C++/SWIG typemap passed by reference

Question

I have the following C++ code that I want to be usable from Python. The wrapping is made with SWIG.

Header file:

#ifndef FSINDEXTRANSFORM_H
#define FSINDEXTRANSFORM_H

class FSIndexTransform
{
public:
typedef int IndexVec3;

void Transform(const IndexVec3 indices, const IndexVec3 begin1, const IndexVec3 begin2, IndexVec3& result) const;
};

#endif

Source file:

#include <iostream>
#include "FSIndexTransform.h"

void FSIndexTransform::Transform(const IndexVec3 indices,
                                const IndexVec3 begin1,
                                const IndexVec3 begin2,
                                IndexVec3& result) const
{
std::cout << "OK" << std::endl;
}

SWIG header:

%module FSIndexTransform

%{
#include "FSIndexTransform.h"
%}

%include "FSIndexTransform.h"

I am trying to use the generated Python module as follows:

from FSIndexTransform import FSIndexTransform
transform = FSIndexTransform()
transform.Transform(1, 2, 3, 4)

According to SWIG documentation, const IndexVec3 and IndexVec3& arguments should be processed the same way. But this is not the behavior I observe:

Traceback (most recent call last):
File "test.py", line 13, in <module>
    transform.Transform(1, 2, 3, 4)
File "/projects/fsdm/dev/st15435/FlowSim/FSDM/trunk/test_fsindextransform/bin/FSIndexTransform.py", line 101, in Transform
    return _FSIndexTransform.FSIndexTransform_Transform(self, indices, begin1, begin2, result)
TypeError: in method 'FSIndexTransform_Transform', argument 5 of type 'FSIndexTransform::IndexVec3 &'

When looking to the FSIndexTransform_wrap.cpp, one can see that the translation is not done the same way for all parameters:

FSIndexTransform::IndexVec3 arg2 ; 
FSIndexTransform::IndexVec3 arg3 ;
FSIndexTransform::IndexVec3 arg4 ; 
FSIndexTransform::IndexVec3 *arg5 = 0

I didn't manage to use (or to understand) similar discussions I have found.