[Cython] non-virtual methods

[Vitja Makarov]

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


-- 
vitja.