On Thu, Jul 21, 2005 at 04:54:07PM +1000, John Pye wrote:

I have some nice unit-checking code here as part of the freesteam project, http://pye.dyndns.org/freesteam/docs/class_units.html This class prevents things like "1 * bar + 3 * kg", and also ensures validity of things like "Density rho = 5 * kg / (2 * metre2)"

It will work with _very_ simple expressions only, in particular, it is impossible to check expression pow(m1, 4-2*eps-2*j) - pow(m2, 2-2*j)*pow(p, 2-2*eps)) (where m1, m2, p have the same dimension) in this way.

Does anyone have any comments on the advisability / feasibility of trying to do this,

I don't think this code (or any other implementation playing with overloading of operator=, operator+, etc.) is suitable for GiNaC, since: 1) C++ compiler is unable[1] to do symbolic manipulations, 2) GiNaC overloads all these operators in its own way, 3) in some simple cases (say, polynomial or rational expressions) it is possible to do run-time checks in a far simpler way: symbol M; symbol L; symbol a("a"); symbol b("b"); ex test = a*M/(b*pow(L,2)); assert(test.coeff(M)==1); assert(test.coeff(L)==-2); Best regards, Alexei