Should round/floor/ceil really be generic?

[sharkdp]

Using round/floor/ceil/… on dimensionful quantities is sometimes useful, but it's also dangerous, because the output depends on the unit in use. au, a C++ compile-time unit library, solves this problem by providing round_in<unit>(value) instead. We could potentially do something similar. round_in(unit, value) would work, but is prone to argument reversal errors.