On Apr 8, 2008, at 9:40 PM, Steven Watanabe wrote:
AMDG
Howard Hinnant wrote:
template <class T, class U> decltype(true ? T() : U()) Min(T&& a, U&& b) { return b < a ? b : a; }
Should this really work if T of U is a reference type and thus cannot be default constructed?
You're right. Not by current language rules. The reported error message could have been better. By coincidence I'm dealing with a similar problem here: http://home.twcny.rr.com/hinnant/cpp_extensions/time2_demo.html , and dealing with it via a promote trait, quite similar to what I've seen in boost. I.e. the Min signature might look like: template <class T, class U> typename promote<T, U>::type Min(T&& a, U&& b); With the *default* (and preferably standardized) promote trait looking like: template <class T, class U> struct promote { private: static T t; static U u; public: typedef decltype(true ? static_cast<T&&>(t) : static_cast<U&&>(u)) type; }; // promote is specializable for client-defined types -Howard