________________________________________ De: boost-bounces@lists.boost.org [boost-bounces@lists.boost.org] En nombre de Eric Niebler [eric@boost-consulting.com] Enviado el: sábado, 12 de abril de 2008 9:28 Para: Boost mailing list Asunto: [boost] A C++ puzzler
I recently had a C++ problem and found an answer that tickled my brain. In the spirit of Car Talk on NPR, I thought I'd share it in the form of a puzzler. [...]
Hello Eric, I am not sure if this is what you have in mind, since from your description is not clear how the input types are represented: I've assumed they're just the args of a class template with a fixed number of template parameters: struct default_t{}; template<typename T> struct holder_base{typedef T type;}; template<> struct holder_base<default_t>{}; template<typename T,int> struct holder:virtual holder_base<T>{}; template<typename T1,typename T2,typename T3,typename T4,typename T5> struct common_type_base: holder<T1,1>,holder<T2,2>,holder<T3,3>,holder<T4,4>,holder<T5,5>{}; template<typename T1,typename T2,typename T3,typename T4,typename T5> struct common_type:common_type_base<T1,T2,T3,T4,T5> { typedef typename common_type_base<T1,T2,T3,T4,T5>::type type; }; template<> struct common_type<default_t,default_t,default_t,default_t,default_t> { typedef default_t type; }; Best, Joaquín M López Muñoz Telefónica, Investigación y Desarrollo