<mp-units/framework/quantity_concepts.h>
template<
typename Q,
auto QS>
concept QuantityOf = Quantity<Q> && QuantitySpec<MP_UNITS_REMOVE_CONST(decltype(QS))> &&
ReferenceOf<MP_UNITS_NONCONST_TYPE(Q::reference), QS>;
Satisfied by all quantities with the reference satisfying ReferenceOf<QS>.