/*! \static Add a callback fired when any Comm starts */
static void on_start_cb(const std::function<void(Comm const&)>& cb) { on_start.connect(cb); }
/*! Add a callback fired when this specific Comm starts */
/*! \static Add a callback fired when any Comm starts */
static void on_start_cb(const std::function<void(Comm const&)>& cb) { on_start.connect(cb); }
/*! Add a callback fired when this specific Comm starts */