template<typename T>
	auto trait()
	{
		using Tag = typename T::Tag;
		T *t = dynamic_cast<T *>(this);
		if (!t) {
			return std::nullopt;
		}

		if constexpr (std::is_reference_v<decltype(t->get(Tag{}))>) {
			return std::optional(std::reference_wrapper(t->get(Tag{})));
		} else {
			return std::optional(t->get(Tag{}));
		}
	}