ISWT
I would suggest that you have a pod_quantity for defining the various constants so that they can be safely used during the dynamic initilization phase.
template<class Unit, class T = double> struct pod_quantity { //like quantity but without constructors/assignment operators T val_; };
constants.hpp
pod_quantity<si::velocity> c = { 299792458 };
cgs:: the code would suddenly have a bug because there would be no way for the compiler to know
The problem with this is that you lose the type-safety of forcing explicit value+unit construction of quantities. That is, if someone decided to express the constant in cgs units instead and just did a global search and replace for si:: - that the specified constant value was meant to be in SI units. By requiring constructs like quantity<si::velocity> c(299792458*si::meters/si::second); you would get an error here: quantity<cgs::velocity> c(299792458*cgs::meters/cgs::second); because there is no meter defined in cgs. There has to be a better solution to the dynamic initialization problem...anyone? Matthias ---------------------------------------------------------------- Matthias Schabel, Ph.D. Assistant Professor, Department of Radiology Utah Center for Advanced Imaging Research 729 Arapeen Drive Salt Lake City, UT 84108 801-587-9413 (work) 801-585-3592 (fax) 801-706-5760 (cell) 801-484-0811 (home) matthias dot schabel at hsc dot utah dot edu ----------------------------------------------------------------