But wait, there is hope: you can do this:
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template<class A> struct ordinal { void * tag() { static int const tag_; return &tag_; } template<class B> bool operator<(ordinal<B> const& other) { return std::less<void*>(tag(), other.tag()); } };
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This solution should also be MT safe.
Unfortunately, this doesn't function at compile-time. That is, what I really want to be able to do is: struct system1 : ordinal<...> { }; struct system2 : ordinal<...> { }; struct system3 : ordinal<...> { }; typedef mpl::list<system2,system3,system1> list_type; typedef mpl::sort<list_type>::type sorted_list_type; where mpl::less<> can be defined for ordinal<...> It seems like a hard (maybe impossible) problem... Matthias ---------------------------------------------------------------- Matthias Schabel 2859 Glen Oaks Drive Salt Lake City, UT 84109 801-706-5760 (cell) 801-484-0811 (home) matthias at stanfordalumni dot org ----------------------------------------------------------------