I would like to store lists inside a map value. I can: typedef /*boost::intrusive*/list< ClassBase > ClassList; typedef unordered_map< Unit*, ClassList> ClassMap; ClassList someList; And everything works fine, But: ClassMap someMap. And add to access the list: classMap[ pUnit ].push_back( aClass ); I get errors: Thanks, Dan. I get: 1>C:\cpp\boost_1_42_0\boost/intrusive/list.hpp(1478) : error C2248: 'boost::intrusive::list_impl<Config>::list_impl' : cannot access private member declared in class 'boost::intrusive::list_impl<Config>' 1> with 1> [ 1> Config=boost::intrusive::listopt,safe_link,boost::intrusive::default_tag,1>,unsigned int,true> 1> ] 1> C:\cpp\boost_1_42_0\boost/intrusive/list.hpp(117) : see declaration of 'boost::intrusive::list_impl<Config>::list_impl' 1> with 1> [ 1> Config=boost::intrusive::listopt,safe_link,boost::intrusive::default_tag,1>,unsigned int,true> 1> ] 1> This diagnostic occurred in the compiler generated function 'boost::intrusive::list<T>::list(const boost::intrusive::list<T> &)' 1> with 1> [ 1> T=CmdBase 1> ] 1>C:\cpp\boost_1_42_0\boost/intrusive/list.hpp(1478) : error C2248: 'boost::intrusive::list_impl<Config>::list_impl' : cannot access private member declared in class 'boost::intrusive::list_impl<Config>' 1> with 1> [ 1> Config=boost::intrusive::listopt,safe_link,boost::intrusive::default_tag,1>,unsigned int,true> 1> ] 1> C:\cpp\boost_1_42_0\boost/intrusive/list.hpp(117) : see declaration of 'boost::intrusive::list_impl<Config>::list_impl' 1> with 1> [ 1> Config=boost::intrusive::listopt,safe_link,boost::intrusive::default_tag,1>,unsigned int,true> 1> ] 1> This diagnostic occurred in the compiler generated function 'boost::intrusive::list<T>::list(const boost::intrusive::list<T> &)' 1> with 1> [ 1> T=CmdBase 1> ]