From: "Richard Peters" <r.a.peters@student.tue.nl>
The bigint type proposed for the C++ standard library does not permit the use of expression templates. Using expression templates has a positive and a negative aspect: A significant speedup can be gained using expression templates. The downside is that templates cannot deduce the correct type of expressions, for example: template<class T> void f(T a, T b) will not work when invoked as f(x + y, x - y), because x + y returns an object of type different from x - y. Because the C++ standard library proposal specifies the result type of the operators to be of type const integer, a library implementing that proposal cannot use expression templates.
PMFJI, but I wonder whether this would work: template <typename T, typename U> void f(T a, U b) { typedef typename <magical_incantation<T, U>::type V; f_impl<V>(a, b); } a and b can have different types, but then magical_incantation computes a common type to which both can be converted and the implementation function can be invoked with that type. I may be off base, and you may have already tried this approach, but I just wanted to mention it if it could help. -- Rob Stewart stewart@sig.com Software Engineer http://www.sig.com Susquehanna International Group, LLP using std::disclaimer;