Cython C++ static methods in a template class

Question

Problem

I have a template class in C++ that has a static method. It looks more or less like this:

template<typename T>
class Foo {
    static std::shared_ptr<Foo<T>> doSth();
}

so in C++ you would call it like: Foo<Int>::doSth();. In Cython however, the way to call static methods is by using the classname as a namespace:

cdef extern from "Bar.h" namespace "Bar":
    shared_ptr[Bar] doSth()  # assuming shared_ptr is already declared

but this has no notion of templates. Obviously, simply passing Foo<T> as a namespace doesn't work, because it translates to Foo<T>::doStr() in C++, no concrete type is substituted for T.

Question

How would you do that in Cython? Is there a way, or a workaround?

Answer 1

Static methods are now directly supported by Cython; the namespace hack is no longer necessary or recommended.

cdef extern from "Foo.h":
    cdef cppclass Foo[T]:
        @staticmethod
        shared_ptr[Foo[T]] doSth()  # assuming shared_ptr is already declared

cdef shared_ptr[Foo[int]] shared_ptr_value = Foo[int].doSth()

http://docs.cython.org/en/latest/src/userguide/wrapping_CPlusPlus.html#static-member-method

Answer 2

Note: This answer was right at the time it was written (and does still work) but you should now use @Robertwb's answer to this question instead to do this properly.

---

I don't think you can do it directly in Cython. You could create very thin wrapper of a normal (non-static-method) c++ template function

template <typename T>
std::shared_ptr<Foo<T>> Foo_T_doSth<T>() {
   return Foo<T>::doSth();
}

and then wrap this method in Cython

cdef extern from "..."
    shared_ptr[T] Foo_T_doSth[T]()

---

As an aside, the recommended way of wrapping static methods in Cython looks to be (from https://groups.google.com/forum/#!topic/cython-users/xaErUq2yY0s)

cdef extern from "...":
   cdef Foo_doSth "Foo::doSth"()  # not declared as a memeber

(by specifying the actual function to use as a string). This doesn't help you here because it doesn't cope with templates. It may have been me who mis-advised you on the way you were trying...