Std::start::deferred. FutureWarning: Downcasting habits in `exchange` is deprecated and can be removed in the future version. To retain the outdated habits, explicitly phone When the perform f returns a value or throws an exception, it's stored in the shared state obtainable in the std::future that std::async returns into the https://alphawireless.com/future-proofing-american-utilities-why-900-mhz-is-critical-for-utility-communications/