A discussion recently came up on the NumPy mailing list, and it inspired
me to focus on this usability issue:
cdef extern from "test.h":
ctypedef int type_a
ctypedef int type_b
cdef type_a* ptr1 = NULL
cdef type_b* ptr2 = ptr1
Now, it might happen (like with NumPy) that type_a and type_b are
defined as seperate types on some platforms and the same on others
(through #ifdefs). Partly this is relied upon currently, making the
situation a bit confusing, especially for new users.
Possible solutions:
1) Make all external types pointer-incompatible. So "ptr2=ptr1" above
will always fail, and an explicit cast is needed.
2) Introduce a new keyword, something like unknown_size:
cdef extern from "test.h":
ctypedef unknown_size int type_a
ctypedef long type_b # we know this is always "long"
...
which trigger pointer-incompatability with anything. NB! At the same
time, all external primitive types are checked for the right declaration
in Cython at module startup time:
if (sizeof(type_b) != sizeof(long) || ((type_a)-1) != ((type_b)-1) ||
((type_a)0.5) != ((type_b)0.5))) { /*raise exception*/ }
(Not sure if that float check will work though, might need to do a
division instead.)
3) Complex interaction with the C compiler so that Cython and the C
compiler work "in one step". The Cython core is simplified so that it
never checks pointer assignment compatability, but rather take any error
the C compiler gives and translates it back to an error to the Cython
user. Obviously not a short-term solution but if this is a long-term
solution it might be enough reason not to bother with this for now. This
seems to be the most stable solution, but it does give away the
possibility to seperate the Cython and C compilation stages as some
people are fond of doing.
Dag Sverre
_______________________________________________
Cython-dev mailing list
[email protected]
http://codespeak.net/mailman/listinfo/cython-dev
