Andy Little wrote: I believe that pqs is a great solution
for SI quantities. The primary purpose of a physical quantity library is to cater for common practise, rather than being some sort of tool kit for ad-hoc unit systems to be created. Defining a unit system is a non-trivial task. The dimensional analysis part is trivial really. The difficult part is output and to be honest I havent seen a library apart form pqs that tackles this well. Output is messy even in the SI. I believe that users ( including myself) want simplicity. I dont want to have to spend time creating output facilities or making complex typedefs for commonly used SI quantities. The design of an SI quantity library is possible because they have published detailed definitions of their base units and the output format.
Again, it's probably just me, but this all sounds backwards to me. I certainly agree that adding a "generalized dimensions" library as a layer over an SI quantities library is not a good idea. But wouldn't it make sense to develop a core dimensions/units library without any predefined dimensions in it and develop the SI quantities library as a layer above that? I am not proposing that the dimensions library should be distributed without predefined SI dimensions and units; that would of course be silly. I am just proposing that the underlying infrastructure of the library (I am assuming that the physical dimensions and units are not hardwired in the library from top to bottom) be exposed, so that someone like me can build our own customized dimension/units system (analogous to but different from the SI units). But it appears that the only people willing to devote effort to developing such a library are people who always use SI quantities and are not familiar with applications that don't use them. So I will now bow out of this discussion (until that indefinite time in the future when I can submit actual code for the kind of library I want), but I would encourage all of you to move ahead with the SI quantities library. It definitely sounds like a very useful library to me.