mp_units::quantity_spec<QS, Args...>::operator()

template<
    typename Self,
    typename FwdQP,
    QuantityPoint QP = std::remove_cvref_t<FwdQP>>
requires (mp_units::explicitly_convertible(QP::quantity_spec, Self{})) &&
            requires { typename quantity_point<make_reference(Self{}, QP::unit), QP::point_origin, typename QP::rep>; }
[[nodiscard]]
constexpr
QuantityPoint auto
operator()(this
    Self self,
    FwdQP&& qp);