"Neal D. Becker" wrote

Thanks for the links. I am currently using ublas for this. It has promote_traits in traits.hpp. This does what I need, and is part of the current boost release.

Sure... I am using Alex Gurtovoys, promotion_traits.hpp so I'll certainly take a look. One observation... As I have been moving along with my physical quantities library, I have been discovered that 'generic' result_types need this : template<...> binary_operation<LHS,plus,RHS>::result_type operator + (LHS lhs, RHS rhs); rather than template<...> promote_traits <LHS,RHS>::result_type operator+(LHS,RHS); Rationale ...for more complicated types results of (say) multiplication arent the same as for (say) addition. And for UDTs the value_types too may be compatible but different, so they need nested result_types. Another useful extension is to use enable_if, for selective overloading of operator functions. I have wrapped this up in a modified binary_operation ie binary_operation_if<Predicate,LHS,plus,RHS>::result_type operator + (LHS lhs, RHS rhs); This works well when multiplying UDTs by numerics ie int double etc, where The predicate can be "is_this_value_type a compatible value_type for my UDT". This can save a large amount of work overloading operator functions. regards Andy Little