<mp-units/framework/quantity_spec.h>template<
typename Self,
typename FwdValue,
RepresentationOf<Self{}> Value = std::remove_cvref_t<FwdValue>>
requires (detail::explicitly_convertible_to_dimensionless(Self{}))
[[nodiscard]]
constexpr
Quantity auto
operator()(this
Self,
FwdValue&& val);