Help with implementing == and != operators in enum class

[eddiehoyle]

Hello,

I'm having trouble implementing equal/not equal operators on an enum class.

See the following example:

#include <pybind11/operators.h>
#include <pybind11/pybind11.h>

namespace py = pybind11;

enum class Food {
    Pizza = 0
};

template<class T>
inline bool operator ==(const Food& a, const T b) {
    throw std::runtime_error("__eq__");
    return false;
}

template<class T>
inline bool operator !=(const Food& a, const T b) {
    throw std::runtime_error("__ne__");
    return false;
}

template<class T>
inline bool operator +(const Food& a, const T b) {
    throw std::runtime_error("__add__");
    return false;
}

PYBIND11_MODULE(_example, m) {
    py::enum_<Food>(m, "Food")
    .value("Pizza", Food::Pizza)
    .def(py::self == py::float_())
    .def(py::self != py::float_())
    .def(py::self + py::float_());
}

And testing with this code:

import example

if __name__ == '__main__':

    # No-op
    example.Food.Pizza == float(1.25)
    example.Food.Pizza != float(1.25)

    # RuntimeError
    example.Food.Pizza + float(1.25)

I see:

Traceback (most recent call last):
  File "/.../main.py", line 9, in <module>
    example.Food.Pizza + float(1.25)
RuntimeError: __add__

I just can't seem to trigger the exceptions in operator == and operator !=. Can anyone help me with where I'm going wrong?

Versions:

• Python-3.7
• pybind11-2.8.1