mp_units::quantity::operator*=

template</* implementation-defined */ Q2>
requires detail::ScalarValuePreservingTo<typename Q2::rep, rep> && requires(rep& a, const Q2::rep b) {
      { a *= b } ‐> std::same_as<rep&>;
    }
constexpr
quantity&
operator*=(Q2 const& other) &;

template</* implementation-defined */ Value>
requires requires(rep& a, const Value b) {
      { a *= b } ‐> std::same_as<rep&>;
    }
constexpr
quantity&
operator*=(Value const& val) &;