Re: [Boost-users] variadic template function using fusion vector

Roman Perepelitsa wrote:

2010/1/13 noman javed mailto:noman_bwp@yahoo.com>

You can do that, but execute must be a function object instead of function.

#include

struct execute_impl {

template <class Seq> struct result { typedef void type; };

Yeah, used to be that way. And works (by "coincidence" :-). Fusion has been changed at some point to use the boost::result_of protocol for result type computation. Thus, to really get to the argument vector you'll have to write: template< typename Signature > struct result; template< class Self, class ArgSeq > struct result< Self(ArgSeq&) > // <- NOTE: deducing // [... defines type memember 'type'] Anyway, in this very case the result type does not depend on the arguments and so it's sufficient to just write: typedef void result_type;

template <class Seq> void operator()(Seq const & s) const { // s contains all arguments passed to execute. } };

boost::fusion::unfused execute;

int main() { const char* s = "hello"; int n = 42; execute(s, n); }

Here "execute" suffers from perfect forwarding problem, which you can solve by using perfect forwarding adaptor. There is one in p-stade http://p-stade.sourceforge.net/egg/doc/html/egg/function_adaptors.html#egg.f... and also I remember seeing one being proposed for boost, but I can't find it.

Once Fusion's Functional adapters used to attack the Forwarding Problem themselves. Today, there's Boost.Functional.Forward (and .Factory in case u want to e.g. fusion::invoke constructors). Regards, Tobias