Overloading the 'or equals' operator globally for an enum

Here is how to overload the |= operator globally for an enum in C++.

class MyClass {
    public:
    enum Property {
        NoProperty = 0, Flat = 1, Orange = 2, Soft = 4
    };
    //...//
};

inline MyClass::Property&
operator|=(MyClass::Property& a, MyClass::Property const b) {
    a = static_cast<MyClass::Property>(static_cast<int>(a)
                                     | static_cast<int>(b));
    return a;
}