Cython & C++: passing by reference

Question

I am a noob with Cython and C++, so I have a question on argument passing. I want to avoid passing a copy of an argument in the following scenario:

# somefile.pyx
#distutils: language = c++
from libcpp.vector cimport vector

def add_one(vector[int] vect):
    cdef int i
    n = vect.size()
    for i in range(n):
        vect[i] += 1

cdef vector[int] v
for i in range(100000):
    v.push_back(i)
add_one(v) # <-- ??

I want the method add_one to just modify v "in-place." I believe in C++, you can achieve this by pre-pending the argument with &, which means that any changes to the pointer is passed to the pointee. That way, you don't have to worry about passing a pointer or the actual object, i.e.

add_one(v); # in c++

Can I do the same in Cython, or do I have to explicitly change the arg type to a reference instead, i.e. def add_one(vector[int]* vect)?

Answer 1

Found the answer to my own question. Apparently, you can pass by reference, but the function MUST be cdef'ed, not def'ed. i.e.

# somefile.pyx #distutils: language = c++ from libcpp.vector cimport vector  cdef void add_one(vector[int]& vect):     cdef int i     n = vect.size()     for i in range(<int>n):         vect[i] += 1  cdef vector[int] v for i in range(100000):     v.push_back(i) add_one(v)