overload opertator

[hbadi]

Hi,

I have a class A with a method operator+(A a) and also a constructor with a double parameter (defined as py::init )
I 'd like to write such expression a+2.5 with an automatic cast, is it possible ?

Best regards.

[jiwaszki]

Hi, of course it is possible. It is all in docs: https://pybind11.readthedocs.io/en/stable/advanced/classes.html#operator-overloading

If you have your operator defined like this (where _n is some member of your A class):

double operator+(A a) const { return _n + a._n; };

Then you are able to bind it with:

cls.def(py::self + py:self);
cls.def(py::self + double()); // this cover your case of automatic cast

[hbadi]

Hi @jiwaszki

1 - What's because the operator+ is not const, i'm using an external library where operators are not const... How can i deal with ?

2 - Moreover, given a construcor A(double) why the definition cls.def(py::self + py::self); won't automatically cast double as A (like C++ does) ?

Thanks.

[jiwaszki]

1. One way is just to use lambda, easy and clean:

  cls.def(
      "__add__", [](A &self, A &other)
      { return self + other; },
      py::is_operator());

2. If you want that you probably need custom type caster which is more advanced, refer to this: https://pybind11.readthedocs.io/en/stable/advanced/cast/custom.html#custom-type-casters

[hbadi]

Hi @jiwaszki

For sure, lambda helps a lot !
As i understand there's no way to write cls.def(py::self + py::self); with a "non-const" operarator definition A operator+(A a) { return A(_n +a.n); };, it's compulsory to write A operator+(A a) const { return A(_n +a.n); }; ? event if c++ does accept it (even without -fpermissive) but not pybind11.