Struct template is_filter<T, typename boost::enable_if< boost::is_base_of< filter

Struct template is_filter<T, typename boost::enable_if< boost::is_base_of< filter_base, T > >::type>

boost::signals::is_filter<T,typename boost::enable_if< boost::is_base_of< filter_base,T > >::type> —

template<typename T> 
struct is_filter<T, typename boost::enable_if< boost::is_base_of< filter_base, T > >::type> {
};