[boost] fusion unfused_typed problem

From: Christian Holmquist (c.holmquist_at_[hidden])
Date: 2007-07-10 11:41:52

There seems to be some problem with fusion::unfused_typed<> and empty
sequences, at least the way I'm trying to use it.
The example below doesn't compile with boost::fusion::vector<> as the
Sequence parameter to unfused_typed<>.
Any clues, someone?

template<class Sequence>
struct foo
{
    template<class Sig> struct result;

    template<>
    struct result<foo(Sequence)>
    {
        typedef void type;
    };

    void operator()(Sequence const& seq) const
    {

    }

};

void bar()
{
    {
        typedef boost::fusion::vector<int> vec;
        boost::fusion::unfused_typed<foo<vec>, vec> f;
        f(1); // This works
    }

    {
        typedef boost::fusion::vector<> vec;
        boost::fusion::unfused_typed<foo<vec>, vec> f;
        f(); // this fails, error message below.
    }
};
1>c:\studio8\thirdparty\boost\boost\fusion\functional\adapter\detail\nullary_call_base.hpp(51)
: error C2027: use of undefined type 'foo<Sequence>::result<Sig>'
1>        with
1>        [
1>            Sequence=vec
1>        ]
1>        and
1>        [
1>            Sig=foo<vec> (boost::fusion::vector0)
1>        ]
1>
c:\studio8\thirdparty\boost\boost\fusion\functional\adapter\unfused_typed.hpp(76)
: see reference to class template instantiation
'boost::fusion::detail::nullary_call_base<Derived,Function,Enable>' being
compiled
1>        with
1>        [
1>            Derived=boost::fusion::unfused_typed<foo<vec>,vec>,
1>            Function=foo<vec>,
1>            Enable=true
1>        ]
1>
c:\studio8\thirdparty\boost\boost\fusion\functional\adapter\unfused_typed.hpp(86)
: see reference to class template instantiation
'boost::fusion::detail::unfused_typed_impl<D,F,S,A,EO>' being compiled
1>        with
1>        [
1>            D=boost::fusion::unfused_typed<foo<vec>,vec>,
1>            F=foo<vec>,
1>            S=vec,
1>            A=0,
1>            EO=true
1>        ]
1>        c:\fail.cpp(86) : see reference to class template instantiation
'boost::fusion::unfused_typed<Function,Sequence>' being compiled
1>        with
1>        [
1>            Function=foo<vec>,
1>            Sequence=vec
1>        ]
1>c:\studio8\thirdparty\boost\boost\fusion\functional\adapter\detail\nullary_call_base.hpp(58)
: error C2027: use of undefined type 'foo<Sequence>::result<Sig>'
1>        with
1>        [
1>            Sequence=vec
1>        ]
1>        and
1>        [
1>            Sig=foo<vec> (boost::fusion::vector0)
1>        ]

Regards,
Christian