QtCreator crashes as soon as i open the attached C++ file

enum foo_t { A, B, C, D };

constexpr foo_t parent_of(const foo_t f) { return (f < D) ? static_cast<foo_t>(f+1) : D; }

template <typename T>
union index_ptr_t {
    unsigned int index;
    const T* ptr;
};

template <foo_t> struct Dummy;

namespace impl {

template <foo_t f>
struct dummy_impl {
    index_ptr_t<Dummy<parent_of(f)>> parent;
};

template <>
struct dummy_impl<D> {};

}  // namespace impl

template <foo_t f>
struct Dummy : impl::dummy_impl<f> {};

struct DummiesSet {
    index_ptr_t<Dummy<A>> a;
    index_ptr_t<Dummy<B>> b;
    
    void operator=(const Dummy<A>* _a) {
        a.ptr = _a;
        b.ptr = a.ptr->parent.ptr;
    }
};