For integers, we really can do something similar in one line with:
enum class qty_t : int64_t {};
That's a good positive example. Sadly not so sanguine for double or complex.
 
While we are technically out of luck for other types, a wrapping aggregate struct isn’t that horrible (though potentially with an attribute that hints it wants the abi of the wrapped field).
I'm not so skilled. I find it a wee bit horrible especially w.r.t. constructors.

Still, cloning, and possibly cloning with extensions, seems a useful thing. Perhaps too useful though ;-)

--Matt.