AMDG Matthias Schabel <boost <at> schabel-family.org> writes:
1) The target unit may only have one instance of each tag (no repeated tags with different systems). Otherwise, the conversion becomes ambiguous.
If the source has only one instance of each tag than it should be easy too.
But in general we should assume that constructs like this are legit:
quantity<SI::volume> V(1.0*SI::meters*imperial::feet*CGS::centimeters);
where the system of the result type defines the conversions
imperial::feet->SI::meters CGS::centimeters->SI::meters
to get the conversion factor...this is unambiguous in all cases, AFAICS.
I didn't mean that it shouldn't be valid. I meant that both should be allowed. Otherwise, conversions are not necessarily reversible. In Christ, Steven Watanabe