C++ Helper function to get nullptr constructed instance if nullptr ctor is available, default constructed instance if nullptr ctor is not available

empty_instance.h

template <typename T, typename = std::void_t<>>
struct empty_instance
{
    static T get() { return T{}; }
};


template <typename T>
struct empty_instance<T, std::void_t<decltype(T{ nullptr })>>
{
    static T get() { return T{ nullptr }; }
};

template <typename T>
T get_empty_instance()
{
    return empty_instance<T>::get();
}