In my code I have a system as outlined by the following code:

// Base class to make derived objects polymorphic
struct Base {
    virtual ~Base() = default;
};

void registerData(int*) {}

template <typename Derived>
struct RegisterMixin {
    static int (Derived::*dataPtr); // Defined for each derived class

    RegisterMixin() {
        auto* derived = static_cast<Derived*>(this);
        registerData(&(derived->*dataPtr));
    }
};

struct MyDerived: Base, RegisterMixin<MyDerived> {
    int myData; // Will be set by the enclosing system
};

template <>
int MyDerived::*RegisterMixin<MyDerived>::dataPtr = &MyDerived::myData;

int main() {
    MyDerived derived;
}

The indent is that whenever an object derived from RegisterMixin is constructed, its data member will be registered in a global map so it can be controlled by an enclosing system.

If I run the program with UB sanitizer it complains about the static_cast<Derived*> in the RegisterMixin constructor that the object is not of type Derived. I assume the error is justified because the RegisterMixin constructor runs before the Derived constructor.

However I don’t actually do anything with the derived object, I only access its address. Is there any way to achieve what I’m trying here without invoking UB?

https://godbolt.org/z/YK8dKc47W