Hi, I'd like to see support for variadic template arguments, such as this:
test.h:
template<typename RetT, typename ... VARARGS>
RetT foo(VARARGS ...);
test.pyx:
cdef extern from "test.h":
cdef RetT foo[RetT, ... VARARGS](... VARARGS)
def test():
cdef int i = foo[int, float, int](1, 2.5, 3)
This would allow Cython's libcpp to easily support many of C++11's new
types, including std::tuple and std::function.
Support for the latter in particular would prove quite useful in passing
around function pointers between Cython and C++.
I have tried to implement this feature myself, but I'm entirely
unfamiliar with Cython's codebase, and all my attempts ended in
unsatisfactorily hacky, unstable code.
I believe that any experienced Cython developer on this list would be
able to properly implement this in a matter of a few hours, as it seems
like a rather minor feature.
The current workaround for the non-existance of this feature involves
typedefs for every possible number of arguments, like this:
template<typename ... Ts>
struct S {};
using S0 = S<>;
template<typename T0>
using S1 = S<T0>;
template<typename T0, typename T1>
using S2 = S<T0, T1>;
template<typename T0, typename T1, typename T2>
using S3 = S<T0, T1, T2>;
then exporting all of S0, S1, ... individually in the .pxd file.
This is inconvenient, but acceptable.
Now assume that S has a member function f,
template<typename ... Us>
void f(Ts..., Us ...);
due to the nature of C++, the same trick as above does not work, and the
user will be forced to clutter the C++ code with a function body for
every possible len(Us). Even worse, the .pxd file will now contain a
quadratic number of wrappers (one for every possible combination of
len(Ts), len(Us)), all of them extremely prone to mistakes.
Thanks for reading,
~ Michael
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