Use accessor syntax in cython for cpp classes - c++

Question

If I have a class defined as follows in C++
class sample
{
private:
int data;
public:
sample()
{
data=0;
}
int get_data()
{
return data;
}
void set_data(int data)
{
this->data = data;
}
};
and I want to expose it to cython code using:
cdef extern from "sample.cpp":
cdef cppclass sample:
sample() except +
int get_data()
void set_data(int n)
Is there a way to expose the getter and setter in that class in such a way that they can then be used in cython using syntax such as:
a = obj.data
instead of
a = obj.get_data()
I know it is possible to do that by wrapping the class in cython defined class, but I would like to avoid that avoid that overhead.
Maybe I am asking for too much.

Answer 1

Disclaimer: I don't know cython, so I cannot say if the following will be fine for cython. However, my strategy would be to implement access via s.data already in the C++ code to keep the bindings slim and straightforward.
C++ has no attributes, but one can emulate them:
#include <iostream>
template <typename T,typename M,M (T::*getter)(),void (T::*setter)(M)>
struct Attribute {
T* parent;
Attribute(T* parent) : parent(parent){}
operator M() const {
return (parent->*getter)();
}
void operator=(const M& m){
(parent->*setter)(m);
}
};
class sample
{
private:
int data_;
public:
sample()
{
data_=0;
}
int get_data()
{
return data_;
}
void set_data(int data_)
{
this->data_ = data_;
}
Attribute<sample,int,&sample::get_data,&sample::set_data> data{this};
};
int main() {
sample s;
s.data = 42;
std::cout << s.data;
}
Output is 42. Note that I had to assume a int parameter for the setter. To enable also const int& a bit more will be needed.

Answer 2

Using the definition of the sample c++ class in the accepted response above by #idclev 463035818, and copied here for convenience:
#include <iostream>
template <typename T,typename M,M (T::*getter)(),void (T::*setter)(M)>
struct Attribute {
T* parent;
Attribute(T* parent) : parent(parent){}
operator M() const {
return (parent->*getter)();
}
void operator=(const M& m){
(parent->*setter)(m);
}
};
class sample
{
private:
int data_;
public:
sample()
{
data_=0;
}
int get_data()
{
return data_;
}
void set_data(int data_)
{
this->data_ = data_;
}
Attribute<sample,int,&sample::get_data,&sample::set_data> data{this};
};
I tested declaring that C++ class in cython with a flat public property, and ... it works! This does the job.
cdef extern from "sample.cpp":
cdef cppclass sample:
sample() except +
int data
Testing that and instrumenting the accessors in the example shows that the accessors are properly called.
Many thanks to everyone! That was very helpful.