Method add_base

include/pybind11/pybind11.h:2394–2405

    template <typename Base, detail::enable_if_t<is_base<Base>::value, int> = 0>
    static void add_base(detail::type_record &rec) {
        rec.add_base(typeid(Base), [](void *src) -> void * {
            return static_cast<Base *>(reinterpret_cast<type *>(src));
        });
        // Virtual inheritance means the base subobject is at a dynamic offset,
        // so the reinterpret_cast shortcut in load_impl Case 2a is invalid.
        // Force the MI path (implicit_casts) for correct pointer adjustment.
        // Detection: static_cast<Derived*>(Base*) is ill-formed for virtual bases.
        if PYBIND11_MAYBE_CONSTEXPR (!detail::is_static_downcastable<Base, type>::value) {
            rec.multiple_inheritance = true;
        }
    }

    template <typename Base, detail::enable_if_t<!is_base<Base>::value, int> = 0>
    static void add_base(detail::type_record &) {}