Matthias Schabel wrote:
1) I do not need a library that insists on defining some "system of units" to which everything gets converted.
A major design goal of mcs::units was to allow users to work in a system that matches their problem. These can be physical units, but can be anything else, also...
But I don't want the user of the library to have to define a "system" of units just to use a function in the library. If there is, say, a function that takes a distance, a mass, and a time and does computations with them, the user should be able to feed into that function arbitrary units for each of the three without having to use the dimensions library to define a system first. So the thing I didn't like in your version of my sample code is the need for a template parameter called "System". I think in another post you yourself indicate how these defined-by-convention "systems" of units used by physicists cause some awkwardness, because a system might not define the units for momentum to be equal to the units of mass times the units of distance divided by the units of time, creating the need for extra conversions. I am pretty badly prejudiced as a mathematician. I think within a single code module, one should forget these arbitrary man-made conventions and code using mathematically consistent units (so the units for the product of two dimensions are always the product of the the units of the two dimensions, etc.). This yields in my opinion much cleaner mathematical formulas with simpler constants and therefore cleaner code as well. My view is that conventions like SI units should appear only in the interface to the module, and the first thing that the module should do on entry is to convert everything to a mathematically consistent set of units, rather than a set conforming to a rather arbitrary convention. (I'm sorry if I sound like a closed-minded cranky old mathematician, but that's exactly what I am.)