Dag Sverre Seljebotn wrote:
> Robert Bradshaw wrote:
>> Very good point. I've forwarded this onto Danilo who's working on C++
>> support.
>>
>> On Jul 23, 2009, at 12:56 PM, Martin Albrecht wrote:
>>
>>>> 1) Do you have any priorities for features you'd like to see sooner
>>>> rather than later?
>>> While debugging and fixing an issue in the current PolyBoRi wrapper
>>> with
>>> Alexander Dreyer we noticed the following behaviour in Cython which
>>> doesn't
>>> mix well with C++:
>>>
>>> Consider the following code:
>>>
>>> cdef BoolePolyRing ring = pbenv_ring()
>>>
>>> where pbenv_ring() returns a reference to the currently active
>>> PolyBoRi ring.
>>>
>>> This is fine because Cython doesn't care whether a variable or a
>>> reference is
>>> returned. However, Cython re-arranges the code as follows internally:
>>>
>>> cdef BoolePolyRing ring
>>> ring = pbenv_ring()
>>>
>>> This is fine if BoolePolyRing is a C data structure because in C
>>> declaration
>>> is never code execution. However, this is not fine in C++ where
>>> declaration
>>> may be code execution: the default constructor.
>>>
>>> (In our case the default constructor for BoolePolyRing would define
>>> a new ring
>>> and mark it as active and thus render the later assignment useless)
>>>
>>> So my nr.1 feature request is to not re-arrange declarations if C++
>>> is the
>>> language Cython compiles to.
>
> Note that this alone will not solve very much -- it will still only work
> for classes with constructors without arguments. Just doing this would
> just waste time IMO.
>
> This particular problem has been discussed to great length on the Cython
> list several times -- to recap quickly:
>
> 1) At first, one should probably disallow code like that (all C++
> classes must only be used through pointers -- so "cdef BoolePolyRing*
> ring").
Sorry, please ignore this:
>
> Note that without further definition of how this should work,
>
> ring = pbenv_ring()
>
> is nonsense anyway ("cdef BoolePolyRing ring" means stack allocated
> memory, not reference counted or similar).
I realize what you mean now.
--
Dag Sverre
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