Cython & C++: passing by reference

c++, cython, pass-by-reference, python, reference

Solution

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)

Problem

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)`?

Original source