Recently, I've been in need of a holder class for strings with external linkage but I didn't find an mpl datatype that could wrap an externally defined entity. Instead of creating a quick solution working for my needs I thought the mpl library could benefit from a generic holder class similar to the integral constant holders. <code> template<typename T, T N> struct external_c { // make it a nullary metafunction typedef external_c type; typedef T value_type; // correct? requirements? typedef integral_c_tag tag; // can't make a static compile time constant but only a static // function static value_type value() { return N; } // implicitly convertible to its runtime type value operator value_type() const { return this->value(); } }; // e.g. extern const char string1[]; const char string1[] = "string1"; extern const std::string string2; const std::string string2("string2"); int main() { external_c<const char* const, string1> x1; external_c<const std::string&, string2> x2; std::cout << x1 << "\n"; std::cout << x2.value() << "\n"; return 0; } </code> The name 'external_c' is just a quick idea and would have to be changed anyway with c++09's possibility to use types with internal linkage in template programming. Would it be reasonable to integrate this into the mpl? Any comments? Klaus Triendl