e r wrote:

Steven Watanabe wrote:

...

AMDG

e r wrote:

...

// probably not what result_of::transform expects, based on compile // errors (below) template struct result{ typedef typename Metafun::type type; };

Fusion uses Boost.ResultOf. http://www.boost.org/doc/libs/1_36_0/libs/utility/utility.htm#result_of

In Christ, Steven Watanabe

Thanks. I read the link above before posting as well as the proposal:

//example from proposal. struct square_ { template<typename T> struct result { typedef T type; }

template<typename T> T operator()(T& x) const { return x*x; } };

but I'm not qualified enough to deduce the right answer in my case. i thought id would be like this:

template<typename Arg1> struct fun{ template struct result{ typedef typename Metafun::type type; };

template typename Metafun::type operator()(const Metafun& meta,const Arg2& arg2)const{ typedef typename Metafun::type result_type; return result_type(args,arg2); } };

but apparently it's not correct. I guess I can't fully make sense of F::result::type. any hint here would be really helpful.

thanks!

I may have made a little bit of progress here... struct fun{ template<typename Signature> struct result; template<typename A> struct result{ typedef A type; }; template<typename A> A operator()(const A& a)const{ return A(); }; }; typedef boost::result_of::type result_type; BOOST_MPL_ASSERT( ( mpl::is_same< result_type, my > ) );

Steven Watanabe wrote:

AMDG

e r wrote:

...

I may have made a little bit of progress here...

template<typename A> struct result{ typedef A type; };

Yeah. That's the idea. I generally use function_traits rather than partial specialization. In your original example (untested):

#include #include #include

struct fun { template<class Sig> struct result { typedef typename boost::function_traits<Sig>::arg1_type arg1_type; typedef typename boost::function_traits<Sig>::arg2_type arg2_type; typedef typename boost::remove_cv::type>::type Metafun; typedef typename Metafun::type type; }; // ... }

In Christ, Steven Watanabe

Much appreciated, thanks! made changes as suggested and works. but i can't get this simple algorithm to work (errors shown in the code below). please help. algorithm: map fusion::vector to fusion::vector and call {identity<X>::type(arg):X=A,B,C,...} via transform. use the result to copy construct fusion::vector. *.cpp typedef boost::fusion::vector2,boost::mpl::int_<1> > vec1_type; typedef boost::range range_type; range_type::result::type result( range_type::create() ); vec1_type vec1 = result; // error: no matching function for call to ‘boost::fusion::vector_data2, mpl_::int_<1> >, mpl_::int_<0>, mpl_::int_<1> >::vector_data2(const boost::mpl::identity >, const boost::mpl::identity >)’| *.hpp template struct apply_wrapper{ template<typename T> struct apply{ typedef metafun<T> type; }; }; template struct apply_wrapper_to_seq{ typedef typename mpl::transform::type type; }; struct range_fun{ range_fun(){} template<class Signature> struct result { typedef boost::function_traits<Signature> fun_traits; typedef typename fun_traits::arg1_type arg1_type; typedef typename boost::remove_cv< typename boost::remove_reference >::type metafun_type; typedef typename metafun_type::type type; }; template<typename Metafun> typename Metafun::type operator()(const Metafun& meta)const{ typedef typename Metafun::type result_type; return result_type(); //for now arg2 ommitted for simplicity } }; template<typename Result> struct range{ typedef typename apply_wrapper_to_seq<Result>::type wrappers_type; struct result{ typedef typename fusion::result_of::transform< const wrappers_type,range_fun>::type type; }; //ommitting const causes compile error static typename result::type create(){ typedef range_fun f_type; BOOST_MPL_ASSERT((mpl::equal));//mpl_::failed (see below) return fusion::transform(wrappers_type(),f_type()); } }; no matching function for call to ‘assertion_failed(mpl_::failed************ boost::mpl::equal, mpl_::int_<1> >, boost::fusion::transform_view >, boost::mpl::identity >, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_, boost::fusion::void_>, boost::range_fun, boost::fusion::void_>, boost::is_same, mpl_::arg<-0x00000000000000001> > >::************)’|

Steven Watanabe wrote:

AMDG

e r wrote:

...

typedef typename boost::remove_cv< typename boost::remove_reference >::type metafun_type;

This should be typename boost::remove_reference::type.

...

typedef typename metafun_type::type type; };

In Christ, Steven Watanabe

Oh! I should have spotted that. Thanks for following up throughout!