AMDG Matthias Schabel <boost <at> schabel-family.org> writes:
I'm working with Steven Watanabe on a demo implementation of the library that allows heterogeneous units from different systems to be mixed, so each dimension carries its own system information along with it. The main problem with this is that it these heterogeneous composite units make it difficult to define functions that are restricted at compile time to a specific unit system. With concept extensions to C++, it ought to be possible to mitigate this issue, but at the moment I don't see an easy way to get both features at the same time...
It can be done using SFINAE. However, 1) All the dimension lists need to be processed twice. 2) Partial ordering doesn't work. 2 is solved by concepts. 1 is not. I've been wondering whether that information can be encoded in the system. Here are the basics for when each fundamental dimension has a unique unit. template<class DimensionMap> struct heterogeneous_system {}; template<class DimensionMap> template<class DimensionMap, class Tag> struct unit_info<heterogeneous_system<DimensionMap>, Tag> : unit_info<typename mpl::at<DimensionMap, Tag>::type, Tag> { }; template<class DimensionMap, class Tag, class System> struct base_unit_converter<Tag,heterogeneous_system<DimensionMap>,System> : base_unit_converter<Tag, typename mpl::at<DimensionMap, Tag>::type,System> { }; namespace MGS { typedef heterogeneous_system< mpl::map< mpl::pair<length_tag, SI::system>, mpl::pair<time_tag, SI::system>, mpl::pair<mass_tag, CGS::system> >
system;
typedef unit<system, energy_type> energy; energy g_m_squared_per_sec_squared; } In Christ, Steven Watanabe