----- Mensaje original ----- De: Peter Dimov <pdimov@mmltd.net> Fecha: Viernes, Noviembre 3, 2006 9:48 pm Asunto: Re: [boost] programmatically building a bind composition? Para: boost@lists.boost.org
Fernando Cacciola wrote:
Besides the error, that's the general way to go? (when I can only use tuple/bind of course)
Defining the function object directly without going through bind, as suggested by Bryan Ewbank, may be easier. The pseudocode is trivial: [...]
I think the following should do, but I don't have here a powerful enough compiler (i.e. supporting boost::result_of) to try: #include <boost/tuple/tuple.hpp> #include <boost/utility/result_of.hpp> template<typename Const> struct cons_bind; template<typename F,typename G> struct cons_bind<boost::tuples::cons<F,G> > { typedef boost::tuples::cons<F,G> cons; typedef cons_bind<G> next; template<typename Arg> struct result:boost::result_of< F(typename next::template result<Arg>::type)
{}; template<typename Arg> static typename result<Arg>::type call(const cons& c,const Arg& a) { return c.head(next::call(c.tail,a)); } }; template<typename F> struct cons_bind<boost::tuples::cons<F,boost::tuples::null_type> > { typedef boost::tuples::cons<F,boost::tuples::null_type> cons; template<typename Arg> struct result:boost::result_of<F(Arg)> {}; template<typename Arg> static typename result<Arg>::type call(const cons& c,const Arg& a) { return c.head(a); } }; template<typename Tuple> struct tuple_bind { tuple_bind(const Tuple& t):t(t){} typedef cons_bind<typename Tuple::inherited> helper_cons_bind; template<typename Arg> typename helper_cons_bind::template result<Arg>::type operator()(const Arg& a) { return helper_cons_bind::call(t,a); } private: Tuple t; }; // testing #include <cmath> #include <iostream> int main() { typedef boost::tuple< double (*)(double), double (*)(double)
tuple_t;
tuple_t t(std::sin,std::cos); tuple_bind<tuple_t> tb(t); std::cout<<tb(0.0)<<std::endl; }; HTH Joaquín M López Muñoz Telefónica, Investigación y Desarrollo