[Cython] non-virtual methods

[Vitja Makarov]

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.

-- 
vitja.