011 21:17:
>>>>>>>>>>>
>>>>>>>>>>> I tried final classes:
>>>>>>>>>>> 2. In this example foo call is done through virtual table
>>>>>>>>>>>
>>>>>>>>>>> cimport cython
>>>>>>>>>>>
>>>>>>>>>>> @cython.final
>>>>>>>>>>> cdef class Foo:
>>>>>>>>>>>     cdef foo(self):
>>>>>>>>>>>         print 'haha'
>>>>>>>>>>>
>>>>>>>>>>> def test():
>>>>>>>>>>>     cdef Foo a = Foo()
>>>>>>>>>>>     a.foo()
>>>>>>>>>>>
>>>>>>>>>>>   __pyx_t_1 = ((struct __pyx_vtabstruct_3yyy_Foo
>>>>>>>>>>> *)__pyx_v_a->__pyx_vtab)->foo(__pyx_v_a); if (unlikely(!__pyx_t_1))
>>>>>>>>>>> {__pyx_filename = __pyx_f[0]; __pyx_lineno = 12; __pyx_clineno =
>>>>>>>>>>> __LINE__; goto __pyx_L1_error;}
>>>>>>>>>>
>>>>>>>>>> Right, this is not implemented yet. Feel free to do so. Also see
>>>>>>>>>>
>>>>>>>>>> http://trac.cython.org/cython_trac/ticket/474
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>> 3. I can't use final decorator for methods (error reported)
>>>>>>>>>>
>>>>>>>>>> http://trac.cython.org/cython_trac/ticket/586
>>>>>>>>>
>>>>>>>>> What is the prefered syntax keyword inline or final decorator?
>>>>>>>>
>>>>>>>> "final" is the right option here.
>>>>>>>>
>>>>>>>> They are orthogonal concepts. Only because you declare a method "final"
>>>>>>>> does
>>>>>>>> not mean you want to inline it, and just because you declare it "inline"
>>>>>>>> does not (necessarily) mean that you cannot override it. Admittedly, the
>>>>>>>> semantics of an overridable inline method may turn out to be somewhat
>>>>>>>> obscure and error prone, so I think it's a good idea to let "inline"
>>>>>>>> imply
>>>>>>>> "final". But not the other way round.
>>>>>>>
>>>>>>> But both inline and final methods should bypass vtab, right?
>>>>>>
>>>>>> Yes. But in the "final" case, it's always clear which method implementation
>>>>>> to use - it's not overridable, so there is only one choice. In the "inline"
>>>>>> case, it could still be overridable and we may have a subtype of the
>>>>>> declared type in our hands at runtime, thus choosing the wrong method at
>>>>>> compile time. That's why only the "final" case is safe.
>>>>>>
>>>>>> Note that I'm only talking about the semantics of the qualifier themselves
>>>>>> here. If we allow "inline" methods, I think we should force them to be
>>>>>> "final" as well. But that's a practical choice, not a semantic implication.
>>>>>>
>>>>>>
>>>>>>> Also I'm not sure about C inline qualifier here.
>>>>>>
>>>>>> That's what "inline" requests.
>>>>>>
>>>>>>
>>>>>>> I see three options:
>>>>>>>
>>>>>>>  - non-virtual: bypass vtab
>>>>>>>  - final: non-virtual, non-overridable
>>>>>>
>>>>>> How would you want to bypass the vtable in the "non-virtual" case if the
>>>>>> method is overridable?
>>>>>>
>>>>>>
>>>>>>>  - inline: non-virtual, C inline qualifier is used
>>>>>>
>>>>>> Correct.
>>>>>>
>>>>>
>>>>> Ok.
>>>>>
>>>>> I think it's better to implement final method then user could choose
>>>>> to use inline qualifier or not.
>>>>>
>>>>
>>>> I tried it here:
>>>> https://github.com/vitek/cython/commit/ddf80a80dc75aced2cd92dc32afa77a7bcf2de02
>>>>
>>>> There is one problem: vtab bypassing should be enabled if final method
>>>> is defined in the same module.
>>>> I don't know how to check that final method comes from cimport (it's
>>>> okay with pxd, the problem is pyx)
>>>>
>>>
>>>
>>> https://github.com/vitek/cython/commit/6e91fc257a683018ba6be340d384f9a7c34ef425
>>>
>>> Here is update version. I've add tree asserts and final method's prototypes.
>>>
>>> --
>>> vitja.
>>>
>>
>> I've created ticket for compiler crash when cython.final is used
>> inside pxd file:
>>
>> http://trac.cython.org/cython_trac/ticket/722
>>
>> Also I've updated final methods test case (added tree path assertions)
>> https://github.com/vitek/cython/commit/92edb09419c9b77a792f7c43e6ddd760b00c4e74
>>
>>
>> About declaration origin detection may be it's a good idea to have a
>> flag at scope level something like is_pxd_scope or
>> is_declaration_scope?
>>
>
> It seems to me that I found a way to fix pxd/pyx cimport problem. I've
> created pull request:
>
> https://github.com/cython/cython/pull/59
>

I've add support for inline methods, now you can declare inline method
in pxd file:

cdef class Foo:
   cdef inline foo(self):
       return 1




-- 
vitja.


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