Would there be any interest in a library for attaching units (physical or otherwise) to numeric variables, so that the type system could enforce dimension- and unit-consistency in all calculations, and convert semi-automatically between compatible units? To make this a little more concrete, here's a sketch of the kind of code such a library could enable: --- quantity<meters, double> distance(1.0); quantity<newtons, double> force(5.0); quantity<joules, double> work = distance * force; quantity<calories, double> work_cal = unit_cast<calories>(work); work_cal = work; //Compile error or implicit conversion, // possibly depending on compiler flag quantity<watts, double> power = work; //Compile error- incompatible types --- This library would be somewhat similar to the dimensional-analysis code given by Abrahams and Gurtovoy in their book[1], but with two major enhancements: - it would be defined in terms of specific units (as Abrahams and Gurtovoy suggest in an exercise), rather than general dimensions, so it could catch unit-consistency errors as well as dimension-consistency errors, and it could convert between compatible units - it would allow client code to extend the system with arbitrary units in arbitrary dimensions I should note that although I gave the example in terms of physical units for clarity, I intend this library to be useful not just for physical calculation, but for numerical calculation in general. Almost any time software deals with numbers, it's really dealing with *quantities* (numbers that measure something in terms of some unit), and errors can result if variables with different units are inappropriately combined. The purpose of this library would be to allow developers to prevent those errors with strong typing and compile-time checking, as well as to somewhat ease the task of converting between units when necessary. I know there's been a lot of discussion of units for a GUI library, so I'm especially interested in what people involved in that thread think of this idea- I want to make something sufficiently powerful to be useful in a context like that. [1] http://www.boost.org/libs/mpl/doc/tutorial/tutorial-metafunctions.html