How do I pass one C++ class (reference) to another when using Cython?

Question

I'm trying to wrap a C++ module using Cython such that I can use it in Python.

The module has multiple classes some of these have methods that have object references to another class as arguments.

So lets say I have c++ classes called "foo" and "bar"- and cython wrap them thus:

cdef extern from "foobar.hpp" namespace "foobar":
    cdef cppclass foo:
        pass
    cdef cppclass bar:
        void kungFoo(foo &f)

Now I want to make a wrapper class so that I can use it in Python...

cdef class pyFoo:
    cdef foo *thisptr
    def __cinit__(self):
        self.thisptr = new foo()

cdef class pyBar:
    cdef bar *thisptr
    def __cinit__(self):
        self.thisptr = new bar()
    def kungFoo(self, f):
        self.thisptr.kungFoo(f.thisptr)

Well this results in "Error compiling Cython file." and "Cannot convert Python object to 'foo'".

I think that this is because the cdef cppclass foo makes foo a "Python object" associated with the c++ class. However, this clever transformation doesn't seem to go back the other way when I need to pass it as an argument to another c++ class.

This seems like a basic issue with cython to me - but I can't seem to find any solution after a couple of hours on google.

Any help most welcome.

Thanks!

Answer 1

Specify type for the f parameter. So make it this:

def kungFoo(self, foo &f):
    self.thisptr.kungFoo(f)

Or this:

def kungFoo(self, pyFoo f):
    self.thisptr.kungFoo(f.thisptr)