std::map<std::string, resource::StandardLinkImpl*, std::less<>> links_;
/* save split-duplex links separately, keep links_ with only LinkImpl* seen by the user
* members of a split-duplex are saved in the links_ */
std::map<std::string, std::unique_ptr<resource::SplitDuplexLinkImpl>, std::less<>> split_duplex_links_;
std::map<std::string, resource::HostImpl*, std::less<>> hosts_;
std::map<std::string, resource::StandardLinkImpl*, std::less<>> links_;
/* save split-duplex links separately, keep links_ with only LinkImpl* seen by the user
* members of a split-duplex are saved in the links_ */
std::map<std::string, std::unique_ptr<resource::SplitDuplexLinkImpl>, std::less<>> split_duplex_links_;
std::map<std::string, resource::HostImpl*, std::less<>> hosts_;