Hello, Code below, first what I'm trying to do is... assign a value to a adapted struct (BOOST_FUSION_ADAPT_ADT), which works fine if both are of the same type or convertible: template<int I, class Seq, class V> typename std::enable_if< std::is_convertible< typename fusion::result_of::at_c<Seq, I>::type, V>::value ,void>::type assign(Seq& s, V& v) { fusion::get<I>(s) = v; } Some of my input is string, and the struct member is bool, unsigned int etc. In this case I'd need to know the type to convert from string. boost::fusion::get returns the attribute_proxy for the adapted struct, so does at_c<>::type. template<int I, class Seq, class V> typename std::enable_if< !std::is_convertible< typename fusion::result_of::at_c<Seq, I>::type, V>::value /*&& !std::is_same<typename std::decay<V>::type,std::string>::value*/ ,void>::type assign(Seq& s, V& v) { std::stringstream ss; ss << v; ss >> fusion::get<I>(s); } Obviously this does not compile. Is there any trick to get to the type of the proxy? One idea I have is decltype(fusion::get<I>(s).get()), but not sure if I can get this to work in an enable_if... thanks, Jens Weller