I'm looking at the Boost::Units classes to help eliminate a family of programming errors, but there is one thing that I'm having difficulty with: I have a collection of objects of my own type that pertains to units - these are of a fixed type, with instances per type of unit. I'd like to somehow be able to map from the units constants that Boost uses (e.g. boost:units:si:watts) into my objects (return the correct instance for "watts"). Obviously, there's going to be some hand coding to make that happen - it is unlikely to be possible to generate that mapping automatically. Ideally, what I'd like to do would be to have something like template <typename Unit> struct MyMapper { static const MyUnitInfo info; }; template <> const MyUnitInfoboost::units::si::watts::info(/*ctor parms for my type */); and do things like: MyMapperboost::units::si::watts::info to get the appropriate structure. However, since all the various Boost units are in a type hierarchy to express dimensionality, I'm at a loss how to compose a template to allow something like that to happen - it certainly isn't as straightforward as the above, since Boost units instances of varying types, not typenames. Likewise, just defining some form of map: std::map mymap = boost::assign::map_list_of (boost::units::si::watts,MyUnitInfo(/* my parms*/)) (boost::units::si::ohms,MyUnitInfo(...)); won't work as the types for the Boost constants are all different as far as I can see. Is there some base type all the Boost::Units constants extend, such that I could test for that?