[Cython] non-virtual methods

[Vitja Makarov]

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)

-- 
vitja.