Dear Martin, Please look at the first line in the Boost Design and Programming Guidelines : http://www.boost.org/more/lib_guide.htm#Guidelines It may be that some compilers optimize the current code better than others and that some do very poorly. Also in accordance with the aforementioned guidelines we have not focused primarily on performance or performance testing. There is no fundamental reason why the code should not be able to be optimized away, but achieving that for many compilers may need to be left for later. It certainly will never happen without a putative starting point. Finally, if a nominally compile-time unit system incurs as much overhead as you seem to believe, imagine the cost of a runtime system... Cheers, Matthias