"Dave Steffen" <dgsteffen@numerica.us> wrote in message news:17642.19283.854773.973499@yttrium.numerica.us...
I don't know how to do that, but I'm absolutely sure it's what your users want.
Sorted as a quick test in my local copy of Quan FWIW. I added a metafunction to query the unit : allow_implicit_unit_conversions<StaticUnit>::type // bool_ true or false (of fixed_quantity<StaticUnit,NumericType>) Modified the fixed_quantity ctor to query the unit. added a conditional explicit ctor allowing conversions and voila: #include <quan/length.hpp> int main() { quan::length::m L1(1); quan::length::mm L2 = L1; // line 6 L1 + quan::length::m(L2); // ok } e:\Projects\Test\test.cpp(6) : error C2440: 'initializing' : cannot convert from 'quan::length_<Value_type>::m' to 'quan::fixed_quantity<StaticUnit,NumericType>' with [ Value_type=quan::quantity_traits::default_value_type ] and [ StaticUnit=quan::meta::unit<quan::meta::components::of_length::abstract_quantity,quan::meta::si_unit::milli>, NumericType=quan::quantity_traits::default_value_type ] Constructor for class 'quan::fixed_quantity<StaticUnit,NumericType>' is declared 'explicit' with [ StaticUnit=quan::meta::unit<quan::meta::components::of_length::abstract_quantity,quan::meta::si_unit::milli>, NumericType=quan::quantity_traits::default_value_type ] Also works for addition etc. In this quick mod a Macro decides whether the particular implementation of a StaticUnit returns true or false. but you could create a Static where that is a policy parameter I guess.. I'm not sure if this is important enough to do that, but if it is, it is no great problem to add it. regards Andy Little