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