create and pass a functor that assigns a new auditor generator to the one in the engine, and then tells it to play i do for example: write_blocking_command(assign(engine_.auditor_gen, p)); write_blocking_command(boost::bind(&engine::play_auditor, boost::ref(engine_))); assign() is just a utility template to make creating functors that do assignments easier.. boost::bind is used to make all passed functors 0-ary (e.g for binding member functions to their instance or binding arguments to the functor.. and write_blocking_command is just a utility function that disables the GUI until the acknowledgement from the engine has come back to the GUI,, The command ringbuffer is just a ringbuffer holding boost::fucntion<void(void)> objects.. typedef ringbuffer<boost::function<void(void)> > command_ringbuffer; Examples from here: https://github.com/fps/jass/blob/master/main_window.h https://github.com/fps/jass/blob/master/assign.h https://github.com/fps/jass/blob/master/engine.h Regards, Flo