[Boost-users] [fusion] trouble with transform

Subject: [Boost-users] [fusion] trouble with transform
From: Gennadiy Rozental (rogeeff_at_[hidden])
Date: 2011-11-12 01:22:32

Hi,

 I have code similar to the following snippet:

#include <boost/fusion/container/list/list.hpp>
#include <boost/fusion/container/list/convert.hpp>
#include <boost/fusion/container/generation/make_list.hpp>
#include <boost/fusion/algorithm/transformation/transform.hpp>
namespace fusion=boost::fusion;

template<typename T>
class A {
public:
    struct B {};

    B   make_b() const  { return B(); }
};

template<typename T>
A<T>
make_a( T const& )
{
    return A<T>();
}

struct make_b {
    template<typename Sig> struct result;

    template <typename DS>
    struct  result<make_b(DS const&)> 
    {
        typedef typename DS::B type;
    };

    template <typename T>
    typename T::B
    operator()(T const& t) const  { return t.make_b(); }
};

int
main()
{
    namespace fusion=boost::fusion;

    fusion::as_list( fusion::transform( 
                       fusion::make_list( make_a( 1. ), make_a( 1 ) ), 
                       make_b() ) );

    return 0;
}

it fails to compile with an error like this:

... rather long context here
..\..\../boost/utility/result_of.hpp:83:1: error: 
invalid use of incomplete type ‘struct make_b::result<make_b(A<double>)>’
test.cpp:27:35: error: declaration of ‘struct make_b::result<make_b(A<double>)>’

What am I doing wrong?

Any help appreciated,
Gennadiy